I just replaced the 5.8L engine in my 1989 F250 with one from a 1994 truck (less than 80K miles, good compression). I had to use the upper intake manifold, distributor, and exhaust manifolds off of the old engine to make all of the emissions equipment hook back up correctly. It has new ignition module, cap, rotor, plugs, wires, and coil. Started up and ran fine when cold but had a rough idle and less power on the freeway once it got warmed up. MAP sensor, throttle position sensor, water temperature sensor, intake air sensor, idle air control and timing all checked out OK. No codes set during KOEO or KOER tests. I finally changed the oxygen sensor today and it is 95% better, the idle is still a little rough. One mechanic suggested that the fuel injectors that I used from the '94 engine might be different from the ones from the '89 and causing a slightly rich condition. I'm considering taking it to a smog station to see if it is running rich but does anyone know if the injectors are compatible? I still have the old ones and can switch them if necessary. Do I just need to drive and let the computer re-learn the optimum default settings?

 

I don't think there would be an issue with the injectors between the years. Now the ones your using may be dirty and need to be cleaned.

 

What color are each injector? Do they both look the same? Did you also change plugs?

 

I believe the injectors will be the same. I believe both will be yellow.

By the way: 5.0 and 5.8 injectors are the same.

 

Injectors are the same but I suspect they may need a cleaning and the computer will need a few drive cycles to re-learn what this new motor will needs. Did you change the distributor drive gears? The '94 motor should have a roller cam in it while the '89 had a flat tappet, that means the old distributor had a cast iron drive gear and the '94 has a steel gear and you need that steel gear, the cast iron gear will be quickly worn down working against the harder steel camshaft gear.

 

would that steel gear be ok on the flat tappet cam ?

 

The injectors from both motors are yellow, I was going to check the pulse width on the new ones but it's a hassle to get at several of them. The fuel pressure in the fuel rail is spot on and stays rock solid after the engine is shut down so I don't think there is a problem with any of them leaking. I did replace the plugs before installing the engine. I believe that it was running lean at first since engine speed would increase at idle if I partially blocked the air intake or gave it a short shot of carb cleaner into the throttle body. Both of those conditions went away after I replaced the oxygen sensor. I did not know about the difference with the distributor drive gear, though, so thanks a lot for that tip. I'll get that swapped out.

 

Not 100% sure but I believe on a flat tappet cam you have to run a cast iron gear, or brass.

 

I was going to post this also and i agree....when the battery is disconnected for 15 minutes the eec's adaptive memory is erased. That is where the computer has learned certain things from the engine to keep it running as smoothly as possible. When it is wiped clean you need to keep driving for a few hours at all speeds and conditions for the eec to relearn.

 

Thanks again for the help. I'm going to swap the drive gear for the distributor tomorrow and then drive it, I'm pretty sure that it's all sorted out. It's been a great work truck and I think I'll get several more years use out of it.

 

One more follow up. Even after several driving cycles, I still had mild problems at cruising speeds and excessive idle speed that would take over three minutes to drop down, turning into a loping rough idle. After lots more reading and testing I stumbled across some reference to clearing the computer codes after making repairs. I had no idea that the computer used those stored codes in it's calculations for current optimum running adjustments, but after clearing all codes and driving it for a couple of days it's running a lot better. Still has an occasional rough idle, especially after a hot re-start, but I'm going to give it a few more days of driving and see what happens.

 

Yes, that is what I was saying in the above post when I said, when battery is unplugged eec's adaptive memory is erased. Adaptive memory is where the eec learns what it needs to do based on the running condiiton of your to make it run smoothly as possible and is stores it in adaptive memory until needed.

 

Thanks, I missed that. I thought that the stored codes were just a log of past errors and didn't realize that they affected the adaptive memory. Learned something new.