What do I do next?


Asked by Sep 14, 2014 at 03:44 PM about the 1987 GMC Sierra

Question type: General

I have an 87 gmc high sierra 5.0. I
changed the fuel filter, fuel pump and
sending unit. Just put new plugs and
plug wires and the timing is set. It still
has hesitant take off and today it
backfired. Help please

6 Answers

Backfired through exhaust or back through intake?

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Double check timing and make sure it's not too retarded..if in doubt advance it a little more than specs. Also double check the plug wires are on right..if even two are swapped it will run but a plug will ignite when an intake valve is open. After that, have to start looking at cam timing. I think it has a chain, but if high mileage it can actually stretch and jump a cog

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Way excessive lean will also cause an induction backfire

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The way I check cam timing in a pushrod engine is get #1 at about 10 BTDC compression stroke and look at...even feel rocker arms to be sure both valves are closed.

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Ok thank you

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