Truck stalls when warm

[jay_0283]

Any help would be greatly appreciated...

So i have recently bought a 93 Chevy K2500 with the 6.5L TD...
It starts up and idles good. when its warm it stalls out as if its lacking fuel. But it restarts after cranking for under a min... helps if i play with throttle. I have replaced the lift pump. i can hear the lift pump running when the key is in the run position ( even when not running ).

I checked and installed a new fuel filter by the intake, someone had previously removed it. it is full of fuel when idling, when i checked it after it stalled it was not full, but that was before the filter was installed.

I have opened the valve at the front for bleeding fuel ( by oil fill ) and put the hose into a bottle, if truck is not running with key on i get a steady flow of fuel, but with truck running at idle i get none...

i had the truck out yesterday and it lost power and speed and eventually stalled...

I have read about guys cranking up the fuel on the injection pump but am not sure if that might help...


Any ideas would be greatly appreciated.

[Robyn]

Hi

Welcome to TDP

There should be fuel at the front drain line with the engine running.

Check to be sure lift pump is running when the engine is running.

If the lift pump does not continue to run once the engine starts the transfer pump in the IP will in some cases continue to pull the fuel to the IP, but not always, and this will cause the stalling.

The lift pump must run while the engine is running....

The oil pressure switch may be the culprit as it operates the lift pump after the engine starts.

Check or replace the fuel pump relay.

[DmaxMaverick]

Welcome aboard!

Any help would be greatly appreciated...

So i have recently bought a 93 Chevy K2500 with the 6.5L TD...
It starts up and idles good. when its warm it stalls out as if its lacking fuel. But it restarts after cranking for under a min... helps if i play with throttle. I have replaced the lift pump. i can hear the lift pump running when the key is in the run position ( even when not running ).

I checked and installed a new fuel filter by the intake, someone had previously removed it. it is full of fuel when idling, when i checked it after it stalled it was not full, but that was before the filter was installed.

This indicates a large air leak in the system, likely between the lift pump and fuel inlet in the tank (pumping air into the system).

I have opened the valve at the front for bleeding fuel ( by oil fill ) and put the hose into a bottle, if truck is not running with key on i get a steady flow of fuel, but with truck running at idle i get none...

The fuel valve near the thermostat housing is the water drain (dirty side-bottom of the fuel filter). The air bleed valve is at the top of the filter housing cap. Opening the water drain will not bleed air, but drain pressurized fuel as it enters the FM).

i had the truck out yesterday and it lost power and speed and eventually stalled...

I have read about guys cranking up the fuel on the injection pump but am not sure if that might help...


Any ideas would be greatly appreciated.

Increasing the fuel volume at the IP will do nothing to diagnose/fix your current problem. Visit that later if you wish, but forget about it, for now.

Everything indicates you are getting a lot of air into the system while running. This could be due to a large air leak, or the lift pump is not pumping while the engine is running. The injection pump will draw fuel, even when the LP isn't pumping. This will exploit the slightest of air leaks that won't normally (with working LP) won't be an issue, and often won't leak fuel when under pressure. Install (temporarily) a fuel pressure gage at the water drain outlet. Fuel pressure at idle should be 4-10 PSI and remain steady. If it is below that, the lift pump is not up to the task, or something is changing while it's running. If it starts out good, but falls off, either the pump is failing, losing 12V power (likely the OPS-Oil Pressure Switch), or is sucking in air (the lift pump does not pump air very well, but it will pull it in with great efficiency).

[jay_0283]

I have installed a new fuse and relay direct to the lift pump to make sure my OPS wasn't the problem (I do plan on removing this). It started better, and had way more power to start out, but did the same losing power. it did start much easier after it stalled.

I will put my pressure gauge on the water drain and see what it reads either tonight or in the morning.

Any ideas of where to look first for a possible air leak? back by tank???

I have also tried running it with the diesel cap off (thought maybe vacuum in tank)

Thanks for the help so far, any advice is much appreciated.

[DmaxMaverick]

Remove the OPS? Unless you plan on replacing it with an electronic alternative ($$$ and no more reliable), leave it. Using it to power a relay (which powers the LP) removes the load from it, and from then on they usually last a very long time. The problem with using it to supply power to the LP (OEM) is over time the contacts become weak and eventually fail due to the continuous high load. Using it to supply power to a relay completely removes that burden.

Once you've properly eliminated the LP and still have the issue, on to the leak(s). There may be one large leak, or perhaps several smaller ones. On the older trucks, everything is suspect, but if the lift pump is pumping, that leaves the plumbing before it. Metal lines rust, and rubber lines crack. The sending unit in the tank is also suspect, as they often rust, creating pinholes above the fuel level. One way to check that is, test with low fuel and also with a full tank. If it's worse with lower fuel, the sender unit plumbing is a likely suspect (but probably not the only one). You can also pressurize the tank (low air pressure, 5 PSI or so) and look for external leaks. If there are no external leaks, then it's likely the sending unit. Still, all the fuel plumbing on an old rig should be replaced, eventually.

[jay_0283]

Truck has a new LP installed yesterday.

[DmaxMaverick]

OK.

Try this. Get it warm, about where it will "normally" stall. Have handy a bottle (or several) of cool water. As soon as it indicates it might stall, slowly pour the water onto the injection pump. If the condition improves and it doesn't stall (until it warms up again), repeat the process a few times. If pouring water on it seems to help keep it running, the IP is worn out and must be rebuilt or replaced. Quite possibly a result of running with no filter.

As the engine warms up, so does the fuel and IP. As the IP warms up, the tolerances open. Add warm (thinner) fuel and the IP may not be able to provide enough fuel pressure to pop the injectors.

You may have several issues, simultaneously. Address them one at a time. Begin with the easiest or most obvious.

[trbankii]

Once you've properly eliminated the LP and still have the issue, on to the leak(s). There may be one large leak, or perhaps several smaller ones. On the older trucks, everything is suspect, but if the lift pump is pumping, that leaves the plumbing before it. Metal lines rust, and rubber lines crack. The sending unit in the tank is also suspect, as they often rust, creating pinholes above the fuel level. [snip] Still, all the fuel plumbing on an old rig should be replaced, eventually.

This past year I went through and replaced everything from the sending unit to the IP (IP is next on my list when I have the funds) - sending unit, fuel and return lines, lift pump and OPS, fuel filter housing (and filter), and line to the IP. Replaced the brake lines while I was in there too. I was getting some fuel weeping down around the bellhousing and showing up along the framerail where the lines ran, but the truck still ran - sorta… Most of the components were suspect (heavy corrosion on the outsides due to salted roads in the winter) and the remaining few items seemed worth replacing with all the trouble it was to do the work. The filter housing was replaced because a new unit was cheaper than the parts to seal up the old one. As I was pulling lines out, in quite a few places they literally snapped in two rather than bending.

I have to say that the truck runs much better than it has for years. As DMax says, you can have a bunch of little issues that don't really show up, but together they all affect performance.

As an aside, until I disassembled everything, I didn't know there was a heating element in the fuel filter housing. I swear that has improved startup performance this past winter.

It's an absolute b**ch to get to everything. Getting to the lines between the transmission/bellhousing without removing the trans was probably the worst part. But it was definitely worth doing if you're considering regular use of a 25-year-old vehicle.

[ronniejoe]

This sounds to me like an internally worn injection pump. How many miles are on it?