An intriging Problem
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Supreme Member
Joined: Jul 1999
Posts: 1,556
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From: Adrian, Mi, USA
Car: 1988 Pontiac Firebird Formula
Engine: 5.7 TPI
Transmission: 700R4
An intriging Problem
Hey folks, here's a good one for ya.
The Vehicle: 1988 Chevy Blazer (sorry, not F-body......)
350 TBI
Automagic Tranny
The engine has 2400 miles on it, but has been in the truck for about a year. (assorted transmission problems....) Just long enough for the warranty to run out. I have checked the ignition system, get a nice fat blue spark from the tester, I have changed the spark plug from a known good cylinder. Leakdown is less than 10%, and the cylinder builds about 125 lbs. on a compression test. I have verified that there are no vacuum leaks, fuel pressure is good. The problem is that the number 7 cylinder is dead. The spark plug from this cylinder was kinda black, other plugs were a nice shade of tan.
Now I seem to remember something about GM having a problem with the back cylinders running lean on some of the TBI motors. However, I don't want the customer to spend a couple hundred dollars on a new manifold, and not solve the problem.
I am open to any and all suggestions, I know you folks out there are pretty smart, I have already received a great deal of help from you on my Firebird. (which is currently down for the count, that &%#$$ borg warner rear end went out......)
Thanks Folks.
The Vehicle: 1988 Chevy Blazer (sorry, not F-body......)
350 TBI
Automagic Tranny
The engine has 2400 miles on it, but has been in the truck for about a year. (assorted transmission problems....) Just long enough for the warranty to run out. I have checked the ignition system, get a nice fat blue spark from the tester, I have changed the spark plug from a known good cylinder. Leakdown is less than 10%, and the cylinder builds about 125 lbs. on a compression test. I have verified that there are no vacuum leaks, fuel pressure is good. The problem is that the number 7 cylinder is dead. The spark plug from this cylinder was kinda black, other plugs were a nice shade of tan.
Now I seem to remember something about GM having a problem with the back cylinders running lean on some of the TBI motors. However, I don't want the customer to spend a couple hundred dollars on a new manifold, and not solve the problem.
I am open to any and all suggestions, I know you folks out there are pretty smart, I have already received a great deal of help from you on my Firebird. (which is currently down for the count, that &%#$$ borg warner rear end went out......)
Thanks Folks.
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Joined: Jan 2000
Posts: 19,675
Likes: 314
Ploegi,
As I'm sure you're aware, lean isn't black. Is the owner one of those notorious "non-warmup" hard drivers? You may have oil problems in that cylinder making the carbon, not fuel. It sounds unlikely at only 2,400 miles, but there may be seal/ring/gasket damage allowing some oil into that chamber or intake runner.
As I'm sure you're aware, lean isn't black. Is the owner one of those notorious "non-warmup" hard drivers? You may have oil problems in that cylinder making the carbon, not fuel. It sounds unlikely at only 2,400 miles, but there may be seal/ring/gasket damage allowing some oil into that chamber or intake runner.
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