Technical Question

[Benny The Mule]

All,

I have a 1988 Blazer with a 350ci TBI with 200,000 miles on it. It has good compression, no blowby and runs smooth.

It has decided to start smoking (right bank) under heavy acceleration or high RPM deceleration. It is a 4sp standard.

It will not smoke AT ALL under normal driving conditions or at hot or cold start up.

I'm stumped.

[9498clay]

is it white or black smoke.. white smoke could be fuel not burning completely for a number of reasons ..black smoke would be oil leaking.. valve seals or the oil rings worn id pull the plugs and check the condition hope this helps

[oldyeller]

i think it's the other way around on the color of the smoke?

[dd38]

Black smoke - Raw/Unburned fuel
White smoke (steam like) - Water
Lite/Very Lite Blue smoke) - Oil, Auto Trans. Fluid, Brake Fluid


First thing,What color is the smoke?
Does it smoke when first started?
Does it foul any plugs? If it does is it limited to just 1 cylinder?
Do the plugs on that bank look all the same (gas/oil soaked)?
And compared to the other bank, how do the plugs compare?
Is the compression range euqual all the way (1 thru 8 - within 10-15% Dry Test)?
Did you do a 'Wet and Dry' compression test?
What about a "Leak Down" test?
Is it using oil or getting worse gas mileage or having coolant needed to be added?
Power booster seem to work o.k. (vacuum type)?
How is the Master Cylinder level for the brakes?


As you can see there is a lot to take into consideration. Hope this helps.

[Benny The Mule]

Black smoke - Raw/Unburned fuel
White smoke (steam like) - Water
Lite/Very Lite Blue smoke) - Oil, Auto Trans. Fluid, Brake Fluid


First thing,What color is the smoke? Blue
Does it smoke when first started? No
Does it foul any plugs? If it does is it limited to just 1 cylinder? No
Do the plugs on that bank look all the same (gas/oil soaked)? all the same no oil soak.
And compared to the other bank, how do the plugs compare? Same
Is the compression range euqual all the way (1 thru 8 - within 10-15% Dry Test)? Yes
Did you do a 'Wet and Dry' compression test? Just dry tested
What about a "Leak Down" test? All cylinders have l some leak down (200,000 miles)
Is it using oil or getting worse gas mileage or having coolant needed to be added? Using oil, mileage the same, no coolant leaks
Power booster seem to work o.k. (vacuum type)? Yep
How is the Master Cylinder level for the brakes? FULL LOL

As i said, i am stumped. This just started recently and i thought broken oil ring but i can drive all over town without a drop of smoke. Mash on it hard and i can't see the cars behind me.


As you can see there is a lot to take into consideration. Hope this helps.
Reply With Quote

[dave41]

smoke

valve seals

[Frasson118]

Wouldn't valve seals clear up shortly after start-up?

Also, how can you tell which bank is smoking if it only does it under heavy acceleration (you'd be in the cab)? Smoke out the exhaust, or from under the hood?

[tccaz]

My guess would be too much oil or the crankcase isn't venting properly, and yes valve seals would clear up after it warmed up.

[mr south 59]

PCV valve.

[Benny The Mule]

Frasson (Jerry) Dual exhaust exits both sides behind tire (can see it in the mirror)

Mr South, PCV has been replaced.

Valve seals a year ago to stop smoke at start-up.

Dang! most likely an oil ring..........it's coming out.

Thanks guys, at least i know now I'm not losing my mind.

[9498clay]

na benny u got us all over the map on that one good luck i hope u get it staightend out

[dd38]

If you think that is the problem, before you tear it down do a Leak Down test to single that particular cylinder out so you can concentrate on that one (Rings, Guides). Why do you say LOL on Master Cylinder?

[83earnhardt]

Hard acceleration shows a hard drop in vacuum available. I would bet on the PVC valve also as that is vacuum related. Black smoke right bank would eliminate a fuel problem because fuel dumps on both banks at same time. I would drop a PVC valve in for the cheap price it is. Next possibility is valve seals as they are easy and cheap to replace on the motor. However if you have a valve seal problem it would show on the plugs which cylinder it is if it is smoking that bad.

[83earnhardt]

PVC should be PCV, I have done too much irrigation lately.

[Benny The Mule]

If you think that is the problem, before you tear it down do a Leak Down test to single that particular cylinder out so you can concentrate on that one (Rings, Guides). Why do you say LOL on Master Cylinder?

Just for the fact you provided quite a list and i have tried everything already, at the end i had to LOL.

This would not bother me if it came on gradually. This happen from last time i drove the vehicle until the next time i drove it.