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

[Scott ZHP]

Originally Posted by victell

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

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.

[victell]

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.

Originally Posted by 80stech

Have you driven with the maf disconnected (before starting engine) ?

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.

[andrewwynn]

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.

[X5chemist]

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.

[andrewwynn]

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.

[80stech]

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.

[andrewwynn]

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.

[80stech]

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.

[Bdc101]

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.

[victell]

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