M42 won't start

[nando]

Aluminum head rebuilders says: exhaust valves not seating, due to carbon buildup. Fairly common with the M42s they said. The flash carbon buildup was probably due to a minor overheat...

hmmm

could that also cause compression loss?

[Hick]

yes, but a leakdown test is a better test for bad valve seating

[BBY1104]

Glad to see problem was fixed. 280k wow, great shape for the milage

[Funkmasta]

yes, but a leakdown test is a better test for bad valve seating

a leakdown only locates the source of a bad compression reading...

The motor ran like a champ once we R+R'd the head. every other factor was the same. weird

[Hick]

I still think kencopperwheat problem was something else. The car wouldnt just stop running even if they headgasket or valves went. The way he says 'it just cranks over but wont fire' means it was something else you guys much of fixed putting it back together.

[KenC]

So the car isn't running again... same symptoms. Have fuel, spark, and timed correctly. Compression is about 80.

Some one on M42 club said that they have seen similar symptoms due to a faulty fuel pressure regulator.
Too much fuel is dumped into he cylinders, which washes away a lot of the oil on the cylinder walls... which can lead to low compression.
He suggested putting a bit of starter fluid in each cylinder and then putting a little bit of oil in each and restarting it.

Seem plausible to any one?

[Nomadic]

So the car isn't running again... same symptoms. Have fuel, spark, and timed correctly. Compression is about 80.

Sorry to hear its not running again. Did the starting problem happen again suddenly, intermittently, or did it get worse over time?

Is it 80 across all cylinders?

Did you try squirting some oil in the cylinders and doing another compression test? A higher compression reading with oil in the cylinders would suggest the rings.

He suggested putting a bit of starter fluid in each cylinder and then putting a little bit of oil in each and restarting it.

Seem plausible to any one?

If the rings are NOT holding much compression, the oil would help the rings seal temporarily. The oil with the starting fluid could start a car with low compression from bad rings. I don't know if it is wise to do this or not. But certainly plausible.

An old Alfa guy told me that putting a fresh head on a block with marginal rings will accelerate the rings demise... but it shouldn't happen that quick...

[KenC]

Update.

I dumped a ton of oil (a cap or two) into each cylinder and checked compression again. It was around 200 on all of them.
We put everything back together, dumped more oil in, then it fired right up.
I don't think it's the rings because this hasn't been a consistent problem. Also, I checked compression about two months ago on a luke warm engine and it was 190-200 on all cylinders (with no oil added).
I'm going to buy a new fuel pressure regulator today and pop it in this weekend.

[Nomadic]

Any further updates? Still running strong? I'm curious if the regulator did the trick.


My #4 cylinder is a bit low on compression but comes back up with oil.. I'm planning on replacing the injectors and the pressure regulator to see if #4's compression comes back up and smoothes things out.

Cheers,

[blueboi69]

Hi!

I have more or less the same problem. To take the story short, I figured it out that, the injectors don't let the fuel go into the cylinders.

The injectors are working fine, I've tested them separately.
Fuel goes until the injectors with pressure.
Sparks fire.

If a few drops of fuel fuel go on the intake valves, the engine is almost starting. At least it fires a few times. I am sure there is something wrong with the injectors management.

How can I test it? I see 3 wires. One is Red-White, it has 12V. The others also have 12V, when I crank it dropes to 10V, but I think it should go to ground, isn't it???
I changed the Crankshaft sensor and the camshaft sensor and I also tried a different ecu. Enginge still won't start.
I can't hear the injectors clinking. What voltage should I see from the ECU? I think is must be ground, that's how the ecu controls the injectors. I'm using a simple multimeter and maybe it can't respond so fast if the ecu is switching ground so fast. Any other solution?

Please help! :)

[SergioM42]

You sure? These things lose compression when they sit for a like a week (valves not seating or stuck piston rings, I have no idea the exact cause). Pretty much what was described in this thread.

Listen to the engine carefully when it's cranking and you'll be able to tell it sounds like there is no compression stroke and the starter is turning it over just a tad too easy.

No reason to panic, keep cranking it and keep listening... the compression will slowly start to come back until one cylinder catches and another and it will fire. Play with the throttle and keep it alive until the engine smooths out and you're back in business.

Personally, I would not spend any time tearing down such an old engine to find the root cause. In every day use the engine fires and runs great and comps out at 200 psi when warm.

[blueboi69]

yep, It was the cable going to the injector. The +12V wire was broken.... now it's runnin :)