e34 540i hot start issue

[Fordkoppie]

My e34 540i6 is doing its utmost best to infuriate me as much as it possibly can with a recently developed intermittent hot starting issue. The starter would swing like crazy, but with not a single hint of taking.

When the car is cold, it always starts.

It has also never died after already running.

I tested the coilpacks, and none of them have any spark when the car is performing its little tantrum.

I tried a different crank position sensor off another M20 engine I have, and the problem persists. It would start only sometimes when hot.

Then I tried a fresh battery, and while its definitely better, the problem still presents itself every now and then.

Someone suggested that it might be the key, but I tried the spare key with no noticeable improvement.

Even tried to push start when its in this “mode”, but it simply won’t take.

Any suggestions?

Matches?

 

[Blue Shirt]

It sounds like a bad connection on a sensor somewhere, which intermittently prevents the DME from sending signals to the coil packs.

Since you already tried replacing the crank sensor, perhaps try some of the others like the throttle position switch, camshaft sensor, knock sensors, coolant temp sensor?

 

[Fordkoppie]

throttle position switch, camshaft sensor, knock sensors, coolant temp sensor?

I can disconnect any of these while its still cold, and it would start.

PS - not running as it should, but it does actually start

 

[Blue Shirt]

Dodgy MAF connector?

Is there a fuel pressure switch on the M60B40? Perhaps you have low fuel pressure when the pump is hot (or has overheated) and the lack of fuel pressure tells the DME to shut down the coil packs?

My last guess would be to get a new DME relay into the fuse box.

 

[ChefDJ]

Matches?

After reaching the 200k milestone??? :RedNo:

 

[Blue Shirt]

Oh, another suggestion, I remember that E36's of the era suffered from cracked solder joints on the DME circuit board. This would typically kill the DME intermittently when it gets hot. Its worth a look inside the DME if you cannot isolate the problem to a faulty sensor or dodgy connection somewhere.

 

[Fordkoppie]

Dodgy MAF connector?

Is there a fuel pressure switch on the M60B40? Perhaps you have low fuel pressure when the pump is hot (or has overheated) and the lack of fuel pressure tells the DME to shut down the coil packs?

My last guess would be to get a new DME relay into the fuse box.

Starts fine without a MAF.

I am unsure about a fuel pressure switch. I think its a mechanical FPR

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Oh, another suggestion, I remember that E36's of the era suffered from cracked solder joints on the DME circuit board. This would typically kill the DME intermittently when it gets hot. Its worth a look inside the DME if you cannot isolate the problem to a faulty sensor or dodgy connection somewhere.

Thanks.

As a last resort I would check this, because I would prefer not to break the seal on th std ECU.

But if that is where the problem lies, it needs to be done. Will definitely keep it in mind.

 

[Blue Shirt]

Have you tried removing a plug when it fails to start to see if the plug is wet (flooded) or dry?

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As a last resort I would check this, because I would prefer not to break the seal on th std ECU.

But if that is where the problem lies, it needs to be done. Will definitely keep it in mind.

Try a new DME relay first before opening the DME.

 

[Fordkoppie]

Have you tried removing a plug when it fails to start to see if the plug is wet (flooded) or dry?

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As a last resort I would check this, because I would prefer not to break the seal on th std ECU.

But if that is where the problem lies, it needs to be done. Will definitely keep it in mind.

Try a new DME relay first before opening the DME.

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No I have not removed a plug yet. But I do know this car is programmed/wired as such that the fuel pump does not turn on if there is no spark.

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Thanks. That is a brilliant suggestion.

 

[maximus]

A solid kick would do

 

[naushad]

my merc did the same thing, crank angle sensor

 

[Budleigh]

^ what he said.

 

[Blue Shirt]

Mr Ford, is the 540i running again?

 

[Fordkoppie]

With the fresh battery, it has done the no starting thing once, so I am driving it everyday now to see if the problem wont reappear.

2 days so far with no issue. In the process I actually hope the suspect component fails completely, so I know once and for all what the hell it is.