Hi all,

 

I bought a manual TT that had recently had an engine rebuild but still had some problems. I took a chance on it... this is generally my preferred approach, it's more fun... kind of.

 

When I picked up the car, I discovered that it smokes on overrun; decent plumes after engine braking at low speeds, then when the throttle is reapplied or if the engine settles at idle (typically when pulling up to a junction or slowing and accelerating between speed humps). No smoke when accelerating or at start up / idle. I have been doing a lot of googling and reading a lot of old forum threads about these symptoms, but none of them finished with a conclusive result. I will make sure that this thread has a conclusion even if it takes a while to figure out.

 

Advertised spec:

Engine rebuilt by Outlaw Customs

Wiseco forged pistons

Eagle rods

AEM series 1 ecu

615cc Nismo injectors

NA rear diff and hicas deleted

Rebuilt turbos

Stainless steel custom exhaust with H pipe and Greddy back boxes

HKS blow off valves

Currently running 380hp, mapped by DWR Performance

 

 

 

Culprit #1 - PCV

 

I noticed that the car had too much oil in it, and thought that maybe the PCV pipes are pulling oil up into the intake plenum during vacuum, which would then get burned off as the engine idled or accelerated. I looked into the balance tube holes and there is oil in the plenum.

 

I then did an oil change and deleted the PCVs for good measure (into a catch can), the pipes were full of oil! I also swapped the spark plugs from Iridium BKR7EIX (which sit too far in the head) to NGK PFR6B11C gapped to 0.035.

 

I have only driven the car around five miles since, at first it seemed much better but the smoke problem returned. Perhaps I need to drive it a bit more.

 

Should I also reroute the breathers at the front of the engine?

 

 

My next potential culprits are:

 

Culprit #2 - turbo seals

 

Culprit #3 - valve seals

 

Culprit #4 - piston rings

 

 

... anyone want to add to the list of possible culprits?

 

Cheers.

Edited February 19, 20196 yr by MattDaKav

I had exactly the same problem. Ended up to be a cracked piston. Both leakdown and compression was showing good numbers. Did change pcv valves and hoses at first which had no change.

I had exactly the same problem. Ended up to be a cracked piston. Both leakdown and compression was showing good numbers. Did change pcv valves and hoses at first which had no change.

 

:excl:

 

Uh oh!

I had exactly the same problem. Ended up to be a cracked piston. Both leakdown and compression was showing good numbers. Did change pcv valves and hoses at first which had no change.

 

Cracked crown?

 

Do you know what caused the crack on your engine?

My guess was a bad job done by a specialist and the way previous owner treated the car. Knock sensor was non operational. And the car was running increaed boost with no tune. It is all fixed now

Just had a look at your spec. If it is what it says it shouldnt be the case for you. But it doesnt hurt to get a camera in while doing a compression test.

I had exactly the same problem. Ended up to be a cracked piston. Both leakdown and compression was showing good numbers. Did change pcv valves and hoses at first which had no change.

 

I found your old thread about this: https://www.300zx.co.uk/forums/showthread.php?181790-I-am-losing-it-need-advice

 

It does sound very similar although you mention that it only happened when warm, pretty sure mine is initial driving when cold too... if anything, it seems to smoke less as it warms.

 

I'd be interested to know if the crown(s) showed any damage as I might be able to see something similar when I put the endoscope down the plug holes.

 

Cheers.

Piston had a crack on the top about 1mm from the side. While it was taken out it actually broke off. I guess the piston ring tension was the only thing holding it together. So i was close to a disaster. I do not have any pictures unfortunately.

I’d guess a ring land

Cracked crown?

 

Do you know what caused the crack on your engine?

 

Cracked pistons are caused by detonation, primarily through timing or if the motor has been run too lean at high rpm

Quick update here... I've been super busy and haven't done any more investigation into the cause of the problem, but I have been using the car occasionally with no issues other than the smoke itself.

 

I went for a proper two hour hoon last week, the most aggressively I've driven it, and it didn't miss a beat.

Edited April 29, 20196 yr by MattDaKav

Hi all, I've still been enjoying the Z, even with the occasional cloud of smoke.

 

However, the rev limiter is set pretty low, I guess as part of the safe map to try to protect the (potentially) damaged engine... The spark cut limiter fouls up the plugs. I have been running the NGK PFR6B-11C gapped to 0.035" ... do you think that I could get away with using a slightly hotter plug at 1 bar of boost?

 

I see that the PFR5B-11B was the stock plug before this was superseded to the 6.

 

Thanks.