Gain extra benefits by becoming a Supporting Member Click here find out how!

Classic Performance Products Classic Industries
American Auto Wire
Danchuk Catalog
Hellwig Products IncPerformance Rod & CustomNu-Relics Power Windows

Username Post: 91 350 TBI Engine rebuild + idle issues        (Topic#327386)
Forum Newbie
Posts: 13
Age: 27
Loc: Tennessee
Reg: 08-08-15
08-08-15 05:54 PM - Post#2567374    

Hi all, thanks in advance for any help i could get on this scenario. Im not exrtremely knowledgeable on the subject of engines, but competent enough to understand.

So recently i bought a 91 c1500 5.7l that had a rebuilt motor. The mechanic is high spoken of, and i am to believe he did it correctly, from having the heads worked to replacing all the necessary parts (plugs, wires, pistons, rings, v. seals and guides, etc.) The truck itself is in great condition for having 200,000+ miles on it. I live in area with emissions, when i took it up there, they flagged it for smoking. Upon further investigation, it does smoke blue. So oil is being burned somewhere. It never smokes on start-up, and only smokes after a warm up, but never alot of smoke no matter the circumstances. A very high rev will produce more, but never a cloud. I was wondering if maybe the rings still havent seated?

Also, the truck has a very erratic idle. Only after the truck has warmed up, and i am at a stop light, the trucks rpms will steadily and slowly drop from around 7-800 rpms almost to stall, then it will surge back up and repeat this process until im allowed to go. If i put it in park, then back into drive during this process, it's likely to stall. Im stumped on these 2 issues, and being that im not very knowledgeable on these things. I could use the assistance. Im also limited on the tools i have without seeing a mechanic, which i do not have the money for at the moment.

Emissions is my biggest worry at the moment, i need tags on the truck to get to work. The idle issue is annoying but not crippling.

Thanks again for any and all help i could get.


Posts: 32

Loc: South Central USA
Reg: 09-20-15
09-20-15 10:08 AM - Post#2576851    
    In response to ChevyCuriousity

There are only a few ways a 4 stroke gasoline engine can burn oil .

A - Some how sucking in oil through the PCV system . Check to see if anything is wrong in that system . ( the engine is not over full of oil , is it ? )

B - Oil going past the valve seals . Look in on line parts catalog & see if you can find pictures of the valve seals for the engine . Pull 1 or both valve covers and visually inspect to see if the seals are there & look OK . May need to do a compression test on each cylinder . Make sure you write down the numbers for each cylinder .

C - Past the piston rings . Do a compression test , if you have not already done one . Make sure you write down the numbers for each cylinder .

Now take an oil squire can and squire engine oil , through the spark plug hole of # 1 cylinder . Do the compression test again . Let the engine spin several times & see if the pressure is going to pump up any . Write the number down . Repeat for the rest of the cylinders .

If the oil raised the pressure significantly , the rings are not sealing properly . Is this because they have not seated properly , yet ? Or , are there other problems ?

I do not know . Might try driving it pretty hard , then easy . In several cycles , to try to make the rings seat ?

Have you driven it enough to see if it is actually consuming significant quantities of oil ?

Has it actually failed an emission test ?

Best of luck to you .

God bless

God bless


Icon Legend Permissions Topic Options
Report Post

Quote Post

Quick Reply

Print Topic

Email Topic


FusionBB™ Version 2.1
©2003-2006 InteractivePHP, Inc.
Execution time: 0.082 seconds.   Total Queries: 16   Zlib Compression is on.
All times are (GMT -0800) Pacific. Current time is 04:14 AM