Question about 1986 Oldsmobile Ninety Eight

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Back fires under load and is sluggish at times

1986 olds 98 -- 3.8 liter
Car will back fire under a load and is sluggish. Catalytic converter has been changed, fuel pump, ignition module, have all been changed. the car has about 160,000 miles on it. The transmission and timing chain were replaced when the car had about 100,000 miles on it. We recently did a compression test and all cylinders were around 125 psi.
The plugs and wires have been changed in the last 6 - 10,000 miles and when we did the compression test all the plugs looked good. Do you have any idea why this car would be back firing?

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Backfires means that pressure is high and gas is igniting before it should. This happens under load because loads require more horse power than torque. Although the 6cylinder should normally be OK with 86octane. Try something higher and see if you get the same issue. Higher octane gas means it can handle higher compression and thus would eliminate the problem.

If you are already using high octane, switch gas stations for about 2weeks (enough to clean out old gas) if you regularly use the same gas station.

Also, the compression should be presented as a ratio. Cylinder position at start of stroke vs cylinder postion at bottom of stroke (not exact but something like this). 10:1 is about right

Posted on Jun 24, 2009

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Crank position sensor? oxygen sensor?

Posted on Jun 24, 2009

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Have you checked the coils? It has three above the rear valve cover right?

Posted on Jun 24, 2009

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