Help Needed - Blue Smoke, only After Idling When Hot

[Erik]

Could really use some help, so I?ve updated and am posting this again.

Of late, I?ve noticed a couple of times when the car is warm, and sits running for a while, it blows a puff of smoke out of the back, once I start accelerating.

Looks like it?s gotten a bit worse of late, so I did a little investigated. She did get a good Eye-talian tuneup the other day, with some ZR-1 appropriate highway speeds. Through all of it, no signs of any smoke. Actually, I?ve been impressed with how little oil it burns overall. So I don?t think there are any major issues inside the engine.

Poked around here a bit, and came up with some references to the lower (?) fuel injector housing gaskets going bad, and letting oil up into the plenum, which then burns off in the first acceleration. Sounds exactly like what I am experiencing. Oh, and mine only does it out of the right exhaust pipe.

Anyone have any thoughts on this? What parts do I need to address it? What else is worth doing while it?s this far apart?

Thanks again, everyone.

[dredgeguy]

Lazy O2 sensor on one side? Might explain only one side.

[Paul Workman]

Once had a similar (very similar!) symptom that turned out to be a combination of IH/head bolts loose, & being a '90 it came w/ no primary valve stem seals.

Like yours, a puff of blue smoke when first getting on it after sitting for a few days.

Being that it is a '90, I was aware of the fact there was no primary valve guide seal on the primary valve. But, Marc Haibeck machined the primary guide to accept those seals (done when I had the heads off for porting - 91+ models came with seals on both valves).

Anywayz... new gaskets (Jerrys Gaskets) and some BLUE LOCTITE thread adhesive applied to the IH bolts (AND the same treatment for the windage cover too) stopped the oil seepage/smoke issue.

[XfireZ51]

Is it blue or white smoke?

[A26B]

Some symptoms & sources of momentary exhaust oil smoke, without excessive oil consumption.

1. PCV System. Most always affects L exhaust only:
Accumulation of oil in plenum from PCV system. Oil enters plenum through PCV vacuum source on L side of plenum behind T-body. Oil gravity flows to rear of plenum and enters mostly into #7 cylinder. Exam of #7 plug may show light oil coloration.
Not a cause for concern and has very little effect on engine performance.

Solution: Install Oil "Catch Can" system.


2. Injector Housing/Cyl Head Gasket. Can affect L and/or R exhaust.
Infrequent occurrence but known as potential source of oil smoke in exhaust. Most often occurs in high mileage engines.
Over time, injector housing bolts become loose, reducing clamping force on gasket. Differential pressure between intake vacuum and crankcase vent port causes gasket to migrate towards intake runner & communicate. Considering the injector housings have isolated passages for 3 different functions, (i) intake runners w/vacuum), (ii) crankcase ventilation and (iii) coolant @16psig, the need for absolute gasket sealing is essential.
Communication between intake runners & crankcase ventilation passages will result in oil laden vapor contamination, i.e. burning oil.

Solution: Replace Injector Housing Gaskets

3. Exhaust Valve Stem Seals. Can affect L and/or R exhaust.
Only the 1990 model LT5 engines did NOT have exhaust stem seals. All other models, 91~95 have both exhaust & intake valve stem seals.
Typically, any noticeable oil smoke in the exhaust, only occurs at startup or after extended idle and is not normally detrimental to engine performance.

Solution: Install Valve Stem Seals on Exhaust Valves. NOTE: This is not doable without significant cost to R&R cylinder heads to install seals. Not recommended or necessary for engine performance unless engine is very high mileage or damaged otherwise.

[Erik]

Some symptoms & sources of momentary exhaust oil smoke, without excessive oil consumption.

1. PCV System. Most always affects L exhaust only:
Accumulation of oil in plenum from PCV system. Oil enters plenum through PCV vacuum source on L side of plenum behind T-body. Oil gravity flows to rear of plenum and enters mostly into #7 cylinder. Exam of #7 plug may show light oil coloration.
Not a cause for concern and has very little effect on engine performance.

Solution: Install Oil "Catch Can" system.


2. Injector Housing/Cyl Head Gasket. Can affect L and/or R exhaust.
Infrequent occurrence but known as potential source of oil smoke in exhaust. Most often occurs in high mileage engines.
Over time, injector housing bolts become loose, reducing clamping force on gasket. Differential pressure between intake vacuum and crankcase vent port causes gasket to migrate towards intake runner & communicate. Considering the injector housings have isolated passages for 3 different functions, (i) intake runners w/vacuum), (ii) crankcase ventilation and (iii) coolant @16psig, the need for absolute gasket sealing is essential.
Communication between intake runners & crankcase ventilation passages will result in oil laden vapor contamination, i.e. burning oil.

Solution: Replace Injector Housing Gaskets

3. Exhaust Valve Stem Seals. Can affect L and/or R exhaust.
Only the 1990 model LT5 engines did NOT have exhaust stem seals. All other models, 91~95 have both exhaust & intake valve stem seals.
Typically, any noticeable oil smoke in the exhaust, only occurs at startup or after extended idle and is not normally detrimental to engine performance.

Solution: Install Valve Stem Seals on Exhaust Valves. NOTE: This is not doable without significant cost to R&R cylinder heads to install seals. Not recommended or necessary for engine performance unless engine is very high mileage or damaged otherwise.

Thanks Jerry. The order will be coming in shortly.

I figure 1 and 2 are the easy bets. 3 will have to wait.

Do you sell catch can kits?

I THOUGHT I bought all the PCV related stuff from you? Do you keep easily accessible records of my previously made purchases? Anything I missed?

IIRC, you had one of the two under plenum PCV valves. Do you carry both now?

Anything else worth doing while we replace the Injector Housing Gaskets?

[Erik]

Is it blue or white smoke?

Looked blue to me.

[Erik]

Lazy O2 sensor on one side? Might explain only one side.

The O2 sensors are new, but that of course doesn?t mean much. However, this only happens on the first acceleration after idling a while. Once it?s gone, no oil burning to be seen, hot or cold, regardless of how I push it.

[Erik]

Once had a similar (very similar!) symptom that turned out to be a combination of IH/head bolts loose, & being a '90 it came w/ no primary valve stem seals.

Like yours, a puff of blue smoke when first getting on it after sitting for a few days.

Being that it is a '90, I was aware of the fact there was no primary valve guide seal on the primary valve. But, Marc Haibeck machined the primary guide to accept those seals (done when I had the heads off for porting - 91+ models came with seals on both valves).

Anywayz... new gaskets (Jerrys Gaskets) and some BLUE LOCTITE thread adhesive applied to the IH bolts (AND the same treatment for the windage cover too) stopped the oil seepage/smoke issue.

Thanks, Paul!