Join Date: Aug 2011
Location: Fayetteville, AR
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Did you seafoam.the motor to cure the dieseling? And all of your possible problems above could cause dieseling, so the issue is not resolved, just alleviated. The dieseling will probably return if you don't get to the root of the problem. Your poor economy correlates with the seafoaming, in that if you have had the problem for a while, you probably had excessive carbon build up on the cylinders due to the fuel not being completely burned, and the seafoam got rid of some of that carbon. I am still leaning toward timing. You need to get the timing checked out, and inspect the distributor cap and rotor to see if there is any indication of arcing. Also, with the issue being when the car is warm, it is probably not the whole cause, if the cause of the problem at all, but it could also be a plugged catalytic converter. But that is about the last thing I would check. And yes, check your fuel pressure. I know autozone rents fuel pressure testers. Someone else will have to continue from here, because I know how to see if the fuel pressure regulator is working on a fuel injected car, because the pump primes, and you don't start the car, just leave it in the on position and see if the pressure bleeds off. But on a carbureted car, I haven't done it before. If it is an electrical fuel pump, I would think the procedure would be the same, but for a mechanical fuel pump, I am clueless.
One other thing. Check the ignition coil and the ignition control module. Autozone also tests these. When I test an ignition controls module, I actually cycle it on our tester 12-15 times, because that heats them up like they would be when running in a car. I have seen them pass when cool, but start failing as they get warmer and warmer. Which could also explain your problem, runs fine when cool, like crap when hot. Weak spark=incomplete fuel burn and poor economy.
I am not telling you the definitive problem and solution, just trying to help you troubleshoot the problem. But DON'T start throwing parts at the car without having them tested. Many of the ignition and fuel.components can be tested, and ruled out or confirmed as the problem.