m20b20 L-jet starting issues

[PinkyToe]

Hello all, I have been lurking the forum for some time in the process of fixing my 520i L-Jet and have finally come upon an issue I cant find the answer to.
Basically when I turn the key to start the car everying happens as normal, idiot lights come on, fuel pump primes and car starts as normal. The issue I face is that when the key returns to the run position the car stalls, lights stay on and all systems still have power but the car ceases to run. I had recently sone some work in the fuse-box reparing a loose connection and though I had maybe bumped something else loose but I cant find any system that isnt getting power. Checked injectors, fuel pump, main-power/fp relay, coil and distributor. I dont beleive there is a break in any of the circiuts, which is backed up by the fact that when I hold the key just out of the starter position I can get the car to idle/rev. Can't find a reason that the ignition switch is bad as all positions of the switch send 12v when selected.
This led me to believe that maybe the one of the sensors that the ecu references when in the idle loop is bad. I thought that may cause the ecu to fall on its face when car is in run position but cant find any evidence to support that. Bentley manual unfortunatly does not cover the Australian delivered m20b20 models but I do have the haynes manual covering this specific model just forget it when going home to fix the car . I pulled the sensor connected to the side of the distributor which I beleive is the reference sensor (correct if wrong) but car failed to fire when starting telling me that its fine. Next step is to test the ecu, have purchased a second hand ecu just waiting on it to arrive to see if that fixes the problem.

(I did notice there was an extremely similar thread covering almost exactly the same issue but the answer was never posted )

[jdb]

Well this is a tough one as that wiring for the Ljet system has a few different configurations.
I do not have the exact diagram to look at, but something close.

So, just take a look to see if you have a ballast resistor located between positive term. Of the coil (+ or 15) and the term. 15 of your ignition control unit. It would make sense it has failed as there is a small term. 15a, that comes off the starter solenoid that powers the coil while cranking.
You could check for power at the coil term. 15 with a test light. It should be powered with key on at all times, not just while cranking the engine.

Hope that makes sense, please let us know what you find,

Jeff

[Mike W.]

Excellent suggestion by jdb, I've very familiar with L jet and that didn't even cross my mind.

I would look at a simpler,at least for first step, troubleshooting. Bridge positive and ignition at the switch, or where ever. Temp of course. but set it up so you have power even if the ignition switch is off. Then start it. If the switch is the problem, it should keep running. If something else, like a bad resistor pack, then it would not stay running. Sure sounds like the switch from here though.

[PinkyToe]

Thankyou guys for the suggestions, I will try that next time I’m with the car.

[PinkyToe]

So, back with the car this weekend. 
Had a look and my model is the one without the ballast resistor, only has the ignition module next to the coil. Also the wiring diagrams in the haynes manual for the Australian delivered models show no mention of a ballast resistor either. 
Tested a new ecu and no change in the condition, on the plus now I have two working ecu's incase I fry one 
Tried bridging the ignition switch 12v and didn't change the issue either. Still runs and idles when held just off the start position on the switch. 
So now I can eliminate the igntion switch, the ecu as failure points. By my logic, I can pretty much pin it down to a failure in the wiring somewhere as I know the car runs fine.

If the switch is the problem, it should keep running. If something else, like a bad resistor pack, then it would not stay running

 

Also a little confused as to what you were refering to with the resitor pack here jdb. 
As for now i'm going to go through all the connections involved with that ignition switch wiring and check for power and ground as I was playing with them earlier in the project chasing a no start issue so may have taken something off and forgotten to put it back on. 

 

[JohnH]

What work had you carried out before you started having problems? Cam belt? Distributor? Water pump?
If you are not careful doing any of those you can upset the distributor timing.

[jdb]

Early ignition systems, and those with points and condenser ignition systems, used a Ballast resistor to drop voltage at the coil to about 8 volts after starting to protect the coil from heat and burning the windings. Later systems used a resistor wire.

I am pretty sure if you monitor power to your coil + terminal and when you get power and when you don't at that terminal, you will be on to finding the root cause of this issue.

So with key on but engine not being cranked over, is there power to + terminal of coil?

I hope this helps find the issue, I am sure it is frustrating.

Jeff

 

[PinkyToe]

 

What work had you carried out before you started having problems? Cam belt? Distributor? Water pump?
If you are not careful doing any of those you can upset the distributor timing.

I’ve done the full timing belt, water pump, dizzy cap and rotor a while ago whilst fixing other issues. Before I started chasing this starting issue I had a complete no start caused by the main 12v supply to the fuse box being loose. In try to fix that issue I changed the alternator brushes/voltage reg and had been playing around with the ignition switch. Despite my efforts to find something out of place everything seems in order under the dash. 

I am pretty sure if you monitor power to your coil + terminal and when you get power and when you don't at that terminal, you will be on to finding the root cause of this issue.

So with key on but engine not being cranked over, is there power to + terminal of coil?

Key in the run position I have 12v to term. 15 of the coil. I think your right jdb about the coil, becuase when the car dies it just stops flat and doesn’t stutter or stumble so I think it’s losing spark not fuel but I could be wrong. I’m going to check through the ignition system today with some help and try to see if anything fails when going from start to run positions.

[JohnH]

 

What work had you carried out before you started having problems? Cam belt? Distributor? Water pump?
If you are not careful doing any of those you can upset the distributor timing.

I’ve done the full timing belt, water pump, dizzy cap and rotor a while ago whilst fixing other issues. Before I started chasing this starting issue I had a complete no start caused by the main 12v supply to the fuse box being loose. In try to fix that issue I changed the alternator brushes/voltage reg and had been playing around with the ignition switch. Despite my efforts to find something out of place everything seems in order under the dash. 

 

So, you have sucessfully started the engine after changing the cambelt? The distributor is driven off the small pulley and its very easy to move that when refitting the belt, which will change the distributor timing.

[PinkyToe]

Yes after changing all those parts I was able to start the engine and it actually ran really well. Although on these m20 L-Jet motors the dizzy runs off a gear on the crankshaft. Timing im sure is good, I have a timing light there and could check it again. I suspect the problem is more electrical as when I hold the key just off of the start position sometimes I can trick the car into running for a few seconds before the starter tries to engage again, in this position it revs and sounds as normal. 
I was wondering if anyone knew exactly which sensors the motor references when cranking over and if this is different to the sensors it references when idling/warming up as maybe this is causing the car to die. 
Also I tested the ignition control module as per the e30 wiki states 

The only checks you can do to the control unit are to ensure that it is getting a supply. On the Siemens unit, remove the large round 8 pin plug and check for voltage (ign on) between pins 3(+) and 6(-). Pins should be numbered inside the plug. On the Bosch unit, check between pins 4(+) and 2(-).

when I did this I only had 10.6v at the plug, maybe this could be a lead into the cause of the issue. 

For now I think it would be best to figure out if the car is cutting fuel or spark or both when it dies, so I can hone in on where the problem really lies. I will keep updated as I do some more testing tommorow. Any further suggestions are welcomed ass swell 
 

[JohnH]

Sounds like the ignition switch to me. Did you test it as per Bentley? Did you remove the switch from the column and turn the mechanism using a screwdriver?



I recently had a similar problem, hence the photo. I fixed mine by replacing it with a spare I had knocking about.

Maybe someone has taken one apart. I couldnt workout how to, without destroying it.

Try bypassing it by running a wire from battery positive (+) to terminal 15 on the coil. Hook up the wire, turn the key to Start, then let it go. Lets see what happens.

[PinkyToe]

John,
I tried a couple things, 
I bypassed the switch by bridging 12v from the switch to the run wire (green one I beleive) 
I also tried jumping the coil term. 15 straight to bat + and still had the same issue. 
This tells me that the ignition system from the coil back is not apart of the issue but im not sure how true that is. I'm starting to lean towards the injectors as the issue but what do you think?
 

[Mike W.]

Guessing M20 distributors are similar to M30 L jet electronic ignition, you can probably rock the rotor back and forth enough to generate a spark. At least you can on M30s. Much easier than cranking it all the time.

[Aldo525]

Read this post very quikly, so not sure if the Ignition module is OK???...some similar issue in my father's e30 318i many years ago. The culprit was a bad "Telefunken" ignition module (the one with two round connectors)

 

[PinkyToe]

Aldo, 
I somewhat suspect the same issue. When I checked the voltage into the ignition module it only showed 10.6v and I couldnt seem to get a reading from the pulse generator on the distributor. do you know how he went about testing his, mine is a seimens unit? 

[PinkyToe]

I have been attempting to do some diagnosis today and still I cannot find a fault in the fuel or ignition systems. I know that all the major components are working as the car can and will run with the start held just off. I was wondering if anyone knew or had any information as to what changes between the starting system and the running system. Are there any sensors that are bypassed when starting or any systems introduced when in the run/idle mode. I think that this is where I am going to find a solution. 

[Mike W.]

I have been attempting to do some diagnosis today and still I cannot find a fault in the fuel or ignition systems. I know that all the major components are working as the car can and will run with the start held just off. I was wondering if anyone knew or had any information as to what changes between the starting system and the running system. Are there any sensors that are bypassed when starting or any systems introduced when in the run/idle mode. I think that this is where I am going to find a solution. 

Without a schematic I can't say for sure, but probably...

On earlier L jet cars, power was supplied to the coil thru a resistor in the run position and straight 12V in the start position. Electronic ignition E12 used separate resistors that look like resistors, earlier point type cars used a transparent wire that had resistance built into it, but no visible resistor. Also power is supplied to the thermo time switch which in turn operates the cold start valve for up to 8 seconds I believe, if it's stone cold.

I've got all the E28, US market ETMs, but nothing for a 520i. If you can point me towards on I can tell you.

[Aldo525]

Aldo, 
I somewhat suspect the same issue. When I checked the voltage into the ignition module it only showed 10.6v and I couldnt seem to get a reading from the pulse generator on the distributor. do you know how he went about testing his, mine is a seimens unit? 

 

 

Here is a "How to test" the Ignition Module. In spanish but if you need I can translate the procedures. I think you have the second (bottom) IM. Brands are Telefunken, Siemens and I remember (but not sure) Temic.

[JohnH]

LE-Jetronic from Haynes 1560.
 

[PinkyToe]

These images show the Siemens style ignition module that’s on my car. 

 



 



 



 

[Mike W.]

I've spent some time looking at it, mostly Johns diagram but they seem to be the same except for the handwritten color changes, which troubles me wondering if someone made changes or if things just changed over the years.

Anyway, simple story is everything goes thru the fuel pump relay. The ignition switch is not shown so I can't really tell there, but there's nothing that shows an input that would come from it. The fuel pump relay powers the fuel pump, the electronic ignition, the injectors and the coil. I'll continue to look at it a little more but at this point that relay is my best guess. US spec E21s had a similar relay even with K jet instead of L jet and they were known to be problematic. But I'll look more later.

[Mike W.]

OK, with more time on it I found where a start signal goes to the fuel pump relay and the ECU, along with the starter of course and the diagnostic connector. Not knowing exactly how the FP relay works, it's possible once the start signal is lost, the relay drops out. I'm reaching a bit here as I don't know exactly how that relay works.

I've marked it up with some colors, black would appear to be hot, going to the coil among other places.

The yellowish brown would be the start signal from the key.

Green is what I think makes the electronic ignition electronic, so it would probably be a negative voltage, only in a pulse after a trigger from the distributor body.

Red would be 12V, I'm not sure if it comes from the FP relay or the ECU, along with supplying voltage to the injectors, AFM and throttle position switch. I think 15 terminal is what actually turns on the FP relay, but on the K jet E21s I'm more familiar with I think it has to be triggered first by the starter, then the ECU sees that the engine is running and keeps the FP relay on.

Yes, there's a lot I just covered and it's confusing. Broken wiring is always a possibility too. One of your problems troubleshooting is so much is controlled by the FP relay, but only when it's cranking or running. I keep going back to the FP relay as the source of the problem, but I can't say for sure. Open the image in a new tab to get a readable size image.

[PinkyToe]

Thanks Mike,
I had a crack at bridging it earlier but I wasn’t sure my bridging harness was doing what I intended so I moved on. I’ve had the fp relay open before to check the function of it and I may have damaged it in the process. Peninsula BM sells replacements so I’m going to order a replacement. I will update with the results. 
 

[PinkyToe]

Swapped in a "new" second hand relay from peninsula bm and viola. Now she starts and stays running when the key disengages. 
Thanks all for the help   
Now on to the next issue 
 

[Mike W.]

Swapped in a "new" second hand relay from peninsula bm and viola. Now she starts and stays running when the key disengages. 
Thanks all for the help   
Now on to the next issue