Early Model Fuel Delivery Problems

[davtbaum]

Hey Guys,

Backstory: This weekend I took my 87 325is out to an autox (its first autox, new owner :) ) and noticed that by my third run, WOT >5k rpm was causing the car to lose power. The motor wasn't stalling, but it would sit at 5k during WOT and slowly decrease RPM if held for more than 10 seconds. In the lower ranges, however, the car idled and felt normal.

Since then, I did some research and went out to test the fuel pressure coming into the fuel rail. The gauge I bought from Autozone was pretty shit and not accurate (it read ~1.5psi when teed pre and post FPR when I definitely had pressure), so I jumped the fuel pump relay for 30 seconds following this test: http://forums.bimmerforums.com/forum...-fuel-pressure (sixth post, Aleman). I only got 400 ml to spit out, with an inconsistent flowrate, so I assumed that it was one of my pumps.

So here's the thing, I've replaced both the inline and in tank fuel pumps and filter for this car right when I bought it 2 months ago. I can't imagine one of them has failed. I have however noticed that the inline pump has been noisy, and also changes pitch after the car is warmed up.

I have a couple questions:

Is it possible that my newly replaced inline pump has gone bad? Does the whine imply malfunctioning?

I haven't even considered the FPR - as the fuel pump test I performed wasn't cranking the engine, so the vacuum line wouldn't have been activating the regulator. In the case that the FPR was the culprit, could it have caused the low volume of fuel even though the engine wasn't cranking?

Edit: I just pulled the inline filter and bench tested it, it was pushing out fluid nicely. Also there are no leaks in the system that I can tell or smell.

Thanks for the help guys!
-David

[Golfer_705]

The engine must be running for your fuel pressure test. the gauge should be hooked inline before the FPR. Where your fuel line comes into the fuel rail is a great spot. Post FPR readings means nothing. With the engine running you should see about 44psi with the vacuum line removed from FPR and capped on the intake side. With the line reconnected you should see about 36psi. Both readings at idle. The fuel pump will not turn on with the key on engine off giving false readings. With the fuel pressure gauge hooked up you could always go for a drive and see if the fuel pressure drops off when you feel the engine loose power.

While replacing the intank pump did you see if the tank was rusty inside? If it was it could cause the intank pump to starve under WOT. When I purchased my car it had been sitting for a while and had a similar problem like yours but my engine would stall if I did not get off the throttle. It ended up being a rusted fuel tank.


The fuel pump
wine does not indicate a malfunction. It is common with externally mounted fuel pumps. That's a reason why new cars have the pumps in the tank as well as for keepin the pump cool.


Hope this helps to answer some of your questions!

[davtbaum]

Great help, thanks!

As of now I am almost 100% certain it is rust in the tank. I had another look and it is pretty bad, I can see a slight coating of sediment on the filter of the in-tank pump and rust on the siding of the tank.

I've found a really helpful post here by Jlevie 3rd post in

http://spece30.com/forum/43-fuel-system/48274-fuel-tank-replace-it-clean-it-or-let-it-ride

where he has described literally the exact symptoms on his 87is. The autox must have caused some of the rust to mix and clog the filter during WOT. Definitely going to replace the tank this week, and hopefully get some of that e30 power back :)

[Golfer_705]

Draining and flushing the tank is required for warranty of the pump. Surface rust is common, scally flaking is bad. You may be able to recoat. There has been 20+ years for crap to build up in your tank. You should drain your tank and pressure wash it out and see what you have. Double check your fuel pressure test. It would be a good idea to go for a drive. A FPR is $50 and maybe a few bucks to flush and recoat your tank vs guessing its the tank and throwing a hundreds at it. You already spent the money on the fuel pressure tester might as well take advantage of it.