Dies While Driveing, Key Off/on And Fires Back Up?

Wackfox · Apr 24, 2016

I have a 1993 5.0. It's a cam intake heads supercharger build with T5. Runs great the little over 400 horse but I on Occasion it would have a miss. Like the ignition would shut off just for a split second and come back on. finally today while driving it actually killed and while still rolling I turn the key off and back on and it fired off took. It happened a couple other times. Each time if I turn key off back on it fires and runs fine. Any ideas?

nickpic · Apr 24, 2016

Check the ignition switch. Overtime they start to split and can give intermittent issues. Replacement is around $15 on LMR. Mine just had to be replaced

Noobz347 · Apr 24, 2016

Other things to look at:

TFI
Fuel pump
Fuel pump relay
PiP
Reseat the EEC and connector
Reseat custom chip if this applies
Remove of-the-shelf junk chip if this applies

Normally, I'd recommend the Cranks but No Start Checklist but your problem is intermittent.

jrichker · Apr 24, 2016

Another vote for replacing the ignition switch...

Recall on Ford Ignition switches:

Revised 7-June-2014 to add Torx bit picture and source. Also added replacement ignition switch wiring pigtail picture, part numbers and sources.

Some of the symptoms of ignition switch problems are things that don’t work or are intermittent like radio, turn signals, wipers or heater.

There was a FREE recall on Ford ignition switches. They overheat and sometimes catch fire. That burns up the steering column and sometimes the car interior. Since this is very old information, you may not be able to get the switch replaced for free anymore. The auto parts stores sell the switches for $13-$15.

While you are working on the switch, check the wiring and connector closely. A replacement connector with new wiring pigtails is available from most auto parts stores

AutoZone and Advanced Auto Parts have the same Part Number: 434 - may have to order, not always in stock

Advanced Auto Parts alternate part number: PT5534

Saleen0679 was nice enough to dig this up for us awhile back: Replace a 1979-1993 Ignition Switch Assembly

Torx bit set from Advance Auto Parts

Autocraft torx bit set – have small hole in tip for tamper proof screws.
Part No. AC571/W1386 Cost approx. $12 +tax

Diagrams courtesy of Tmoss & Stang&2birds

Ignition switch wiring

Fuel, alternator, A/C and ignition wiring

Wackfox · Apr 26, 2016

Thank you for the suggestions. Changed the switch tonight. Rain for next 5 days so won't be able to test it out but the switch positions feel much more solid now. Fingers crossed this was the issue.

Wackfox · Apr 26, 2016

Well. That didn't work. It actually got worse but I can get it to kill with rotating the key back just a bit. Zero rpm on tac when it kills. Think maybe try new key switch next.

jrichker · Apr 27, 2016

Wackfox said:
Well. That didn't work. It actually got worse but I can get it to kill with rotating the key back just a bit. Zero rpm on tac when it kills. Think maybe try new key switch next.

The zero RPM is because the power to both the tach and the ignition shut off. Look closely at the switch wiring connectors for evidence of heat damage.

Wackfox · May 1, 2016

Everything looks fine. Connectors and wires all look good but now it seems to happen more often after I replaced the ignition switch. Rewired the MSD still happens. I even changed out the actual key switch and still happens. Seems to happen more often if i hit a bump, but it also died while idling in the driveway. Strange. Everytime it dies, you have to take the key to ACC then back to on and it fires. Think I will try to bypass the MSD if I can figure out the wiring and see if that help.
Not sure what else to do but it real hit a nerve!!!

jrichker · May 1, 2016

Have you checked the computer power relay? It is located above the computer on the passenger side. You have to remove the passenger side kick panel and speaker to get to it.

It is difficult to get at unless you have small hands and an eyeball on a stalk like a snail. If the relay is bad or the wiring is damaged, it will produce the symptoms you describe. The clue is do the radio, AC/ heater blower or wipers cut off when the engine dies? If they don't, then the relay is most likely the problem source.

Does the radio, AC/ heater blower or wipers cut off when the engine dies? If it does, the problem is in the ignition switch wiring or the power feed to the ignition switch.

Wackfox · May 1, 2016

Ok, let me run another test with the all the accessories on and see what happens. Started to snow.. this should be interesting...lol......
Thank You!

Wackfox · May 1, 2016

Oh the world of Fox Bodies. I don't drive in rain, so wipers never been on, Have not had time to change the heater core out in the last yr (hehe) so heater fan has not been on. So I turn all that stuff on and drive it and now it wont kill. This morning I got it to kill 8-10 times, now I cant get it to kill to test the above. ugh. Maybe the relay needed some current pulled through it to clean it up.... Will let you know what happens.

jrichker · May 1, 2016

wackfox said:
Oh the world of Fox Bodies. I don't drive in rain, so wipers never been on, Have not had time to change the heater core out in the last yr (hehe) so heater fan has not been on. So I turn all that stuff on and drive it and now it wont kill. This morning I got it to kill 8-10 times, now I cant get it to kill to test the above. ugh. Maybe the relay needed some current pulled through it to clean it up.... Will let you know what happens.

The radio, AC/ heater blower or wipers don't use that relay to function.

Diagrams courtesy of Tmoss & Stang&2birds
Fuel, alternator, A/C and ignition wiring

Wackfox · May 1, 2016

So. All accessories stay on when it kills. No stumble like fuel or anything just... Off. Seems like it may do it more over bums... Fires right back up every time. I guess I go after this ecu power relay. Any tips on this?

jrichker · May 1, 2016

Wackfox said:
So. All accessories stay on when it kills. No stumble like fuel or anything just... Off. Seems like it may do it more over bums... Fires right back up every time. I guess I go after this ecu power relay. Any tips on this?

Only that it is very difficult to get to if you have large hands.
Find someone with small hands and some mechanical talent and bribe them to help you...

Remove the passenger side speaker and kick panel.
One screw on the bottom of a diagonal plastic strap holds the computer in place. Remove it and pull the computer down. The computer power relay is above the computer. Removing the passenger side speaker allows you see the relay and wiring, so you might want to do that first.

Wackfox · May 1, 2016

Got it out. The ecu was loose in there. Not sure if that could have caused and issue. The strap was not screwed on so ecu was banging around a bit. Got the relay out. Can't seem to find one at a parts store. Have to order I guess, unless someone knows the Napa number or something.

jrichker · May 2, 2016

Wackfox said:
Got it out. The ecu was loose in there. Not sure if that could have caused and issue. The strap was not screwed on so ecu was banging around a bit. Got the relay out. Can't seem to find one at a parts store. Have to order I guess, unless someone knows the Napa number or something.

How much skin did you lose in the process?

Wackfox · May 2, 2016

Ha. Lots. Great place to hide it... The new relay is not going back in the same spot that's for sure.

Wackfox · May 2, 2016

Well. . That didn't fix it. it back fires from time to time after a key cycle so don't think it's fuel. So weird. Just dies. No stumble at all

Wackfox · May 2, 2016

What I mean is after it kills I turn key from run Back one click and back to run it pops and runs so there is fuel in there. When it dies you MUST take key back Before trying to start. You can crank all day and it won't start of you don't take key back then forward. I'm at a loss. Any ideas. Codes are as follows. 15,84,15,84,10,18,33,18,33. Supercharger so No EGR with erg fooler plug. And I removed the spout to see what happens so that's why those codes. Also has a programable chip. I did bypass the Msd and it happens more I think.

JohnnyChimpo · May 2, 2016

Years ago on my old 87 notch I had these same issues, two separate incidents... What ended up crapping out (and this took forever to find out) was that control module on the distributor. I replaced the entire distributor with an MSD unit and never had the issue again. With the car running, I literally tapped on the module with a screw driver and the car died. Instantly. The second incident, my car was having similar symptoms'ish. Car would die, sometimes start back up-really intermittent and it eventually left me stranded. I can't remember exactly what it was but we tried everything. Car had spark, fuel etc and by chance, I was messing with the coil and the cluster of wires between the coil and battery while the car was running (like poo) and bam, it came back to life. It was some loose connection within that cluster of wires. Just throwing out ideas fwiw...

It's been 8 years since my last 5.0 so I apologize in advance if my terminology isn't up to par.

Dies While Driveing, Key Off/on And Fires Back Up?

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