i just purchased a 1992 f150 xlt that was super clean but had a blown head gasket and a leaky oil pan gasket. The motor had 182000 miles and i was gonna have to pull it out anyways so i decided to change it because i found another 5.0 that had been rebuilt before for only $300. SO we've swapped the motors and put all new gaskets on the new 302. THe new motor has great compression. Since the rebuilt 302 was from a deiffent year we had to swap all the engine wiring harnesses and distrubutor because it was slightly older and had differnet plug ins. We also swap the upper intake and throttle body to the rebuilt engine. Now that we've reinstalled the rebuilt engine and trans we've been having a lot of trouble getting the truck to run properly. Let me explain. When engine is cold it turns over for about 2 sec and fires up. Engine runs pretty good at idle but is a little choppy but when you rev the engine up it runs awsome. The big problem is when you cut the a/c on or put the truck in drive. When you do this the idle drops to 500-600rpms and loses oil pressure unless you give it gas to keep the idle up. However when you give it gas with a/c on or truck it drive it struggles to run and wants to die. Also it takes longer to crank up when engine is warm/hot, about 5-7sec. We have tired running sea foam through gas tank, vacuum lines and throttle body. We installed another iac valve just to see if it made a diff and it didn't. I tested all plug ins and sensors on intake and throttle body to make sure they are getting power to the sensors. We tried pulling the neg cable off battery to reset ecm but still cant seem to find the problem. Its beating us up and we neeeeeeed hhhhhheeeeellppppp. Low on cash and have now way to have it hooked to scan tool at this time b/c its gona require a tow and dont really understand the whole paperclip thing to pull codes. Also pls keep in mind the exhaust isnt installed b/c we cut it off at the manifold to make it easier to pull engine and trans. Eventually we are gona run true dual from manifolds back. There is an egr tube that runs to the exhaust thats not hooked up and an o2 sensor also. I was told it wouldnt have that big an effect on the performance of the new engine as long as we didnt run it forever like that. Note>>>>we installed some injectors from old engine b/c some were broken. Intake and throttle body came off old motor which was running perfect and so did some of the sensors. We also couldnt find any vacuum leaks.

 

without the oxygen sensor reading anything, the computer is dumping as much fuel possible because it thinks its running lean or its getting wrong signals(which it is). you'd be surprised how much a little sensor can affect driveability. couple questions here-
does the new motor have a bigger cam?
any mods at all on the new engine?
how old is the gas being used?
what do you have the ignition timing set at?
hook exhaust up and start from there.

 

well right now the engine sounds like it has a bigger cam but that is unknown for sure. Hard to tell if when they rebuilt it that installed a bigger cam or if its just a characteristic of the lopping idle issue it's having. The way we set the timing is arranged the engine at top dead center and intalled the distributor the adjusted the distributor once we got it running. We just put new gas in today with sea foam. Its kinda a bummer cuz we cut it with a sawzaw and it's not driveable so we are gona have to get it towed to the exhaust shop and then back home. Do you think it will be better if we just kinda line the exhaust back up somewhat so we can install the o2 sensor or will it just defeat the purpose.

 

did you put a timing light on it? there are too many things going on at once that can cause running problems. you need to get the exhaust hooked up without any leaks to get an accurate O2 reading. you need to pull out the spout and set the distributor to 10*btdc then plug spout back in and see what you got after that. i can not say that the timing and O2 are your issues but sometimes you have to get everything else right to figure out the main problem. i would get a haynes/chiltons manual for helpful info. you can pull codes using the check engine light. this site will help you retrieve codes- http://fordfuelinjection.com/?p=13

 

OK, sorry it took so long but we now have installed the o2 sensor and changed the tps, now when the a/c cycles the engine idle does compensate for the load. However I just purchase a scan tool and pulled dtc codes cyl. 8, 412, 121 172,213,334,411,538,and 632. Honestly, I dont even know where to start. The truck still has no power and is running bad. Any suggestions? I feel like im fighting a losing battle.

 

Disconnect the battery to clear the codes, then see which ones come back.