I have a 1991 ford F250 2wd with a 6 cly straight. I had a motor with 132000 miles. when i motor went out due to pre ignition which ruined two cylinders and cracked the head. I put new motor in and the truck and it repeated this problem again . know after changing allmost all timing related parts and a third motor it's starting over again. can my problem be with my computor or what.

Thanks gary

 

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Have you replaced the plugs, wires, cap and rotor? Did you use the same distributor each time? A vacuum leak can cause lean condition which will cause detonation. Check all the vacuum canisters and lines, and make sure that all the unused ports are plugged off.

 

thanks for the reply . yes i have replaced all plug wire,new cap,rotor buton,and distributor all parts on it. as far as my vacuum canister it has a ole in it but the guy that put the engine in said didn't need it.

 

Do you mean the charcoal canister or the coffee can looking vacuum reservoir on the fender? If it's the coffee can one then you do need it, it's part of the heating and cooling system. It keeps constant vacuum going to the servos that control the blend doors in the cab. In a '91 it's fuel injected, make sure that all unused vacuum ports are capped off, and make sure that your fuel pressure is correct.

 

yes that is what i mean coffee can looking vacuum looking unit the man said he could bypass it and it would hurt . i guess thats why my defrost doesn't work proprely know thanks. gary

 

I would think more on the lines of a bad radiator (plugged up), fan clutch, thermostat, water pump, bottom radiator hose (no spring inside).

Also what is your rear end ratio, and is it a standard or automatic?

 

thanks for your response the radiator was flushes with new engine. not sure on rear end it is a automatic.