E6 350 Fuel Problems

[critter]

Hi Guys, I'm new here hope someone can help. I recently bought a 1986 R688ST dump truck, seemed like a solid truck but in the first 3,000 miles dropped the T2070 Tranny, then the front rear (both fixed now), and now a fuel problem. This is an E6 350 with an Ambac 300 pump, starts and runs great (cold) but now after driving 30 mins or so then shutting the engine off when you try to start while engine is hot it will start and run maybe 5 seconds skip a few times and shut down. You can wind it over til the batteries are nearly dead it will finally start and run fine again. It starts fine cold, but does this every time hot. Where to start? Just changed oil and all filters, all lines look ok.

Thanks

[blackdog2]

Its sound likes block lines or plugged vent or cap make sure your pulling your fuel and return to the same tank .

[j hancock]

After the trans and rear end work, have you had the truck out on the road? As it is being driven does it seem like it is running out of fuel?

When it won't start, try unscrewing the filters to see if the filters have fuel right to the very top.

If you are not getting fuel to the filters, you can try GENTLY pressurizing the fuel tank with compressed air to see if fuel is flowing to the filter. Sometimes fuel lines look ok but the inner liner has collapsed.

[critter]

All fuel lines go to the same tank. Yes I've had the truck out to haul 3 loads of grain since the drive train work its like a new truck on the road. I don't know what the fuel is set on the guy before me pulled a 963 cat with it (over weight), but when you stomp the pedal everything behind you turns black doesn't seem to be any loss of power. The fuel line from the tank to the pump is hard plastic like air brake line. This all started when I serviced it I'm gonna get another fuel filter and try again. Where is the bleeder screw for the hand primer?

Thanks

[2stacksuperdog]

The old O-ring might be stuck on there from the old filter since it happened after the service. Never seen a mack with a plastic line. You have to crack the main line to pump. My advice is to put 2 new lines from tank to motor on.

[Lmackattack]

Replace feed and pickup lines, they'd re cheap and easy to do. May want to replace the vent valve as well unless the fuel cap is your vent. There may be a check valve in the fuel return or feed. May want to replace that as well. If it still has issues it may be the pick up pump can't keep up at idle. This little pump hangs off the main fuel pump and has the in and out lines attached to it.

[blackdog2]

Its always good to to change the check valves in the transfer pump. Ive had people call they gone through several cans of either and it still wont run change the valves and it starts up

[critter]

Thanks for all the replies, I talked to 3 different injector shops today got the same answer from all 3 places. According to them since it is only a hot problem it is weak plungers in the pump which equals rebuild. One told me he would drive that truck across country just don't cut it off, but if you do shut down pour a jug of cool water over the pump and it will crank right back up. Gonna try that next. Any tips on removing the pump and timing?

Thanks

[krismoriah]

I too have an 1986 RD688 and had similar problems. I had a sticky plunger. There is a little tool that my pump shop let me borrow that i took the plungers out of the barrel and had them faced up and new o-rings put on. There was rust down in the plunger that tore the o-rings. If thats all it is you dont have to take the pump off, just the lines going into the pump and use the little tool to pull the plungers. The tool is plastic and looks funny but it pulls them right out. Not a hard job at all and cheap if that is your problem..if not then idk.

[critter]

Thanks, i'll ask about the tool tomorrow.