1990 bmw 520i missfrie problems E34 M50

[rbooth]

Hi i am new to this fourm i hope you can help me

I have got a bmw 520i E34 M50 engine when the car is idleing it is a bit rough but when you try and set off it missfires and pops (backfire) i have changed the plugs and it was ok for about 50 miles then it started again?? but is ok far up the rev range???


i have got a multi meter and tested the lamba sensor and the volts just stay the same 0.5 i think?? (is this right)

i have just tested the coil packso tonight by tring to mesure the resistance and it just comes up -0.521 then jumps to 0.825 ect it is all over the place is this right

It only use to do it when warm but it is starting to do it cold now ????


Please help!!!!

[gatman187]

I have a very similar problem on my 520i M50 e34 1991, i haven't had a chance to check the risistance of the coil packs yet but suspect its either the MAF or a faulty coilpack, so if anyone can help us both, please

[Big Evil]

Multimeter is not going to help with the O2 sensor (LAMBDA). That requires an oscilloscope which has a much faster refresh rate than your meter, or use of a scan tool.

The resistance on your coils however are not right. You SHOULD get a solid reading. If the meter display is walking around then you have an open....that's bad.

The MAF won't cause a hard misfire, it would cause crappy idle, hesitation, and crappy fuel mileage across the rev range. Not saying that it ISN'T your problem but with the reads on the coils, its NOT LIKELY your problem.

When you ohm the coils out you're are unplugging them and removing them from the car? (totally isolating them) If you're getting those reads then I'd say its time for a trip to the salvage yard with your meter and find some replacements. Then see what's what.

[gatman187]

Nice one big E, a good place to start the investigation, i have to say with my car its defo worse first thing in the morning but even when warm the problem persists more in the lower rev range and is a bit intermitant at highter revs..what should the readings be on the coil pack, is 0.8ohms correct?

[Big Evil]

Not positive on the spec (you can probably find one in a service manual), best bet is to compare the readings of several coils to find consistency. Those values will change with temp, heat increases resistance. Cold contracts the metal and can enlarge and open in a coil. Worse when it's cold then rough when its warm. Good bet that's what you're looking at

[gatman187]

Right ok so i sorted the missfire it was the coilpack!! i found out that the spec is 0.8ohms across the two outer pins, but, when i measured all the coils, the risistance was correct. So i fired up the engine and started from the firewall uncliping each coil connector inividualy, one after the other listning to the engine and it was number two coil missing and it was indeed the windings, the inner windings typical.....still she runs like a dream again thank god!! thanks for all your help

[Big Evil]

Nice job