Loss of Power

#1

I have this problem were I seem to lose power after about 4 or 5 laps on track. In losing power I mean most likely torque. The car take longer to raise the RPM’s and the shift points move farther down the track. Lap times drop a little as well. There is also a large dip in the torque curve at the 4500 RPM range. This is what has been done to date:

New fuel pump
Replaced O2 sensor (not sure I got the white wires hooked up right or if it matters)
Swapped AFM
Swapped ECU
Tested Coolant temp sensor
Tested TPS

Car seems to run better without the O2 hooked up but still loses power after the 4 or 5 laps. Fuel pressure seemed to stay constant at about 42-45 PSI with the adjustable fuel pressure regulator.

Today I was thinking that maybe the coil is heating up or something but am really out of ideas and hate to just order a bunch a parts hoping to fix the problem. Any ideas??

Thanks,

Michael O.

#2

Michael - I am sure someone with more experience will weigh in on this for you. Bentley suggests several things as possible culprits, beyond what you have already done. 1) suboptimal/clogged fuel injector, and 2) an intake air/vacuum leak.

I had a 240 z that had a coil issue when it got hot, but it was much more dramatic than what you are noting - missing badly, cutting off, etc.

Best of luck,
Ed

#3

your mention of wires for the O2 sensor have me wondering if you bought aftermarket? Mine wouldn’t idel right with the aftermarket that was in the car and the major supplier of OEM for my shop offers generic but not for 325’s. I am sure there is a reason.

I’m no BMW expert, but I’ve heard of the "dip" from several other competitors at the track.

What year car? You mentioned fuel pump, but what about the filter, regulator and damper? Also, do you ahve the later car with the single pump or do you also have an in-tank?

#4

For the O2 sensor I went to Advance Auto and picked up the least expensive 4 wire Bosch O2 they had and cut off the harness and spliced on the BMW harness. There were two white wires that I think feed the heater and I don’t think it matters on which one goes to which one.

I assumed that all Bosch O2 sensors were the same and it looked just like the one I removed. The loss of power happened even with the O2 not hooked up.

The car is an '88 and has only one fuel pump in tank. The fuel filter is new as of April when I built the car. I have an Adjustable fuel pressure regulator and I don’t think there is a damper on any of the lines. Fuel pressure may be adjusted a little low as it is around 43 at idle but don’t remember for sure.

Michael

#5

That sounds exactly like the problem I had, though I saw it on the first lap. The cause turned out to be rust in the fuel tank collecting on the inlet screen and starving the engine of fuel. Except for the fact that you say that say that the fuel pressure stays up when this happens (I presume you have a live gauge) I’d be inclined to say that you are having the same problem. Are you sure that the fuel pressure doesn’t drop?

#6

Well, on the dyno the pressure did not drop but the guage is under the hood. I will take a look at the pump and filter just to make sure. When I replaced the pump the old one did not show signs of rust building up on the inlet.

Michael O.

#7

check your cap and rotor.
I had the same problems and after a new fuel pump, coil, plugs and valve adjustment i figure it out.