I just had someone replace the motor in my F150. My truck is an '87 but the replacement motor is a 1990, 4.9 (300ci straight 6). I don't know how long this newer motor sat at the junk yard or anything on it's history. I've put new plugs, wires, distrib. cap, rotor, oil & filter. The shop that swapped motors for me supposedly cleaned the fuel injectors. How (what process), I don't know?

The motor idles high, cold & warm, and it chugs/hiccups a little, not real bad, during low-speed acceleration. It chugs whether the motor's cold or warm. High speed acceleration is fine; For instance: Going 45 mph or more it takes the gas fine.

Cold idle: 1250 RPM
Warm idle: 1100 RPM

I suspect the timing is advanced too much but didn't know if I should adjust the timing or the idle first. I see a setscrew on the manifold that looks like it's for adjusting the idle but I don't know for sure how to turn it 'cause there's not a slot in the top of it. Looks like there's a nut on it, just below where it enters the manifold.

If the timing is advanced which direction do I need to turn the distributor to retard it? While facing the engine from the front of the truck, I'm thinking I need to turn it clockwise to retard and counter-clock to advance. Is that right?

Also, I've seen post that recommend cleaning something, I think was called the IAC(?) and something else with contact cleaner. How do I go about doing this?

Thanks for taking the time to try to steer me in the right direction, I really appreciate it!

HH

 

I'd put my money on a vaccumm leak somewhere. Maybe an old dry-rotted hose they reused or maybe they forgot to attach a hose somewhere.

 

I'll check it out and post back.

Thanks for your thought.

HH

 

now i don't know if you have a efi motor in there. but my 94 with the 4.9 hicupus at idle. now i idle at the same rpms as u do, hot and cold in park or neut. i know that my egr valve is starting to go and i was told thats whats causing my hicups. you may want to also have your egr valve checked out. it runs with the vacume system so check the small lines that run to it for cracks and breaks. good luck

 

My motor is EFI. There are a few vacuum lines that look a little rough. I meant to post back before now but have been so busy that I forgot about it. Needless to say, I haven't had time to replace the lines, yet. Hopefully I'll be able to sometime next week. While I'm at it I'll check out the EGR valve, too.

Thank ya'll for the input!

HH