Erratic Misfire m70

[SergeBMW]

The car is finally up and running in great shape. The last of the work, driveshaft and pressure accumulators were replaced yesterday, the ride is amazing. Now when I went to enjoy the car for the day, I got a pretty bad misfire which was very random at times. It would come and go, and by the end of the day with some testing, the car had bogged down so much that it would not rev past 1500rpm and sounded as if it was choking out, the check engine light came on. As soon as I let off the throttle and give it gas, it would go again, but with a misfire. It misfires very randomly and could not pinpoint it to any one cylinder. I checked each one by disconnecting the fuel injector cable on each of the 12 cylinders, each one would cause a noticeable consistent misfire note. The misfire would sometimes happen above 3k or at 1k at any speed.

After shutting off the car for 10 min and restarting it, there was no misfire, and car revved up perfectly fine. 3 minutes in and it came back. Sometimes consistent, sometimes very erratic, happening every 2 seconds or so. Im going to connect BMW DIS tomorrow and see what that says.

- DKs have been cleaned and tested
- 2 new distributors and rotors
- 12 new plugs
- 2 new fuel pumps
- Replaced hoses from fuel pump to sender
- Tested throttle POT (working normal)


The misfire was very slight but really started happening a day or 2 before the new pumps went in. This got worse a day after I put in 2 new fuel pump units from Amazon/ebay, they were 30 a piece or so and have read good from them. I had driven the car home from the mechanics today without a hitch, was driving beautifully.
I have 2 fairly new BOSCH pumps I pulled from a newer 750 a few years back, they look brand new but use the newer connection plug, not the studs you screw the cables on to. I didnt want to hackup my wiring. Should I try these?
Another thing to note. I have HIDs installed and they seem to go green on a bit after going WOT and letting off the gas. That green similar to when they are warming up. Not sure if this means anything or that they just dont have that great of a ballast. The OBC test #9 shows a consistent 13.50v to 13.70v when accelerating.


Sorry for the long thread

[shogun]

you mention that the misfire went away after stopping the engine for 10 minutes or so. Make me thinking if the problem is heat related? Some solder bad joints in the EML control unit or other parts? Just n idea, do you have a spare EML module for testing?

[unity]

How soon after driveshaft repairs did this happen exactly? First run? I would verify the O2 sensors are not criss-crossed at the connections.

[SergeBMW]

you mention that the misfire went away after stopping the engine for 10 minutes or so. Make me thinking if the problem is heat related? Some solder bad joints in the EML control unit or other parts? Just n idea, do you have a spare EML module for testing?

EML module was replaced about 2 years ago which corrected the no start issue I had when I bought the car. The other unit is dead. I will try today while the engine is cold to see if there is a change.

How soon after driveshaft repairs did this happen exactly? First run? I would verify the O2 sensors are not criss-crossed at the connections.

I thought of this as I was going to sleep, but I know it must have started maybe later in the day. I drove the car home for 20 min without a problem, parked it for 2 hours and then 10 min into my 25min drive it started to misfire especially accelerating from 40mph. Car shook as if it was out of balance but stopped as soon as I put the transmission on idle and rpms dropped. The economy gauge was also very sporadic during that time, pointing to a misfire.

Maybe swap the connections?

[SergeBMW]

UPDATE: I ran each bank on its own to further look into the misfire. I had one cylinder which had a very very slight change, but upon running it on 1 bank at a time, I found cylinder 11 had no change when I pulled the injector plug. Removed the plug, was fine, tested for spark on boot with tester and I got a weak and very erratic spark. Closer inspection showed a damaged or missing sparkplug nipple fitting inside the boot, and also noticed the boot arcing to ground from the back, where it is damaged as well.

Replaced it with a fairly short lead I had laying around from my 735i days, and voila, smooth as a seeing machine.
Problem is, I still get that bogging down on heavy or light throttle. It is random and sometimes a simple lift of the throttle and back on gets the car running like a champ. It's very random. Sounds almost like 1 DK keeps dropping off. I never did a DK synch since it's not too easy to do here with traffic, but I will try. Currently have the car battery leads disconnected from battery and shorted ptgether and ignition to ON. Have never done a reset on this car yet.

I also tapped the MAFs and DKs, moved cables to see if it changed anything. Very erratic, CHeck Engine comes on when it bogs down. I doubt it's my new cheaper fuel pumps because just a lift and back on of the throttle and the car accelerates all the way to redline.
No EML light.

[unity]

I wish I could recall my EML issue. I had the same problems long, long ago. No ELM either, so it was not really like one whole side shutdown but felt a lot like it. I made posts but I think the problem cleared itself up. But I had replaced SOOOO much. All new ignition, etc. Might have been the crank sensors which are easy to test.

[SergeBMW]

Definitely is a bank dropping out, unable to pinpoint which one. Seems to be worse on uphill acceleration or hard turns, but still will happen randomly on straight and level road.
Maybe clogged fuel filter? I had one pump in the tank for 2 years while I was working on the car getting it roadworthy, maybe the other dried up and is clogging under fuel demand?

Today I took a corner and gave it gas, it bogged down and actually stalled out completely.

[shogun]

Some quick and dirty tests:
squeeze the fuel lines where they come up left side engine bay. Same pressure? If different or one no pressure, one pump is the problem.
http://bmwe32.masscom.net/sean750/fu...t/Fuelpump.htm
http://bmwe32.masscom.net/sean750/fu...Regulators.htm
The M70 has 2 pumps, so 1 for 6 cylinders, each:
Bosch part number is 0580112507 (according to an old repair book)
operating pressure is 3 bar
conveying capacity at 12 V 1.7 liter/minute
capacity against counterpressure 875 cc/30 seconds
power consumption 5.5A

[SergeBMW]

I had pinched both hoses and they felt the same, also drove the car around with one fuel pump each and drove fine. Slow but just fine. Both pumps were replaced by aftermarket cheaper pumps that matched OE specifications for pressure and fuel flow.

Last night the car was worse, could barely pull into traffic without it bogging down (nearly suicidal at rush hour). Took it to the gas station, filled it all the way up and voila... No bogging down, no hesitation, nothing! What the hell.

My thoughts:
- I do not have the return line connected to the fuel pump pod, so it is just hanging freely spraying return fuel anywhere. (ran out of proper length hose) Maybe the pump holder is running dry on heavy throttle with low fuel levels? I have heard others that never even connected a hose back on the return and let it spill into the tank from the barb without issues.
- Fuel pump has an internal seal fault where if it is not covered completely in fuel, air gets sucked into the line? I do not have another pump to test except for the newer style Bosch with the connector plug. I would really like to not hack up my original circular ends on the fuel pump wires.
- Maybe some of the sediment on the bottom of the tank gets sucked onto the prefilter element and prevents fuel from entering when the fuel level is low? (I would think this would occur regardless of fuel level)


I believe the regulators are ok for now due to the fact that the car runs fine with a 1/4 tank and above. I cant gauge exactly how low the fuel level drops to cause this issue as my fuel sender is damaged. I am currently ordering nichrome 80 resistance wire to repair the damaged wire on the sender itself.

[shogun]

Check once more if the fuel pump set is correctly corrected inside the tank at the bottom. I noticed that when I changed my pumps last year. I pushed the fuel pump unit into the receiver and it did not click, so the unit was not correctly installed, removed it once more and pushed it in till the 2 clips clicked into position. http://bmwe32.masscom.net/sean750/fu...t/Fuelpump.htm
Anyway, you now know the problem is the fuel pump unit

[shogun]

Serge, did you fix the problem 5 years ago? What and how did you fix ?

M73 also had such problem tech-tip-bmw-v12-engine-vacuum-leakage-correction-cold-running https://atlanticmotorcar.com/casestu...old-running-2/
https://www.bimmerforums.com/forum/s...ad-misfire-m70
https://www.bimmerforums.com/forum/s...-Weird-problem
https://www.bimmerforums.com/forum/s...-on-cold-start
https://www.bimmerforums.com/forum/s...L-Engine-light

Lambda (O2) Sensor
This code is stored when the engine temperature is >70C and the Oxygen Sensor value is out of range or not present. Check the Oxygen Sensor wiring and the operation of the sensor. The value should fluctuate between 0.02 and 0.85V. Slow fluctuation indicates a polluted Oxygen sensor and negative values indicate a damaged sensor. Note: Cars without Catalytic Convertors will incorrectly store this code

Lambda Control
This code is stored when the DME detects excessive deviations in the air-fuel mixture (too rich or too lean) for longer than 10 seconds. Possible causes: Fuel tank ran empty, Incorrect Fuel Pressure, Injector valve defective or coked,
Engine Temperature Sensor defective, Secondary air leak, Fuel evaporation control system defective, Air Flow Meter defective and/or the combustion is being disturbed by mechanical failure (Spark plugs,, compression, intake/exhaust valves, etc.

1215 Air Mass/Volume Sensor
This code is stored if there is a break or short-circuit at: Air Mass Flow Meter or its supply wires or the voltage supply to Air Mass Flow Meter insufficient. Cable damage is the most common cause of this trouble code.

1223 Coolant Temp. Sensor
This code is stored when a short to plus or a break in the wiring at the Coolant Temperature Sensor or its supply wires may exist. Check the wiring and the value of the sensor. 8.26-10.56 KOhms at -10C, 2.2-2.7 KOhms at 20C, 290-364 Ohms at 80C

1224 Intake Air Temp. Sensor
This code is stored when a short to plus or a break in the wiring at the Intake Air Temperature Sensor or its supply wires exists. Check the value of the sensor. 2.2-2.7 KOhms at 20C, 760-910 Ohms at 50C

1243 Crankshaft Pulse Sensor
This code is stored when signal from the Crankshaft Pulse Generator is implausible (absent or out of range). Check the Crankshaft Pulse Generator and the wiring.

1251 Fuel Injector 1 (or group 1)
Check the injector valve for coking and proper spray pattern. Check the wiring from the DME and the output stage of the DME. Code 1283 may also be stored when the defect is intermittent.

In the 12 cylinder model the Injection system is treated as two 6 cylinder systems joined at the crank. This means there are two ECUs in the system. To access the second ECU depress the gas pedal to the floor 6 times. Some models will return implausible blink codes if the ECU has failed or if the power is interrupted during operation. Removal of the control units harness and reconnection after 10 minutes seems to resolve most of these problems

[SergeBMW]

I honestly for the life of me cannot remember what I did to fix the issue Erich. I've tried recalling that time period but was quite busy with other things at the same time.

The only things I can remember doing where the following:
- Replaced entire fuel sender with newer model which allowed me to use the original BMW pumps from a donor car
- Replaced coil to distributor wire (You sent me one as mine had eventually broken in 2, not sure on the time this occurred)
- Fuel lines in the tank were not rated for fuel submersion and went very VERY soft (probably caused fuel pressure loss)

Have you had any success with your friends car yet? I do apologize for the late reply!

[shogun]

Have you had any success with your friends car yet? I do apologize for the late reply!

yes, fixes, replaced: distributor/rotor + 2 old original BMW ignition wires, the M70 requires spark plug boots 5000-OHM. Over time, the metal film resistor contained in the plug connector decomposes (oxidizes) + the ignition spark becomes too weak. When we tested the old wires, could only measure ~ 1000 ohm.
changing the original spark plug boot https://www.bimmerforums.com/forum/s...park-plug-boot or replace with a new set ignition from me

[SergeBMW]

I'm glad you got it fixed, the more I think, I believe my issue was due to that bad coil wire. I still have to get a set from you at some point. Do you still have plenty left over?
I have a rats nets worth of old ignition wires as they have been failing one by one and I'm sure most of them are not up to spec anymore. Not sure when I will get to it.
My E32 has been stored away in a garage with my family while I live in Colorado. I have a few things it needs but luckily I am able to use it when I visit.

Been enjoying my E39 M5 that I found here in CO for now.

[shogun]

my version ignition wire sets I have available ex stock, no problem. Or you try to repair your old ignition wires as per my link above, but the original spark plug boots 12121710707 are pretty expensive, 1 piece ~ $30. spark plug boot 12121710707, Insulating sleeve 12121736142, Round connector 12121705656.
Or try a cheaper solution with a ZLE 185 Spark Plug Connector (122mm) with Wood Screw wire Connection 122mm long, 5000 Ohms resistance, $12.99, used on BMW http://www.kingsbornewires.com/product-p/zle%20185.htm
But before you order check their shipping cost, K-wires ship via UPS Ground and the shipping charge will be displayed in your online shopping cart.
Local as well as international shipping has been increased a lot.