engine stalls

[jerheff]

just bought 87 gmc with na6.2. drove it home 70 miles, but stalled once before topping off both tanks. is it possible for tank switch to have a nuetral area between the l & r tank. the guy i bought it from was running 50% BIO. tried driving it next day stalled at intersection and has become worse. the glow plug light came on and off as I was trying to limp home. would start and then die. now can hardly get it to stay running. black smoke when it does run. no block heater. should glow plug light come on and off. new fuel filter installed. new to 6.2 and diesels. thanks jerry

[john8662]

Stalling can be caused by a failed fuel lift pump not getting fuel up to the fuel filter. But, if you've changed the fuel filter, and did the prime routine to remove the air out of the filter, than the lift pump is likely fuctioning.

The problem with Biodiesel is that it is NOT compatible with the older rubber fuel lines, and will deteriorate them. The problem with this (besides leaks) is that the parts of the line that are deteriorating float around in the fuel lines, clogging fuel filters or worst, getting past the fuel filter (think line from filter to Injection Pump) and into the pump.

At 50%, that truck was in the danger zone (others running it can chime in at any time here!).

Anyways, more things to check.

Double check you're getting good fuel pressure. Using the model 80 fuel filter housing (square filter mounted on firewall setup) connect a 1/4 fuel line (clear preferably or whatever you have) to the petcock located on the top of the filter housing (top left side). Then open up the valve on the top of the filter houing (1 complete turn will work here) and crank over the engine. You should be able to get a HEALTHY flow of fuel out of the hose and into your Coke bottle that the other end of the hose will be in. If this checks out, your lift pump is working.

Next, you'll need that 1/4" ID piece of clear hose (hardware store variety) to replace a piece of hose already in the system. Take and remove the hose coming out of the injection pump (top-front of the pump) and replace it with the same length clear hose to the return fuel rail (just like it is now).

What this will do for you is allow you to view air coming out of the injection pump when the engine is running. So, get the engine running and able to idle, and watch for bubbles, if just steady fuel is observed, then the problem might not be air in the system. IF you observe steady bubbles coming of the hose througout the running time of the engine (before it stalls) then you have an air leak in the system.

The fuel tank switch module always comes to mind when thinking of a fuel starvation problem. This could very well be. How well does the switch control both tanks? Can you switch from tank to tank. You will be able to physically hear the switch working. You press and hold the switch to swap tanks. Some switches just swap nearly immediatly, not these. You have to hold the button for the desired tank for nearly 10 seconds to complete the swap. You can listen to the motor in the switch, it makes a kind of binding sound when it's done.

Hope this helps!

J

[jerheff]

I did what you wrote and was able to get her running again. left the clear hose between the IP and the return. notice a little hesitatation of throtle response though. any thoughts? thanks jerry