I have an 88 f150 with a 4.9 L. I currently have an issue where it will misfire and kinda like spit while under load which is either normal driving or when I have heat, lights and wipers on etc. it really just chooses what it wants to do and when it does it. I’m getting the right fuel pressure and I don’t have any vacumn leaks. Me and the main mechanic that’s worked on it are thinking that it could be distributor since the last distributor started to go out and did similar things just not as aggressively. If it is distributor like we’re thinking is there any reason why they go out so often? The distributor we put in wasn’t new but it was in good condition. It’s been happening for a couple months now and I’m just now being able to afford to do anything about it. Any advice helps

 

Welcome to FTE

There are only 2 things in the dist. that can really go bad that you can replace.
The first that I would try as they can cause all kinds of crazy things to happen is the TFI / the gray IGN box bolted in the dist. with all the wires going into it.
Most of the time they just stop working and no spark but we are finding more and more the TFI and the DSII boxs do some strange stuff like miss fire lack power or stop working (motor shuts off) but in a hour or so will start back up till it heats up and dose it again.
It dose not hurt to replace it to see if it changes anything and if not you have a spare.

The other thing is the pick up coil. Some have had strange things happen from it going bad.
There is a ohm spec to test it but I dont know what that is. I would also test when it is warm as that seams to be when most of the issues happen.

The last but have not seen it on electronic dist. the upper shaft bushing wears and the shaft gets play and changes the gap between the pickup coil and the star .
On my 81, DSII dist., the plate the coil assy is on should have plastic bushings it rides on that are on for vacuum advance.
Mine was missing the bushings to the plate rocked changing the gap.
When I replaced the pickup assy. I found the coil hit the star? Dontknow why but it did and would hardly run.

I was able to take the old pickup coil assy and new one and make one that worked and have a steady gap.
So far a few 1000 miles it has been good no miss under load like before.
I also had 1 vary bad, fouled, plug. plugs had 28K miles and that really fixed the miss.

Oh becasue you have EFI have you pulled codes to see what the computer has to say?
Dave ----

 

The midnight ignition check: with it idling in the darkest conditions you can manage, carefully inspect all ignition-related components looking for any electric blue light at all; try revving the engine too while looking.
I had a misfire under load that developed last summer a few weeks after putting in new plugs, wires, rotor, cap, &c. In the dark, a very faint blue glow could be seen down in the bottom of the #1 plug well. I replaced that wire, but it still missed, so then put in a(nother) new plug, which solved the problem. Fining that with an ohmmeter and standard troubleshooting procedures would have been very time consuming, if they even worked at all.