Starter engaged while driving

[ScubaSteve]

So I had a strange problem yesterday while driveing down the road about 75mph I had the starter engage. I pulled over and shut the engine down and everything shut down with the key and when I restarted it was fine for a few minutes and the starter engaed again. I disconnected the cable that goes to the started at the starter relay on the right fender and drove home with no problems. A little history on the truck I have a 351W carbureted with Duraspark distributor and module. On the "S" terminal of the relay I have the original start signal wire, A wire that triggers my fuel pumps when cranking and a wire to the ignition module to retard the timing at startup. On the "I" terminal of the relay I have a wire to bypass the ballast resistor or the coil at start up. I will list what I think is a list or possible causes and see if anyone has had anything similar happen or if they can think of anything i am forgetting.

Starter Relay Sticking: This is not the problem because it doesnt happen at start up it happend after the engine is already running.

Ignition switch: I dont think this is the problem as it happens while driving with the truck in drive so the neutral safety switch should stop the ignition switch from activating the starter.

Wire connected to the "I" terminal of relay: This wire has voltage any time the engine is running so if this was the problem It should be trying to start all the time.

Wire on "S" terminal for fuel pump: If voltage was applied to this wire it could cause my problem I checked the connections and could not find any shorts. This wire is connected to an oil pressure switch and it applies power to close the fuel pump relay when cranking and when the oil pressure comes up the switch is flipped and the fuel pump relay gets its power from an ignition source.

Wire on "S" terminal for the ingition module to retard timing when cranking: I think this may be my problem. I noticed that for a few miles before this happened i had some sputtering on hard acceleration. I disconnected the wire from the "S" terminal and the truck is running better and I have not experianced any more engine cranging when driving. With the wire disconnected from the "S" terminal and the key on I have .33 volts coming from the ignition module. I know .33 volts is not very much but I am concerned I may be getting more current as the module warms up and would expect this to be 0 volts.

Has anyone experiencedanything similar and has anyone ever had the ignition module malfunction in a way that it delivers current to the "S" terminal on the starter? The module on my truck is only a few months old but its not a Motorcraft. I ordered a Motorcraft module and it will be here in a couple days. I plan to install it and see how the truck runs. Right now the truck is running fine with the wire disconnected from the "S" terminal but I dont trust this module.

[Gary Lewis]

I think you may have figured it out. I've not had the ignition module do that, but it sure could. And if you having some other symptoms of a failing module then that's probably it.

One way to ensure this doesn't happen is to put a diode in the wire such that the relay can supply power to the module but not the other way 'round.

Please let us know what you find out.

[ScubaSteve]

I think you may have figured it out. I've not had the ignition module do that, but it sure could. And if you having some other symptoms of a failing module then that's probably it.

One way to ensure this doesn't happen is to put a diode in the wire such that the relay can supply power to the module but not the other way 'round.

Please let us know what you find out.

I was thinking the same thing about the diode. I am going to install a diode in both the fuel pump and ignition wise on the "S" terminal. Until then I am planning to leave the Wire disconnected. I will also check for voltage on that wire when I get my new module this week. I am curious if I will see the same .33 volt or 0 volt, I am hoping its 0. Thanks for the reply and I will report back with any new information.

[Gary Lewis]

I was thinking the same thing about the diode. I am going to install a diode in both the fuel pump and ignition wise on the "S" terminal. Until then I am planning to leave the Wire disconnected. I will also check for voltage on that wire when I get my new module this week. I am curious if I will see the same .33 volt or 0 volt, I am hoping its 0. Thanks for the reply and I will report back with any new information.

Solid state circuits can present odd voltages when using high-impedance meters, so I’m not too surprised at the .3v reading. But a diode sure won’t hurt.

[ArdWrknTrk]

I'm pretty sure the I terminal should have spark retard, fuel pump prime and full voltage to the coil.

It should only be energized when the starter is engaged.

There should only be the red blue relay trigger on the S terminal.

I've never seen a DSII wired the way you say yours is.

(but I will have to check the EVTM)

[ArdWrknTrk]

I'm pretty sure the I terminal should have spark retard, fuel pump prime and full voltage to the coil.

It should only be energized when the starter is engaged.

There should only be the red blue relay trigger on the S terminal.

I've never seen a DSII wired the way you say yours is.

(but I will have to check the EVTM)

The diagram from the 1986 EVTM seems to show only the fuel pump 'prime' wire connected to the I terminal of the starter relay, by a blue fuselink (T)

Coil power comes straight from the ignition switch, and retard is coming from C121 upstream on the same red/blue wire....

[Gary Lewis]

The diagram from the 1986 EVTM seems to show only the fuel pump 'prime' wire connected to the I terminal of the starter relay, by a blue fuselink (T)

Coil power comes straight from the ignition switch, and retard is coming from C121 upstream on the same red/blue wire....

Good point, Jim. I missed that.

[ScubaSteve]

I'm pretty sure the I terminal should have spark retard, fuel pump prime and full voltage to the coil.

It should only be energized when the starter is engaged.

There should only be the red blue relay trigger on the S terminal.

I've never seen a DSII wired the way you say yours is.

(but I will have to check the EVTM)

I am using a painless wiring DS2 harness so the schematic in the manual does not match up. The reason for having the fuel pump prime and ignition retard on the "S" terminal is because the wire to the ballast resistor bypass will have 8 volts at the "I" terminal when the engine is running. This will not be a big problem for the fuel pump prime as its going to an oil pressure switch and the current does not actually go anywhere but for the ignition retard the 8 volts will keep my ignition retarded all the time not just at startup. Thank you for looking into the schematic for me. I should have mentioned the painless harness in my first post.

[ArdWrknTrk]

Good point, Jim. I missed that.

I'd be interested to figure out what wire is connected to the 'I' terminal (that is hot in run)

From the schematic it doesn't seem the retard wire to the module should be back feeding.

Having it connected at the 'S' terminal is essentially the same as shown.

Though you have to wonder what else has been changed???

There's certainly been a bunch of creative harness modification!

[ArdWrknTrk]

I am using a painless wiring DS2 harness so the schematic in the manual does not match up. The reason for having the fuel pump prime and ignition retard on the "S" terminal is because the wire to the ballast resistor bypass will have 8 volts at the "I" terminal when the engine is running. This will not be a big problem for the fuel pump prime as its going to an oil pressure switch and the current does not actually go anywhere but for the ignition retard the 8 volts will keep my ignition retarded all the time not just at startup. Thank you for looking into the schematic for me. I should have mentioned the painless harness in my first post.

Looks like we posted about the same time, and I missed the Painless harness while reviewing the EVTM.

I would put a diode in the coil wire and move the coil, fuel pump and retard wires to the 'I' terminal.

This will solve any backfeed from the coil and leave only the trigger (through the NSS) connected to the Start (relay trigger) terminal.