DrDoe

Background:
Car was shaking in idle. Indy shop replaced plugs, distributor and wires. It's still shaking after parts replacements and the shop pointed to no compression on V8 cylinder #4. All other cylinders read 140.
Took to another dealer for diagnostic and dealer said car needs a new engine.
Car runs fine and no CEL but shakes violently in idle. Coolant reservoir showed low fluid but no leaks were found. Muddy sludges were found at the oil filling cap. Oil drained and no metal dust were found.
Question:
Assuming passenger side head gasket is blowed. Can it caused no compression on 1 cylinder? Should it be low and not zero compression?

Plutoe

It's a new block---don't you love those value auction cars

DrDoe

Not helpful

Plutoe

You got professional help that you don't believe and or won't accept---what's your point!

DrDoe

How can coolant leak caused zero compression on one cylinder?

Astro14

Coolant leak won't cause zero compression.

Blown head gasket will cause a coolant and/or oil leak and may cause a compression drop, but doubtful that it will go to zero.

Broken valve, broken piston, completely worn bore...the things that cause a zero reading are mechanical, and expensive to fix.

And it doesn't run fine with zero compression on one dead cylinder. It runs. And that's a testament to a Mercedes engine, but it doesn't run fine.

A compression test isn't hard to do. You might want to verify the readings. I would like more detail from the dealer on "Needs new engine" - how did they conclude that, exactly?

Sludge on the oil cap is a sign of moisture in the oil. Could be coolant. Could be lots of short trips leading to moisture. Doesn't prove anything. No metal particles in the oil proves nothing as well. You could have a broken valve where the pieces went out the exhaust. Or a broken chunk of piston in the oil pan that won't fit out the drain plug.

Only time I've ever seen zero PSI, there were big broken parts in the engine. Big, broken, parts.

BenzVince

anytime a zero compression in one of the cylinder, is essentially a dead cylinder, which either your valve broke or stuck, or blown piston. SO yes, you will need a new engine. It sucks, but it's ultimately up to you what you're gonna do, scrap the car, or get a new engine.

DrDoe

I thought so about the relationship between the coolant leak and no compression. Thanks for the confirmation.
Questions:
1. The distributor, plug and wire were replaced but if any one of those was defective then it would still give no compression right?
2. Can bad seal or blown piston be replaced by removing the cylinder head? Why can't the engine be rebuild?

tusabes

a rebuild will cost $4000-8000
a good used engine will cost $400

there are so many good used engines out there it makes no sense to spend labor time to rebuild . Just swap in a used engine

wallyp

A leak-down test will tell you immediately what the problem is. A tester is installed in a spark plug hole in the affected cylinder, and compressed air is blown thru the tester into the cylinder. A gauge on the tester tells the amount of leakage, and the hiss of escaping air tells where the leak is. Hissing at the oil filler port on the cam cover shows damaged piston or cylinder wall. Hissing at the MAF or throttle body shows a damaged intake valve. Hissing at the exhaust pipe shows a damaged exhaust valve.

Zero compression is more often a valve problem. A head crack or failed head gasket bad enough to show zero compression would be blowing huge quantities of coolant out of the system. A broken piston would usually make a lot of noise, and would cause heavy smoke from the exhaust.

It is possible that you could fix a failed valve by pulling only the affected cylinder head, but the labor and parts cost would be close to the same as installing a used engine.

DrDoe

I wish that I could do a compression test right now but I can't. Head cover is off. Upper intake manifold is off. Fuel rail is about ready to come off. Then lower intake manifold and the head.
I'm almost there.
I'm pausing because of couple suspicious issues:
1. Plug on the problem chamber can be removed by hand.
2. Ignition wire to the problem chamber had corrosion. Perhaps no contact?
Do I put things back or do I go all the way and remove the head? What would you do?

tusabes

Maybe the spark plug was never installed fully by the Indy shop , that could cause no compression

wallyp

Do you actually mean that the cylinder had zero compression, or do you mean that the cylinder had a hard misfire? Huge difference!

DrDoe

Indy shop said no compression in one cylinder and all others are good. I wish I do compression test myself before taking things apart but I didn't.
Engine is shaking in idle mode and it could be from ignition source from the evidence. I stick a camera into the trouble cylinder and the pistol looks fine. Cylinder walls also look fine with no vertical scratches. Trying to look at the valves but the camera angle isn't co-operating...

DrDoe

I got some images of the head valves finally. I don't see any burnt marks
Wall and piston images
I think I'm going to put things back to see if it's still shaking or not

wallyp

My first priority would be to determine what the actual compression is in the affected cylinder.

kraut56

stick a finger into the plug hole and have somebody crank it for a few turns.
Might be wise to make sure the engine does not actually start.
You will know if there is compression or not.
Good luck!
Alternate: Buy a cheap compression gauge.

If you get more involved, crank the engine without ignition, and listen: if there is no compression you will hear the engine speed up momentarily in a steady rhythm.

... of course there is always DAS, if you can get it.

mrmotoguzzi00

If you've torn it down this far, then your mechanically inclined and I would buy a decent compression gauge and check it myself

DrDoe

I'm learning. The passenger valve cover is back on but the upper intake manifold and the throttle valve body are still out. Is it safe to do the compression test at this point?

Mashoodsharaf

I have two engines for sale if you're located in California. Send me a pm if You are interested

wallyp

Should be safe to check the compression - if you make certain that both the injection and the ignition are dead, dead, dead.

DrDoe

In the last couple of weeks, I put everything back together and had hard time with timing. It would crank but won't turn over.
Finding the TDC was easy but positioning the distributor was quite a challenge. I nailed it today and the engine is back to life.
It wasn't shaking at all and the compression all 8 cylinders are good. Disconnected distributor wire was the culprit.
This is the case of dishonest professional at the indy shop and a lousy diagnostic job at the dealer.

AlexMercedes

This is why I never trust my car with anyone.

Always do repairs yourself, and you will never go through any bs problems, because if you disconnected something you would reconnect it right on the spot. Instead of some lousy tech not caring about anything and the stealership trying to throw as much bs at you as they possibly can just to make the most money out of you.

Welwynnick

Did the shop actually do a compression test on all cylinders?

With a mis-firing engine, it's easy to jump to the worst conclusion, but the cause is often much more benign.

Nick

tusabes

So the Indy shop that replaced the distributor didn't do it properly ? I would demand a refund of at least the labor bill if not the full invoice