Can't get the engine to idle

[davidm2232]

I have a 1970 M35A2. It runs great, starts perfect at 15F and overall runs really smooth. The issue I have is I can't get it to idle. If I hold my foot on the pedal, it will sit at 800 rpm all day. But to get it to idle on its own, I have to pull the throttle lock out and keep it at around 1200. Anything less and it will slow down and stall. I turned the idle speed all the way in and that didn't really do much. Only had the truck a few months and haven't really gotten a chance to drive it much. Maybe ran 2 gallons of fuel through it. The guy before me let it sit for a while too, had issues with the fuel filters clogging. I have all new filters in it and besides the idle, it runs great. Taken it up the road a few times and it pulls good. I put some Marvel and Powerservice in the diesel and Seafoam in the oil as I do on all my diesel stuff. I do a lot with the VW TDIs so am familiar with diesels but nothing mechanical like this deuce. Any tips on where to start? I really don't want to put much money into it, I have enough other projects that are money pits.

 

[cattlerepairman]

As for easy things to check:

- sticky fuel shutoff at the injection pump. If it is fully stuck, engine won't start but if it hangs up a little, it may cut enough fuel to not let it idle properly. That is the lever behind the small lid on the side of the IP.

- you said you changed the fuel filters. Did you retain the canister style? The new filters (depending where you bought them) may have come with a gasket that does not fit properly and can let air in. That would be enough to cause a problem at idle.


- someone reported water at the bottom of the fuel tank causing this as well. I would think that could cause longer term damage to the injection pump/hydraulic head as well.

- further down on the list....was the injection pump replaced? Might be out of timing. A failing hydraulic head also causes difficulty idling; it cannot maintain pressure.

Checking fuel pressures never hurts. On top of the tank is a boss with an unused port; NPT thread; a gauge there should read about 7-10 psi from the in-tank pump. At the secondary filters, a gauge in the filter base port should be....trying to remember...65ish or more at about 1500 rpm.

A good time to locate, download and use the 465 engine troubleshooting manual!
Time for the good deed of the day:

LDS465-1 Multifuel Engine Troubleshooting Manual

Attached the Trouble Shooting Manual LDS-465-1 Multifuel Engine. G.

www.steelsoldiers.com

 

[davidm2232]

As for easy things to check:

- sticky fuel shutoff at the injection pump. If it is fully stuck, engine won't start but if it hangs up a little, it may cut enough fuel to not let it idle properly. That is the lever behind the small lid on the side of the IP.

- you said you changed the fuel filters. Did you retain the canister style? The new filters (depending where you bought them) may have come with a gasket that does not fit properly and can let air in. That would be enough to cause a problem at idle.


- someone reported water at the bottom of the fuel tank causing this as well. I would think that could cause longer term damage to the injection pump/hydraulic head as well.

- further down on the list....was the injection pump replaced? Might be out of timing. A failing hydraulic head also causes difficulty idling; it cannot maintain pressure.

Checking fuel pressures never hurts. On top of the tank is a boss with an unused port; NPT thread; a gauge there should read about 7-10 psi from the in-tank pump. At the secondary filters, a gauge in the filter base port should be....trying to remember...65ish or more at about 1500 rpm.

A good time to locate, download and use the 465 engine troubleshooting manual!
Time for the good deed of the day:

LDS465-1 Multifuel Engine Troubleshooting Manual

Attached the Trouble Shooting Manual LDS-465-1 Multifuel Engine. G.

www.steelsoldiers.com

The fuel shutoff plunger seems to move very freely, so that is good. I only replaced the filter under the radiator, I have not done the ones on the engine myself. I ordered 2 new ones so I can replace them myself. I have no idea on the history of the pump. It will run very slow with my foot on the pedal, no smoke and runs smooth, so that leads me to think timing is good. There is no in tank pump, it looks like there is an electric pump in-line and that appears to work. I'll see if I can get a gauge and check some pressures. I see a chart in the manual you linked so I should be able to compare to that.

 

[cattlerepairman]

Depending on the clarity of your injector return lines, can you see air bubbles with the engine running? While I recommend following the decision trees in the manual, methinks air leaking into the fuel system is high on the list. Once fuel flow picks up at higher rpm the injection pump can handle it, but at low flow there is too much air for maintaining injector pop off pressure. But, what do I know....

 

[Floridianson]

30 psi minimum at idle and 60 minimum at high idle.

 

[dmetalmiki]

The fact it starts well is odd...As that problem occurs when the 'dreaded button' drops off the quill inside the Hydraulic Head....Smaller stroke..less fuel delivery and power at low RPM's.,
And As cattlerepair man stated.." But what do I know"...

 

[davidm2232]

As that problem occurs when the 'dreaded button' drops off the quill inside the Hydraulic Head

Would it get worse? It did have a small problem idling but was fixed with pulling the throttle lock out a bit. Now I can't get it to idle stable under 1200 or so with the lock. So whatever it is has gotten worse. My gauge said around 20 PSI down near idle, but it kept stalling so it was hard to get an accurate reading. Hoping the new fuel filters is the cure but I doubt I'll be that lucky.

 

[Floridianson]

Would it get worse? It did have a small problem idling but was fixed with pulling the throttle lock out a bit. Now I can't get it to idle stable under 1200 or so with the lock. So whatever it is has gotten worse. My gauge said around 20 PSI down near idle, but it kept stalling so it was hard to get an accurate reading. Hoping the new fuel filters is the cure but I doubt I'll be that lucky.

Yea you might need to see why you are low on idle pressure and as said it should be 30 psi minimum not 20 at the filter bleed. Can be filters and can be other things that are easy to check.

 

[dmetalmiki]

That's waaa't 'appens, when that unbelievably stupidly designed (Idiot) 'Bit' falls off.
.( Regularly).
Rotate the engine until the Hydraulic Head comes up and out, After all disconnects have been performed.
DO NOT ROTATE the engine after that,
Afix a NEW button and a NEW CLIP.
Re install.
Vroom vroom! Fixed. OH, AND with NEW filters.

BUT..Try NEW FILTERS FIRST.

 

[cattlerepairman]

As an added insult, the Chinese manufactured HH have an improved button and clip that are beefier, better made and seem much less prone to falling off.

 

[ToddJK]

I won't speculate too much, but the other guys had some good idea's on the IP. First things first though, change those filters! Dirty fuel filters can starve an idling engine but the engine will run in some cases when given more fuel due to fuel pressure increase from the IP. My old deuce did that and because I didn't filter some oil once, that's all it took to clog the filters up.
Another thing to note, is too drain the primary of any water (located under the radiator) just in case if that's really old fuel, diesel will absorb water so that's a possibility. If you're getting a lot of water drainage, I'd add a bottle or two of heet to the tank or even a bottle of 90% isopropyl alcohol as it does the same thing, run that tank out of fuel and use fresh diesel.
I would just do all the easy and cheap fixes first then move on to the more complicated costly fixes.
Keep us updated so if future members have the same issue, they may be experiencing a similar issues with a similar fix.

 

[davidm2232]

Filters should be in tomorrow or Saturday. That is definitely my first step. Going to fill the primary with Diesel Purge. That stuff works magic on everything I have put it in. The guy I bought it from had some issues getting it to run. I guess the filters were totally clogged and full of water. He replaced them but very possible there is junk in the tank and old fuel. I've only ran maybe 3 gallons of fuel through it since I bought it, so not really enough to get fresh fuel through it. I'm hoping to get it registered so I can put some road miles on it.

 

[Bill Nutting]

When I bought my 934 it had sat in a lot for eight years. There was no water in the fuel but the truck ran bad. It could hardly pull itself up a mild grade. We dove it 1,000 miles home putting fuel additives in at every fill. By the time we got home it was flying up those hills. I would suggest a long ride to use up that old fuel. Put heat in it to get ride of water in the system. You might have to replace your filters more than once if there is crap in the tank. Take an extra set of filters with you. You will know better where you are when you have fresh fuel in it.

 

[ToddJK]

When I bought my 934 it had sat in a lot for eight years. There was no water in the fuel but the truck ran bad. It could hardly pull itself up a mild grade. We dove it 1,000 miles home putting fuel additives in at every fill. By the time we got home it was flying up those hills. I would suggest a long ride to use up that old fuel. Put heat in it to get ride of water in the system. You might have to replace your filters more than once if there is crap in the tank. Take an extra set of filters with you. You will know better where you are when you have fresh fuel in it.

It's surprising how many issues arise with old fuel, lol.

 

[dmetalmiki]

HA! well spotted (dog!). I have fitted 4 chinese heads in this last year..No problems..And yes..the clip and faster system on them IS better.

On the subject of Old Fuel,..When in the forces..In some free time...'We' (Buddies), err..(UM)..No one looking?...
Pulled a war time I.H.C. half track out of ........... And when we got it 'Home' (Base)..we towed that thing for about 50 feet..And it FIRED RIGHT UP!!
We drove that thing all over..Well we did Until the ***base commander >Confiscated<It FROM US it..And had it blown up on the RANGES..
Shame!.
Humph!..We went and 'pinched 'another one..
*** Repeat!..Darn.
We took up sunbathing swimming and table tennis...

 

[Floridianson]

I still want to know why there is low idle pressure. So when you get the new filter changed double check pressures. On a side note it really does not need the 30 psi at idle to start and Idle. Had a truck with the system over pressure valve on the secondary removed and truck still started and idled just fine. How bout another spit ball you said you adjusted the idle screw but if the fuel control is set to low on the Head it wants to shut down because the plunger sleeve is riding to low on the plunger. Is you FDC bypassed?

 

[rustystud]

As an added insult, the Chinese manufactured HH have an improved button and clip that are beefier, better made and seem much less prone to falling off.

Cattlerepairman, where can you find these Chinese Hydraulic Heads for sell ? I've been gone for a while and haven't heard of them.

 

[cattlerepairman]

Cattlerepairman, where can you find these Chinese Hydraulic Heads for sell ? I've been gone for a while and haven't heard of them.

https://www.chinahanji.com/01_hd90100.htm

I bought mine directly from them. I am sure someone, one of the vendors, imports them, but don't know.

 

[davidm2232]

Well, I got the filters changed last night and it runs... not worse haha. There was a brown slime covering the inside of the filters and housing, so I'm thinking contamination is definitely part of the problem. There is Diesel Purge, Marvel Mystery, and Powerservice in the tank, so that should help. I'd really like to get some fuel through it. Hard to burn much just driving around the yard though.

 

[INFChief]

Probl

Well, I got the filters changed last night and it runs... not worse haha. There was a brown slime covering the inside of the filters and housing, so I'm thinking contamination is definitely part of the problem. There is Diesel Purge, Marvel Mystery, and Powerservice in the tank, so that should help. I'd really like to get some fuel through it. Hard to burn much just driving around the yard though.

Problem solved? Make sure the lines are tight and not sucking air. Those canister gaskets (O-rings) don’t always seat properly and the canister won’t seal.