Starter engaged while driving

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.

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.

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.

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....


 

Good point, Jim.  I missed that.

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.

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!

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.

The brown wire is connected from the "I" terminal to the coil down stream of the ballast resistor. This provides 12 volts when cranking to the coil but it is also recieving 8 volts from the ballast resistor when the engine is running.

LOL I think we are posting at the same time. I will be adding the diode to the wires on the "S" terminal but i could also add a diode to the wire from the coil on the "I" terminal and move everything to "I". That would keep it from back feeding and the worst thing that could happen would be my timing would be retarded and no chance for my starter to kick in.

Right.  
So put a diode in that brown wire so it can't backfeed the retard or fuel pump circuits and leave only the 919 wire connected to 'S' on the starter relay.

I think this is the cleanest and most positive way to eliminate your problem.

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Looking at the '86 EVTM I don't see any electric pumps for a 351. Only 5.0 and 7.5l engines.

http://www.garysgaragemahal.com/electric-fuel-pump-control.html

Did you swap engines or eliminate the mechanical pump on the timing case?

It was originally a 5.0. All of the original fuel pumps and wiring are installed on the truck I'm just triggering the fuel pump relay with a 3 terminal oil pressure switch.

Okay. This is beginning to make more sense now, as a 5.0l would trigger the pumps from the ECM which you don't have.

So I recieved the new Motorcraft ignition module today. I believe the issue that caused the starter to engage was with my ignition module. I still have not hooked up the wire to retard the ignition at start up as the diodes i plan to use have not arrived but I am thinking about not hooking it up at all. The trucks starts very easy hot or cold so I dont realy think I need it. With the new ignition module the engine idles smoother, the throttle response seems better and no more stumble at wide open throttle.

I think you’ve solved the problem, and if you don’t need the retard function then there’s no need to hook it up.

But, you might get even better throttle response with more initial timing, and then you might need the retard function.

I am planning to check and reset my timing this week. The truck is idling a couple hundred RPM higher with the new module and I am thinking that if voltge was shorted to the retard wire inside the module it may have had my timng retarded a little bit all the time. I had the timing set to 13 deg and im curious if its not a little higher now. I had some problem with my timing moving around a few months ago but I thought the distributor may have slipped. so i locked it down a little tighter and marked it with a sharpie. Now im thinking it may have just been the module moving the timing around. I know plenty of people have said it before but if your using DS2 ignition stick with the Motorcraft brand module. You cant trust the parts house brands for this part.