93 CHEVRLET 1/2 TON WORK TRUCK WITH 4.3 LITER

1993 All Other Makes All Other Models

Tiny

lilblutruk

July, 31, 2006 AT 11:13 AM

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?

FOUND 1177 RELATED QUESTIONS

6 Answers

Tiny

demearsjr

July, 31, 2006 AT 1:13 PM

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

Tiny

lilblutruk

August, 4, 2006 AT 12:59 PM

[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

demearsjr

August, 4, 2006 AT 11:39 PM

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

lilblutruk

August, 14, 2006 AT 11:10 AM

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

demearsjr

August, 16, 2006 AT 9:30 PM

That could cause it.

Tiny

lilblutruk

August, 24, 2006 AT 5:23 PM

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.

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