Limp Mode

[rjjablo]

I have been chasing Limp Mode in my 1991 850, 185 K Miles, sometimes it will pull fine up to 4-5 K sometimes it will not, slightly lumpy idle, The Check Engine Light on the left is always on. The one on the right Starts out being on but once the car warms up it goes away

Already done
Resealed Intake Manifolds
New O2 Sensors
New PCV System
I had two dead plug wires and replaced with Shoguns
New Autolite Plugs, I ordered the NGK's
Cleaned Commutators on Throttle Bodies
Pulled the plugs and they look good I can post a picture if I need to

Tested my MAF Sensors and got correct voltages. Went ahead and tested my Coils, car was warm but not hot.
Primary resistance per the Manual is .8 Ohms
Drivers side measured .4, .5 and .6 never stabilized tested it twice
Passenger side measured .3 and .4 never stabilized tested it twice
Secondary Resistance per the manual is not measurable,
I tested mine and got 11.26 for the Drivers and 11.25 for the Passengers.
Coil Wires are brand new
Time for some new Coils?

[Belgiumbarry]

for what it's worth.... with 1 MAF no bank worked, problem switched banks as i switched MAF's ... i tested the MAF's ( with a air blower ) and all voltages seemed OK.... perhaps i did it not correct , but i did not find any clue on the "bad" MAF .
2 new MAF's and problem was gone !

[rjjablo]

As part of my MAF testing I unplugged each of them in turn. Motor hesitated a little and kept on running the same, Limp mode bypassing the need for the MAF Sensors?

[Belgiumbarry]

don't know rjjablo , my engine doesn't run at all with 1 MAF disconnected !

[rjjablo]

I reseated the 6 and 12 Sparkplug leads into the 90 degree elbow. It appears to have solved Limp Mode problem. I still have a continuous CEL light(One on the left) but motor pulls hard to 5K and trans shifts correctly. Check engine light on the right comes on at start but goes away in a minute or so. I am going to drive it like it is for a while and swap plugs when I get the new ones. I still think both coils are suspect

Tried doing the Stomp test and got nothing either doing it 5 or 6 times

Picture of the Plugs

[spitfire980]

I reseated the 6 and 12 Sparkplug leads into the 90 degree elbow. It appears to have solved Limp Mode problem. I still have a continuous CEL light(One on the left) but motor pulls hard to 5K and trans shifts correctly. Check engine light on the right comes on at start but goes away in a minute or so. I am going to drive it like it is for a while and swap plugs when I get the new ones. I still think both coils are suspect

Tried doing the Stomp test and got nothing either doing it 5 or 6 times

Picture of the Plugs

Can you please explain what you mean by reseating the 6 & 12 leads into the 90 degree elbow?

[shogun]

To change the cylinder ID sensor on cylinder 6 & 12 from the old ignition wires onto my new ones, one has to unscrew the 90 degree angled plug which goes onto the distributor, install the CID the correct way (one direction only works correct, see link) and then screw in the plug again, as shown here https://www.bimmerforums.com/forum/s...6#post30163176

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.)
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.

[cartoonz]

What is the the resistance on those Autolite plugs?

[Belgiumbarry]

it is a copper plug..... but 4 K Ohm....

[rjjablo]

I am going to swap out for the NGK's Tommorow

What is interesting driving it. It will be in Limp Mode if I put it in Drive and Sluggish etc

Put the 4 Speed in 1st and it runs great, pulls hard etc

[8eights]

Because the car is Limping you too safety and protecting at the same time, Other gears will be fully available soon.

[rjjablo]

Measured Primary Resistance while it was hot out 87F and a lot hard slog home thru traffic. 1.6K Ohms. Versus 8K Ohm by the books and erratic when it was just warm

Getting a pair of new Bosch Coils

[8eights]

Are you getting fuel to both banks? I don't usually see the coils being intermittent, They usually work or they don't, Have you tried swapping your Air Flow Meters or testing them? Unplug one and see if it dies, If not Plug it back and unplug the other, If either makes it die, That's the good AFM.

[rjjablo]

Unplugging the MAF sensors causes it to hesitate but keeps on running

[8eights]

That's good, Could well be your plugs as mentioned.

[rjjablo]

With new NGK Plugs idles a lot better still has a lumpy idle but no longer wants to almost stall, Still with the Main Check Engine line on. Coils were ordered this morning.

[rosakirk12]

Replace coils periodically. There cheap. Very likely problem. I would do CPS then pulse Generators. I do not get good results from the short CPS. I recently had one drop off line never went into limp mode. Turns out bad connection where CPS and generators connect under oil filler spill J box


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[rjjablo]

Replaced Coils with Bosch. Idles better and no longer wants to stall. Will drive it again to work tommorow. Pulls to redline in D and shifts better. Still does not have that absolute smooth idle and does not pull hard off idle.

[Pneill316]

Did you replace the wires? I had a limp home problem a long time ago, turned out it’s was started from a gas leak above the #12 plug. Reseating it would fix temporarily but ultimately I needed a new wire. Gas leak was just a lose clamp on a hose.

[8eights]

OP:

How are your fuel filters? CEL go off??

[rjjablo]

OP:

How are your fuel filters? CEL go off??

New Plug wires and I ordered new fuel filters and they will be here on Friday. I also can replace all the potentialy rotten fuel line back there

Left CEL is still on

[rjjablo]

New Fuel Filter, No real change, Hoses were getting rotten, worth it to do it anyway

Will reset car/drain capacitors tommorow according to Shogun's instruction if nothing there, I will pull Cluster and see if one of my two EML Lights are out Per Shogun

[rjjablo]

Drained Capacitors according to below and Check Engine Light went off, of course it came back on in about 5 seconds after I started it and remained on at low RPM, Went out to do the TB synchronization and it went off, When I was done I dropped it into Drive and it came back on but went off when I took it to 5K again in drive.

Sounds like the Throttle Bodies are out of Sync at idle but close enough as the RPM's Rise?

Time to send them to Dragon850?
The reset procedure is billed as a ‘cheap fix’. It does often give good immediate results, however if there is something wrong with your car then over a 2-8 week period the car will likely return to its original state.
The reset procedure removes all mean values stored by your onboard computer that control engine timing, fuel use etc. As you continue to drive the car, the stored values ‘average out’ to best suit the engine condition.
If your car has for example a leaking intake manifold gasket or broken O2 sensors, the readings are quickly going to become ‘corrupted’ with incorrect information.
This can lead to the engine running too rich or too lean (check your sparks for evidence). Within a short period of time the car will return to rough idle as the underlying problem has not been fixed.
That said – the reset procedure can reset values that are no longer applicable. You may have replaced something on the car (e.g. Catalytic Converters) thus causing a sudden change in normal engine running. The readings stored over 10-20 years will suddenly not suit you recently modified car. The car will however read new values in and average out over time. The Reset procedure simply speeds that process up.
The long and short of it is that this procedure can sometimes fix rough idle and transmission timing and seems to improve the cars performance. However with existing underlying issues as outlined above – it won’t be long before the problems return. Perhaps this procedure could be used if you’re trying to sell your E32 ;-)
Procedure:
1. Disconnect battery cables, first negative, then positive.
2. Cover and protect the battery posts! Leave no potential of a battery short circuit.
3. Turn ignition to position II.
4. Connect both battery cables ("SHORT") for at least 10 minutes. This step drains a capacitor in the ECU/TCU. (Covered the battery with a thick, dry shop towel to prevent actually shorting the battery! – careful of arc welding the back seat! As the battery is still in place, and the cables aren't that long, you could use a very long Craftsman screwdriver and two small vice-grips to actually clamp the negative and positive cables to the metal shank of the screwdriver.
5. Wait 10 minutes - then ignition off, key out.
6. Reconnect battery positive, then negative.
7. OBC says "PPPP", reset time. Start and idle the engine for 5 minutes, then off for five, then out for a drive.
8. Now, with the car in lowest gear (one or two depending on your make), accelerate until at least 5000 rpm is reached. Allow the car to slow to idle, and then repeat two more times. Let the car idle for 5 minutes. All Done!
9. Idle should smooth out over 10-12 miles; shifts should be immediately smoother

[shogun]

Could be the problem of the DKs, the resistance material in most cases wears off in the area where the wipers make contact with the material most of the time when engine is running = idle and low RPM range. The major concern is the amount of wear on the resistance material. When the wipers wear thru the resistance material, the resistance readings sent back to the EML will not longer be correct or may fluctuate wildly during throttle plate movement. This will set off the EML light and initiatea “limp home” mode.
You can measure them, on my website http://twrite.org/shogunnew/topmenu.html click on the left side index reference data >>>DK electrical reading 750 / DK input details : small PDF file

[rjjablo]

I pulled the Gauge cluster because the Check Engine Light came on and never turned off. I read your thread about needing two Check Engine lights or Limp mode happens. Rear of my cluster is different than what you had and has a spot for two light bulbs for the Check Engine Light and only one bulb. I ordered some and will give that a try also