Hello, new owner and member. I have a 1990 F150 5.8 truck. Cannot seem to fix the issue it has and asking for any help. I’m a mechanic by trade but even this has me stumped. It has a new reman 5.8 engine. It spitters, stumbled and pops through the intake. Barely drives me and won’t idle well. i have replaced as follows:
-New pick up in distributor
- new ICM on distributor
-new fuel pump per po who couldn’t fix this issue
-new map sensoe
-new coil
-new tps sensor
-new ect sensor
-new air intake temp sensor
-verified timing is set 10 degrees btdc
-removed o2 sensor to see if cat was stopped up. no change
-cleaned and installed additional ground wires

Im out of ideas. anyone got anything?

 

I would verify that the correct firing order is being used and check the routing of the spark plug wires. Crossfire between spark plug wires was an issue on some of these engines.

 

Did you time it with the SPOUT connector removed? If you did not you need to remove it and then time it again if you can get it to operating temp. Otherwise you’ll just have to time it by sound and then once it reaches operating temp use the timing light with the SPOUT removed then set it 10 BTDC and I’d make sure it’s lined up correctly on the timing pointer I just timed mine and I didn’t line it up right I thought another spot was where it lines up and it was pinging so bad it sounded like a Cummins.
And did you use the #1 cylinder plug wire. I’ve heard of something of these engines being different than others with where #1 one is located. Or I’m just crazy.
sorry if I’m just stating basics to you I know you said your a mechanic. I’m no mechanic but I figure if maybe you forgot to do something this could help. I’ve heard a lot about people forgetting to remove the SPOUT and then it’s wrong.

 

I set the timing with engine off, cylinder 1 at top dead center on the compression stroke. the rotor was pointed directly to number 1 on the cap. with it running at this setting it sounds worse when the distributor is turned either direction.
I failed to mention i also replaced the PCM with a new reman unit. and verified it had good capacitors as these are known to be bad on the 12A650 pcms

 

Did you pull KOEO and KOER codes?
I learned with these OBD1 systems even if there’s no light it could still have a code.

 

This is a short video
https://youtu.be/v4PzOo5L1C0

 

Did you verify fuel pressure at the rail?

 

Just did the test. 35 psi at idle and 40 when revving the engine.
Here is a video of it running:
https://youtube.com/shorts/Ef_M0tre4jU?feature=share
i’m out of ideas guys i have tried every single thing i know.

 

https://www.therangerstation.com/tec...gitcodes.shtml

Here’s the codes library for the 2 digit

I couldn’t tell you what codes your getting I had to buy the obd1 scan tool cause I never read the check engine light flashes right.

Never saw anything about replacing plugs? If you haven’t get Motocraft copper ones only. If you did and they’re not motocraft copper get those. On another forum I use they are dead set on motocraft copper only in these engines.
And only motocraft ignition parts but the plugs are what they are big on the other forum.

Maybe unplug each individual cylinders plug wire while running if you won’t get shocked doing so, see which ones causing the misfire.

Spray some propane around the engine bay or just brake clean if you’re not worried about the fire risk. see if any vacuum lines are leaking and plug a vacuum gauge into it.

Clean IAC?

How different does it run if you unplug the SPOUT? Does it run better or worse? Maybe the new PCM isn’t controlling its timing right.

My cap and rotor, on my 302 made it run terrible. Maybe sand down points see if that helps if they are old?

Again, I’m just spitting out everything I think of I don’t really know what you would do to properly diagnose it.

Try a KOER (key on engine running) test if possible and not done already. There’s different procedures depending on what sensors your truck has or doesn’t have

https://youtu.be/cVFpQkl0mnY


Skip to 5 minutes for the KOER

 

***Posting the solution for anyone else with this issue. It was a faulty TFI module. Replaced it and relocated it using a hand made extension harness for the pip side of things and mounted it to an old xbox heat sink and she’s good as gold now **