M70 Banks cutting out on cold start

[derrith]

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.

[shogun]

Check the ignition wires and boots, etc. they must be in spec.
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.) = total 6kohm
rotor 1.1 +/- 10% kohm

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

[cartoonz]

wrong resistance plugs... big time wrong.

[rosakirk12]

wrong resistance plugs... big time wrong.

Yes should be Bosch F8LCR or NGK ZFR5F


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[cartoonz]

The Bosch F8LCR's have been extinct for a decade... the F8LCR2's are NLA too...
While I have 60 of them stored in my vault, you will not find any anywhere.
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.

[derrith]

Definitely installed 12 Bosch 7959 which resolves to F8LCR. Purchased via rockauto at $1 or so each. I'll go back to NGKs and hope that resolves the issue. Will follow back up.

[cartoonz]

NOT the same plugs. BMW & Bosch pretend they are, but the resistance is 5k, not 1k. Go back and use the dual electrode NGK 2288 BKR6EK's

[M6csi]

The Bosch F8LCR plugs are still available from BMW. Just bought 2 sets (24) recently. With discounts, they are approximately $10-11 each.

[cartoonz]

haha... NO, they are NOT the 1k F8LCR plugs...

[M6csi]

This is the merchandise.

[derrith]

Update! Replaced the wrong Bosch plugs with NGK 2288s. About 95% of the problem has resolved. Thank you.

I am still occasionally getting the car going into limp intermittently when cold. I suspect vacuum leaks and am planning to disassemble and reseal the whole top end. Valve cover gaskets are noticeably leaking so might as well.

[JDP530]

This is the merchandise.

I am pretty the R1 designation on body of plug denotes 1K resistance.

[M6csi]

Update! Replaced the wrong Bosch plugs with NGK 2288s. About 95% of the problem has resolved. Thank you.

I am still occasionally getting the car going into limp intermittently when cold. I suspect vacuum leaks and am planning to disassemble and reseal the whole top end. Valve cover gaskets are noticeably leaking so might as well.

From my experience on my coupe, vacuum leaks will result in bad cold starts, CEL coming on during fast idle during engine warmup (light will go off once excelerator is engaged), but likely will not trigger the limp home mode. The 2 instances when the ‘lhm’ were activated on my 8: Severe engine misfire caused by the defective original ignition wires (fixed with new wire sets and new BMW F8LCR plugs. The other time was a defective alternator causing the car to run on battery power only. The batteries were not being recharged due to a bad ground within the alternator... bad exciter wire circuit. Fixed charging issues with a rebuilt Bosch alternator.

[M6csi]

I am pretty the R1 designation on body of plug denotes 1K resistance.

Don’t know whether these BMW F8LCRs are NOS plugs that have been sitting for decades on dusty distribution warehouse shelves or they are newly manufactured by Bosch for BMW only.

[derrith]

Well, I definitely have the bad idle on cold start and CEL at idle. Driver’s side plug wires are only a few years old, passenger side I don’t have records on. Still got all the donuts around the wires. System is charging at appropriate voltage and I have no evidence of any issues with the batteries or charging system. Thanks for the additional insight.

[JDP530]

I think all of the issues I had with misses, monetary loss of power at highway speeds, 'limp home mode', etc, were related to old oem and aftermarket CIS sensors. Got new BMW sensors on the car and I am not experiencing these issues now.

[8eights]

This is the merchandise.

haha... NO, they are NOT the 1k F8LCR plugs...

You sure? I have about 5 sets of the same also under my Dog house, Would hate i bought the wrong one's a year ago, Tia!

[JDP530]

This is the merchandise.

Could you check the resistance of your plugs? I think the R1 does designates a 1K ohm resistor but I cannot find values for Bosch plugs. Would be interesting to know.

[M6csi]

I’ve somehow misplaced my new set of F8LCRs, so no dice on checking the ohm readings. A couple of old and used F8LCR plugs (20k miles) both tested roughly 1.5k ohms.

[JDP530]

I’ve somehow misplaced my new set of F8LCRs, so no dice on checking the ohm readings. A couple of old and used F8LCR plugs (20k miles) both tested roughly 1.5k ohms.

Do the old plugs have the 'R1' designation on the insulators?

[shogun]

Here is the old thread, the BMW spark plug chart for 8 series from 2005:
840Ci (E31) M60 All Bosch F7LDCR Non-adjustable, NGK BKR6EK Non-adjustable
840Ci (E31) M62 All Bosch F7LDCR Non-adjustable
850i (E31) M70 All Bosch F8LCR .028” - .032” (0.7 – 0.8 mm)
850i (E31) M73 All Bosch F9LCR2 Non-adjustable
850CSi (E31) S70 Bosch F8LCR2 Non-adjustable

https://www.bimmerforums.com/forum/s...ch-plugs/page3

[JDP530]

So i decided to try an experiment that several others on here have already done and that is using the MSD Blaster Coil 8207 along with some platinum plugs and so far I have not experienced any issues over several hundred miles. But car is down right now while I rebuild rear suspension.
IMG_20190121_143140619.jpg
IMG_20190121_143152661.jpg

[M6csi]

Exactly the same. Also BMW F8LCR plugs. Actually tested @ 1.340k ohms. Suppose plug resistance go up slightly as they ‘aged’ and the mileage piles up.

[M6csi]

Another used plugs. This one reads 1.163k ohms.