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Low Comp And Blue Smoke Only Sometimes?

femno

By femno,
in Engines & Forced Induction

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femno Grand Master

femno

Posted
Posted

Hey all heres my probs, im kinda thinking the engines gonna need to come apart anyway, but its driving nuts what all this could be.

When i take off, i get a puff of blue out the back. Then if i slightly boost it (bout 5psi or more), more blue shit. But it will only do this sometimes, say i drive to work, it'll do it. Then when i drive home, no blue at any time at all.

Then sometimes when i crank the car over to start, i can hear it doesnt sound right, low comp on one cylinder, anyone can clearly hear it. But only sometimes when i crank it.

When i exit the car with the timer going, i can hear it missing out the exhaust. but only sometimes.

Did comp tests, came up with an even 155 give or take a couple. Engine HOT but this is when the cranking sounds fine and no miss. The engine has done 8,500 ks, forged acl pistons n rings. Valves were reground and new nissan stem seals used. Hi-flowed turbos done with the engine.

No oil in the cooler piping or breather pipes, running 18 with tuned PFC. How can these problems possibly be intermittent? and ive been watching out the back while im driving lately like a hawk to see. I havent changed anything at all, this has all started suddenly.

Soz for the novel, any insight would be good.

Cheers,

Mat.

*sighs*

Yawn Mentor

Yawn

Posted
Posted (edited)

Sounds like my car, except mine does it all the time :D Rebuild time for me haha

I had low compression on cylinder 6 which eventually got worse till its 0 comp now

Edited by Yawn
Taso84 Mentor

Taso84

Posted
Posted

Blue smoke usually means that oil is coming out the exhaust.

If it only does it when the engines cold remember that hot metal expands so the oil is probably not getting thru a gap that is present only when the engine is cold.

I hope for ur sake its a turbo on the way out and not a busted ring.

femno Grand Master

femno

Posted
  • Author
Posted
Blue smoke usually means that oil is coming out the exhaust.

If it only does it when the engines cold remember that hot metal expands so the oil is probably not getting thru a gap that is present only when the engine is cold.

I hope for ur sake its a turbo on the way out and not a busted ring.

Well, when the blue smoke happens, the car is at NOT, when driving, i always let the car warm before i drive it anyway, ive done that all its life. I never drive unless its at about 40deg.

Haha ive got a feeling it is something serious...

femno Grand Master

femno

Posted
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Posted
i would suspect your turbos for the blue smoke.

Yes head was fully reco'd; revalve regrind reset clearances etc etc, genuine nissan stem seals used...i guess that still doesnt eliminate them though.

Could very well be a turbo or two, would a faulty turbo leak oil only sometimes though? Once again theres no excessive oil in the IC piping or breather system.

A vacuum leak or dirty afm wont cause low comp on cranking, what would, but only sometimes?

Green_s13 Proficient

Green_s13

Posted
Posted

how do you know the low compression on cranking?? have you tested this? i have never heard low compression on seen the results. the other thing is a dirty crack case breather but i would have thought this would be a all the time thing

femno Grand Master

femno

Posted
  • Author
Posted

Its easy to hear. Kinda hard to explain...if you pulled one spark plug out then cranked the engine thats what it sounds like.

Im leaning toward valve stems and seals.

After much discussion i think a problem has been caused by the head porting. The lower part of the valve guide was removed during the porting, and i think this has caused valve stem and seal wear, this could explain the intermittent low comp issue if the valve is worn from side to side, it would only seal sometimes?

Is that a worthy point?

femno Grand Master

femno

Posted
  • Author
Posted
Low comp when cranking needs to be proven. DOnt assume it is. A lazy battery can cause they symptoms of low compresion when cranking.

But it doesnt do it all the time...straight after it was doing it, i tried to catch it and did a comp test quick, but everything was ok, and it suddenly decided to crank fine.

GTRsean Grand Master

GTRsean

Posted
Posted

I had a missfiring issue at idle and low load, low revs. Thought I'd lost a cylinder.

Checked compression,plugs for oil etc, all ok.

Cos it has cams, it's a little more missleading.

Wiggled the injector plug and miss went away. Fixed that up and shes all good.

Little things, always the little things.

I'd go with the turbo seals for that one, followed by valve stem seal.

NXTIME Grand Master

NXTIME

Posted
Posted

I agree...just ask TO4GTR about his "miss". Changed engine and miss was still there. Ended up being a blocked injector. :thumbsup:

I have a similar problem with my engine/turbos....blue smoke on overrun. Check turbo seals and then stem seals. Both are better than a piston ring issue.

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