1989 e32 750iL miss-fire

[7e32]

Hi,

I think i am getting a miss-fire.
Symptoms are, when the engine is running the car shakes even when standstill.

Car was serviced about 8 months ago, so had oil, oil filter, coolant/antifreeze, fuel pumps, sparkplugs, air filters, coil packs, rotors and arms changed.

The only thing that was not changed was the HT leads as i could not find a decent price for a direct swap/replacement.

Could this be related to the HT leads? If so, how can i diagnose this?
Or maybe a vacuum leak somewhere? If so, how can i diagnose this?

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[shogun]

To check the HT leads and fuel injectors is relatively easy. Remove the sound absorbing cover on top of the engine. Let engine run in idle and the remove the connectors from the fuel injectors one by one for a few seconds and re-connect. If idle changes when one is removed = that one is o.k., if nothing changes, then tht one is defective. To remove the FI harness plug push the metal clip down to release and then pull, do not pull out the clip, some people do it the wrong way and lose clips, here is a pic of such plugs
http://napolperformance.com/4-rc-fue...l-obd1-gm.html
Same test do with the ignition wires as the next step. When one is removed, idle/running condition should change, if nothing changes, that one is bad. I have for the spark plugs and wires an inline spark tester, costs abt. $10, quickly diagnoses problems with all ignition systems , just cnnect the tool between the spark plug and the plug wire, then you can see the sparks, here you can see it working on a gardening tool https://www.youtube.com/watch?v=eQBtzk-dGYM
Here you can see some bad ignition wires on a 750 and he installed my ones then http://www.bimmerboard.com/forums/posts/767718/
Note: never pull on the HT lead, that can damage the lead, pull and wiggle and twist on the boot. There are also Spark Plug Plier Boot Removal Tools available.

You can also measure the ignition wires and other parts
M30/M70 ignition system data accdg to Bentley
Coil primary, coil code # 2051118335 terminals 1 (-) and 15 (+) resistance 0.50 ohm
Coil primary, coil code # 20510171101 terminals 1 (-) and 15 (+) resistance 0.37 ohm
Coil secondary, coil code # 2051118335 terminals 15 (+) and 4 (ctr. resistance 6.0 kohm
Coil secondary, coil code # 20510171101 terminals 15 (+) and 4 (ctr. resistance 9.0 kohm
spark plug ends 5.0+/- 10% kohm, shielded plugs 1.0 +/- 20% kohm, spark plug wires 0 ohm (approx.) = so intotal around 6 kohm
rotor 1.1 +/- 10% kohm

M70 firing order: 1-7-5-11-3-9-6-12-2-8-4-10
crankshaft position/rpm sensor:
540+/- 10% ohm

from workshop manual
distributor rotor 1+/-20% kohm
angled/shielded connectors 1+/- 20% kohm
spark plug connectors 5+/- 20% kohm
cylinder identification sender coil resistance at 20 degree C (68F) <1 ohm
pulse sender/crankshaft position sensor coil resistance 540 +/- 10% ohm
temperature switch for e-box cooling E32 750: switch on at 44 +/- 3 degree C, switch off at 36 +/- 3 degree C.

Ignition wires for DIY I have on stock, see E31 8 series forum my thread FS Ignition wires for M70 and M73 engine. Maybe you can also get something in the U.K., cheaper for shipping and no import duty.

Vacuum leaks testing: remove the engine sound absorbing cover. Let engine run in idle and spray some starter pilot or brake cleaner around the intakes and pull/push the intakes up and down. If idle changes, there is a vacuum leak.

[7e32]

Thanks, will give it a go

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[unity]

If you go with new crank position sensors, go OEM. People have complained about other brands. I went with the second best to OEM and have an occasional EML failure. Once in a while I may even notice a slight miss, very minor, a couple times before it goes into limp mode. I still have not setup the laptop to diagnose the EML code. But a miss-fire form spark or injector would typically not result in such a sensitive fault being caused. So I suspect I have to replace my crank position sensors again, not an easy project. In your case, I do suspect fuel/spark issue though. It could even be the O2 sensors. I had a rather bought idle at times, especially after cold starts, that new Bosch sensors too care of.

[shogun]

some info on spark plugs for the M70, copied from the E31 forum:
My 1991 850i/A is having an odd running problem. I recently replaced the spark plugs. The NGK dual electrode ones were very worn and I had a set of 12 Bosch copper FR8LC+ I swapped in. Since then when I start the car it runs with super low power, feels like one bank for the first 3-5 minutes of driving and then goes back to regular function. Wondering if this is related to the spark plugs or something else? No check engine light or eml light occurring.
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wrong resistance plugs... big time wrong. Should be Bosch F8LCR or NGK ZFR5F. The Bosch F8LCR's have been extinct for a decade... the F8LCR2's are NLA too.The BEST replacement plugs I have found - that truly are 1k resistance - are the NGK 2288 BKR6EK plugs. Funny dual electrodes, but they work flawlessly. The NGK ZFR5F plugs are still 5k resistance and will cause aging ignition components to complain, often resulting in no pulse generator signals at #6 & #12 and random misfires.