SOLVED: Need help with bogging and misfires, persistent P0171 & P0174 lean DTCs
 

SOLVED: MAF was at fault

Conclusion: even if there are no codes for MAF and the live data seems to be responding correctly, the MAF may still be at fault. Disconnect the MAF before starting the engine, then drive the vehicle. If there is a change then the MAF is likely at fault. Thanks 80stech for the tip.

-----------------------------------

My 2003 3.0 X5 has a bogging and misfire condition that I cannot seem to find the root cause. I have reached the limits of my knowledge and am asking for help before I waste more money replacing good parts.

History:
Check engine light after miles of highway cruising (sustained high vacuum driving). Codes:
- P0171 & P0174 System too lean banks 1 and 2. No drivability issues.
Performed smoke test using DIY tester. Didn’t notice any leaks but test area had a slight breeze and may have blown away any light wisps. I'd say test did not reveal any major leaks but because of conditions there may have been small leaks(s) I didn’t see. Valve cover gasket was leaking oil and could be a source of vacuum leak so replaced:
- New valve cover gasket
- New OEM NGK BKR6EQUP spark plugs
Cleared codes and drove vehicle only periodically to keep battery charged. CEL did not return at this time.

Drove 5 miles to friend’s house to replace rusted rear subframe and install rear muffler sections from LCI V8 model. Vehicle sat without being started while I slowly did work on the weekends. After about 3 months started engine to maintain system voltage during the many, many, many rounds of brake bleeding and ABS pump activations to get air out of the ABS system. This is when the drivability problems began. Engine would start, idle ok, then slowly misfire more and more until finally stalling. Upon restarts misfires began immediately. The only way to keep engine running was to continually feather the throttle. Thinking something might have crawled into the MAF and fouled the heating element:
- Sprayed MAF with CRC Mass Air Flow Sensor Cleaner.

Cleared codes (did not record codes), restarted and misfires went away for a few minutes then slowly came back. Finished subframe job, installed new rear mufflers, cleared codes, and drove home. Reduced power while driving. When almost home misfires began again and engine started bogging badly. Barely got it home. Removed new spark plugs to inspect:
- New spark plugs now look darker than the old ones I pulled out (possibly rich and fouled from the misfires?)
Retrieved codes:
- P0171 & P0174 - System too lean banks 1 and 2
- P1343 - Misfire cylinder 1 with fuel cut off
- P1345 - Misfire cylinder 2 with fuel cut off
- P1346 - Misfire during start cylinder 3
- P1350 - Misfire during start cylinder 5
- P1348 - Misfire during start cylinder 4
- P03XX - Misfires on all 6 cylinders

Rented fuel pressure tester. Started engine:
- Fuel pressure slowly rose to 52 psi after about 30 seconds (took too long to rise? and psi too high at idle, spec 36 - 46 psi)
- No pressure change when disconnecting vacuum hose to fuel pressure regulator
- Under wide open throttle fuel pressure drops to 50 psi

Suspecting soft-fail fuel pump:
- Replaced fuel pump
No change.

Performed compression test to check for blown head gasket:
- 200psi average all cylinder compression pressures = OK
Suspected a faulty rented fuel pressure tester, rented another one, this one new. Same results, fuel pressure very slowly rose to 52 psi, dropped to 50 psi under WOT. Tried tester on another X5, fuel pressure rose more rapidly to spec. Determined fuel tester was not faulty.

Removed intake boot to check as source of vacuum leak
- No cracks or damage to intake boot
Per an Xoutpost thread for checking the CCV system:
- Removed oil filler cap to feel for excessive vacuum, moderate vacuum found indicating CCV likely ok
Removed DISA to inspect, found flap door stuck in one position. Took apart and found hex cam slipped one position
- Repaired DISA and re-used old DISA O-ring.
No change

Suspected possible clogged exhaust due to mufflers sitting outside for months, maybe something crawled in and blocked it. Following another Xoutpost thread on clogged/plugged exhaust observed O2 upstream sensor live data with Foxwell 510:
- O2 voltage at idle hovers around 0.030v
- O2 voltage at part throttle jumps to about 0.800-0.600v then immediately drops to 0.030v
- O2 voltage at wide open throttle jumps to about 0.800-0.600v then immediately drops to 0.015v
O2 results indicate no clogged or blocked exhaust, but instead lean condition. Is this the correct interpretation? While monitoring live data it doesn’t look like there's any upstream vs downstream rapid sensor switching going on, but I'm not sure how responsive the Foxwell is.

I only have two suspects going forward. One is a faulty fuel filter/pressure regulator combo due to the incorrect fuel pressure readings. But after wasting money replacing a good fuel pump I am hesitant to replace it without being more sure. The other thought is vacuum leak(s). If I remember correctly under wide open throttle the DME should operate under open loop and ignore O2 sensor readings. My thinking is that wide open throttle should mask all but the largest of vacuum leaks. I might be wrong on DME operation though. I may need to buy a real smoke test machine and try to find a windproof garage to test in. Garages are not common here in Hawaii.

My other issue is I'm not sure how to use some of the live data on the Foxwell 510. It has options like 'multiplicative mixture adaptation', but its value is 0.00 with unit %. There's 'additive bank mixture adaptation', but its 0.00 with unit ms. It also has 'adaptation 1 engine throttle' with a value of 0.48 but the unit is blank. There is more but I'm not sure what they are, how to use them, or if they're even reading accurately.

OK! That's all I've got so far. I would like to use diagnosis to determine failed parts instead of replacing good ones, but I don’t know where to go from here. Any ideas or help is appreciated.

The fuel pressure should rise instantly, so if the gauge is hooked up properly (depressing the schrader valve) the problem is the fuel filter or maybe a pinched line or restriction.

I thought about a pinched line from this poor guy who found the same thing after a bunch of part replacements. In his scenario the fuel pressure would go down to 30-40 psi. Mine drops to 50, but no further.

Possibly, might have to replace it as process of elimination.

I hadn't thought of this. Will do another fuel pressure test.

similar, but not, problems with mine; extended searching for ???
 

victell- my '01 X5 3.0i has had a similar problem with lean codes and also showed a misfire code P1345 - Misfire cylinder 2 with fuel cut off, IIRC, just once, in the 2.5 years I've owned it, but I've not yet located the source of the problem, yet. Fortunately, I've used a work-around to keep the CEL/SES/MIL boogeyman away, since the problem started.

The difference between your X5's problem and mine is that mine has never had any driveability problems, with the engine having had just about everything renewed in the three years before I traded for it (by the PO, specifically as the conditions that our car-for-car swap demanded), including plugs, coils, O2 sensors, vcg, Vanos, chain & guides. The only components I've had to change are the exhaust cam position sensor (two codes thrown concerning that was enough warning for me!), a new oil cap & gasket (some blow-by on top of the beauty cover), converting the noisy & cracking viscous fan assembly for a hi-power electric fan, and lastly, swapping the OE MAF sensor for a $20 Amazon unit (more details later).

I followed much the same path you've tread, testing with a homemade smoke tester, out in the open, with the same results you had, for the same reasons, but I've also used carb cleaner spray (which I've used previously on other cars to find vacuum leaks) with similar zero finds. Visual inspections also negative, as was the fuel pressure test (the regulator was brand new, I found out later, so I wasted $75 for the tester and attachments, I guess), and I rebuilt the DISA valve with a G.A.S. kit, so there would be no question concerning it.

I've used a Foxwell NT510 Elite to graph O2 sensors, also, and they were OK, looked at all the live data, compared readings before and after adaptations cleared, and have done hundreds of test sessions using it and once or twice using INPA (but prefer the Foxwell). Nothing much to see, except high fuel trim numbers on both banks.

Concerning fuel trims: mine were so high back in late '21 and early '22, that I'd get the "money light" on (as Eric O. on South Main Auto youtube channel likes to say), and as the next emissions inspection was coming up, I tried taking out my OE MAF sensor (Siemens), which I had previously cleaned with the proper cleaner several times, and replaced it with a $20 ($23? at the time) Chinesium "MostPlus" sensor from Amazon. X5chemist had suggested doing that, as he had much earlier (and still reports that his is performing fine, now 2+ years later).

Immediately, after the swap (and resetting the fuel trims to zero), my MAF readings were much better, and correspondingly the LTFT's (long-term fuel trims) have become lower (better) ever since, though they are still going as high as +9% long-term, in stop-and-go low-speed driving (which is 99% of the only 1500 miles...in the 2.5 years I've driven it), and the long-terms fall to as little as +4%, during the very few extended highway trips it's been on). Either the OE MAF was underreporting airflow, or the cheap replacement is overreporting it, but it's been a good work-around, that I can live with (the X5 passes inspections, the exhaust smells clean, and it is what it is). I had an Amazon refund coming awhile back, so I used it to get a second cheap MAF, as a spare!

Back in Oct.-Nov.'23, I was shopping for a factory-built professional (or semi-pro) smoke tester, after I figured my two previous home-built testers were insufficient. After much ado, after getting & sending back, two cheap-ish units that were broken or defective as built, I finally ordered a better one (which the two cheap others were clearly clones of), the AutoLine Pro EVAP Smoke Machine Leak Tester – Shop Series https://www.amazon.com/gp/product/B0...e?ie=UTF8&th=1
Attachment 83984
from Amazon, to further test my X5 for the phantom vacuum leak I'm sure that MUST be out there, somewhere.

I've got vacuum caps, replacement silicone hoses, and clamps standing by, waiting for the day when I can take over the single garage bay that my wife's precious Lexus sits in, take out the obstructing plastic crap covering the rear of the engine, and smoke test the X5 again. We live on a semi-rural sandhill, with wind-blown sand & oak debris always present (plus feral cats, squirrels, rats, mice, scorpions, spiders, snakes,etc. always trying to get into the garage), so I usually can't open up dust & dirt sensitive components or areas, while outside on my plywood work platform, that I use for external component maintenance.
Attachment 83987

I also have halogen & LED worklights, an endosope, inspection mirrors, Rhino Ramps (so, in case I suspect a vacuum leak near the fuel pump, I can get under there), etc., standing by, but things keep popping up to prevent my smoke test.

• 1) holidays,
• 2) cold or wet weather (N.Texas type),
• 3) constant ongoing projects that my wife needs my help on,
• 3) old age health (73 y.o.),
• 4) just in the last two weeks: the precious Lexus started up smoking & sputtering, so I opened up the engine covers, found a rodent nest, inspected for damage (found none), tested (with Foxwell & Torque Pro app for codes, and found none), then ....see this thread https://www.clublexus.com/forums/es-...r-coolant.html

So, now I'm going to smoke test two vehicles (guess whose vehicle will get tested first, hahaha), to find what, if anything, is really amiss. victell- I wish you luck, I'm hoping you find something, anything, as a longtime mystery problem can drive one nuts, after awhile.

https://youtu.be/IyRaz1q9HEM?si=2rHo0JRBmSYA8j72

This video is after replacing FPR.

Before I replaced it the pressure bounced with every injector pulse on the order of a psi.

https://uploads.tapatalk-cdn.com/202...c702cd5cda.jpg

https://uploads.tapatalk-cdn.com/202...d37802cf11.jpg

Had very simulator errors suggesting vacuum leak. The thing is: e53 doesn't know the fuel pressure it does the matu assuming 50.0 psi and any time it isn't, it will send less or more fuel.

In the video above I was wot rev and it would pull the psi down like 1.5 psi but at idle it was rock steady.

https://uploads.tapatalk-cdn.com/202...a7bc85bafa.jpg

I thought I took a measurement of the small o-ring but that was the only problem. Gas under pressure was getting past and throwing off the regulation.

What are MAF readings? Do you see any oil residue on the intake?

80stech, good call on the fuel rail shrader valve. Swapped with a different one and response from the tester is much better now.
andrewwynn, looks like my fuel pressure is now behaving similar to your video. Here's a video of mine:




workingonit, I also tried spraying different areas to find vacuum leaks but some places I cannot get to with the spray so I couldn’t be confident. I’m coming to the conclusion that a well-built smoke machine with a still environment to work in is essential. Interesting that the chinese MAF worked well for you. I did not have such luck with them on my previous X5, but that was years ago and maybe the quality has gone up s
ince. I’ll keep that in mind.


X5chemist, video below of my MAF readings but I’m not sure how to interpret them. I noticed residue inside the intake at the DISA port, but nothing wet to the touch. Is that significant?

That’s really slow pressure build!

It’s not that hard to get the FPR out.

I would pull the filter/FPR and check those o-rings. For about a buck you can likely resolve.

Query; ever have hard starts at random times? That was another symptom of wife's car when the FPR o-ring failed.

It looks like a slow build but I suspect the rental tester + adapter + swapped schrader valve probably didn't allow max volume flow to the gauge 100%. But at full throttle the fuel pressure stayed pretty solid.

I have not had hard starts at random. This X5 may run like crap most of the time, but it is eager to do so and the engine starts promptly every time.

I had this one morning with my e36. I went through a whole diag ordeal and panicked that the engine was shot. But all it was, was the circular plug for the ignition wire harness wasn't totally plugged in. It was half way in. It ran fine sometimes, I even drove it for 45 minutes the night before, and the next day it starts misfiring like that and would come and go.

I discovered it would change as I hit the valve cover, and that the harness was just moving slightly. Looked at that screwed the plug in properly and it's good. I doubt it but maybe that's all it is, check electrical connectors.

Can you please describe your DIY smoke tester and method?

I have a decent compressor-fed "Stinger" smoke tester bought on amazon and on 2 recent occasions, my indie has found vacuum leaks I was unable to find.

If the gauge is slow to respond going up it can be slower going down, or not go down at all under load so that needs to be dealt with to get an accurate picture of the fuel system. Does the gauge drop 5 or 10 PSI instantly as soon as the pump shuts down? More than once were the OP has not done a fuel pressure test before and doesn't know what things should look like get fooled by the gauge/connection. +1 one one the smoke tester, not the most reliable way to prove no vacuum leaks me thinks ;)
++ fuel pressure test includes driving under load with the gauge taped to the windshield, again common thing for a DIY'er to be fooled by not doing properly.

OP is your pressure gauge fluid-filled?



It looks like the slow speed is just due to gauge damping that Andrew's gauge may not have had.



If you use it to check the pressure on other things does it respond just as slowly?

What's the fuel reading in grams/sec?
Are any intake runners showing signs of oil residue? Mine had a vac leak along the intake seam.

Need help with bogging and misfires, persistent P0171 & P0174 lean DTCs
 

What I'm noticing is the pressure didn't go to 50 until started. Or should hit 50 at key on. If you key off then key on does it go to 50? In any event I'm getting some deja Vu.

It'll take half an hour but no$ to pull the FPR and look at the o-rings. At the age of the car I'll need surprised it's not flattened like mine was

https://youtube.com/shorts/AEjiWbrrP...VEy8TkHUtTdSzm

Ok I checked the connector and wiggled the harness with the engine running, no change.

I used a version of the smoke machine below. Manually blew smoke into the intake boot just after the MAF. The DIY tester was leaking smoke from the cap and the test area was windy. What method did your indy use to find the vacuum leaks?

https://i.imgur.com/8BRwtk8.jpeg

I’ve now removed the schrader valve from the fuel rail and adapter, and opened the tester’s purge valve until fuel filled the hose up to the gauge displacing the air making it fluid filled. Previous fuel pressure video was a taped-to-windshield drive but did not do that this time as I couldn’t get a leak-free tester setup and didn’t want to risk it. Response is much faster now, but overall the same. Video below.



I do have oil residue inside my intake (pics below). How would an intake vac leak cause this? For fuel reading do you mean volume test or Foxwell fuel consumption live data?

https://i.imgur.com/LCjPfzQ.jpeg

https://i.imgur.com/sLC9cOc.jpeg

https://i.imgur.com/iVvlTYq.jpeg

Manually ? You mean like blowing on a hose or something???

To do a decent smoke test, you need 10 minutes + of steady smoke at a steady pressure. and you need to introduce smoke in several locations...like the brake booster...as well as the intake.

My Indy used a professional-grade smoke tester that costs $1,000's...

You need to get a proper smoke test done...I suggest you pay a tech to do one.

Need help with bogging and misfires, persistent P0171 & P0174 lean DTCs
 

That jiggle at isle exactly matched mine with the FPR leak!

After the fix it rests exactly 50.00 and doesn’t waver at all.

That’s the sign I was looking for! 90% certain FPR is your problem. When FPR is working properly the needle should be rock stable at idle.

https://youtube.com/shorts/AEjiWbrrP...VEy8TkHUtTdSzm

I recall a video in 2021 I made with my E66 N62 having an unstable fuel pressure like shown above. The FPR is integrated into the fuel filter, but I've since changed the filter assembly. Currently repaired multiple issues on the engine but I will have to check and see if this one is still remaining, and look into the regulator.

OK, I didn't watch the first video before. The gauge does rise on the slow side but also drops when the pump shuts off (pressure drops to regulator setting but should hold there) which is good because it verifies that the gauge will drop with the actual pressure. The second video you start the engine just as the pump shuts off to prime and gauge is dropping. Under load though means highway speed and full throttle if you want to rule out fuel. Are the codes coming back up after regular driving?

https://youtu.be/IyRaz1q9HEM?si=ikZwuoHyqUeTPKNx

The 3.0 version of e53 should run the fuel pump for about 6 seconds at key on. Note that the pressure does not drop before I crank the engine.

The comfort start models act differently and maybe your 3.0 has the more advanced start. (you can tell because the car will keep cranking when you release the key from crank position).

In any event the video above is after replacing the FPR. The bad FPR had the shaky needle at idle. Had handfuls of odd random misfire and occasional long cranks before the replacement.

After replacing the FPR the needle was rock steady at idle. At the autopsy was when I discovered the o-ring was toast and almost certainly the only problem. I could have just replaced 30¢ o-ring vs. $75 fuel filter plus FPR.

I didn't mind though the fuel filter was getting pretty full. Cut that in half to check and yeah it did it's job charcoal colored fuel on the dirty side it was very dirty. I think the odometer was about 160-170,000

If you haven't realized already, andrewwynn's vibrating needle, FPR o-ring theory is a load of crap.

Except it's exactly what happened. Those are the before and after videos from FPR swap and the only defect found post mortem was a horribly defective o-ring.

I am in fact correct far more often than I'm wrong. Prove me wrong. Fluid only flows from high to low pressure very simple laws of physics. FPR works by having excess pressure that is held back to release a regulated pressure. This means there is higher pressure coming from the pump than is coming out of the FPR. If there's a leak in the feedback it's not going to function as designed that's exactly what I measured.

If you have a better explanation for the measured results that came along with a fixed car then share them and be less of a ass while doing so.

The air intake runners show no sign of oil. Right where the runners connect to the side is where the seam can leak.
The inside looks normal for a high milage intake. I was surprised how clean mine was except for the DISA area.

Locally, a shop charges $125 for a smoke test.

My money is on an undetected vacuum leak…

you can get a decent unit for $100+, but you'll need peripheral equipment
 

from another thread, just now I agree with Effduration, it would be better to have a professional shop do your smoke testing, rather than piece together a homemade tester (in my case, a sauerkraut jar + soldering iron + $7-10 manual siphon pump), or make one that you have to blow thru a hose to furnish the air. I wasted money making my failed tester (twice), time doing that, and more time ordering and sending back two Chinesium cheapo testers; finally, I bought a decent one on Amazon (third time's is a charm), in November, but only got around to testing it today (preliminary to the actual smoke test, just to see if it works..it did).

I'll have to get a sealing bladder to keep the smoke in (unlike Lucas Electric equipment, famed for letting the smoke out, haha). That'll add another $25+ to the $101+ I bought the tester for (Black Friday deal, plus I got Amazon to throw in $25 credit, due to the fiasco caused by my previous two tester orders...it was a differnt brand). So, in all, I will have spent $101 for the good tester + $25 for the sealing bladder I'm ordering, minus the $25 I was credited...equalling $101 for the complete test outfit I'll use.

Of course, the same tester is up to $120 now, + $25 for the bladder ($145 total), but that doesn't include a compressor at home (which I would assume most of us DIY'ers have, mines a Husky 20-gallon), but I'm not adding that into the cost to test. If one doesn't have a compressor already, Autoline offers the same tester, but it has a small air supply attached, for another $10 @$130 (bringing the cost to test up to $155).

So, why didn't I get my BMW tested at a pro shop?

• 1) there are no BMW Indy shops within 40-50 miles (except for one that is a glorified tire shop/ricer shop),
• 2) the two local shops I went to last year (general mechanics) quoted me $150 and $160 for a smoke test, and
• 3) I have five old vehicles that need maintenance off & on, including emissions and engine bay smoke tests (I've had to redo several Evap systems at home, had to test & replace leaking gas caps, too, and now the intake smoke test on the X5); whereas I used to have a friend, back in the day, that had the gear at home, now I will, so I the gear I've bought should pay for itself several times over.

I could be wrong, and might never find any leaks, nor have to repair Evaps again, but at least I'll have the gear, which I can pass on, later, to friends or relatives.

Some less common air/vacuum leaks on the M54... one or sometimes two small vacuum caps on the rear of the intake manifold; they split and fall off. The tubing/vacuum valve that controls the secondary air pump is also back there. Dipstick o-ring where it enters the oil pan. The vacuum tube leading to the fuel filter/FPR splits; this leak will only be visible under the car. Any/all of the CCV hoses can crack.

I have a $50 smoke tester; the paint gun+regulator type and it works great to find leaks.

For sure! Mine had two with real back cracks. I'm surprised it didn't set any codes.

+1 for "paint gun+regulator type" smoke testers
 

Since I was unsuccessful at sealing-off the intake tube, I was unable to keep the smoke flowing further down the line in sufficient quantities to spot any leaks. I was stuck holding the vinyl/rubber glove in place (before the eventual leak), so I couldn't move to look at the rear of the engine, the SAP system above the exhaust manifold, nor underneath the truck at the fuel filter/FPR system.

I also couldn't see down to the dipstck O-ring connection, but I had a close look at the DISA, ICV, intake manifold (with the cover still on, unfortunately), and the flexible air intake tube, and saw zero leaks. I did say that I had 10+ minutes of smoke before the glove split, but that was probably closer to 3+ minutes, in actuality. Not enough time or smoke for a detailed exam.

I'm pleased with my Autoline $100 "paint gun+regulator type" smoke tester, used in conjunction with my 20-gallon air compressor, but the 4-mil Nitrile gloves just weren't working well enough in this application; a purpose-built "Universal Bladder Adapter" should solve the sealing problem. I will still have to remove the cowl cover. though, to be able to adequately view the rear of the engine, especially the two caps and the SAP vacuum control valve back there..

You can double/triple the glove


Sent from my iPhone using Tapatalk Pro

The openings wouldn't stretch far enough, being medium size (as both my wife and I use them); maybe large size gloves might've worked (if doubled). I'm ordering the Bladder Adapter today, so the gloves won't be needed.

Oh I must have had bigger gloves mine worked great


Sent from my iPhone using Tapatalk Pro

Same; I buy L/XL in 6mil; stretch it over the MAF, cut off the pinky tip and stuff the smoke hose in it secured with a small zip tie.

Just looked at OP's MAF reading... 52kg/hr at idle?? I'd expect 11-16kg/hr.

I think that was at "cruise". When he buttoned off it dropped pretty quickly to around 20kg/hr and still dropping....

The fuel pressure readings are close enough to spec that I do not believe it is a factor. I don't think volume is to blame either because under wide open throttle there'd be a steady decline in pressure as the engine consumes more fuel than the system can supply. This is what happened when my e30 had a failing fuel pump; idle and cruise pressure would be fine but would drop 15-20 psi under load. Even at 15 psi below spec the e30 would run decently, just down on power. It doesn't make sense that the X5 would fall completely on its face with 50 psi fuel pressure at the rail. As far as the fuel pressure drop when the pump is shut off, this was because the tester fitting leaked the whole time the system was pressurized.

Vacuum leak(s) seem more likely now. There was a suggestion to have a shop run a smoke test but I am more confident in my efforts and attention in finding these leaks than our local indy shops. I have ordered a self-powered smoke machine that puts out an advertised 6L/min @ 19psi which is significantly better than the cobbled-together thing I borrowed earlier. I've also ordered replacement DISA O-rings from G.A.S.

Now to find an enclosed garage to work in or wait for a dead calm wind day - both rare in Hawaii. Will report back.

I didn't upload the whole video but yes MAF reading drops down to ~14 kgh at idle.

You can use a big tarp over the hood to calm the wind for smoke testing. I've done similar when I had a 40' ladder on the roof worked perfectly to hold the top over my head but it's a thought vs. using a garage if you can't find one.

The fuel pressure should drop (to the regulator setting and then hold) when the pump stops because of the way the syphon jet system is plumbed in. As long as you are confident that the pressure will stay up under a full load (throttle and rpm) and you are not getting fooled by the gauge connection (happens more than you would think) then you can rule out the fuel system. It was the first thing that needed to be looked at especially since all the trouble started with work being done. Are codes coming back? is the bog and miss consistent ? An all of a sudden vacuum leak bad enough to cause that much trouble and not be obvious is a tougher sell for me. Maybe the CCV or brake booster ?? Have you driven with the maf disconnected (before starting engine) ?

better than no garage at all
 

I've considered buying a portable shelter for working on my cars & trucks, four of which have to be left outside the 3-bay garage.
Attachment 83997Attachment 83998

Presently, bay 1 (with a manual single roll-up door) holds my home-built camping trailer plus automotive equipment; bays 2 & 3 (together, sharing the big automatic electric roll-up door) hold home repair & yard-working tools & mowers on one side, the wife's Lexus in is the middle, and there are antiques & spare furniture (all covered) on the other side. That's why I haven't been able to put my X5 into the big spot, where the Lexus lives, yet.

I work on my vehicles outside in the wind (it's always windy, with sand & Oak tree debris tossed in), and I've tried using a 10x10 Ezy-Up canopy for covering a car when I've got it apart, sitting for more than a day on my work station (3.25 sheets of 4x8x 3/4" thick plywood, over a sand & gravel base).
Attachment 83999

That hardly works to keep the summer sun off, much less a light rain, and there's no effect on the wind. I worked on my wife's old Cobalt, off and on for three years (mystery brake problem), using up two canopies that were destroyed by heavy rains. I'd never leave another canopy up for long, as destruction is inevitable.

A stronger-built portable 12x20 garage shelter would've been better, especially with sidewalls blocking the wind. I'm still considering getting one, if I ever have another maintenance problem lasting for very long. I think the Lexus will get parked under the portable garage, since the feral cats might get into an open engine bay outside, but not a locked & sealed Lexus.

We use a similar tent for our cook tent for our big annual family reunion. It would work well for car repair and you can take the canvas off when not needing just leave the tent poles up.

A really bright flashlight helps too. Check the DISA diaphragm to ensure it's holding vacuum. And remember, when you find "a" problem, it might not be the only problem. P0171/P0174 are almost always large air leaks; but they might not be big enough to cause drivability issues; so thee might be something else fishy.

I found a place to do a breeze-free smoke test. The local mall's parking structure has a section that is rarely used and out of the way. The smoke test revealed one split on the intake boot small elbow. The split is relatively small and I don't think it could cause the heavy bogging and no power conditions.
So I tried this and the engine immediately ran better. No bogging and the power was back, all the way up to redline. The best it has run in months. I cleared the codes, did a couple more drives and the only code that came back was P0102 for Mass air flor sensor.

Due to only finding one small vacuum leak and the engine running fine with the MAF disconnected, I believe the MAF is failed. Which is confusing because there was never a fault for the MAF and it's live data seemed to indicate it was functioning.

Nevertheless, this is the strongest diagnostic test result so far. I'm planning to buy a new MAF and intake boot. But before I buy, is there anything I'm missing out on or not considering?



Smoke test machine notes and lessons:

The $70 Solary smoke tester from amazon worked pretty well. It lightly pressurizes the system and makes plenty of smoke. The included rubber cone fitting was too small for the intake boot. I tried using a funnel duct taped to the boot but it would not seal no matter how much tape was used. The smoke pressure easily pushed past the tape, filling the engine bay with smoke. I then got a pvc plumbing cap and 1/8" brass barb from the hardware store and it fit and sealed.

Something I realized about using a pressurized smoke machine is when it reveals a leak smoke pours out and quickly fills the engine bay with smoke. This makes it difficult to see any other leaks, especially ones that might be smaller. So after the intake boot is replaced I'll do another smoke test to make sure there's no additional leaks.

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Need help with bogging and misfires, persistent P0171 & P0174 lean DTCs
 

MAF sending incorrect data will cause either rich or lean codes there's no feedback to know it's the problem. The car will assume MAF is correct and do the math wrong for how much fuel to add.

Don't cheap out on the boot. I bought a knock off boot not to be cheap but for fast shipping and the fake copy had ribs around the small tube but it wasn't actually corrugated! So it wasn't flexible and kinked!

Of course I didn't realize until I already cut the old one in half to remove (the house clamp installed at the factory was blocked by itself and not accessible.

Cordless leaf blower would work wonders to blow smoke away to keep looking for other leaks.

Wow! Y'all want to make me smoke mine out of curiosity. I replaced several parts during a coolant refresh. It's the intake seams I'm worried about. Luckily, I have a lead on a good replacement.

The last time I had intake leak was the giant gasket on the disa valve. I just wrapped with a couple wraps of oatey fastape Teflon. (my go-to because it has a built in indicator: it's gray and turns black under pressure). Test fitting will reveal if you have enough. I used once to stop a leak at the lower radiator hose temp sensor. I bought o-rings to fix it proper but in the 3.8 years after the temp repair it never leaked. The bag of o-rings outlasted the car.

The DME will usually not set a code that points directly to a MAF because there are too many variables involved. DIYers often think that codes point directly to a part that needs to be replaced which is not true. Mixture codes are usually thought if as "oxygen sensor" codes but they are valid for anything that might be affecting the mixture including the MAF.
The only way to rule out a MAF is with a known good unit.
DO NOT buy a cheap MAF.

Best example for me as it happened with 3 of the 4 cam sensors on our two m54 motors. Never have I ever gotten a cps related error it was always some performance issue like random misfire combined with a certain type of stall. It would be amazing to have error pointing to the exact part.

If you haven't tried yet, rapping on the MAF with your knuckles will sometimes reveal (engine stumbles) a bad one, this does not rule out the MAF if the engine doesn't stumble though.

I took all that apart to replace the starter last week, and found that the numerous gaskets and grommets were all showing age. I am actually ordering most of them to replace because I've fought the same AFR codes in the past and those are some of the few things I haven't replaced. I agree with 80stech on the MAF... I am hoping not to have to buy a brand new one but eventually it is probably in the cards. If only to make sure it works.

I plugged the MAF back in and it ran like crap immediately. Then I tapped and knocked on it a few times but no change. At this point I'm still pretty sure its the MAF.

I have a Febi Bilstien intake boot in my FCP cart, but not sure which MAF to buy. Any recommendations or experience on these options?

Bremi $114 FCP
VDO $193 FCP
VDO $295 Turner (not sure why its more expensive at Turner)
Hella $88 Turner

I got the VDO from FCP. Sadly the car was killed by a deer within a year I wish I'd have thought to swap it back in still had the original.

SOLVED: MAF was at fault.

New intake boot and MAF arrived from FCP. Installed the intake boot, performed smoke test, found no additional leaks. Started engine, still ran terrible.

Installed new VDO MAF mass airflow sensor, started engine, immediately ran better. I have driven about 100 miles on since the MAF replacement and no MILs or drivability issues to date.

Conclusion: even if there are no codes for MAF and the live data seems to be responding correctly, the MAF may still be at fault. Disconnect the MAF before starting the engine, then drive the vehicle. If there is a change then the MAF is likely at fault. Thanks 80stech for the tip.

good for you updating your fault. too many forums out there, always a hit and run and never come back to update.

Cheers! :thumbup:

This CAN indicate a bad MAF...but a vacuum leak is more likely if the car runs better when unplugging the MAF..


Happy to see you fixed it and thanks for coming back to post a follow-up...

Yes, the conclusion isn't really accurate but good to see it fixed and good to see the follow- up post! ;)