Losing power at 2500 rpm. Help please.

[Vdubmt]

I picked up this 87 325e 5speed a few weeks ago and it's driving me mad.
History- After I picked it up I had the timing belt and water pump changed. After they did that the tech said that he test drove and noticed a missfire. When he pulled one of the injectors he noticed it was clogged and looked like rust was in the gas. He replaced one plug, the fuel filter and sent all of the injectors out to be cleaned and rebuilt. The car ran fine for the little bit that I drove it in the last two days.

Current problem- I started the car up and drove to the store fine with no issues. On the way home as I was driving the car started to bog out around 2,500 rpm. It happens through out all of the gears. Feels like as once it hits 2500 rpm it's not getting any fuel at all. I limped home like that and with the car in neutral it revs up to red line. Why would it rev high in neutral but not go past 2,500 in gear? Could it be an air leak? Possible the fuel pump?

I've done searches and have seen people with the same issue but can't find any solutions in any of the posts. Please help if you can. I love this car and just want to drive it which I haven't been able to do since I've bought it. Thanks.

[bloodsnot]

Current problem- I started the car up and drove to the store fine with no issues. On the way home as I was driving the car started to bog out around 2,500 rpm. It happens through out all of the gears. Feels like as once it hits 2500 rpm it's not getting any fuel at all. I limped home like that and with the car in neutral it revs up to red line. Why would it rev high in neutral but not go past 2,500 in gear? Could it be an air leak? Possible the fuel pump?

Short answer is yes, it could be an air leak. Look up the engine->vacuum control diagrams for your car on RealOEM.com and go check all of the hoses on your car for old, hard, brittle rubber and for cracks. You can spray carb cleaner around the fittings as a secondary check or do a smoke test to really rule out air leaks.

I don't think it's the fuel pump because the fuel pump load doesn't vary with engine load on these cars. The system is pressurized by the pump and the variations in fuel demand are handled by varying the timing injector pulses.

It still very well could be a fuel issue and with your mention of poor flowing injectors I would say it's likely that the fuel filter change was long overdue so your entire fuel setup is suspect. Perhaps the fuel pressure regulator on the end of the fuel rail is on its way out.

I would start by testing the fuel pressure by t-ing in a fuel pressure test gauge right before the fuel rail to see if these power loss issues correspond to drops in fuel. You should be able to get the test gauge to rest near the wipers with your hood closed so you or your navigator can watch it while you drive.

If this problem doesn't seem to be related to fuel pressure then I would look to the air flow meter or ignition components such as spark plugs and wires amongst various other things. Do you have a Bentley manual? There are some thorough troubleshooting guides in there.

[bmwstudent]

Check or replace fuel filter, engines require a lot more fuel accelerating under load than they do just revving with no load.

[Vdubmt]

Thanks for the replies. The fuel filter was replaced three days ago while the injectors were cleaned. Does make sense though that you would need more fuel under load than in neutral.
I'm going to try to poke around under the hood tonight when I get off of work to see if I notice any vacum lines that are obviously leaking. I forgot to mention also the external fuel pump has been whining since I purchased the car but had been operational. When it was in the shop, they said that it should be for for a while. I was thinking that it started to fail. I'm going to also probably just replace that even if its not the issue. It'll be piece of mind anyway.

[Andy348]

I had a very similar issue (cut out at 3500rpm) and was caused by rust in the fuel tank accumulating around the pumps and choking them when the car was under load. It was fine in neutral.

[Vdubmt]

I had a very similar issue (cut out at 3500rpm) and was caused by rust in the fuel tank accumulating around the pumps and choking them when the car was under load. It was fine in neutral.

Interesting. I know that the car had been sitting for a while and I'm assuming that's why the injectors were clogged up with rust. If I do not find any issues with vacum leaks, I think this will be where I concentrate. What did you do to get rid of all the rust. I'm assuming there is still rust in the tank. Should I drop it and have it cleaned. Is there a way to flush the lines out? Thanks for the help. I want to enjoy driving this thing and as of now its been a headache.

[Andy348]

An easy way to check is to take out your rear bench and pull out the in-tank pump. Using a flashlight and a stick you can scrape the bottom of the tank and see if the gas gets cloudy. My tank had rust both inside and outside so I replaced it entirely ($220). There are services that will coat the tank, though not sure what they cost.

Not sure about flushing the lines though.

[Vdubmt]

Did you pick up a new tank locally or order one online. I think I seen one on pelican but they wanted $700. I haven't really done any looking further than that though.

[Andy348]

Ordered one from autopartswarehouse.com. I got a replacement one (cheapest, ±$200) but coated it with rubberized coating beforehand so it didn't rust.

[Vdubmt]

Thanks. I'm going to check for vacum leaks and may just redo the whole fuel system even if that isn't causing this problem. Appreciate the help everyone.

[bimmerboy709]

check if your plug wires are arcing on your exhaust mani. That was my issue.

[Vdubmt]

check if your plug wires are arcing on your exhaust mani. That was my issue.

I will look for that. I haven't and probably won't have time to look at it until the weekend. I ordered a new fuel tank, pump, and fpr for it. The filter was changed and the injectors were cleaned and rebuilt last week. I'm hoping this will take care of of any fuel/rust related issues it might have. Also have an air intake boot to put on. When I purchased the car I noticed that it has electrical tape on the boot so I ordered one before all of this. I'm going to assume from the tape that it has a crack in it. Thanks for the replies. I will keep you posted in what I find. Any other suggestions, please feel free to chime in.

[bloodsnot]

Any other suggestions, please feel free to chime in.

Avoid throwing any more money at it until you've smoke tested all of the vacuum connections :)

[Vdubmt]

Avoid throwing any more money at it until you've smoke tested all of the vacuum connections :)

Still going to concentrate on vacuum. I had planed on changing out the fuel components regardless due to the rust that was found in the injectors and fuel rail along with the noisy fuel pump.

[etienne81]

Would second the recommendation to check the plug wires. I had a similar problem solved with new wires.