Backwards problem - it starts but I can't shut it off with the key!

[philbobaggins52]

Hi all! Phil here, Adelaide in Australia. Over the last 4 years I have been restoring a 1986 F100 302 4WD C6 which spent it's first 20 years as an ambulance in country NSW. Over the last few months I have been rewiring it, virtually from scratch. I have installed a Kwikwire 22 circuit wiring harness. Because the engine uses EFI, I decided to open up and copy the relevant parts of the EEC IV harness and connect them to a new 60 pin connector and sensors etc, and overlay this harness onto the Kwikwire job. Long story short, the engine starts readily (both EEC and fuel cut-off relays obviously work fine, along with an unknown list of sensors). The problem is, when I turn the ignition switch to off, the engine keeps happily running. I suspect the ignition switch wiring but my limited understanding of the start-run-stop process means I don't know where to look to resolve this issue. FWIW, I put a toggle switch in line of the pin 30 power feed relay to the high pressure fuel pump, which does cause the engine to stop when switched. My main difficulty is that I have been unable to find any references to the start-stop sequences when you have the ecu controlling ignition and fuel delivery etc. I mean, if I knew the sequence, that should give me clues where to look for whatever is latching the fuel delivery and ignition circuitry to "on"". So, can anyone please point me towards a resource that describes this sequence? Any thoughts would be very much appreciated! :)

[Gary Lewis]

Welcome! Glad you joined.

You may want to post the same thing in the main section as it'll get more attention than here. But we can work on it here if you want.

By the way, we have a map (Bullnose Forum/Member's Map in the menu) and can add you if you'd like.

As for your problem, I think you have a mis-wire in the ignition switch circuit such that the W/LB wire going to the coil is hot even with the key off. The way the ignition circuit works is that the EEC causes TFI module to ground the DG/Y wire on the coil and then take the ground off when it wants to fire a plug.

But you must also have power to the EEC when the key is off or it wouldn't be telling the TFI module to fire the ignition. So something is pulling in the EEC Power Relay. And that W/LB wire is what pulls the relay in, so if you have power to the coil you also have power to the EEC.

[ArdWrknTrk]

Welcome Phil!

You're going to find ignition diagrams and testing information in the EVTM pages. https://www.garysgaragemahal.com/start--ignition.html

This would be Documentation/Electrical/EVTM's/appropriate year.

Not all years are shown because much of it is redundant and it's a lot of work for Gary.

A 5.0l Windsor for 1986 with EEC-IV ignition, start and run is linked, but there is much more to the manual if you follow the steps above.

 

[grumpin]

Welcome!

[philbobaggins52]

Welcome! Glad you joined.

You may want to post the same thing in the main section as it'll get more attention than here. But we can work on it here if you want.

By the way, we have a map (Bullnose Forum/Member's Map in the menu) and can add you if you'd like.

As for your problem, I think you have a mis-wire in the ignition switch circuit such that the W/LB wire going to the coil is hot even with the key off. The way the ignition circuit works is that the EEC causes TFI module to ground the DG/Y wire on the coil and then take the ground off when it wants to fire a plug.

But you must also have power to the EEC when the key is off or it wouldn't be telling the TFI module to fire the ignition. So something is pulling in the EEC Power Relay. And that W/LB wire is what pulls the relay in, so if you have power to the coil you also have power to the EEC.

Hi Gary! Thank you so much for such a speedy and helpful reply! It feels as though a load has already been lifted :).

I will study your words and diagrams asap and hopefully find the mistake(s) in my wiring - I expect the answer will be obvious as soon as I know it! I will give you feedback on progress as it happens.

FWIW, I had the engine running for a good five minutes this morning and it sounds mechanically sweet and with a steady exhaust note (I have to time it accurately next). All very promising!

Again, many thanks :)

Kind Regards, Phil

 

[philbobaggins52]

Welcome Phil!

You're going to find ignition diagrams and testing information in the EVTM pages. https://www.garysgaragemahal.com/start--ignition.html

This would be Documentation/Electrical/EVTM's/appropriate year.

Not all years are shown because much of it is redundant and it's a lot of work for Gary.

A 5.0l Windsor for 1986 with EEC-IV ignition, start and run is linked, but there is much more to the manual if you follow the steps above.

Thank you Jim for taking the time to help - very much appreciated! :)

Kind Regards, Phil

[philbobaggins52]

Welcome!

Thanks Dane! I can tell there is kind help aplenty in this Forum! Good to be here :)

Kind Regards, Phil

[Gary Lewis]

Hi Gary! Thank you so much for such a speedy and helpful reply! It feels as though a load has already been lifted :).

I will study your words and diagrams asap and hopefully find the mistake(s) in my wiring - I expect the answer will be obvious as soon as I know it! I will give you feedback on progress as it happens.

FWIW, I had the engine running for a good five minutes this morning and it sounds mechanically sweet and with a steady exhaust note (I have to time it accurately next). All very promising!

Again, many thanks :)

Kind Regards, Phil

Welcome. I think you'll find it is a simple problem, but it might be tricky to find. However, we are here to help regardless of how deep the problem is.

[philbobaggins52]

Hi again Gary! After a week where life got in the way and a mild bout of food poisoning, I have some preliminary feedback on the issue :). My son and I followed your clues re coil voltages, without finding a cause of the symptom. We were suspicious that maybe somehow the alternator was holding up whichever circuits had latched on while the engine was running (because even disconnecting the battery wouldn't stop it). We found that disconnecting the exciter wire enabled the engine to shut down instantly by turning the key to off! A little bit of internet searching on alternator circuitry suggested that it was indeed possible to have this non-stopping sequence if something is missing from the circuit (likely in my case because I am adapting a Kwikwire harness to EFI control). So, I put a 6 amp diode between the exciter wire and the alternator. Like magic, the engine now turns on and off correctly! What I also discovered on the original Ford harness were two light bulbs in the exciter circuit which I had omitted from the rewire. Does it seem likely that these bulbs (they look like dash display plug-ins) are essential for correct running of the alternator? I have not yet completed wiring in the instrument cluster, so there are no connections to the cluster as yet (and no gauges like oil pressure/charge etc). I do wonder will the alternator function properly as wired - can you please make some observations about all this?

Again, many thanks for your support! ::))

PS - please feel free to add my location to your map :)

[ArdWrknTrk]

Hi again Gary! After a week where life got in the way and a mild bout of food poisoning, I have some preliminary feedback on the issue :). My son and I followed your clues re coil voltages, without finding a cause of the symptom. We were suspicious that maybe somehow the alternator was holding up whichever circuits had latched on while the engine was running (because even disconnecting the battery wouldn't stop it). We found that disconnecting the exciter wire enabled the engine to shut down instantly by turning the key to off! A little bit of internet searching on alternator circuitry suggested that it was indeed possible to have this non-stopping sequence if something is missing from the circuit (likely in my case because I am adapting a Kwikwire harness to EFI control). So, I put a 6 amp diode between the exciter wire and the alternator. Like magic, the engine now turns on and off correctly! What I also discovered on the original Ford harness were two light bulbs in the exciter circuit which I had omitted from the rewire. Does it seem likely that these bulbs (they look like dash display plug-ins) are essential for correct running of the alternator? I have not yet completed wiring in the instrument cluster, so there are no connections to the cluster as yet (and no gauges like oil pressure/charge etc). I do wonder will the alternator function properly as wired - can you please make some observations about all this?

Again, many thanks for your support! ::))

PS - please feel free to add my location to your map :)

Hi Phil,

I'm not Gary but in the US if your truck came with a charge indicator lamp you need to retain it because it provides 'exciter' current to the field winding of the alternator. This is a light green wire a red stripe (iirc it's circuit 904???)

The lamp would be jumpered on the cluster flex circuit with a 512ohm resistor so if the filament breaks the alternator will still charge.