My sons 90 F150 with a 5.0 had a burnt valve. It ran good other than the missing cylinder from the burnt valve. We built another 5.0, bored, new pistons, heads worked and now it is missing like crazy. It will not pull a greased string from a cats butt.
We put plug wires on it before tearing it down so we didn’t renew them. I replaced the distributor since the gear on the old one was chipped and had a lot of wear. New plugs, water pump just about everything replaced.
If it were something other than all the electronic and fuel injection I probably could fix it. It will backfire some, not all the time. It misses sitting idling and when it’s revered up it sounds much better, but when trying to drive off it doesn’t have any power regardless of rpm.
The egr valve was disconnected when we got the truck and it appears it may have had a smog pump, but it too is no longer on it.
I have checked the timing and actually set it with a light. I think I have tried it anywhere from 0 to 10 degrees BTC.
If anyone has any suggestions, I’m listening. My son really needs his truck, but I’m lost as a ball in high grass.
Any help would be greatly appreciated.
Thanks

 

I kinda suspect there is a possible timing problem , might need to remove dist and reinstall from scratch.
It would not be the first time two plug wires were reversed, recheck yet?

 

Found out since I used a 95 engine for the rebuild, I had used a HO set up so I had it cross wired really bad.
Runs a whole lot better, but it has a miss/sputter from about 1700 RPM UP TO 25 hundred RPM.

Still struggling at this time,

Thanks for your help.

 

did you disconnect the spout connector when you set the timing?

do a power balance test. this will id which cylinder is misfiring.

if you don't have a scan tool...disconnect injectors one at a time if they are accessable...if not pull the spark plug wires off one at a time( use insulated spark plug wires pliers) and note if the rpm dropped. the cylinder that did not drop rpm is the faulty cylinder

swap the spark plug, plug cable and see if the misfires follows the swapped part. if not compression test

 

I know with older vehicles we pulled a plug wire to locate a misfiring cyl, but sometimes the high voltage created because it had no place to go would wipe out the ign module just as a bad plug wire could.

 

its possible. the best way to do it is to pull all the spark plug wires off the dist cap...insert a 1 " section of washer fluid tubing on each tower (8cyl = 8 pieces of tubing) and set the wire on top of the tubing.

the secondary discharge will conduct thru the tubing into the sp wire. to short out each cylinder without any potential arcing....touch a grded test light to the tubing. the spark with flow thru the test light safely to grd, not reaching the spark plug.

 

I timed it with the “spout” unplugged. Seems to run fine.
The only opportunity we have is driving down the road going thru the gears (5 speed) any where from 1500, 1700 - 2000, 2500 it will seem to miss. I have noticed it seems more like it dies for a moment. The tach drops just for a split second then it good. This doesn’t happen all the time, just occasionally. It’s just like you switched the ignition switch off and back on. We have checked connections and all seems fine. Don’t remember this happening before we rebuilt the engine. I guess it could be a naked wire somewhere shorting out, but it is driving me nuts trying to figure it out.

 

What you can try if you want to,
Connect a test lite to the wire coming from the ign switch to the coil power supply. You will need to use a long piece of wire so you can see the test light inside the vehicle, then drive it and observe if the light flickers any time. It is a good visual check to rule out the ign switch and wiring to the coil. It was a good test for use on the older vehicles.

 

if the tach is dropping out...sounds like an ignition problem...tach signal is probably off the ignition

 

With engine off the codes my reader pulled are 10, 11 and 31.
With engine running I got codes 40, 44, 77 & 52.
I drove it for a few minutes this evening and it would cut off or miss occasionally. But it really doesn’t seem to have very much power. It couldn’t pull a greased string out of a sick cats butt .

Is there something up with the HO motor versus the non HO? I used a 95 engine which was a HO versus a non HO that was in the truck. I found out that the firing order was different and changed that, now It runs smooth, just doesn’t have much power.
Son said this morning on his way to school, he pulled out on the road, but the truck had almost dead!
Since the firing order was different, would the injector wiring also need changed?