M35A2 idle surge.

[DutchmanZ]

In addition to my 1953 M35 gasser, I now own a 1978 M35A2C. The story is it sat 6 or 7 years after it drove to where it was sitting. The PO said it sat a few weeks and then wouldn’t start. He had the IP off and replaced the hydraulic head because it was stuck. Once it started it had a huge idle surge and was smoking a lot. I have since got it running again and it has the same idle surge. The tach cable is broken so I’m not sure rpm’s but it’s at least 300 rpm surge. I don’t know how to tell which pump I have (letter code) I suspect the HH is wrong because the number on it seems to be from a 5 ton. Engine is a LDT465-1C according to the engine plate. Any help with identifying the parts as correct or not or suggestions to look at for the surge would be appreciated. The radiator is out so I can’t run it very long. The in tank lift pump is dead but it has an external pump that’s working. It’s getting fuel pressure to the filters. It needs a little shot of ether to start too. The timing marks are also lined up correctly.

 

[cattlerepairman]

You do not mention hard starting and low power, so I assume the injection timing is correct and not 180 degrees out.

Simple things first - what do the fuel filters look like? New primary and secondaries and then re-assess. Yes, the filters can really cause super annoying running and idling problems!

Idle adjust...maybe it needs to be turned up a tad to be 750-800.

A 5ton HH on an LDT should work just dandy.

Do you make sure the fuel control rod is properly attached and seated? I remember reading that stiff fuel controls and a plunger that is not moving freely can cause what you describe.

Have you been driving it a lot? Sometimes, putting it under a good load and driving the crap out of it helps things settle down.

I'd do all that before starting to tear deeper into it.

 

[DutchmanZ]

Cattlerepairman,
It won’t start without ether so I guess I’ll call that hard starting. I didn’t mention that I just purchased it last week. It’s still partially disassembled (fan, rad and grille are off) from when the IP work was done those 6ish years ago, so I’ve only ran it twice for 30 sec or so. My thought was the issue started after the IP work for the no start condition but it was running fine a few weeks prior to the no start. He said it surged and smoked like it’s doing now and he figured it was a bad IP and never spent any more time/money on it. I didn’t want to reassemble if I had to take it all back off. Would it start at all 180 out? I didn’t verify TDC on compression stroke, just TDC. Other than bleeding the fuel system and unsticking the fuel shutoff, I’ve checked fluids and put fresh batteries in. I can’t seem to attach a video from my phone.

 

[DutchmanZ]

M35A2 Idle surge

youtube.com

This is what it does once it starts. It’s not happy but I feel it’s worth putting money into at this point. I didn’t even know if the engine was sound but it was making air and oil pressure.

 

[Floridianson]

You said checking the fuel shut off. I'm going to guess you're talking about the fuel control unit assembly. If that's hanging up in the idle position that could cause surging you might want to double check that again. You can run the engine with the timing shutdown rod cover off and watch to see if that is moving/ surging. The arm coming up from the governor going to the fuel control unit assembly should not be moving when it's idling or in other words the fuel control assembly unit should not be moving. When you need to shut the motor down you can use your finger and just push the fuel control unit assembly towards the firewall.

 

[Elk1111]

You might have a leaking fuel line which would cause the hard start and the surge also.

 

[DutchmanZ]

You said checking the fuel shut off. I'm going to guess you're talking about the fuel control unit assembly. If that's hanging up in the idle position that could cause surging you might want to double check that again. You can run the engine with the timing shutdown rod cover off and watch to see if that is moving/ surging. The arm coming up from the governor going to the fuel control unit assembly should not be moving when it's idling or in other words the fuel control assembly unit should not be moving. When you need to shut the motor down you can use your finger and just push the fuel control unit assembly towards the firewall.

Yes, the fuel control was stuck. I got back to the shop today. The deuce started (with ether) and idled perfectly. It ran for about 45 seconds, slowed down and then died. I worked on the in tank pump which was bypassed with an inline pump. The connection was corroded and fuse missing in the terminal assembly. I cleaned it all up, replaced the in tank hose and the pump ran. Never got the filters to bleed out after that. So, either the filters are plugged or the pump is too weak. I’ll pick up filters tomorrow and go from there.

 

[Floridianson]

What I'm saying is you can watch that fuel control unit assembly and if it's moving just grab it with your fingers and hold it in one position see if you can get it to idle and stay running not cut out.

 

[DutchmanZ]

What I'm saying is you can watch that fuel control unit assembly and if it's moving just grab it with your fingers and hold it in one position see if you can get it to idle and stay running not cut out.

I followed you but it ran without the surge Sunday afternoon and then died so I wasn’t able to see if the fuel control was moving and causing the issue. Once I get it running again I’ll have to reassess. Thanks for the suggestion!

 

[DutchmanZ]

Update…

I got the new in tank pump swapped into the freshly cleaned fuel tank. Replaced all 3 fuel filters last week so it was just a matter of fresh fuel and bleeding the filters this weekend. I got it to start but still only on ether. Drove it up to the shop and installed the freshly cleaned and tested radiator along with the grille. That lower hose was fighting me but my wife said she would get it. She did. Smaller hands fit in tight spaces better and she’s cool like that. The surge was kinda still there but I think it’s an idle rpm issue. It ran fine with the throttle cable slightly out. The tach cable was broken so I replaced it. Still no tach so it’s either a drive side problem or a tach issue. I ran out of daylight so I didn’t go back and check to see if the cable was actually spinning inside. I do have a return line leak from the filter head to the copper line back to the tank and one on the injector return. I also got the rear axle brakes to bleed out but nothing on the front. Problem for another day. I’m planning to bob this one so I’ll go thru the brakes then since I’ll have the rears completely out. Also scored 5 aluminum MRAP wheels and a spare 395 tire. Can’t wait to really get started on this thing.