more 750 limp mode - SOLVED

[howl9000]

First does anyone have a definitive list of limp mode causes or theories
89 750IL 149K

Right now
I have no start
She cranks fine
I have spark pulses at coils. so I'm assuming I have spark at plugs.
The DK's wiggle at key on ( I replaced both DK's with cleaned ones)
(NO EML light on ) it comes on then 2 seconds later goes off
I have voltage to fuel pumps. at fuses during starting I'm going to say pumps getting voltage
I measured both CPS the Ohms are within range but at the low end. spec 550-650 ohms I get 555 and 560
I measured them at the ECU connector pins 47 to 48 on both ECU's.

I have yet to prove fuel flow. will do 4-3-2020 after battery charge. I drained it.

Curiosities.
No power door locks. the power lock unlock not working.
When I connect the battery the hazard lights flash with switch not depressed
I have to depress it then un_depress to turn off.

how about an anti theft situation? did I trigger something?

I'm stumped guys
I think it's something seemingly not obviously related to start/running

Ron
Cincinnati NO'HIO
If it's fun we just say NO
If found to be FUN we regulate to be NO'FUN
We take having NO"FUN seriously

[shogun]

Hazard light comes sometimes when a battery is connected, especially when battery is low. There were also some bad crash control modules, maybe you remember the old days when we were active on BB, here some pics and there Kharon8 had the same problem http://www.bimmerboard.com/forums/posts/410301/
http://www.bimmerboard.com/forums/posts/149425/
no power to door locks: check the fusible link which goes from battery to the rear seat fuse box, that also powers the GM and RM which are among other things also for locking, that is the fusible link in the black plastic box as shown, the other one inline goes to B+ in engine bay and powers the e-box http://www.bimmerboard.com/forums/posts/377728/
I looks to be that both fuel pumps are not controlled by the EML module, I would check both fuel pumps if they really run and produce the capacity and the required pressure. I usually test it without ignition on, fuse box open, a short wire touching B+ and with the other end I briefly touch on top of fuse 23 and then 24, then I can hear the fuel pumps working and fuel pushed even thru the fuel pressure regulator. Also squeeze fuel fuel hoses in engine bay before and after the test, should be harder then after you powered the pumps.

[howl9000]

I was finally able to test the fuel pumps by jumpering 12v to the fuses 23 and 24
No fuel flow. I removed the fuel pressure regulators at the fuel rails.
This was easier than undoing the 4 inch of flexible fuel line going to each rail.

The rail on side 1-6 passenger side had no fuel in it when I removed the regulator
Rails for 7-12 drivers side had some fuel in it.

Next I'll pull the pumps from the tank and apply 12v
I hope there is no spark so I don't go boom on the porch lol

Any other thoughts?

I have not checked the fuses under the drivers side rear seat yet

Ron
Cincinnati NO"HIO

[shogun]

Looks like you need new fuel pumps, better change both, when I replaced my ones a few years ago, I noticed that with the new fuel pumps I got some leaks near the fuel pressure regulators, before with the old pumps I did not have that, probably did not notice that over more than 25 years the pressure and probably the volume of the original pumps went down a lot. Maybe you also change the 2 fuel filters too.
If you want to go aftermarket, I took some measurements of the original Bosch fuel pumps back in 2016 when I replaced my ones http://www.bimmerboard.com/forums/posts/1264560
My original Bosch pumps lasted 175.000 km and almost 30 years, good quality then.

[howl9000]

more limp mode after fuel pump replacements

read below and keep me straight I'm starting to chase my tale here I think

Are you saying the engine will run with no MAF's?
Then what is the minimum to just run?

Why-I ask ---I have spark on both sides If I pull the coil wires I get pulse on the non running side.and running side
If I pull maf for the non running side no difference. If I pull plug on MAF for running side she stops.

Question I know I have Fuel flow and pressure BUT How do i test if injectors are actually firing?

Fuel AIR and spark to run I don't know how to prove injectors are actually working???

If I unplug the drivers side maf (passenger side feed) the car stops. Telling me only the passenger side of the engine is truly rubbing.. am I right?

any ideas guys?

[shogun]

Based on the Info on M1.1 and M1.3 which is basically the same working principle like your M1.2 for the M70 I assume it still should run in limpmode:
Limited Operating Strategy (LOS)
In the event of a serious fault in one or more of the sensors or their wiring circuits, Motronic will substitute a fixed default value in place of the defective sensor. This procedure is often termed limp home. A serious fault occurs when the signal from the sensor is outside of its normal operating parameters. When operating in LOS the engine may actually run quite well with failure of one or more minor sensors. Since the substituted values are those of a hot engine, cold starting and running during the warm-up period may be less than satisfactory. Also, failure of a major sensor, ie the AFS, will tend to make driving conditions less easy. Once the fault has cleared, Motronic will once more accept the live signal from the sensor. The following LOS measures are taken in the event of a failure
Component..............................Action
AFS........................substitute values are calculated from the TS position. The load signal is fixed to 6.0 ms and the ignition timing to 20° BTDC once the TS contact is open.
http://www.bimmerboard.com/forums/posts/1256627/

Lets wait for comments of other M70 owners.
You can swap the MAF for a test from one side to the other, does the fault change to the other side?
Injectors: touch them, you should feel them clicking. You can also unplug the connector from 1 injector, see if any change in idle or not, then plug back and test the next and so on.
Remember the MAF on passenger side is for cylinders 7-12 on driver side and the MAF on driver side is for the cyl. 1-6 on passenger side. https://www.7-forum.com/bild.php?bil...%20und%20sport
Did you check the donuts on cyl. 6 and 12? Remove spark plug 6 and 12 and see if they fire. Are they wet?

Checked both distributor caps and rotors? Quite often the center pin in the distributor gets lost in action. Haircracks? http://e32b12.blogspot.com/2013/10/i...tric-leak.html

[tsmcg161]

I have a 12/88 750il and I had a situation about a year ago where I lost a bank on the way to work. No EML light but, I was definitely in limp home mode. On the bank that was out I had no spark, no injector pulse and no fuel. I swapped my DME'S , no help. Swapped MAF'S, no help. On my car, on the passenger side there is a relay box. My model has the big black relays and two smaller white relays. I think these relays were changed per production year. Your car and my car are a month apart per production so Im assuming you have what I have, the tall black relays. I swapped them and the problem switched to the other bank. I had a spare relay from my junkyard travels, put it in and problem solved. I don't know why they changed the relay configuration from year to year and I was assuming the tall black relay was for the fuel pump. But I believe on my production year they are DME relays? Just a suggestion.

[howl9000]

I have proven That the fuel injectors on the drivers side of the engine are not working
by spraying starting fluid through the MAF on the passenger side of the car
She smooths out and revs up

What would cause the fuel injectors on one bank not to function?

Ron

[shogun]

The big black relays tsmcg161 is mentioning and the DME main relays: info here , K210, K211, K212, K213 = fuel pump relays + DME main relays aka engine control module relay, they changed positions,
older version http://www.e32-schrauber.de/bmw/date.../arb_08_88.pdf
newer version http://www.e32-schrauber.de/bmw/date...8_88-07_94.pdf
swop DME I and DME II and test.
Swop fuel pump relays or bridge them and test
swop MAFs from one side to the other and test
remove the spark plug on that side which is not working which holds the donut = either 6 or 12, is the spark plug sparking?
Double check distributor and distributor rotor on that side.
Check again the CPS for that side. The testing with a multimeter for ohm is not 100% proof, usually in a shop they test it with an osci to test over the full range of RPM.
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 6
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

[tsmcg161]

Howl9000. Unable to open PM. Encrypted??? Did you swap relays, MAFS and DME,s.Do them one at a time. Its obvious you dont have an injector pulse.

[howl9000]

MY 750 Drivers Side Fuel injector bank is not working

I have swapped everything that can be swapped
I've replaced all 12 plugs
I have spark at all 6 plugs on the driver side
I have fuel flow.

I have spares so I replaced both DME and the EML

The EML light stays on for 2 sec then goes off.

I'm down to what mystery thing is keeping the injectors from not firing
They all measure about 15 ohms
Cylinder Id is .4 ohms
CPS was 560

Stumped in
Cincinnati NO'HIO

[shogun]

Do you have a fault code reader?
Or make a stomp test https://www.bimmerforums.com/forum/s...e-pedal-faults

[howl9000]

yes
the reader always says no fault.

stomp test is on the menu.

hear me out.
no fault: that tells me the DME's and EML "think" everything is fine.
I spray starting fluid in maf on dead side she revs up and smooths out.

I'm thinking a wire common to all injectors.on that side.

I read a owner found some bad wires under the coolant tank going to his dk

I'm going to go wire hunting tomorrow

Ron

[shogun]

probably a wire problem, see also the pic fom Erwin http://www.bimmerboard.com/forums/posts/644209/

[howl9000]

according to the schematic I have the wire color is red/write for 7-12 injectors
1-6 is red/white/yellow

I'll find it.

[tsmcg161]

If you have swapped everything you mentioned with no change, then chasing down the wires is what I would do. Could you send pic of that fuse in the relay box? I couldn't open in PM. Im very curious.

[howl9000]

here ya go

relaybox3.jpg

[tsmcg161]

I do not have that. It is obvious that has been added at some time. Did you inherit this vehicle? or did this issue just arise one day?

[howl9000]

the story is to long to tell.
yes I have had issues with S showing up in the display instead of the E like
SP or SD and the car would just stop running no matter where it was
on the highway at a stop sign.

the car sat for 5 or more years I traded it to a kid for labor
we had it running and in the drive it just stopped
then started in limp mode
then stopped
the fuel pumps died
replaced and she starts in limp mode with no eml

I've traced it to driver side injectors are not firing. thus no fuel to driver side yes the fuel is flowing to that rail.

the kid cut his losses and she is mine still he said to complicated for him.
I haven't heard from him since January

[tsmcg161]

5 years is a long time with no activity. While running, how are you testing the injectors on 7-12, are you using a test light or a noid light on each injector plug? If a car sits for 5 years here in south Texas, chances are that mice and squirrels make them selves at home and they love eating electrical wire.

[howl9000]

I tested with a Fluke multi meter no voltage and no pulses
If I spray starting fluid in that side she revs up and smooths out.

the trunk had a couple of houses and one under rear seat.
I don't see how mice get in a closed car.

the red/white wire goes from a splice where all the drivers side injector wires meet in the wire cover
r down the center of the engine then over to the fuel pump relay
I'll check continuity tonight.

The best mouse one was the blower stopped working the guy opened it up and a mouse was stuck in the cage blocking rotation
I think the pic was on bimmerboard

[howl9000]

can some one tell me which two lines are pressure/pump feed lines and which one is the return line?

I have it from left to right
return line
pump
pump
the big one on the bottom is the filler neck vent line

I don't think its correct

Playing around I got them confused

Last edited by howl9000; Today at 08:05 PM.

[shogun]

Return line is in the center. http://bmwe32.masscom.net/sean750/fu...t/Fuelpump.htm
clean up the cover, next to each hose connector there is an arrow stanped into the cover for the flow direction!
from left to right on your pic, fuel pump to engine, fuel pump to engine, return line http://bmwfans.info/parts-catalog/E3...double_filter/
If I remember correct the connector most left on your pic is fuel pump bank 1 (?). But you can test that on fuse 23 and 24 with a wire bridge to B+ pole.
M70 pumps/each:
operating pressure: 3 bar, conveying capacity at 12 V: 1.7 liter per minute=102/60 minutes, conveying capacity under counter pressure: 875 ccm/30 seconds =105 liters/60 minutes/1 hour, power consumption: 5.5 Amp.

[howl9000]

My paper blew away in the wind.
I knew it was pump pump return
just not the right to left part

who knows now I'm confused
I'm doing new fuel filters
so I'll figure it out or just reroute at the filters.
Only guys named shogun read right to left muhaha muhaha
to many gas fumes today

[shogun]

Just clean the cover, besides each connector there is a arrow stamped into the cover showing the flow direction from ----to, that I know for sure as I checked it on my car when I changed fuel pumps, maybe even fuel pump 1 and 2 (not sure)