Apologies for the long post but I'm at wits end with this issue.

My daily driver is a 1967 International Travelette Crew Cab that I built using a 1990 1st gen Cummins 12v from a 1990 Dodge D250 pickup. Moving to diesel has been wonderful having run gas and propane in my IH prior. I've driven thousands of miles without any issues, validating the reputation of the 1st Gen Cummins 12v as being a bulletproof engine. Once I even got 26mpg on a long trip.

But for the last three years the truck loses power when I least expect it, coming to a point where I can't restart it because for some reason fuel is not getting to the engine. None of the following repairs have fixed the problem and strangely the truck can run for weeks under any variety of conditions and not fail.

• Installed a brand Fuel Solenoid valve
• Repaired all electrical leads to the FSV and KSB valve
• Rebuilt the portion of the electrical harness that activates the FSV and KSB valves
• Replaced the FSV relay - or the equivalent given my unique electrical harness
• Cleaned and replaced any/all faulty ground connections
• Replaced the voltage regulator and harness connector
• Tested that all of the above gets the appropriate voltage when key on and off
• Replaced my primary and secondary fuel filters
• Injector pump, injectors and fuel pump were rebuilt and/or replaced in 2012 and so I'm presuming they're not the issue
• Checked all fuel and air return lines for blockage - no issues there

The most consistent thing I can do to fix this is to simply wait a day and then try starting it up again. 90% of the time this works and I drive until it fails again. The truck starts right up in cold or hot weather, doesn't blow white smoke or show other signs that would help me dial in what's wrong.

But here are the most consistent issues I can figure out that might point to the actual problem.

• Three years ago I had a +40HP fuel pin and 3,200rpm governor spring installed (the truck never failed prior to installing both)
• When I floor it, acceleration takes a while to kick in (1-3 secs) and idle is inconsistent
• When the truck dies, it's as if some part of the fuel system slowly loses access to diesel before becoming completely fuel starved
• And again, most often just letting it sit for 2-6 hours resolves the issue ( although twice that's not been the case)

Has anyone had similar issues with their 1st gen Cummins? Do any of these symptoms ring a bell or remind anyone of one or several things I can do to focus on what's happening here?

I've worked on trucks for years but don't have very good diesel trouble shooting skills. And so for the last 3 years that means driving a truck that I don't trust will break down any time I take it on the road.

Thanks for any help you can pass along!

 

I'm certainly not the most knowledgeable here on 12 valve conversions, but I'll make two points:

1.) That's a killer avatar you're sporting there...
2.) Since this is a conversion, is the fuel tank cap vented?...

...Ben

 

Keep this in mind while you troubleshoot. Fuel is sucked from the tank by the lift pump.

"And again, most often just letting it sit for 2-6 hours resolves the issue ( although twice that's not been the case)"
Your tank is not venting creating a vacuum restricting or stopping fuel flow.
An obstruction that blocks the fuel pickup in the tank.
A section of hose that collapses cutting off fuel flow.
A stuck inlet check valve in the lift pump.

A leak in the fuel line that sucks air would not fix its self.

 

The avatar is something I whipped together to best rep the truck. Cap is not currently vented but will be soon. It's a required fix but not thinking it's what's been causing the issues for the past three years.

Thanks Ben.

 

Understood about the fuel pump and yet when they fail, wouldn't that create performance symptoms across the board?
And while I agree that an air leak in improbable here, but will still check near the turbo just in case.

I wouldn't be able to really diagnose any tank obstruction without pulling and draining it. It's a custom 42.5 gallon tank so that's kinda a big deal.
The lift pump was replaced in 2012, but I see how it might be the source of the problem.
I've checked the hoses and there are no obstructions.

Could the installation of the new fuel pin and governor spring have anything to do with this in your opinion?

Thanks!

 

A 1/16" drill bit is the quickest way......Ben

 

This comment gets two thumbs up.

 

I agree with the others that it sounds like an issue with the fuel tanks and/or lines running to the lift pump. What kind of lines are you using, rubber, plastic, metal? If they are rubber or plastic they can look good from the outside, but could be starting to collapse internally. But it could be something in the fuel pick up in the tank that is getting sucked up and it just depends on it's shape and how it gets drawn up and in that the fuel starts to get restricted.

If it dies again maybe have a couple gallons of fresh fuel and disconnect the fuel line from the lift pump and run it into the fuel can and see if it fires up right away, that would tell you for sure where your problem lies.

 

Has anyone tried replacing the rubber hose between the steel line coming from the tank and the lift pump with a clear tube to see if the pump is sucking air somewhere?

Also I had a diaphragm lift pump fail in less than a year not from the rubber part wearing out but because the mechanical lever connection was poorly done and obviously NOT inspected. Chicom crap strikes again!

 

Here's another idea you could try at the same time...If it happens again, immediately loosen the fuel tank cap and listen for a "whoosh" of incoming air...I know it seems like I'm obsessing over the cap, but I had a very similar problem with an old '66 Chevelle years ago, and an unvented cap was the problem...Your former gasser is the same vintage, and in my case after I fixed the cap (with a drill bit) the problem went away, but I lost five gallons of capacity in the tank because the suction was that strong......Ben

 

A lot of 1st gen Cummins owners replace their OEM fuel pumps with these higher PSI versions. Takes some modification to the insulation on the engine, but seems to be worth it.

 

All the lines were replaced when the truck was built in 2008. They're rubber with metal braided reinforcement and graded to be used with up to 100% biodiesel if I was every inclined. But your comment is really making me think that cleaning and examining the tank might be a valid next move.

 

Funny you should mention it because that's EXACTLY what it sounded like when I removed it today to see where was the best place to drill a hole. Definitely a fix that will make things better. Can you explain the loss of fuel capacity? Wouldn't a vented cap mean little to no back pressure and thus no loss in fuel capacity?

 

In my case I was 100 miles into a road trip after getting the car back from a body shop when I lost power...I'm guessing the original gas cap was lost when they were working on it and they just screwed on whatever was lying around...I heard the "whoosh" when I opened the cap at a gas station, and a guy who worked there drilled the hole through the top which vented it...But by then the fuel pump had sucked a vacuum in the tank which caved in the top of the tank from inside...From then on when I filled up the gauge never went past 3/4 and the most I could get in it was 15 gallons when empty......Ben

 

Looking at the list of fixes. I didn’t see a new lift pump. What is it’s status?

Also, I wouldn’t put it past the rotary injection pump to be worn out after 8 years and however many miles.