first off i am new and my name is ryan. i joined because i can not seem to get this problem fixed. its a 1991 f150 xlt lariat 5.0 lifted a little on 34s.

ok i will start at the beginning. when its cold out and i first start it in the morning it has a little bit of a rough idle, then the rpm's "jump" and it will come back down and sometimes stall, if not it slowly goes up to about 12-1500 rpm then will warm up to normal idle around 7-800. if it stalls its hard to start. after that warm-up it drives great, acceleration is great and when i give it gas it GOES. no problems with power. it backfires too. when i rev it and let go it does it on the way down. during the winter it wont backfire untill it warms up more. now here is the problem. after driving it for about 20-30 minutes the acceleration becomes horrible. when i say horrible i mean if i stomp the pedal to the floor from a stop it putt-putts up to speed untill its in high rpms. it sounds like its struggling soo bad. almost like its starting out in 2nd or 3rd gear or something ha. its not though. if i slowly hit the gas, i mean just barely, it sounds like smoothe acceleration then i stomp it and it actually drops down. otherwise when it cools down after sitting an hour or so it's back to running great with awesome acceleration, but for less time. also it runs hot and overheats. not while driving though. when i turn the truck off and stand near the overflow it will start to bubble over. if i turn it back on it stops and i rev it a little to move the pump and fan more and it cools down. it has never overheated in the 1.5 years i have owned it. and was always just a little sluggish, but never this horrible. not nearly. also when i start it right after i have been driving it for 20 minutes or more, it sounds like it doesnt want to start. almost like there isnt enough juice.

here is what i did. i adjusted the timing. pulled the SPOUT connector and the timing was off about 3 degrees but the mark was steady. now when i plugged it back in to check it the mark was jumping around without about a 10 degree range. it wasnt steady one bit. ultimately i think this is what is causing this problem. first i thought it was an ignition module and i replaced that. it ran better but only a little. i hooked my friends scanner up. the following codes came out:

172-173 EGO not switching always lean 172/ always rich 173
212 no tach imput to spout processor (what i think is my main problem) but my tachometer works. not sure how that whole circuit fully works though from the ign. module.
327 EGR low signal, low voltage.

i replaced the O2 sensor and the EGR position sensor tonight. not sure if i needed a whole EGR valve but i took that off and actually sucked it open through the vacuum hookup so i figured thats functional.

now my friends car timing jumped like this when the resistor wasnt hooked up. they hooked it up it ran fine. maybe mine is bad? i couldnt find it in accordance with the wiring diagram, but i heard they could also be built into the coil. if all i have to do is replace the coil i would love anybody who tells me that. or anybody who tells me what i can do.

any and all help greatly appreciated. thanks

ryan

 

any help please its driving me nuts.

i replaced the coil anyway since it was old and rusted bad. but that wasnt the problem.

i am going to do all the voltage checks as per haynes manual describes tomorrow. but since i already replaced everything it looks like its the pcm, and i have no idea where that is on my truck. anybody know where i can locate this?