M42 won't start

[Jordan]

At this point you have verified compression, fuel, and spark. It should be starting.

If its not... timing is an issue. More important then spark is a properly timed spark.

Pull the valve cover and set the engine to #1 TDC and verify camshaft timing. This will take a few minutes and wipe out a big potential problem.

[KenC]

Pull the valve cover and set the engine to #1 TDC and verify camshaft timing. This will take a few minutes and wipe out a big potential problem.

Is there a resource online on how to do this? I've never really worked on timing, but I'm pretty mechanically inclined.

Also, is there a reason why the timing would have become off after sitting for about 8 hours?

[Hick]

Also, is there a reason why the timing would have become off after sitting for about 8 hours?

No, unless something broke when you turned the car off or tried to start it.

Im at a loss. Spark, fuel... should start.

[M42Technik]

Odd problems, can't help you much lad. When my car wouldn't start it ended up being the fuel pump that went bad after only six months! But you are getting fuel, so I'm unsure myself.

Good luck dude!

[KenC]

I'd like to make sure timing is correct.
Is there a site online that can walk me through it?

Could it be a mixture issue?

[James Crivellone]

you didn't confirm, but did you try the WOT trick? I have seen it start many M42/M20 motors that act like they should start and did not.

[KenC]

you didn't confirm, but did you try the WOT trick? I have seen it start many M42/M20 motors that act like they should start and did not.

Didn't try it. Joe was actually the one tinkering on it today while I was at work.

So would it solve the problem if it starts up at WOT?

[James Crivellone]

Didn't try it. Joe was actually the one tinkering on it today while I was at work.

So would it solve the problem if it starts up at WOT?

On a few of the motors that I've seen it happen, it just solves the starting issue, most are older motors that do consume a bit of oil, however I've never really dug into the issue.

The ECU does run a slightly different map at WOT, so perhaps that aggressive map is what really kicks the motor over. Motronic is so dumb I never go to far into it.

[KenC]

I'll give it a try tomorrow.

[KenC]

UPDATE:

Tried the WOT start - Nothing

Pulled the valve cover off. Rotated the crank to TDC. Cams looked to be pretty perfect. Hasn't jumped a tooth.

We're still baffled at this point.
We decide to compression test it just for shits. I had done this about a month ago and got 190-210 on all four so I wasn't expecting anything too drastically different. Boy was I wrong.

ALL cylinders are reading 80-100psi for compression.

We put the valve cover back on and did a leak down on three of the cylinders - 90% leakage on all of them. We can't find where it's leaking from, but it sounds like the air is coming right back up from the sparkplug holes.

We then do another compression test. ZERO compression now. I'm not sure how in the course of 15-20 minutes I could go from 80-100psi (which is WAY low for the M42) down to absolutely nothing.

We even had a running M42 to compare with so we could rule out the gauges being faulty.

We're pulling the head tomorrow.


WTF could cause that? All of the cylinders have essentially no compression now.

[Hick]

The gauge is wrong, dont tear it down. Squirt some oil down in the cylinder [about a half a cap full] let it sit for a second and do another compression test. That will check the rings.

If the FPR is bad it will dump too much fuel into the cylinder which would cause it to not run also.

Unloader relay, which diverts the power to the starter when cranking could be bad. IE Cranks then when it switches back to 'normal operating' it dosent turn on the fuel pump/injectors/coil/anything.

[KenC]

The gauge is wrong, dont tear it down. Squirt some oil down in the cylinder [about a half a cap full] let it sit for a second and do another compression test. That will check the rings.

If the FPR is bad it will dump too much fuel into the cylinder which would cause it to not run also.

Unloader relay, which diverts the power to the starter when cranking could be bad. IE Cranks then when it switches back to 'normal operating' it dosent turn on the fuel pump/injectors/coil/anything.

We did the ring seal with oil trick, and it didn't really help.

Where is the Unloader relay?

[ak96ss]

If you tested it on another engine, and it worked, I would say the gauge probably isn't faulty, although that obviously doesn't rule out operator error. I would find it hard to believe, though, that you could make the gauge work on one engine, then totally screw it up on all four cylinders of another engine.

Unloader relays are K5 and K7, but that won't help your lack of compression.

Are you positive timing is set right?

[KenC]

Yeah we tested the gauge on another engine to make sure that it wasn't the gauge.

I'll try those relays and swap in another FPR.

Timing:
We put cyl 1 at TDC and the arrows on the cam gears were both parallel and pointing straight out of the head. We can get a cam alignment tool.

[Hick]

The cams line up by placing a straight edge across the blocks all the way at the back of the cams so that there is no gap on the straight edge, best judgement is best, do not need to be perfect.