It cranks but no start

[Towersafety]

I have a 1970 M35A2. It has run great until we got it home from the Memorial Day Parade. Got it home and it just died. Thought maybe it was low on fuel so added diesel and it started. Used it a couple weeks later and drove it about a mile and it died. Added 15 gallons of fuel. Let the fuel pump in the tank run a min and it restarted and went a little bit and died again. Towed it to the barn. Could not get it started. You could hear the pump in the tank running. Came back out next day and still no start (cranks good). A week later same no start. I replaced the pump in the tank and it started right up and ran like a champ. Problem solved. NOT. Drove it about a mile and it died and will not restart. I checked the stop engine cable and it is pushing the kill valve on the engine fuel pump all the way in. When it is running it runs great. I replaced the fuel filters last fall and have maybe a 100 miles on it sense then. I looked through the TMs and could not find anything to help me troubleshoot (I may be looking in the wrong place). Any ideas where to start? I am pritty good with gas engines but diesels (multi-fuel) not so much. It looks simple enough just need pointed in a direction. Thanks

 

[gimpyrobb]

Sounds like you've covered most of the basics. Did you replace the fuel hose from the pump to the top of the fuel tank, those get soft and allow air in. Have you tried letting the truck sit over night and drain the filters the next morning? That would let any moisture settle out if you hit a fuel station that had water in the fuel.

 

[Towersafety]

I did not replace the hose. It looked good so just re-installed it. I did open the drains on the filters to see if they had fuel in them and the fuel looked good. I will do it again when the sun comes up and see what it looks like. I think I will get a fuel pressure gauge and check the pressure out of the tank too. I read in the TM it is supposed to be about 7psi. If that does not work I will pull the fuel filters to see what they look like.

 

[gimpyrobb]

Sounds like a good plan, let us know.

 

[Towersafety]

Update: got a fuel pressure tester and it had the wrong fitting so I opened the drain valve on the fuel filters and the fuel coming out looked good. I then cranked and cranked, no start. I pulled the plug on the fuel line elbow right at the top of the tank. Turned the pump on (with switch on dash) for 10 sec and then went back around the truck and fuel was all over the place. Put the plug back in left the pum run for 10 sec or so and cranked it and after 5 sec or so it started. Runs great. Now to see if it stays that way. My guess is it will go another mile or so. Should I drain the fuel and put fresh in and change the filters just in case? I never pulled the filters so I have no idea what they look like.

 

[FloridaAKM]

Change all three fuel filters to eliminate that roadblock! These filters will sometimes look like they were used to filter rusty pond water from the bottom of the pond. Clean fuel, clean filters, good pump pressure (some run without a functioning intank Pump) & you should be able to enjoy driving, not wrenching so much! Keep us informed!

 

[gimpyrobb]

Update: got a fuel pressure tester and it had the wrong fitting so I opened the drain valve on the fuel filters and the fuel coming out looked good. I then cranked and cranked, no start. I pulled the plug on the fuel line elbow right at the top of the tank. Turned the pump on (with switch on dash) for 10 sec and then went back around the truck and fuel was all over the place. Put the plug back in left the pum run for 10 sec or so and cranked it and after 5 sec or so it started. Runs great. Now to see if it stays that way. My guess is it will go another mile or so. Should I drain the fuel and put fresh in and change the filters just in case? I never pulled the filters so I have no idea what they look like.

Yes yes change them.

 

[Towersafety]

Update: Got the fuel filters today but will not have a chance to change them until Saturday. A friend said he though the vent was not working in the tank and it was forming a vacume. I tried it without the cap and no change it still shut off. I did notice it shuts down about the time it starts to warm up and it will not restart until it cools but it seems to restart everytime once cooled. You do have to crank it a little to get it back started when cooled but it does start. What might it be that could be affected by tempature?

 

[cattlerepairman]

Update: Got the fuel filters today but will not have a chance to change them until Saturday. A friend said he though the vent was not working in the tank and it was forming a vacume. I tried it without the cap and no change it still shut off. I did notice it shuts down about the time it starts to warm up and it will not restart until it cools but it seems to restart everytime once cooled. You do have to crank it a little to get it back started when cooled but it does start. What might it be that could be affected by tempature?

Cause and effect....easy to get pushed down the wrong path. It *could* be a temperature thing, but it is more likely a time issue. It has enough fuel to run for a few minutes, then it shuts off. Coincidentally, it also warms up while it runs. I would strongly suspect a supply problem that allows some, but not enough, fuel flow. Once enough fuel has collected past whatever the constriction is, it will once again start and run for a bit.

Usually filters, but could also be a collapsed line (check the rubber supply and return hose that connects the copper lines at the frame to the IP/secondary filters). The copper line underneath the front cross member is also a prime suspect if you did off roading and could have hit something.

 

[gimpyrobb]

I agree.

 

[Towersafety]

Update: Fixed. I changed the fuel filters end emptied the tank. 3 new filters and fresh diesel. Runs like a champ. The first filter was rusty nasty, the second one kinda rusty and nasty the last one looked pritty good. A friend of mine told me it was not rust but algae. I will order 3 more filters for the shelf and an extra first filter. I plan on adding biocide to the tank to kill anything else then change the filters again after I move (I figure the truck will get plenty of use moving to help get everything trapped in the filters). On a good note I now know what is wrong with my diesel forklift. Guess I need to get a filter for it too.