m35a2 runs rough at startup. Need input

6x6junkie

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have and m35a2 with and ldt465 engine when you first start it up it runs rough like it is not running on all cylinders then when it gets hot running for 10 mins on a 60 deg day it runs great all fuel filters are new and air cleaner is new any info will be a great help thanks in advance
 

brianp454

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Portland, OR
My truck would do that when I got it. I found that turning on the lift pump for a minute or two before starting it would limit the rough time to about 30 seconds. I bypassed the FDC and it never happened again.

You should also look to see if you have any leaks in the fuel supply lines.
 

rustystud

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My truck would do that when I got it. I found that turning on the lift pump for a minute or two before starting it would limit the rough time to about 30 seconds. I bypassed the FDC and it never happened again.

You should also look to see if you have any leaks in the fuel supply lines.
Agree. The way our fuel system is designed there are no one-way check valves in it ( except in the pump which leaks down) . The injection pump also has a small hole for bleeding fuel pressure off. After a night of sitting the fuel in the lines slowly drains back to the tank and the only fuel left is the fuel in the filters. So there can be air trapped in the lines. I also allow my pump to run a few minutes before starting.
 
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bigmike

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Agree. The way our fuel system is designed there are no one-way check valves in it ( except in the pump which leaks down) . The injection pump also has a small hole for bleeding fuel pressure off. After a night of sitting the fuel in the lines slowly drains back to the tank and the only fuel left is the fuel in the filters. So there can be air trapped in the lines. I also allow my pump to run a few minutes before starting.
Ditto to above post. Run the pump a few minutes before starting!
 

daytonatrbo

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My 109 currently has a small leak on one of the injector lines. I have to run the lift pump extra long if I want a smooth start.

My other truck doesn't have any leaks, and about 30 seconds on the lift pump is all it takes for a quick, smooth start.
 

Jeepsinker

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No, something isn't right. None of my trucks have ever done that above thirty degrees. You have an air leak in a fuel line somewhere. You should be able to bump the button and have it come right up to a smooth idle.
 

DavidWymore

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El Centro, CA
'70 in my yard is like that...has a leak on the outlet of the primary fuel filter. If I let the lift pump run extra long, it starts and runs better, probably because the leak lets air into the lines when it's off.

Try cracking the bleeder, I bet you get air. Air bubbles feeding into the IP would make it miss.
 

rustystud

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No, something isn't right. None of my trucks have ever done that above thirty degrees. You have an air leak in a fuel line somewhere. You should be able to bump the button and have it come right up to a smooth idle.

Garrett, you drive you truck daily. Most of us here drive it on weekends so the fuel has a chance to drain back. I have replaced ALL my fuel lines with PTFE hose. There is no leaking going on here, but it will drain back after a few days. I also have Brand New fuel pumps in both tanks. So when I start my truck up after 5 to 7 days setting it will run a little rough if I don't first run the fuel pump for a minute or two. After that it will start on the first spin and run like a top !
 

Jeepsinker

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I understand what you are saying Rusty, and I agree on the concept. What you may not know is that I have four other deuces here that only get started every couple of months at best, and they crank the same as my truck, sometimes one or two will take a half revolution before they catch. Maybe I'm lucky and all my in tank pump check valves work, I don't know. I'm just reporting my experience with proper operation.
 
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