I've been trying to figure out what is causing my engine (1987 EFI F150) to hiccup (cut out) at speed for over a week now and it's still doing it. My apologies for the long post.

It started with a no start condition. When it did start, it ran poorly, the tach was going nuts, and it started cutting out. I traced down a bad ignition module and replaced it. It ran well for a bit and then started cutting out again. I went to pull codes and it took a couple of attempts to get the KOEO to run with my code reader which was highly unusual. I pulled the ECM and found a couple of capacitors that looked like they were on their way out so I replaced it.

It ran great for about 75 miles and then started cut out again. This time I installed a new distributor (for the PIP sensor), along with a new cap and rotor. The plug wires are relatively new and tested out within resistance specs. The ignition coil tested a little flaky on the secondary side, so it was replaced as well.

No luck - it is still cutting out. The fuel filter wasn't very old but I replaced it anyway and checked the resistance in the high pressure pump which came well within specs. A fuel pressure test indicates that I have 45 psi at idle with a spike of 55 psi when the key is first turned on. The gauge wasn't the best, so I haven't been able to test pressure under load.The pressure regulator was replaced in January and doesn't appear to be leaking into the intake manifold.

At the same time the regulator was replaced, the intake manifold gaskets, IAC, vacuum lines, and EGR valve were replaced to fix the wandering idle issue. The vacuum line to the EGR is currently disconnected due to an issue with the control solenoid.

The truck was running well before all of this started. Everything I've done has made it run smoother and quieter, but has done nothing for keeping it from cutting out.

I'm running out of things to look for. The only codes I'm pulling are for items i know about (33, 67) and have been there for a while. The things that I still have on the checklist, but haven't pursued are:

- Code 82 - Seems to be the smog pump control solenoid?
- Fuel pressure test at speed while its cutting out
- Fuel pump relay
- Back pressure from 28 year old catalytic convertors and who knows how many years of running horribly rich due to idle issues.
- Dying Fuel Pump(s)
- Tank selector switch - I only run on front tank due to being told not to use the rear by PO. He didn't say why because the guy he bought it from told him not to. I figure the pump and/or tank is bad.

I would really appreciate a new perspective on this. The truck idles smooth and is strong up until 35-40 mph before it cuts out. I really don't want to drop new pumps & a selector switch in it because it "might" help. I've already done too much of that lately.

 

Fault Code Description. 82 - 3x Crankshaft Position sensor circuit.

You have three different codes plus a vacuum line to the EGR disconnected. What steps have you taken to correct these items?

 

No crankshaft position sensors in '87...

 

When it "cuts out" what is it doing?...does it die? or just sputter? If it dies does it start again right away?.

EECIV is simple, but the wiring is old, is the wiring generally in good shape?...

How are the grounds..especially the main ground to the battery terminal/body location? Have you cleaned those grounds?

In my own personal agony with an 80's Ford EECIV product, bad grounds chased me around for quite a while after buying something someone else worked in...forgetting to fasten all of the engine/body grounds. The fuel relay is a good suspect..again grounds etc.

Have you changed your high tension lead to the diz from the coil?. I once had a new MSD coil fail as well causing cut-out.

Best wishes...

The good news is..it's old enuf to dura-spark..just sayin...and job done. 30 year old wiring..not fun.

another note..I would not expect 30 year old cats to perform well. Truth be told probably plugged.

 

I might add as a comment, your fuel selector switch may not be holding well from one tank to another. In my 83, the default draw (power off) is the rear tank. Of course my 83 is pre-EFI so it is the simple switch.

just another angle to look at..

 

Thanks John.

When I'm going down the road, it's like shuts off for a fraction of a second and then comes back on. It hasn't completely stalled since the ignition module was changed and it hasn't left me stranded.

The wiring has been generally in good shape aside from time worn connectors that I've replaced. I will make it a point to check the grounds in the morning. I've heard of problems with the tank selector switch but really haven't considered it as a possibility. I've got the factory service manuals so I'll dig through those and see what they say about it. The coil wire was changed with the rest of the wires a year ago and is still testing OK.

I'm not sure how much of guts of the cats are there - previous owners may have gutted them already...

If I hadn't already poured a bunch of money into the EEC-IV system, I'd be first in line to convert back.

 

Well, it's either fuel or fire..so a little patience may help you sort it out. remember the injectors need grounds too. In my case with my Ford experience, an engine had been swapped by the PO and the harness grounds weren't connected well. I DO know that the main ground and relay for the computer itself is critical. I hope you aren't experiencing any corrosion issues in your wire leads....too bad you can't do a fuel pressure test from inside the cab..that would tell you a lot also.

You mentioned you changed the diz module, how did the connection from module to diz look?. How about the PIP plug?..any chanch it's shorting out etc? it should be giving bad signal codes, but you never know.

If I were doining an EFI install I would re-locate the TFI module itself making it easier to change/check in the future along with giving it a cooler location as well.

Hang in there..

 

Regarding the distributor - its all new - distributor, PIP sensor, ignition module, cap, & rotor - so there shouldn't be any issue there. That also makes the 2nd ignition module replacement without any improvement.

I'm going to attempt to set up the pressure gauge so it can be watched from the cab while its on the road just to see if the fuel pressure takes a dive or not. At the same time, I'm going to start checking all of the grounds I can - particularly those related to the powertrain.
it may take a bit of time, but there has to be something off somewhere...

 

Fuel pressure is relatively stable with no drop off at higher RPMs. I was really hoping it would drop off and give me one of those "aha!" moments. Since there's no practical way to safely test it on the road there's no way I can catch it when it cuts out.

 

It almost looks like one of those RF interference kind of things. Remember how you make sure how you route #7 and #8 on a V8 away from each other? That's RF interference. At night or very poor lighting with it running, spray water on your wiring to see if you can see any fire flying.

 

Thanks Vince - I'll give that a shot tonight and see what I see.

Grasping at straws here - could problems in the charging system put up that kind of RF? I've had a on and off low voltage issue that I thought was a flaky gauge, but if it isn't low voltage would cause problems as well?

 

Update & Bizarre twist...

Checked the plugs - they're all clean and perhaps showing a little lean - which they would if there's a fuel delivery issue. Took it for a hop over to the auto parts place to return the fuel pressure kit and have the charging system checked (its OK) and as long as I kept it under 45 it was pretty smooth.

Here's the bizarre and probably critical new discovery - if you slam a door or the hood with the engine running, it picks up 500 rpm momentarily and then slows back down. That said - I am now looking for a probable vacuum or electrical issue.

 

Well it would appear that you are checking things out. I wish you well..I probably should've said from my first post that even thought I would desire to be helpful, I actually would rather not get involved in a conversation that involves a system that has been messed with much, especially an EECIV system. The age of these systems along with the effect of corrosion on wiring has left me with an urge to really deal with as complete a factory system as it was shipped with when trouble-shooting problems.

I have a hunch yours is more electrical than mechanical giving the on-off failure. If you or some else has messed with wiring much..a review of what is good may need to be considered when checking wiring gremlin issues...

so..basics..of a TFI system..and it's ALL electrical..

Hang in there..

 

John - your advice has been both helpful and appreciated.

I've got the factory manuals and have printed out the wiring schematics for the EFI system. I just need to pick a starting point and take the time to trace everything down.

 

You might check grounds on both the fenders and the kick panels.