M6 E24 won't start

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smracer9
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M6 E24 won't start

Post by smracer9 »

OK, hoping that many of you that know more than I do can help me out.
87 M6, not running and hasn't for about 5 years. Replaced in tank pump,cleaned tank, replaced fuel filter, bench tested fuel pump (OK), blew out fuel and return lines from fuel rail back, cleaned fuel rail, replaced injectors, and pressure regulator. Replaced cap and rotor.

Has good spark and plenty of fuel. The engine cranks and sounds like it is about to start but.......not starting.

Compression test: 5 cylinders have about 125 #5 cyl. at 100.

Any ideas, suggestions would be appreciated.

Thanks,
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raykoke
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Re: M6 E24 won't start

Post by raykoke »

How old is the fuel?

How are you checking for spark?

Are the plugs wet?

Are the spark plug cables in the proper order?

GL,

Ray
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smracer9
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Re: M6 E24 won't start

Post by smracer9 »

Thanks Ray for the interest.
This ones is a puzzler since I have spark and fuel I am thinking it must be something with the timing. Even when I dump fuel into each plug I still do not get it to fire.

Fuel is fresh, high test
Grounded plug to engine and observed a strong spark.
Plugs are wet
Yess plugs are in the proper order

Thanks
Dave
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Re: M6 E24 won't start

Post by ron »

"smracer9"

We need your location in your profile as requested by admin.
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TN_M6
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Re: M6 E24 won't start

Post by TN_M6 »

Sounds like it has been flooded then flooded some more. I would pull the fuel pump relay and then crank it for a bit to see if it fires. If not maybe dry out the plugs and re-install then see if it kicks over on the remaining fuel or even try ether before putting the relay back. If the timing is close it should try to fire with clean plugs and some combustible present.

Be very careful 'dumping fuel' into cylinders. You can get them so wet they dry out the rings and score the cylinders.

Timing is not adjustable on these cars. How strong is the spark? I've seen a really dirty or moisture laden cap & rotor give some spark but not enough energy under compression. OOPS... I think you said replaced C&R.

From there you could have several problems affecting mixture and if they are even a bit rich they tend to foul or get wet plugs quickly.

Bad FPR, it could even be dumping fuel in through the vacuum hose (easy to check), otherwise a fuel pressure test would help diagnose.

Sometimes a bad CTS or connection causes enough extra fuel and it floods pretty quickly.

More unusual would be something hanging the AFM open commanding way too much fuel.

There's a few things to try.
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Boggie
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Re: M6 E24 won't start

Post by Boggie »

smracer,

Have you resolved your starting issues? If not, I found THIS INFO very useful. When I 'found' my car it had not been run for some time and we couldn't get it started. The Motronic article above provides a methodical, step-by-step test sequence and helped quickly identify a faulty sensor. Once replaced the engine fired up instantly.

Ian
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Brucey
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Re: M6 E24 won't start

Post by Brucey »

smracer9 wrote: Mon Feb 12, 2018 2:56 am Compression test: 5 cylinders have about 125 #5 cyl. at 100.
It is perhaps a bit knackered, judging from those figures.

Q. does the engine fire on eezy-start? If so (and you are certain you have good spark) then you have to look at the fuelling. If not then maybe the compression has passed the point of no return.

BTW the cold start injector alone is usually enough to make the engine fire and then quit after a few seconds, if the main injectors are not delivering fuel. That it does not fire at all suggests that the CSI is not working or that the compression is too low.

The CSI works completely independently of the main injectors; all you need is fuel pressure, a working CSI and a working thermotime switch and it can't fail. The circuit only comes live during cranking. Look in the workshop manual for how to test the thermotime switch.

cheers
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smracer9
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Re: M6 E24 won't start

Post by smracer9 »

Thanks to all that have offered ideas. We worked on the car this weekend. Checked fuel supply, removed hose and pumped fuel into bucket looks like it is getting enough fuel. The return line has been blown out as well. Ran compression test, all are about 125 with the exception of #5 which is about 100.
We have a strong spark and a good supply of fuel. We thought that possibly we had a timing problem where the chain might be off but after pulling the rocker cover found that both cam marks and TDC on the pully line up. We did get a little sign of life by using starting fluid. If I didn't check the fuel flow I would say that the engine is not getting enough fuel but I don't think that is the case since we removed the fuel line and pumped quite about out.

I am thinking we may have an electrical problem.

Have several things to check after reading your posts, hope to get some time on it this week.
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Re: M6 E24 won't start

Post by hornhospital »

Put a pressure gauge on the fuel line and test it. Flow means nothing if you don't have sufficient pressure. Pumping unrestricted into a bucket can show plenty of flow even from a dying fuel pump.
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Brucey
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Re: M6 E24 won't start

Post by Brucey »

hornhospital wrote: Tue Feb 20, 2018 6:51 am Put a pressure gauge on the fuel line and test it. Flow means nothing if you don't have sufficient pressure. Pumping unrestricted into a bucket can show plenty of flow even from a dying fuel pump.
you are meant to test fuel delivery after the FPR, so that you are testing fuel delivery at pressure. That said, you don't know what the pressure really is unless you measure it....

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Ralph in Socal
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Re: M6 E24 won't start

Post by Ralph in Socal »

Brucey wrote: Sun Feb 18, 2018 5:30 pm
smracer9 wrote: Mon Feb 12, 2018 2:56 am Compression test: 5 cylinders have about 125 #5 cyl. at 100.
It is perhaps a bit knackered, judging from those figures.

Q. does the engine fire on eezy-start? If so (and you are certain you have good spark) then you have to look at the fuelling. If not then maybe the compression has passed the point of no return.
I think this is your issue. Those numbers are low for a US M30 B34. They are pathetic for a 10.5:1 euro motor. I don’t have enough experience with M6 CR to know where it should be but I would think it would be closer to the euro motor numbers which should be over 200.

Lost compression has to go somewhere. Valve/Head problems are typical causes of low compression. The no start problem you are experiencing could be due to compression returning air to the intake tract and preventing the motor from inhaling the necessary oxygen for proper combustion. With the injectors providing fuel, the cylinder can quickly get too rich in fuel to combust the mixture. Worse is if it does fire a little bit and sends combustion (exhaust) gases into the intake flow so the air has less oxygen and more fuel getting pumped in

A subjective way to test is to see if you can feel substantial negative pressure at the throttle body. Cover the TB opening with your hand during cranking to feel for the negative pressure. The motor has to inhale fresh air to provide the O2 necessary for combustion. Good luck

Ralph
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Ohio Jon
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Re: M6 E24 won't start

Post by Ohio Jon »

Turns out it was bad injectors. The spare set we had were no better that what was in it. We install the new injector and a fresh set of plugs and it fired right up. There is something so satisfying when you hear a car fire up for the first time that has been sitting for years.
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raykoke
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Re: M6 E24 won't start

Post by raykoke »

Yay!

Set the valves, run it hard, check compression again!

Cheers,

Ray
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hornhospital
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Re: M6 E24 won't start

Post by hornhospital »

raykoke wrote: Mon Feb 26, 2018 2:30 am Set the valves, run it hard, check compression again!
This! ^^^
The compression on my 633 was awful (100 and less per cylinder) before it ran again. Oiled the cylinders, got it running, drove it a while and the power increased noticeably. Checked compression again and it was up in the acceptable range (150-ish psi). The rings were no doubt stuck a bit. Yours probably were, too.
Ken Kanne
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