Adriano350z

Hi guys,

after the rev up rebuild in a company, the engine runs with errors.

I've changed the spark plugs for NGK, Lambda on engine.

After that checked compression of cold motor and on first cylinder it is 4 bar and goes constantly down.

The other ones have 13 bars.

What could been happened?

Thanks for advice.

dkmura

iTrader: (64)

Sorry to hear about your VQ problems. What caused you to have it rebuilt in the first place? As to the lack of compression on #1, there could be many possibilities: defective head gasket or improper torqueing of head, defective rings or improperly installed, problems with the head/valve seats- the list is endless.

Why have you not taken it back to the company that did the rebuild?

Adriano350z

It happened after a broken crank.

The previous owner had allready done something in the engine forged rods, APR, ACL bearings etc.

dkmura

iTrader: (64)

So this was the second rebuild of this engine? Again, have you talked to the shop that did the rebuild this time?

Adriano350z

Correct, it is the second rebuild.

I've spoken to the shop, they say everything was recovered, blocks, etc. all parts were installed as brand new, including ACL Race bearings.

An advice has been given, to look with a camera on 1 cylinder, maybe something foreign has been fallen into.

Maybe the ECU must be reseted?

After the broken crank error like P0301 cylinder 1 misfire, P0300 random/multiple cylinder misfire, P0340 camshaft position sensor bank 1 and P0345 bank 2.



Right now the misfire error is still there.

dkmura

iTrader: (64)

If your compression reading is correct (and you may want to check it again to be certain), than it's a mechanical issue. There's nothing to be "reset" in the ECM that would account for that low a reading in compression.

Adriano350z

Thank you.

Compression was measured twice - same effect.

At least I will look with a camera on first cylinder, that should say what is going on.

Can the work be done on sitting engine, what you mentioned in second post, by current mechanic?

I don't want to pay twice for in and out of the engine.

Jennifer 2

Adriano, when my dad would diagnose an engine in his shop with a low cylinder like you have, he would use his air flow meter to do a ‘leak down test’. By increasing the airflow into a leaking cylinder he could identify the problem. If an exhaust valve is leaking you will hear the sound of escaping air in the exhaust pipes, an intake valve, listen at the throttle, broken piston rings, take the oil filler cap off and listen for a sound in the crankcase. Also take the radiator cap off and check for air bubbles, which would indicate a problem with the head gasket. He listened in other places, but I don’t know what he was checking for.

If the head and its valves were rebuilt, it could be that an overly thick shim was used to set the valve backlash; this would prevent one of the valves from closing completely. This condition could be easily corrected without removing the engine from the car. A skilled and experienced mechanic can usually quickly locate the problem.

dkmura

iTrader: (64)

I concur, a leak down test--done by an experienced tech--could narrow the possibilities.

0jiggy0

iTrader: (13)

Quick check. Put a capful of oil into the cylinder. If the compression goes up its a piston ring issue.

Adriano350z

Putted a camera inside 1, 2 cylinder.

Valves are closed, clean inside, head is rebuild.

I noticed that pistons, as well as valves are 2 hand, maybe from my old engine.

Mechanic investigated and has sad that piston is not broken.

dkmura

iTrader: (64)

Have you done the leak-down yet?

Jennifer 2

Adriano, the camera can’t really tell if one valve is being held open one hundredth of a millimeter or so from a wrong valve adjustment bucket. Also the camera can’t see if someone forgot to put a piston ring on the piston (or broke it during installation) etc.

Adriano350z

Ok, so I will do the leak down tomorrow.

Adriano350z

Today I did a leak down test with oil in a cylinder, the compression is the same 4 bar and goes slowly down.

Jennifer, checked also the radiator cap off for bubbles and there were none of them.

dkmura

iTrader: (64)

This is key: having a skilled and experienced mechanic do the leakdown test can eliminate a lot of possibilities. Since the OP did the test themselves, that didn't happen. At this point, the only thing I can suggest is to have the Z towed to an experienced technician and have them do a full diagnostic of the engine.

Getting advice on an Internet board can only go so far...

Adriano350z

I did was an figurative expression. The car is still in other shop, they have send the engine to another company for rebuild, puutted it in, so the job was done by an mechanic, so they must be the valves.

Mechanic didn't want to do the check procedure as it is nonsense in his oppinion, because the head must be removed anyway.

Happy NYE.

dkmura

iTrader: (64)

OK- that makes more sense. And it sounds like an experienced technician will pull the head in the car and determine what the problem is. Good luck with getting it fixed in the New Year!

Adriano350z

The car was taken to other shop.

It was a piston ring issue, the last mechanic did the leakdown test in a wrong way.

Compression is fine now, but second problem appeared.

The right chain is loose.

eDIT: on other cylinder compression goes to 7 now, engine must be taken out again.

Adriano350z

Engine sounds fine now.

Is the oil pressure on idle 11 - 12 psi, full warm up fine?

Valvoline 5W50 inside.