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1993 All Other Makes All Other Models Repair Question


Topics covered: Body, Throttle body, Vacuum leak.
Mileage: No information provided.

Asked on July 31, 2006

93 Chevrlet 1/2 ton work truck with 4.3 liter

I changed out the intake manifold (chasing an oil leak) in my sisters 93 1/2 ton truck. I have it all back together but when I tryy to start it the trouble begins. I turn the key and the truck will crank then back fire through the throttlebody and start up. I set the initial base timing to TDC as indicated and have checked and re-checked the firing order. When the back fire occures it blows the vacuum lne apart that serves the pcv valve. When I attach the hose while it is running it idles fine but when I give it throttle it will blow the hose off again and run. Any suggestions. I am leaning towards a stuck egr valve or that I have a vacuum leak under the throttle body??
Avatar Asked by lilblutruk

Answer

Replied on July 31, 2006

Souds like a vacuum leak, either around the intake or throttle body.
Make sure all hoses are routed right.

Tiny Answered by demearsjr
0 questions asked
Replied on August 4, 2006

[quote="demearsjr"]Souds like a vacuum leak, either around the intake or throttle body.
Make sure all hoses are routed right.[/quote]

Ok. I have replaced the gaskets around the throttle body and double checked the placement of the hoses. All seem good. I started it last night with some success but when I let it stand for a few minutes and came back to start it again the backfiring returned. Any thoughts?

Tiny Response from lilblutruk
2 questions asked
Replied on August 4, 2006

Do you have a reading on the oil pressure.
If it's reading high check the pcv hose first to see if it's clogged.

Tiny Answered by demearsjr
0 questions asked

Replied on August 14, 2006

The PCV valve and hose are all ok. I read in the manual that the distributor must not even be off by one gear and I suspect it is. Would this cause this type of backfiring due to crankshaft or camshaft positions sensors?

Tiny Response from lilblutruk
2 questions asked
Replied on August 16, 2006

That could cause it.

Tiny Answered by demearsjr
0 questions asked
Replied on August 24, 2006

Ok! Here is what solved the problem. The book calls for the alignment of the indent on the bottom of the distributor gear to be in alignment with the arrow and a 6 that is cast into the casing. This does not exist but it does have a 23 over a large X so I gambled and aligned up these marks. The book also shows that the number one spark plug must face toward the front of the vehicle which is what I did. Woo Hoo!!! It started great and runs perfect.

Thanks for the help. I know now that to be exact is most important.

Tiny Response from lilblutruk
2 questions asked