M1009 Starter Runaway

[aembry1009]

I believe this is a very unique set of circumstances that is causing my starter runaway. I'm working with an M1009 and new Wilson gear reduction starter. Doghead relay mod had already been done.

The first thing I wanted to rule out was that there is enough clearance for the starter bendix to properly retract, as I know this can cause a starter runaway. The starter sounds good and strong and the teeth have roughly .035" clearance. All good.

I decided to remove the large wire for the starter from the 24V (+) terminal block for diagnostic purposes. I connected a test light and checked for power out of the starter relay while a helper worked the key and I was able to simulate the runaway. When the runaway occured, I observed that power had stopped coming out of the relay! Nevertheless the starter circuit was closed.

A separate helper was nearby to quickly disconnect the batteries.

The ignition switch and relay were replaced prior to these diagnostics. My issue is between the relay and solenoid, but I have no idea where else I should be looking. Only other observation that might be useful is that the smaller wire from the (-) side of the rear battery to the "diamond" connector was notably hot after the authentic starter runaway events, though I'm not sure what this could mean.

Any and all of your thoughts are greatly appreciated!

 

[dependable]

Could be the solenoid on the starter is faulty, it happened to me once with a freshly rebuilt gear reduction starter.

 

[aembry1009]

Could be the solenoid on the starter is faulty, it happened to me once with a freshly rebuilt gear reduction starter.

I had tried multiple solenoids, relays, and ignition switches before conducting the diagnostic outlined in the first post. The positive connection at the solenoid was disconnected, yet it still simulated the runaway.

 

[dependable]

Only other observation that might be useful is that the smaller wire from the (-) side of the rear battery to the "diamond" connector was notably hot after the authentic starter runaway events, though I'm not sure what this could mean.

The red wire to the "diamond" connector (on firewall above glow plug relay) is a 12 V feed if truck is wired stock and correctly, so it is a clue. The 12 V current it would carry during start should only be from ignition to relay under dash, not starter load.

So many of these trucks have had their wiring messed with, I would not want to speculate on what is going on without seeing truck. If there is 24V on that connector, something is not wired right, I'd check that next.

If you are just checking with light, you really need a volt meter to determine what is going on.

Might be a good time to compare with known stock truck or study wire diagram in TMs.

 

[aembry1009]

The red wire to the "diamond" connector (on firewall above glow plug relay) is a 12 V feed if truck is wired stock and correctly, so it is a clue. The 12 V current it would carry during start should only be from ignition to relay under dash, not starter load.

So many of these trucks have had their wiring messed with, I would not want to speculate on what is going on without seeing truck. If there is 24V on that connector, something is not wired right, I'd check that next.

If you are just checking with light, you really need a volt meter to determine what is going on.

Might be a good time to compare with known stock truck or study wire diagram in TMs.

I've been all over the truck with a DVOM to sort a bunch of issues. A test light was just more handy for verifying relay behavior.

There is only 12V showing at the diamond connector.


I'm going to try to take a good hard look at the diagrams this evening. I have serious starter circuit gremlins!

 

[dependable]

Don't overlook the possibility the relay is wired wrong or something. Also check you have the right relay, many are same externally but have different internal specs, such as grounded by chassis or externally grounded.

 

[cucvrus]

Is it possible that the starter gear is engaging too deep into the flex-plate gears and getting locked in there?

 

[aembry1009]

Is it possible that the starter gear is engaging too deep into the flex-plate gears and getting locked in there?

Unfortunately, I don't think so. This was one of my first thoughts as well. If you reread my first post, I removed any possibility of a mechanical fault with the starter. The runaway was simulated as the 24V feed was disconnected. The solenoid could not actuate this way.. It's a real head scratcher..

I thank you for your consideration to the issue though. Many invaluable posts from other topics have helped me isolate it this far.

Somehow power is coming in on the purple wire that goes out to the small wire of the solenoid. The relay WILL quit feeding current with the key. Paradoxically, this won't happen without first cycling the key. This would appear to indicate an issue with the relay at first glance.

However, what I observe with the light is that the circuit stays closed even after the light goes out. ALSO, the helper still had the key in the START position when the light first went out. At this point, the key had no effect on the circuit. The light never showed power on the purple wire, but the circuit remained closed until BOTH batteries were disconnected.

I touched the battery cables to the terminals a few minutes later and there was significant arcing, indicating high amp draw. A few minutes later, the circuit opened and I was able to reinstall the battery cables.

SHEESH! This truck has been a pain.

 

[cruzer747]

electrical fault or mechanical fault? If it were mine I would first disconnect the starter relay wire and cobble up a manual feed and manually connect it to the batteries. This test eliminates the starting circuit.

If problem persists after that test would drop the starter but leave the wires connected, ground the case, and clamp/brace it to keep it from moving (these suckers will want to twist and jump if not restrained!) and test it again. If problem, disappears you are getting closer to the root. If it is still there it's definitely a bad starter. It does sound like a faulty starter. You could drop the flywheel cover and inspect to see what the depth looks like while engaged to make sure it isnt going too far and getting hung up like cucvrus stated.

 

[dependable]

Still think it is likely the relay is wiring is off, or wrong relay ( ie chassis grounded, or ground activated, both of which can probably be made to work if you switch some wires around).

However, if you refer to diagram E-1 in appendix of TM 9-2320-289-34, it does show some splices in wire of that circuit. If someone has "modified" the harness, it is possible there is a short or crossed circuit somewhere. I'll add I have never had problems similar to this unless the wire harness was hacked up or someone fried it by hooking up batteries wrong or something. These harnesses don't go bad by themselves.

Did problem start with relay swap (aka Doghead conversion) or with the new starter, or did you change a lot of things at once?

 

[aembry1009]

Still think it is likely the relay is wiring is off, or wrong relay ( ie chassis grounded, or ground activated, both of which can probably be made to work if you switch some wires around).

However, if you refer to diagram E-1 in appendix of TM 9-2320-289-34, it does show some splices in wire of that circuit. If someone has "modified" the harness, it is possible there is a short or crossed circuit somewhere. I'll add I have never had problems similar to this unless the wire harness was hacked up or someone fried it by hooking up batteries wrong or something. These harnesses don't go bad by themselves.

Did problem start with relay swap (aka Doghead conversion) or with the new starter, or did you change a lot of things at once?

I'll verify which relay is installed and add a pic to show the wire orientation sometime today. The runaway does not occur until maybe the third or fourth start attempt. It was the same behavior from the first relay.

I am going to take a harder look at the diagram too. Thank you!

 

[chevymike]

I'll verify which relay is installed and add a pic to show the wire orientation sometime today. The runaway does not occur until maybe the third or fourth start attempt. It was the same behavior from the first relay.

I am going to take a harder look at the diagram too. Thank you!

Is that back to back starting attempts or over the course of multiple hours? If back to back (or relatively short time) it might be a heat induced issues where the solenoid or relay is heating up and sticking.

 

[dependable]

There are two suspect relays (solenoids), one under the dash, one on the starter. It might be good to confirm the one on starter is actually for 24V. It is not unheard of for a 12V solenoid to be on a 24V starter. It is a 24V starter, hopefully. The relay under dash has to be a 12V relay, as in operated by 12V signal from ignition switch.

Relay under dash has 4 wires. Red on is 24V all the time. Black is ground all the time. Purple and white should read around 12V when key is turned in start position. Solid purple sends 24V to solenoid on starter only when the relay has switched (received 12V from purple and white wire). Test these four wires and if above conditions are true, it is almost certainly the relay or starter solenoid, if you are correct in your assessment that it could not be mechanical binding of the starter gear.

One thing to confirm is the starter is not moving at all during start, is bolted up firmly, hopefully with rear support. It is reccommended the starter bolts be replace with the starter. If you did use old bolts, male sure they are strait and threads are in good condition with no sign of being stretched.

I'd check all of the above before I started poking around wire harness, unless you have reason to believe it damaged.