M35A2 runaway problem

[NorthPlainsDrifter]

Hello everyone, what a fantastic site!

I am in the process of buying a M35A2, the previous owner bought this truck restored and drove it regularly until about 2 years ago, since then he only started it every 6 months or so. The last time he started it he said it ranaway. Fast forward till recently, we started it and it still ran away and ran out of fuel while governing the intake, the fuel pump was gummed up and wouldn't spin and was cleaned and now working. Tried starting again to find out that the fuel shut-off was stiff and stuck closed. We can get it to fire up everytime now only to have a runaway, the fuel shut-off will kill the engine when this happens only to get stuck closed. I realize through searches here that it needs taken apart and cleaned. I'm just not sure where the runaway problem is coming from. Does it have to do with the fuel shut-off? Any help would be great!

Thanks!

 

[cattlerepairman]

"Runaway" is not the same as "wide open throttle" (WOT). In the former, the engine typically feeds on fuel OTHER than the fuel supplied by the injection pump, such as engine oil leaking past turbo seals etc. Because of the alternate supply of "fuel", the engine rpms are no longer governed or controlled by fuel shutoff and typically the over-revving engine will self-destruct, unless its air supply can be closed off.

In a wide open throttle condition your anal sphincter may initially clench as tightly as the engine revvs up (speaking from experience), but the engine feeds on its normal fuel supply and therefore responds to the governor and the fuel shutoff. It will revv to its governed redline but not beyond. Annoying, but much less destructive.


Here is some wisdom and pics: https://www.steelsoldiers.com/threads/stuck-in-full-throttle-multi.78640/

M35a2 stuck injector pump

Got a Deuce in with a stuck pump. The fuel shutoff was stuck. Got it to move up and down but it's real stiff and the truck runs full throttle once started. Rack seems to have no effect on rpm. I was thinking of making a little cocktail to run it on of sea foam,wd40,2 stroke oil and diesel. the...

www.steelsoldiers.com

 

[USAFSS-ColdWarrior]

Hello everyone, what a fantastic site!

I am in the process of buying a M35A2, the previous owner bought this truck restored and drove it regularly until about 2 years ago, since then he only started it every 6 months or so. The last time he started it he said it ranaway. Fast forward till recently, we started it and it still ran away and ran out of fuel while governing the intake, the fuel pump was gummed up and wouldn't spin and was cleaned and now working. Tried starting again to find out that the fuel shut-off was stiff and stuck closed. We can get it to fire up everytime now only to have a runaway, the fuel shut-off will kill the engine when this happens only to get stuck closed. I realize through searches here that it needs taken apart and cleaned. I'm just not sure where the runaway problem is coming from. Does it have to do with the fuel shut-off? Any help would be great!

Thanks!

First off.....

Welcome Aboard
Find a bunk, stow your gear, and prepare to get underway

Sounds like you're already getting some good expertise responding to your query.

Again, WELCOME!

 

[NorthPlainsDrifter]

Thank you Cattlerepairman for the links and advice. I'm going to take apart and clean the fuel shut-off and hope that's the problem since it's an easy fix. Unfortunately the truck is across town from me and I can't get back to it for a few days.

 

[cattlerepairman]

Let us know how it turns out! Hopefully that will be the extent of your problem.

 

[NorthPlainsDrifter]

Update, I took apart the fuel shut-off assembly and thoroughly cleaned it, I also made the mistake of taking apart the the splined shaft and didn't mark it. Ugh! I spent quite some time looking at videos and manuals and pretty sure I have it put back together correctly. Now it tries to start then dies, we are getting white smoke out of the stack so I'm assuming it's getting some fuel, not sure if it's too much or not enough fuel. This thing ran when parked so we are kind of stumped. Is it possible the HH is gummed up with old fuel? I'm going to continue researching the manuals to see how the HH works before tearing any more apart.

Edit- After spending a hour reading the R & R thread on the HH removal, I have a few more things to try. Just wish this truck wasn't an hour away!

 

[Floridianson]

Injection pump fuel pin

Hello all , I have an issue with the multifuel fuel pin location. I have an lds2 that I saved for my dump truck that I won't be needing. I have not tried to start it in years. Long story short, the fuel pin was sticking holding it in the off position. I tried cleaning it externally but no luck...

www.steelsoldiers.com

 

[Floridianson]

click on the" injection pump fuel pin" in orange. Post #6 and post #7.

 

[NorthPlainsDrifter]

click on the" injection pump fuel pin" in orange. Post #6 and post #7.

Thank you, that helps a lot!

 

[NorthPlainsDrifter]

Great news! After hours of trying to figure out how the fuel shut-off goes back together, what a pain that was, I got her fired up and running smooth. While messing around with this, I also figured out why we were having a runaway engine, the fuel solenoid for the cold weather fire start was pumping fuel directly into the intake manifold making it runaway. For a temporary fix I just blocked off the fuel line to the solenoid.

Thank you everyone for the tips and suggestions as I couldn't have got it running without the help. I get to drive it home tomorrow! Woo Hoo! Then I'll be able to do a more thorough job of getting it in top shape!

 

[cattlerepairman]

Do yourself a favour and make the temporary fix your permanent fix. Remove the complete flame heater setup and plug the connections. Unless you regularly fire her up in well below freezing you don't need it and if you do need regular cold start help, spring for a KAT 24V ether dispenser that shoots a metered dose into the intake. The flame heater is nice and nostalgic if it works properly and does not leak, but a PITA (as you found out) when it doesn't work right.

 

[NorthPlainsDrifter]

That is a good idea to remove the flame heater, I don't plan on driving it in sub temperatures. The truck is in really great shape, it just has sat for the last 2 years, the gentleman I'm buying it from kept up on the maintenance even when it was sitting. It's going to be a fun truck!

 

[ChrisDeuce68]

Recently bought a 1968 M35A2. The previous owner tried to do some injector pump work. Once he got it back together he said it made a “funny sound” (I know, but that’s all I got out of him), and revved up. I got no details whatsoever about how high it revved or what made it stop. Once I got it home, I found that the engine was free, so I took apart the fuel control rod assembly and found it installed wrong with the fuel pinned at WOT. I got it fixed and running, but it constantly hunts for idle between 500-1100, and the engine is wayyy louder than I think it should be, and sounds like it may have a dead hole. Before I go too deep in disassembly, I was wondering if anyone could answer 2 questions for me: 1. when the fuel control is stuck at WOT, is that a true runaway, or is it still governed to a max rpm somehow? 2. What are some issues that may be easy to look into that would cause this thing to run like crap as a result of this that I can look into before I tear the head off and check for a valve problem?
Thanks!

 

[fpchief]

On the shutoff lever,

Recently bought a 1968 M35A2. The previous owner tried to do some injector pump work. Once he got it back together he said it made a “funny sound” (I know, but that’s all I got out of him), and revved up. I got no details whatsoever about how high it revved or what made it stop. Once I got it home, I found that the engine was free, so I took apart the fuel control rod assembly and found it installed wrong with the fuel pinned at WOT. I got it fixed and running, but it constantly hunts for idle between 500-1100, and the engine is wayyy louder than I think it should be, and sounds like it may have a dead hole. Before I go too deep in disassembly, I was wondering if anyone could answer 2 questions for me: 1. when the fuel control is stuck at WOT, is that a true runaway, or is it still governed to a max rpm somehow? 2. What are some issues that may be easy to look into that would cause this thing to run like crap as a result of this that I can look into before I tear the head off and check for a valve problem?
Thanks!

When I replaced my HH o-rings, mine hunted really bad and I found that the problem was that I had the two screws too tight that hold the fuel shutoff valve. It is the two that get safety wired. I loosened them up to where they were basically finger tight and that fixed it.

 

[ChrisDeuce68]

On the shutoff lever,


When I replaced my HH o-rings, mine hunted really bad and I found that the problem was that I had the two screws too tight that hold the fuel shutoff valve. It is the two that get safety wired. I loosened them up to where they were basically finger tight and that fixed it.

thanks! That sounds plausible and will be easy enough to look into. When I first got the truck running it didn’t hunt, it idled right at 700 give or take, but I had a leaky o-ring and when I got it to stop leaking...the hunting began!

now if only I can figure out if I have a dead hole or not. Any suggestions on determiningthis on one of these? I tried an infrared thermometer but it heats up fast enough I couldn’t tell the difference between the bores

 

[cattlerepairman]

https://www.steelsoldiers.com/upload/M35/TM9-2910-226-34.pdf

Pages 1-18 and1-21 have the drawings for the governor. I suspect that the engine can overspeed if the fuel control rod is incorrectly installed and won't move.

As for the dead hole: Not saying you ought to do it that way, but I put on safety glasses, place a rag around the injector line connection to the suspected dead hole, loosen the nut with engine idling, and listen for change to the engine sound. No change - hole likely doesn't fire.

 

[ChrisDeuce68]

Thanks for the idea, I’ll give that a shot. I’m suspecting valve related issues if it really ran away on the previous owner. I wonder at that point if it’s worth a valve job or if it’s time to go motor shopping?

 

[cattlerepairman]

You can't know until you check. A new OEM head with valves is still available and a lot cheaper than a new motor. If you just need a new valve, I got some clean spares. Pushrods and tappets are readily available.

 

[ChrisDeuce68]

Listened the retaining screws for the fuel control rod just a tick. Was skeptical it would make any difference because it already moved very freely, but my hunting is gone and it has a nice idle now. Thanks for the advice.

now to dig into the valves...

 

[fpchief]

Listened the retaining screws for the fuel control rod just a tick. Was skeptical it would make any difference because it already moved very freely, but my hunting is gone and it has a nice idle now. Thanks for the advice.

now to dig into the valves...

Good! Make sure you safety wire them.