Author Topic: Runs GREAT until it warms up ????? (Read 5707 times)

Justonegear · « **on:** January 01, 2010, 10:17:10 PM »

Hey Guys, need some help. 91 318is, 98K, Runs fantastic until it warms up and then it runs bad on acceleration. Already replaced the 02 sensor, fuel filter, plugs, did the under intake drill to cover all the vac hoses. Ran the stomp test, no codes, tested & cleaned injectors, cleaned intake ports. Still no improvement. Anyone have any ideas, BTW, thanks for any help.

KenC · « **Reply #1 on:** January 02, 2010, 01:13:08 AM »

Fuel Pressure Regulator?

Have you reset the ECU?

Justonegear · « **Reply #2 on:** January 02, 2010, 06:36:08 PM »

Would the Fuel Pressure Regulator only act up after the engine is up to temp? thanks

Justonegear · « **Reply #3 on:** January 11, 2010, 06:28:38 PM »

Still running poorly after it warms up. The thing runs great for the first 3-5 minutes, then it tanks. Almost like it's choking out or starving for fuel. Any ideas.

1991 318is 98K , No codes,already replaced, 02 Sensor, fuel filter, Crank sensor, Cam sensor, Coolant temp sensor, checked fuel pressure, cleaned intake and injectors, new plugs, cleaned up the Vacuum hose mess under the manifold, cleaned air filter, compression test was good, prayed and lit a candle several nights in a row..

Thanks for any help.

DesktopDave · « **Reply #4 on:** January 11, 2010, 07:42:34 PM »

Did you try the fuel pressure test when the car was running poorly? I'm sure you did, just thinking out loud...

There is the intake air temp sensor in the AFM...it's a long shot but worth testing. Could also be a coil or plug wire that's dying a slow death when it's overheating. Those would likely set a code though...very mysterious problem. What mechanical system changes when the car warms up? Thermostat?

Do the sensors perform according to Bentley specs?

Justonegear · « **Reply #5 on:** January 11, 2010, 07:55:45 PM »

Would the Thermostat cause this ? I'm looking into the coils now, If I raise the RPM's very slowly it will almost run fine, but when you try to accelerate fast it stumbles, coughs and shakes. Strange thing is often when I raise the RPM.s over 3000 it will clean up and run well... although this can even be irregular.

92BMW318is · « **Reply #6 on:** January 27, 2010, 01:23:30 PM »

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Justonegear · « **Reply #7 on:** January 28, 2010, 07:33:11 PM »

OK, replaced the AFM, TPS, ECU and the coils, no change. However the car was up to temp when I swapped the ECU and it ran perfect for a few minutes then right back to normal as in running poor. Any other thoughts ?

DesktopDave · « **Reply #8 on:** January 28, 2010, 07:54:13 PM »

Can you test the timing when it's hot? I don't know what it should be when the car is warmed up...

Odd that it'd keep doing this even when mostly everything else has been replaced.

Justonegear · « **Reply #9 on:** January 28, 2010, 09:14:11 PM »

Test timing when it's hot?? if it is possible to do I should be able to do it. I have new plug wires to put on this weekend, don't think that's the prob. I'm about ready to take it to the shop. It's crazy that something somewhere is sending a code to the ECU to retard the timing or something to cause it to run bad

??

flyinglizard · « **Reply #10 on:** January 28, 2010, 09:23:45 PM »

temp sensor?

Justonegear · « **Reply #11 on:** January 28, 2010, 09:39:13 PM »

it acts the same with or without the temp sensor connected, and the coolant temp sensor was replaced.

Choking Hazard · « **Reply #12 on:** January 28, 2010, 11:11:17 PM »

http://www.m42club.com/forums/showthread.php?t=7757&highlight=catalytic

Look at the post from sports.racer
I realize that is opposite of your problem, but pretty easy to try out anyway.

DesktopDave · « **Reply #13 on:** January 29, 2010, 07:11:35 AM »

Quote from: Justonegear;86014

Test timing when it's hot?? if it is possible to do I should be able to do it. I have new plug wires to put on this weekend, don't think that's the prob. I'm about ready to take it to the shop. It's crazy that something somewhere is sending a code to the ECU to retard the timing or something to cause it to run bad ??

I suspect the DME isn't setting a code because a bad sensor is still close enough to spec. Not sure which one. Testing the current off the o2 sensor would let you know if the car is lean or rich.

Testing the timing (with a cheap timing light) would get you the same result...finding out if the car's timing is still retarded for cold start or advanced for hot running.

flyinglizard · « **Reply #14 on:** January 29, 2010, 08:22:36 AM »

AFAIK, all motronic, advances the timing and goes full rich upon cold start. As it warms up, the fuel drops, to run off of the O2 sensor, the timing goes to closed loop, . Some things to look at from a diog shop point of veiw. 1 Is the temp signal valid?? Do the wires go to the thing?? Does disconnecting it make it change run quality? If it runs the same when you disconnect it, it,or the wiring , is not working.
2) Are the injectors clean? As the ECM goes to full lean, the injectors spray very fine fuel mist. Shitty ones quit, or shoot off to the side. At WOT the injector spray pattern problem will fade. WOT is more of a function of quantity.
next) bump the plug gap down to 015. As wires get weak, they look for places to jump. as the gap gets wider, the cross over voltage gets higher and leaks acure. The crossover voltage is highest at max torque, due to the sweet spot of cam timing, fuel load, exhaust lenght, etc. Usually about 3600 in these M 42 cars.
MM