4.8is intermittant loss of power while accelerating
 

The 4.8is started doing this yesterday while applying light throttle at stop lights to reach about 45 mph. It's not consistent and does it at odd times. It did it twice yesterday and today it did it while cruising at about 65 on the highway. It's not constant. No CEL. Some folks have mentioned fuel filter, fuel relay and fuel pump. Someone even mentioned the IVM. What are your thoughts?

Always test a few things before you go throwing parts at it.

Fuel pressure testing is QUICK and simple. Test is for VOL and Pressure
Take a peek at the coil tops. Burnt?
Pull all the codes not just the P codes!

I'm going to pick up a pressure tester today. What should the pressure be at the rail?

50/55 psi

I use this one
https://www.amazon.com/OTC-5630-Fuel...ef_=ast_sto_dp
REV X E85 Super Tester Reusable Ethanol Testing Kit - 5 oz
I also use this as way too many drivability issues are trash fuel. Cheap $12!
Background: Had a dealer once play stump "Mr Wizard" by giving me a multiple comeback car with 1/2" pile of service receipts all around poor performance. Scope showed poor cyl to cyl balance under load with multiple cylinders randomly involved. Fuel delivery (Injectors/pump)? Ignition (coils/Plugs)?, Fuel contamination? Pulled a sample of the fuel to show that the car had 33% water/alcohol mix in the tank. Somebody put it in there either at the pump or his neighbor hates him! :dunno:
Drained the tank, added a can/bottle of injector cleaner, added 1/2 tank of quality fuel. Presto change O, problem gone.

I now live by the "test the fuel FIRST" approach for hard to find drivability issues.

Many thanks! I'll let you know what I find. :)

Bentley Manual says
Idle 36.3-46.4 PSI (system pressure)
Engine off 50.76 =/- 2.9 PSI (Residual pressure)

I'm gonna run the test after dinner. :thumbup:

The tester I bought sucked. It essentially leaked gas out at the gauge. Everything was tight. It's going back to the store tomorrow. I ordered the one you recommended and it'll be here tomorrow.

Yep the cheap ones want to see 5-10 psi from a mechanical pump, not 55PSI from a electric pump. Wait until you see the newer cars with 2200 psi direct injected units.

Or an oil-burner with 26,000psi!! :yikes: :D

The OTC came in today, basically the gauge with a hose and an adaptor. I had to use the adaptor, however, nothing shows up on the gauge.

:banghead:

Does the car start? Can you feel pressure in the hose when you connect it? You should be able to test on a tire. It should measure air pressure as well as fuel.

So, the gauge worked after I checked the adaptor. Only issue is it pissed fuel out all over the engine again. Luckily i caught it quick and shut her down. Also as a side note, the problem I experienced twice on the one day has stopped happening. I'll just change the fuel filter, since it's an overdue item.

Fuel filter can last a half million miles. I'm not aware of any replacement schedule. That said, other than loss of power have you has other symptoms like hard start after a while not using?
I ask because I replaced my wife's fuel filter after I did some measurements that indicated the FPR was shot only to discover post mortem that the o-ring bwtween the FPR and filter was shot.

If you have another car to drive take off your old filter and remove the FPR you should see a small o-ring that is most likey flattened out and stiff and no longer functioning. It is what I observed when I replaced my wife's.

I cut the old filter in half with a band saw to look inside and it to be sure war was filthy at 180,000 miles but I would rate it perhaps 1/2 to 1/3 consumed. It definitely did not need to be replaced and I saw no sign the FPR was defective either only the o-ring bwtween them.

The test i used to confirm the problem was to test the fuel pressure at the rail and leave overnight. I watched the pressure drop ten psi before an hour had passed and by morning the pressure was basically zero. After replacing the FPR, the pressure stayed over 30psi overnight.

The hard starts evaporated as well as the random power blips e g loss of power on freeway onramp.

No, no hard start issues on the 4.8iS. It has the "comfort start" feature, so I just flick the keep and it cranks over. Once in a while it's slightly "extended" but by no means a hard start.

https://uploads.tapatalk-cdn.com/202...8f6cf9e25c.jpghttps://uploads.tapatalk-cdn.com/202...eaa1464887.jpghttps://uploads.tapatalk-cdn.com/202...730750471f.jpghttps://uploads.tapatalk-cdn.com/202...a62832f5d8.jpghttps://uploads.tapatalk-cdn.com/202...5a000bd9f6.jpg

BMW sources a couple different vendors so this is just one possibility. Put your fuel gauge on and start the car. If the needle vibrates around an average of 50 vs. dead stable sign of o-ring leaking.

Then let it sit overnight. I forgot the numbers I had but before was zero psi overnight after was 20-30 psi overnight. If psi drops below say 10 overnight the o-ring is leaking between your FPR and fuel filter. Unlikely three FPR broken or the filter is plugged enough to be a problem.

So here's the saga, was driving the X the other day and it started doing it quite frequently and continuously above 65 MPH. It through a code for fuel adaptation lean. Since I've been busy with work lately I just took it to my indy. Checked the fuel trims were lean. After some more testing he changed the fuel filter, and the trims were perfect and no more bogging down. Attached is a pic of what was coming out of the filter. Just glad that it's over and it only cost me $60.00.

https://live.staticflickr.com/65535/...cfebc97b_b.jpgIMG_5244 by Al, on Flickr

I cut wife's fuel filter in half to post-mortem and similarly black as soot.

Other side cristal clear though. Turned out to be just an o-ring that failed but for $60 I wasnt about to out the black as sin filter back on.