Hey guys. I have a 92 F-150 with a 5.8 engine. About 4 months ago, I had to put a new engine in it. The mechanic putting the engine in got rid of the smog pump because he said it would get better gas mileage. After driving it for a while, it did great. One day it started skipping and I replaced the spark plug wires. It did fine after that until about 2 weeks ago I started it up, and it ran great until it got warm. It then started to idle rough and uneven and runs very rich. While driving it, it hesitates a lot. It also gets awful gas mileage. All the ignition stuff is new. New fuel filter. New EGR valve. New MAP sensor. New idle air control valve. I have no idea what to do now. Someone please help!

 

Sounds like you need that smog pump back!

He is a dirty liar. Smog pumps actually inject air into the catalytic converter during warm up to help get them up to the correct running temperature. Without a smog pump you'll be running rich during start up

Edit: cred to '89F2urd for correcting me

 

Since you mentioned an after-warm-up condition, it would appear that the EEC/computer now had full control (advanced to "closed loop" operation), so there is very likely a fault code.

For example, an oxygen sensor monitors exhaust and adjusts accordingly, you did say running rich.

Lot's of information in the archives about retrieving codes, related problems, etc.

 

It will *not* run rich all the time without a smog pump. It aids in reducing cold start emissions only, and that's it....the computer doesn't even know it's there, or not there. Mechanic is incompetent, agree with you there.

 

OP: pull the codes. If you don't know how, google "pulling codes obd1 f150". It's a very simple procedure, post up your findings and we will have answers.

 

I had my mechanic run all the codes. I can't remember what they were, but he said they didn't have anything to do with why it was running like it is. He is as clueless as I am at this point. The truck runs great on initial start up, and then it "runs stupid" is what the mechanic called it. Any ideas of what it could be?

 

Stupid mechanic. Get that truck away from them before your wallet is empty.

 

Pull codes yourself and post them, please.

 

Cant tell you want is wrong but I do know the car runs in closed loop when cold meaning it is not reading the O/2 and stuff like that. So that should help at least point you in some type of direction. Check the codes and hopefully one of them is telling you a sensor is bad or missing. Should not have anything to do with your smog pump though or ignition components. If it is firing and running smooth when cold then you have fire and fuel. Something is telling the engine to change perimeters after it warms up. Could be the O/2, EGR, BAP/MAP, and as in my case when I first got mine running could be a vacuum leak somewhere that is only opening up after warm up.

 

Had a smoke test done and fixed all vacuum leaks. What kind of code reader do I need and how much will it cost?

 

it would appear that the EEC/computer had control

 

Spencer, Do some searching on here. The code scanner for our older trucks is not quite as good as the new ones but the procedure is pretty simple as well.

 

You don't need a code reader. PLEASE google the procedure and do it. It takes no time at all.

 

Well I'll run the codes in a few days. I don't wanna spend any more money on sensors that won't fix the problem. I just wanna know what's wrong with it and fix it

 

Correct. First thing to do is pull codes, any sensor you've replaced would have shown up in the codes and you wouldn't have wasted your money in the first place.

Obd1 code readers are just as good as obd2....obd2 readers tell you the codes, so do obd1. Obd1 readers are ~20 bucks.