Well, bummer. Who's the chucklehead that suggested changing the ignition switch? What a mouth-breather! Oh, wait, that was me. Nevermind...

Time to put on my orthopedic thinking cap. In your first post, you said the truck dies as if the key was turned off. Is it still behaving the same way? When the engine dies, does the radio also go dead? Same for the temperature and fuel gauges. If you don't move the key from the run position, those two gauges should continue to work. The oil pressure gauge will (accurately) drop to zero because oil pressure drops off when the engine stops.

EDIT: Try the turn signals and heater fan, too. Basically anything you can think of that is controlled by the ignition switch.

Just trying to get a feel if this is an electrical supply issue, or just something acting up in the ignition system.

 

So the switch & the IGN box has been changed anything else?

I would check the coil connection and pull apart any plugs on the IGN side to see what they look like.

The only other thing if wiring is good is the PIP or pick up coil in the distributor.
Dave - - - -

 

It was a honest guess hah. Yes it still acts the same way. It does it at idle, acceleration, or just cruising, as if power was being unplugged. However, the radio, heater, turn signals etc. still operate when it dies. The radio never cuts out. I haven't noticed my fuel and temp gauge when it dies. I'll look out for that next time.

The ignition switch, computer, EEC relay, coil, distributor, ignition module (Motorcraft) and the stator inside distributor (Motorcraft), have all been replaced within the past 6 months. My mechanic is the one who replaced the stator. When I search the stator there are a few different parts that come up such as the PIP, pick up coil, and Hall effect. So I'm not completely sure which is the correct terminology. Unless these are all different??

 

When the truck dies I lose spark from the coil to the distributor unless I recycle the key to off and then back to run. It starts up immediately every time.

 

Have you ever pulled the codes from the computer?

 

Yeah I cant remember the codes off the top of my head but they had something to do with the SPOUT circuit and/or IDM circuit. I tried researching what the IDM was but couldn't find anything.

 

I know for sure one was code 18, which I believe to be the SPOUT/IDM one.

 

Does anybody have a good link for interpreting these codes? Deciphering these first generation EFI codes can be kind of tricky.

If you don't get anywhere with that, I did have one more thought. The way the system is shutting off, as if the key had been turned, got me thinking. These are two quick tests that shouldn't be much of a distraction.

Wiring diagrams here, on page 29 and 60-65:

1986 EVTM - Gary's Garagemahal (the Bullnose bible)

On page 29, look at wire #20, white w/ light blue. Via splice S257 (at the right), this circuit feeds multiple ignition components, including the coil and TFI module. If one of those connectors can be backprobed, rig up a long test lead extension so you can read voltage in the cab. Drive around for a few days like that until the engine dies again. Watch the voltmeter when the engine quits and see if the coil was getting power with the key still in the RUN position.

Next is power to the Electronic Control Assembly (ECA) on page 60 and 61. Power to the ECA, the fuel injectors, and most of the related solenoids is all downstream of the EEC power relay. Follow wire 302 to splice S172 and then on the many branches of circuit 361. Backprobe any one of those convenient connectors and read the voltage as described above. If you lose power here when the engine dies, the EEC power relay itself is failing or it's not getting a proper signal to stay energized.

Oh anyways, monitoring power at those two circuits should give you a good idea how best to proceed.

 

Thanks for this information! So far it hasn't died on me in two days. I haven't touched anything else so I am not sure what is going on lol. I will be reading that article above and when (not if) it dies again ill proceed with those. Thanks again!

 

I'd suggest setting up the voltmeter now, before the next failure.

The test setup doesn't have to be very elaborate. Backprobe a connector with a paperclip or similar. Connect that to a length of spare wire with an alligator clip, clothespin, or whatever is handy. Feed the wire into the cab through an existing hole in the firewall or out from under the hood and around the edge of the door.

With that you can now monitor the voltage present at one of the two points previously mentioned. Who knows, maybe your charging system is on the fritz and causes some of the underhood electronics to act up. The key is be monitoring ahead of time so you can either confirm an electrical supply problem or rule it out when the fault returns.

 

IDM = Ignition Diagnostic Monitor

I had a lot of excerpts from the Ford Powertrain/Emissions Diagnostics FSM explaining this stuff but they were hosted by PhotoBucket.

 

One last thought. I'll throw this out there as one more thing to check, but I don't mean to distract you from checking the computer fault codes.

I had previously suggested monitoring the voltage at the two points in the EFI system. Of course you can only check one at a time, but it will only take a few minutes to initially set up. After that, you can easily swap over to the other test point. I mention those test points again in case your charging system is acting up, and the voltage is swinging high or low. Voltage out of specs (high or low) can cause all sorts of strange problems.

My latest thought is to also check for AC ripple. AC ripple can also cause all sorts of strange electrical issues that defy conventional troubleshooting in a DC circuit. At least it's easy enough to rule out. The following article is from Mercedes, but the test is applicable to almost all vehicles. Even if it all seems like electrical mumbo-jumbo, the test is very simple and only takes a few minutes. For best results, and even though it seems like it wouldn't matter (it does!), take the reading as close to the alternator as possible, not at the battery. A reading of 0.5VAC is the maximum you should see:

Link to AC Ripple Test

Remember, I'm not trying to divert you from following the computer fault codes. These are just a few basic checks you can quickly run to rule out some remote possibilities.

 

maybe because its not running?

is this not a fuel issue?