Cummins 12-valve stalls when hot

[towbar]

My snow blower never had this problem before. The engine comes from a 1995 Dodge truck, the P-pump was reused *as was* many years ago when I rebuilt the engine.

Running cold with good oil pressure and slowly rising coolant temperature there is no problem. Once hot it begins to just power down for no apparent reason under load or totally off load. A restart attempt after a minute or two of cursing has always been successful thus far. If I run it to 2200 then isntead of powerdown it may just become erratic between 1800-2200, it may or may not stall down regardless. I find no issues in the fuel system, but I did notice that a pressure gauge placed into the turbo output is all over the place, probably unrelated and the gauge make is unbranded and it never showed much more than 5-8 psi. Besides, at torque speeds the turbo isn't of much effect anyway, it WAS useful in a truck turning 3,000 rpm back in its day. For now I can just limit ops to low power (1400-1600) sticking to the warmup period.

Any suspects? It's winter here and I ain't too keen on getting tools out into the snow but I could try a few leads.

 

[Coaldust]

I would put a fuel pressure gauge on it.

 

[towbar]

The truck that once had this great engine had a fuel PR sensor somewhere, but that harness and everything that was on it is long gone. I found some gauges but where would I "T" one of them in? What pressure would I be measuring, not the lift pump output I don't think. And assuming that pressure were not up to spec (psi?), that WOULD mean a P-Pump?

 

[towbar]

I would put a fuel pressure gauge on it.

north of the 60????

 

[Coaldust]

Lol. 60 degree N. This is where the Earth bulges halfway as much as on the Equator and the sun is a rare treat this time of year.

Does this beast still have the mechanical transfer pump? Or, did it get an electric?

 

[towbar]

Lol. 60 degree N. This is where the Earth bulges halfway as much as on the Equator and the sun is a rare treat this time of year.

Does this beast still have the mechanical transfer pump? Or, did it get an electric?

I know only too well where 60 north is, I was just trying to sharpen a guess as to whether it's Baffin island or Alaska, or maybe exotic places in northern Quebec like Fort-Chimo once was Spent half my life on the dew line among other wonders.

It has the mechanical lift pump and the hand primer. There are some pressure gauges to T in at the fuel-filter drain-plug, I could be sold on trying a direct reading gauge there with maybe a snubber but I'm really no guru at diesels. Wouldn't the fuel pressure just flicker as the engine stalls regardless of whether it's causing the stall?

 

[Coaldust]

Lol, a raucous trailer park in the MatSu Valley.

The Dew Line, Huh? Wow. My son works for the defenses contractor that keeps the modern day Alaska Early Warning system radar sites maintained. Those places are filled with interesting history.

That particular OEM transfer pump is always suspect. With your boost pressure fluctuating like that, the transfer pump pressure is the first thing I would check. Plus, it’s quick and easy. Just tap into the fuel inlet hose. I’m assuming your filter isn’t plugged and your fuel isn’t turning into wax.

 

[heymccall]

Get fuel pressure gauge on there. Monitor fuel pressure at various speeds. Should sit around 30 psi.
If not, supply is restricted or overflow valve is faulty.

 

[towbar]

Lol, a raucous trailer park in the MatSu Valley.

The Dew Line, Huh? Wow. My son works for the defenses contractor that keeps the modern day Alaska Early Warning system radar sites maintained. Those places are filled with interesting history.

you bet

I was mostly stationed on Fox-Main but did a few trips to Alaska too, forget the station names tho, that was all like in another life, around '72. They might need to revive them, what with all these freakin' baloons capable of hauling a school bus and all...

That particular OEM transfer pump is always suspect. With your boost pressure fluctuating like that, the transfer pump pressure is the first thing I would check. Plus, it’s quick and easy. Just tap into the fuel inlet hose. I’m assuming your filter isn’t plugged and your fuel isn’t turning into wax.

Pretty sure I changed it when I built it but I also have some electric ones I might be able to cannibalise on there provisionally while waitingh for a lift-pump (I'll call the local stores tomorrow, could get lucky). It *is* the lift-pump you mean and not the priming pump that's inside the P right?

 

[Truck Shop]

Also check the lobe that operates the lift pump.

 

[towbar]

Get fuel pressure gauge on there. Monitor fuel pressure at various speeds. Should sit around 30 psi.
If not, supply is restricted or overflow valve is faulty.

Found a small 12v utility pump, might piggyback it on first thing tomorrow. The thing being like temperature senstive though (don't remember if I ran it above 1800 until it got warm and started acting up), it could well be the relief into the return line. Come to think of it, as I prime manually the return squirts back into the tank almost too readily... maybe just an impression.

 

[Truck Shop]

Basically what you are describing is what is known as a Vapor Lock between pump and carb on a gas engine.
The old Ford pumps would also do that when the pump arm would get slack in it. Ran fine cold hot not enough
fuel delivery. I have seen two 5.9's that the lobe for fuel pump was worn down not getting full stroke.
Something to check.

 

[Junkyard]

Inlet to the fuel pump should have a screen on it. Most I’ve seen will unscrew and you can clean the screen out. It’ll be a hex headed piece where your fuel line goes into the pump, pull the line, fitting if it’s just a hose barb, and remove the hex shaped piece (usually brass looking color). I’ve seen many a lift pump replaced without even looking at the screen.

 

[thepumpguysc]

Take pressure reading at the main pump inlet..
I’ll bet my last dollar that the overflow valve is weak or broken..
The Cummins application overflow valve opening pressure is about 25 psi..if u change it to 35 psi it cures a bunch of problems..
I’ll get the p# for ya tomorrow..

 

[Truck Shop]

One thing I never hear anybody talk about or perform-adjusting the valves on a 12V 5.9.
It has a flat tappet cam and valves were to be adjusted in the 75 to 100,000 mile range.
I rebuilt several of those most had scrubbed cams and that's where I found the two with
bad fuel pump lobes. I have asked several have you had the valves adjusted, No it's got
250K on it and runs great, especially after I put a big turbo and did the pump.

 

[towbar]

Gee guys, I've learned more in this thread than I needed to

Took out the overflow valve, it looked good, tested with a pin, spring was ok (it's OEM Bosch). Took the lift pump off and tried it just pressing the cam plunger, looked good and solid, much better made than many I'v seen. Always panicing to adapt someting that I happen to have on hand, things went from bad to worse, it got to the point where I couldn't even keep the engine running more than a few seconds; visions of huge bill for a P-pump , major bucks. We often tend to over dramatise. Thought I was done for the rest of the winter!

Then, while scratching my head I noticed dripping fuel under the fuel-heater where the hose connects it to the lift-pump inlet. It seemed strange, a dripping _suction_ line? With nothing to lose I bypassed the entire heater and everything snapped into place instantly. THEN I took a close look at the now removed hose elbow: it had rubber aging cracks under the bend, an ideal place where one never looks or even sees if looking.

3 pics enclosed, thanks one and all.

 

[towbar]

Gee guys, I've learned more in this thread than I needed to

Took out the overflow valve, it looked good, tested with a pin, spring was ok (it's OEM Bosch). Took the lift pump off and tried it just pressing the cam plunger, looked good and solid, much better made than many I'v seen, sprayed fuel all over myself. Always panicing to adapt someting that I happen to have on hand, things just went from bad to worse, it got to the point where I couldn't even keep the engine running more than a few seconds. Visions of huge bill for a P-pump , major bucks. We often tend to over dramatise. Thought I was done for the rest of the winter!

Then, while scratching my head I noticed dripping fuel under the fuel-heater where the hose connects it to the lift-pump inlet. It seemed strange, a dripping _suction_ line? With nothing to lose I bypassed the entire heater and everything snapped into place instantly. THEN I took a close look at the now removed hose elbow: it had rubber aging cracks under the bend, an ideal place where no one ever looks or even sees anything if looking.

3 pics enclosed, thanks one and all.

 

[towbar]

Dang! Done it again, but this time it only caused surging 1800-2200 and, seeing that I was almost done, I could complete the snow-removal sortie at reduced feed rate. It was an iced up tank fuel hose. See my other thread about this as the topic. I hope I'm done finding these bugs.

 

[Don.S]

Where are you in quebec? I am south west of montreal.

 

[towbar]

Where are you in quebec? I am south west of montreal.

Retired way out here on Chaleurs-Bay after confirming with the Kremlin that 'heaven' as we know it starts at LaPocatière and ends at Gaspé