will compression change affect computer?
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Cargo Master
Joined: Apr 2003
Posts: 2,408
Likes: 5
From: Parkesburg PA
will compression change affect computer?
I have a friend with a 89 F150 shortbox 4x2 with a 302 engine and AOD. The truck had sat for about three years because of a spun bearing. He finally got it rebuilt, but he used higher compression pistons (.030 over) and raised the compression about 1 point. Every thing else is stock, stock type cam, stock rebuilt heads... The reason for the higher compression pistons was that they were free from a Mustang friend. With about 3 miles on the new motor, he tried to get it emission tested. It failed. CO was about 3 times the limit, HC and NOx were right at the limit.
The truck only has about 90k on it, but maintenance consited of only filling the gas tank when it was empty. Since the rebuild, it has new plugs, cap and rotor and a fresh air filter. The truck had a hesitation to it when I drove it, now it has a bad miss.
Do you think that the higher compression is causing the poor running becuase the computer can't compensate? I think that it's probably a bad sensor, or a bad fuel pressure reg, or even a bad/clogged injector. I cann't scan the computer because the owner is in florida with the truck. That was the reason that it was fixed, he wanted to drive it to florida..
He left with about 35 miles on a new motor with obvious problems... "All it needs is to have a few miles put on it... It'll be fine..." It's scary that there are people out there that ignorant....
Thanks for any ideas.
The truck only has about 90k on it, but maintenance consited of only filling the gas tank when it was empty. Since the rebuild, it has new plugs, cap and rotor and a fresh air filter. The truck had a hesitation to it when I drove it, now it has a bad miss.
Do you think that the higher compression is causing the poor running becuase the computer can't compensate? I think that it's probably a bad sensor, or a bad fuel pressure reg, or even a bad/clogged injector. I cann't scan the computer because the owner is in florida with the truck. That was the reason that it was fixed, he wanted to drive it to florida..
He left with about 35 miles on a new motor with obvious problems... "All it needs is to have a few miles put on it... It'll be fine..." It's scary that there are people out there that ignorant....Thanks for any ideas.
Posting Guru
Joined: Jul 2003
Posts: 1,280
Likes: 0
From: alaska
i think you are on the right track, that small of a compression bump shouldnt cause any problem. the miss could be fuel related or possibly spark, somehting called a computer diagnostic at a good tune up shop would pinpoint it and save a lot of frustration , he could pull the plugs and see which one isnt firing it could be somethig as simple as a bad plug wire ,good luck,bob
Thread Starter
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Cargo Master
Joined: Apr 2003
Posts: 2,408
Likes: 5
From: Parkesburg PA
It turns out that 1 the valve lash wasn't set right (What are these shims for anyway???) and the timing was way retarded.
With the valves and the timing set right, the truck passed the emissions with flying colors and runs like a champ.
With the valves and the timing set right, the truck passed the emissions with flying colors and runs like a champ.
