My dad bought a 97 2wd pickup awhile back. During daily driving the truck runs great. Last weekend he drove it from his house in KS to my house in TN. The first 6 or 8 hours of the trip the truck ran great then it started missing and back firing like it was out of time. Almost as if it is firing just before it is supposed to. This only seemed to happen at lower speeds below 45 mph, dad said the truck ran ok at higher speeds. We tried to reproduce the problem when he got here but could not make it happen. The check engine light has never turned on and we did not have a chance to try to pull the codes just in case the light has failed. The trip home was about the same. The truck ran great for the first 6-8 hours and then started missing and back firing. Dad said when it started he pulled over and let the truck cool down for about an hour and then drove for about an hour and then repeated the process. He also said the gas mileage dropped way down on the return trip home when the problems began occurring again.
The only thing I know about the truck other than what has been mentioned is it had an intake gasket failure. As I understand the previous owner replaced the intake gasket and the bearings on the bottom end. I was told the bearing on the #8 cylinder failed due to the water from the intake.
What are your thoughts? I did some searching and suspect the crank sensor or cam sensor but have no real proof. Its just a hunch based on reading. I am guessing it is some type of failing sensor since it takes so long for the problems to show up during driving. Any help or thoughts would be great.
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