Truck stalls after start-up...

85F250Diesel · #1 (**permalink**) 10-28-2009, 11:51 PM

Hi, I've been having problems with my '85 F250 with the 6.9. Manual gp control. (yes, I have motorcraft gps)

It starts ok, but not great, when cold, it does take about 10 seconds of cranking on initial start-up. (even after a 10 second gp burn, 10 sec wait, then 10 sec burn) Right after initial start-up, it'll often idle kinda funny, the RPMs will bounce between 500 and 1500. Sometimes it'll only seem shake a little, like it might be missing, with no RPM change. Revving it helps the idle smooth out. It runs great once its warmed up.

Like I said, it starts ok initially, but then if I get it warmed up real good, and I let it sit for an hour or 2, it'll start, run for 30 seconds, and then die. It won't start again until I bleed air from the system. I've replaced the fuel lift pump, and the return lines, caps, and O-rings.

I've read on here that the water separator can cause problems like this? The drain hose from that has been plugged since I got it.

I'm really at my wits end here. Sorry for the long read.

rupejosh · #2 (**permalink**) 10-29-2009, 12:47 AM

have you changed the fuel filter?im wondering if one of your return line tees didnt get seated or something.it sounds like air is getting in somewhere

lmnr0026 · #3 (**permalink**) 10-29-2009, 03:20 AM

Sounds for sure like air in your fuel filter. I have that problem right now. You going to have to find where the air leak is and fix it. The engine surges when air in the line hits the injectors. I have some clear hose between fuel filter and IP, so I see for sure 100% when air starts getting pushed through it surges, stumbles, and maybe dies entirely. I have a van and have the doghouse and air filter off right now, which is why I can see that so easy.

Luckily I have an electric fuel pump, so I turn the key on and bleed air out of the filter. Catch fuel in a little cup until it comes without air. if she's setting a few days I might need to pump out a pint of diesel before it's done clearing the air.

If you can't do that, you will want to pull the fuel filter and top off with fuel and reinstall, before starting.

Obviously, the best thing is to fix the air intrusion. Could be at the fuel heater in top of the filter housing, or maybe the schrader valve, or somewhere else.

Good luck and let us know where you find the problem.

Lazy K · #4 (**permalink**) 10-29-2009, 06:13 AM

The first thing I would do is get a short length of hard line and bypass the water seperator.

85F250Diesel · #5 (**permalink**) 10-29-2009, 09:00 AM

Josh: No, I have not replaced the fuel filter, but I have a new one sitting around, so I'll probably throw that on there. And yeah, I checked and rechecked those tees, I don't think they are the cause of the problem. I just hate to touch them now though, because I've had the engine to operating temp a few times since they went on.

Lmnr0026: yes, it seems like air intrusion to me as well, I've just run out of things to check. I don't have the fuel heater in the filter housing though, just the schrader valve. Maybe it is leaking air.

Lazy K: Would that be ok? I thought it was a no-no to run diesels without the water separator. Or are you just saying to bypass it for diagnostic purposes?

I read somewhere about a check valve for the return line from the fuel filter? would this fix the problem if the air leak is not in the fuel filter assembly?

rupejosh · #6 (**permalink**) 10-29-2009, 09:59 AM

mine hasnt had the water separator in two years i just put an inline filter on