Archived truck bucking/missing what's going on?

[ScottWright]

Hey all,

I have a 2000 qc, 4x4, lwb, auto. I have an FMS and edge Ez on it. Today coming home from work I went to take off from a light and the truck bucked on accel. After that when I came to stop at the next light the truck was running terrible. It sounds like it is missing, but as soon as you either take off, or come to a complete stop (small load on motor) the miss goes away. It doesn't buck every time either. I was thinking maybe the lift pump was dying, but I got on it hard with the FMS on and it still pulled boost up to normal levels (37psi) The only thing I can think, and I guess this may be likely, Right before it bucked I filled it up with fuel. The first time it bucked at the stop light was only about 500' from the fuel station. Any ideas? Bad fuel? What do I do if I do have 36 gallons of bad fuel?!?!?! lift pump dying? injection pump dying? dirty fuel filter? I pulled the water drain up before I filled the tank, but nothing came out. Is this normal? I bumped the key once and fuel started pouring out immidiately. Could the water in the filter have been frozen or something? Sorry for so many questions, I'm just hoping it's not the VP44. The truck has had a lift pump put on it in the last 6 months. I have the psi sender that came with the FMS but it only tells if fuel pressure drops below 2psi. I just got the banjo this week so its' not been put on yet. HELP!!



thanks,

scott

 

[rbattelle]

Try replacing the fuel filter, first? Someone smarter than me will probably have better suggestions, but that's where I'd probably start first.

 

[ToolManTimTaylor]

Originally posted by ScottWright

I pulled the water drain up before I filled the tank, but nothing came out.

I will bet ya sucked air into the system. You juuust may end up bleeding the system of air by cracking the injector lines one at a time. by doing this :Crack open the injector lines 1,3&4 and cycle the L/P till you see fuel coming out, when you get fuel out of these 3 lines tighten them down and try to start.

 

[ScottWright]

I thought about that maybe the pump sucked air, but the truck starts right up. So I didn't think that would be it. Any chance that the FMS has an intermittent short causing the pump signal to be temporarily interrupted causing it to do it? Doesn't really explain why it misses when it idles though?

 

[ToolManTimTaylor]

Are you using a pump cover that pierces the wire internaly or a wire tap?

 

[ScottWright]

I have the pump wire that pierces the cover. Probably not shorted there, but I was thinking maybe at the firewall hole? I can't really look, it's dark outside and about 1°! lol

 

[ToolManTimTaylor]

The pump covers (Mine included) have been notorious for loosening up over time. DBLCHECK the connections and / or pierce pins. I had to go 1/4 turn more 6 months after putting on the cover. another bout with surging a year later proved yet another tightening.



*BE CAREFUL*



Too much will crack the pc board and render the VP44 useless.



Scott where ya from?

 

[ScottWright]

so did you have problems with it bucking even with the FMS turned off? Would the FMS make it idle bad? I think the idle is higher now for some reason too? Idles in neutral at 950 rpms and 850 in gear. Seems that those numbers were about 100 rpms lower before this problem? BTW I'm in southern michigan. I was surprised with it idling so bad that it wouldn't start this morning in the 12° weather but it started right up. Another strange thing is, the truck has been starting really hard lately. Seems like you have to crank it forever when it is cold. So this morning I did my normal, cycle the grid heater a couple times, but today I tried something a little different. I bumped the starter to cycle the fuel pump, then I did the grid heater cycle. . . wouldn't you know it, the thing fired right up after like 2 turns? I'm really starting to think fuel filter, I'm going to put one in at lunch today so hopefully that fixes it.



THANKS AGAIN FOR THE HELP TDR!