BMW E38 740i misfire - Techwatch Support Forums: Digital & Satellite TV, FTA, Cable, Computers, Mobile Phones, Apple and General Tech Forums

delambo · 11-10-06, 10:12 AM

I was called to a garage to code a scondhand ECU to the vehicle. It was their diagnosis that the ECU was faulty, but now it has the same problem.

The car starts and idles ok. When it revs up there is a very slight misfire but hardly noticable unless you are looking for one. When you drive the car slowly it is all OK and drives well. When you get to 4500 rpm the mil light starts flashing and it has codes 57- multiple misfire detected, and 62 cylinder 2 misfire detected. If you back off the throttle staright away the light turns off and the car runs fine until you get to 4500 rpm again. If when the light comes on you keep your foot on the throttle the light stays on and it cuts the injection pulse to cyinder 2. When the injection pulse has been cut and you switch the ignition off and then start the car again, the car starts on 8 cylinders again until you hold it at 4500 rpm again. If you have a scan tool connected to the car when the ECU kills the injection pulse to cylinder 2 and you clear the fault codes it starts the njection pulse again.

I have swapped (one at a time) the injectors, coil, and spark plugs from number 1 to number 2 and none of this has "moved" the misfire to cylinder 1.

Question 1: Is the ECU supposed to kill the injection pulse if a misfire is detected or is this a fault?

Question 2: What could be causing the problem?

the insaan · 11-10-06, 05:32 PM

have you actually chenged the plugs over, it may also be worth checking the resistence of the HT leads as these can go faulty as well

jakeyfly · 11-10-06, 09:16 PM

Hi
yes ecu will switch injector off if it picks up an ignition fault, this is mainly to save cat failure

the breather on the back of manifold goes faulty causing your type of fault(think its called a cyclone), and allso any air leaks (pipes common) and sometimes maf aswell.

can you check your long term and short term fuel trim when fault is there, allso chech addaptions should give you an idea of fueling
cheers

11-10-06, 10:12 AM	#1 (permalink)
delambo Senior Member Join Date: Sep 2005 Location: infront of my pc Posts: 426 Thanks: 0 Thanked 15 Times in 6 Posts	BMW E38 740i misfire I was called to a garage to code a scondhand ECU to the vehicle. It was their diagnosis that the ECU was faulty, but now it has the same problem. The car starts and idles ok. When it revs up there is a very slight misfire but hardly noticable unless you are looking for one. When you drive the car slowly it is all OK and drives well. When you get to 4500 rpm the mil light starts flashing and it has codes 57- multiple misfire detected, and 62 cylinder 2 misfire detected. If you back off the throttle staright away the light turns off and the car runs fine until you get to 4500 rpm again. If when the light comes on you keep your foot on the throttle the light stays on and it cuts the injection pulse to cyinder 2. When the injection pulse has been cut and you switch the ignition off and then start the car again, the car starts on 8 cylinders again until you hold it at 4500 rpm again. If you have a scan tool connected to the car when the ECU kills the injection pulse to cylinder 2 and you clear the fault codes it starts the njection pulse again. I have swapped (one at a time) the injectors, coil, and spark plugs from number 1 to number 2 and none of this has "moved" the misfire to cylinder 1. Question 1: Is the ECU supposed to kill the injection pulse if a misfire is detected or is this a fault? Question 2: What could be causing the problem? __________________ If it seems too good to be true, it probably is.

11-10-06, 05:32 PM	#2 (permalink)
the insaan The Village Idiot Join Date: Sep 2005 Location: Burnley Posts: 1,616 Thanks: 136 Thanked 101 Times in 64 Posts	Re: BMW E38 740i misfire have you actually chenged the plugs over, it may also be worth checking the resistence of the HT leads as these can go faulty as well __________________

11-10-06, 09:16 PM	#3 (permalink)
jakeyfly Super Drunk Moderator Join Date: Oct 2005 Posts: 209 Thanks: 0 Thanked 0 Times in 0 Posts	Re: BMW E38 740i misfire Hi yes ecu will switch injector off if it picks up an ignition fault, this is mainly to save cat failure the breather on the back of manifold goes faulty causing your type of fault(think its called a cyclone), and allso any air leaks (pipes common) and sometimes maf aswell. can you check your long term and short term fuel trim when fault is there, allso chech addaptions should give you an idea of fueling cheers