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1987 GMC Suburban backfire

I have a 1987 GMC R2500 Suburban with a 454 engine. It has a problem when it’s hot it backfires when going up hills. It doesn’t happen when the car is cold. I just replaced the TBI gasket and the idle air control valve. My mechanic says maybe the timing is off or the wires and plugs are no good. What do you think?

Sounds like you have a good mechanic.

You or your mechanic needs to work through all the normal conditions that could cause this and make sure maintence is up. Just my personal opinion but I think a resource like CarTalk should be used further down the line and not as a starting point in fixing your Suburban.

I will add, don’t be afraid of first doing both a compression test and recording manifold vacuum readings. You may even want to drive up this hill with the manifold vacuum gague hooked up just to see what it reads before you start on repairs.

One note of “trivia”. One day a 70’s Chevy pick-up pulled into the shop and I remarked how it sounded like a boat motor. The boss replied that the engine had a “Mcdonalds camshaft” I looked at him with a bit of “what the” in my eyes and he replied "You know “ground round” GM had a problem, or perhaps better said ,owners that were lax on oil changes had a problem with camshafts that would wear out very early. this condition also existed on very high mileage engines.

It only has 92,000 orignal miles

is the fuel pressure ok? Has the ignition been scoped? How do the fuel trims look on the scanner? A lot of people overlook checking fuel pressure on these vehicles because it’s not easy, but the majority of GM truck driveability issues Of this vintage I see is fuel delivery problems.