Hello all this is my first post in here. I have fished around in here for some answers before posting so I do not waste your time. I bought this truck a couple of weeks ago for $250.00 from one of my customers. The wiring harness was a hack job at best and the engine would crank but no start. I traced the problem to a faulty fuel pump relay. I replaced the harness (junk yard from a 88) and replaced the relay. Engine starts and runs now. I had to set the ignition timing because the distributor hold down was loose. Upon my initial test drive the truck would not get out of its own way off idle. It choked and puked until about 1500 rpm and then would run like hell (with black smoke coming from the exhaust). I brought it back home and started checking a few things and found myself holding the EEC module (ECM) looking at 4 different burnt spots on the circuit board. Replaced the computer and retested and the rich condition went away but the stumble off idle was still there. I traced this to a bad map sensor and replaced it. Wow, what a difference, throttle response is good now.

So all of that brings me to this: It ran good for a couple of days going back and forth to work but now I have a misfire that seems to only be present when the engine is under a load, cruising is ok but when I throttle down to increase speed it misfires badly. Not just one cylinder either. It is a multiple or random cylinder misfire. I have checked TPS (.962 volts closed throttle), i have checked firing order and plug wire routing. Plugs, wires, cap, and rotor were replaced right before i got the truck, wires have no visible signs of a problem. Fuel pressure is 40 psi with regulator un plugged and 32 at idle. My gut says it is an ignition problem, I just can't reason why the multiple misfire problem, maybe a coil but it is new too. Any ideas on this one would be appreciated. Sorry for the long post. Thanks, Mason.

 

I had this problem, it was multible vacuum leaks.

 

Pull the spout jumper and take it for a little ride, won't get any timing advance without it but see if the missing disappears.
If not, if it still miss fires it needs a tune up, yea yea I know just had one, that doesn't mean good quality parts where used. Might be all auto super store junk.
That and go over all wiring real good, hacked up harness is problematic at best with one of these trucks. Find and fix any iffy wires and connections, be sure and solder and use dielectric grease on any repairs made to make them weather proof.

 

"Pull the spout jumper and take it for a little ride, won't get any timing advance without it but see if the missing disappears.
If not, if it still miss fires it needs a tune up, yea yea I know just had one, that doesn't mean good quality parts where used. Might be all auto super store junk."

Great idea- I did not think about disconnecting the spout and driving to test. Thanks. I will post tomorrow how it does.

 

that and make sure the plug wires are well separated-have seen that problem posted here many times-last two on the passenger side cross firing i think it was

 

Yes, if I remember correctly it is 7 & 8 on the driver side- And yes they are all separated and routed as necessary. Thanks for the help though. Keep it comin' guys- something has to give on this persnickety beast!

 

Problem solved- I had 7 and 8 ignition wires separated but they crossed each other near the cap. I uncrossed the two and retested. No more random misfire now. Thanks for the help guys.

 

by crossing fire wouldn't the plugs wires be bad?