I bought a 1993 f150 4x4 that has a 5.8 engine in it, it originally came with a 5.0, the truck is idling high with the new IAC plugged up, if unplugged the truck idles too low, the check engine light does not illuminate when the key is turned on and a scanner will not communicate with the truck, could the truck have the old 5.0 computer in it, and could the old computer cause the truck to run bad.

 

A 5.8 and 5.0 should work fine with the same computer, if everyting else is connected and working correctly. It sounds like you have some wiring problems at very least, though. How do you know the truck originally had a 5.0 and that it now has a 5.8?
Do you know how to identify them without looking at what's printed on the intake? Just wondering if some shifty saleman didn't swap out the upper intakes in an attempt to make some extra bucks.. and it's now causing you problems. Also what's that about the IAC plugged up? A non-functioning IAC would certainly make for a rough runner.

 

the calibration of the computer still can be different. the way i understand it there is a calibration code for the computer on the aft door support.

 

If you have no CEL, and the scanner won't read codes, then you either have a bad computer or a bad connection at the EEC plug.

It will run with the wrong computer, but it won't run well. The computer is expecting 302 cubes of air per two crank revolutions, not 351.

 

have 94 f-150 it did have a 5.0 took it out put a 5.8 in so the stock computer will need a computer chip to change the motor size it will run a little rough but it will still be driveable if you don't

 

On my 94 f150 I had a 302 (worthless in a truck) which drank some water... oops.. I had a '88 351W given to me and we rebuilt it. RV cam and lifters, intake, new rings, oil pump, seals.. The usual refresh. We first tried the 302 computer and it wouldn't idle. So we put in a 351W computer and now it runs fine. We removed all of the emissions equipment as well. So all that's left to do is remove the CEL bulb. I'm not sure why but sometimes it stalls at low speeds when you get off the gas. Lots of power just has a few bugs.

Just my story.

 

My understanding is that it will run, but not right. Only one person that I have come accross on this board says he has no problems running the 5.8 w/5.0 computer. All others say it needs to be reprogrammed.
Why not find a 5.8 computer in a junkyard? What trans is in the truck?
Al

 

I have a 94 f150 came with a 302 in it. I converted it to a 351. Iam still running the 302 computer. this 4X4 has a decent cam, headers, throttle body, 2 1/2 true dual exhaust with 2 1/2 core 18" long glass packs ( yes its loud) It runs like dynamite. Its faster than any truck has a right to be, have put 11,000 miles on it since the covversion, it runs so well I have no plans of changing to the 351 computer al though I bought one when I did the conversion and its still sitting on the shelf in my shop.

 

Good for you. Is it mass air? I'd love to do this, but couldn't get anyone with actual experience except Conanski. I have a 4R70W trans and can't just swap in a 351 computer.

Thanks
Al

 

I have a 87 F150 4x4 stepside, it came with a 5.0. I
did the ford mass air conversion a few years back for the 5.0. Not enough power so I built a 5.8, good cam,roller rockers,edelbrook rpm heads, msd distributor lots power, but still need more. I never did anything to the computer. Is the sparkplug wires in the right firing order?

 

Here is a list of codes for computers so you can compare what you have in the truck to what you should have: http://www.fordfuelinjection.com/index.php?p=17

At the top of that page they show you where to look for the code and the truck computers are listed almost to the bottom.

In addition to the other issues mentioned above, the '93 302 has a different firing order from a 351. In 94-95 the 5.0 MAF equipped trucks would have used the 351 firing order. I'm wondering if that may be why some 351 swapped trucks run okay with the 5.0 computer?

 

that was my thought what year did the truck 302 start using the 351 firing order?

 

I think in '94 with the MAF equipped trucks.

 

Haynes manual says 1995 5.0 and 5.8 used the same firing order.1-3-7-2-6-5-4-8, 1994 and earlier 5.0 1-5-4-2-6-3-7-8

 

Kosmo01: the spark plugs should be wired correctly if it's running alright (1-3-7-2 order in the previous post) but the injector wiring is setup for the old 302 order. You'll want to move a couple of wires to get the injector order correct for the 351 to make it run the best that it can.

I don't think that firing order means beans between a 302 and 351 computers. Being that the computers batch fire four injectors at a time, I really don't think that firing order makes that much difference. On a sequential system, yes it makes a difference (although it will still run decently if the sequence is wrong, just not as good as it could).

Alz: The Ford mass air conversion kit is listed for both the 302 and 351, so I would think that if the 302 has mass air from the factory (like the one you have), it should be able to run a 351 just fine.

Moose94: what year 351 computer are you using?