Jumpy, touchy throttle, can't tow

Opinions Vary

Opinions Vary

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Oct 18, 2012
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I recently completed my P-pump swap on my 00 5 speed. The truck in my signature should give you an idea on what is going on. I hooked it one night to make sure she would stay together and everyone said I needed more fuel so we threw some full cuts at it(not happy) I drive this truck to work and tow with it and pull on the weekends. Anyway, when I am hooked to a trailer, It is very sensitive in the pedal. It starts bucking and jumping. you have to be very smooth with the pedal or stuff it. We changed the gsk to a Bosch 4k and it helped a little but still doesn't tow the way I want. I tried searching but couldn't match my language to what is going on. Any help would be appreciated.
 
Fuel pressure? Mine was jumpy till I got the fuel pressure up and the AFC tuned. It sounds like fuel pressure, return springs, or tuning. Did you try putting the old DVs back in?
 
one weak spring if I remember right on the throttle linkage?

fuel pressure is plenty high. haven't put the old DV's in, thinking about ordering a set of taper cuts.
 
Sounds like a low pressure fuel issue, but it could be the linkage not having enough spring.

I would check to see what your pressure it at coming off of the fuel filter header and then from there if you are low like 3-5psi, I would start with the overflow valve if there are no leaks, and then work my way around to see if possibly the lines have a crack, or your stock mechanical lift pump is going. I had to swap mine around 240k, and my OFV went out at about 290k.
 
Have someone push the pedal in the cab and watch the linkage to see how it returns. The 12 valves I've seen have one spring on the rear of the pump and one on the bracket where the tps goes. I used the apps housing on mine and it is super tight. All you have to do is drill a few holes out, add tappet cover bolts from the ecm to extend it and make a new throttle linkage. Or, try adding another spring if you don't like what you see. What do you have assassin max pressure set at and what do you see @ idle?
 
hydroshok said:
Have someone push the pedal in the cab and watch the linkage to see how it returns. The 12 valves I've seen have one spring on the rear of the pump and one on the bracket where the tps goes. I used the apps housing on mine and it is super tight. All you have to do is drill a few holes out, add tappet cover bolts from the ecm to extend it and make a new throttle linkage. Or, try adding another spring if you don't like what you see. What do you have assassin max pressure set at and what do you see @ idle?
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not sure I understand what you're saying. Do you have any pictures?
 
CorneliusRox said:
not sure I understand what you're saying. Do you have any pictures?
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It's not pretty, but works perfectly. You can see where the 2nd spacer should go. No need for a 12v throttle cable and you can hook the apps back up for cruise control. You also have to trim some metal off for the new throttle linkage and remove both stops to get full travel. I forgot about that stuff. It's been a while since I made it.

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with the set up I have I doubt anyone would be running a stock fuel system. My lines are all brand new braided lines, no leaks. My DTT Assassin is idling around 20-25 and goes up with RPM.
 
I would be willing to bet it is an issue with the springs you purchased. I ran a set of pac brake 4ks in my last pump and they were very touchy. As mentioned above, I added a return spring and it made it more driveable. My current pump from Seth (Farrell Diesel Service) was set up with 5ks and my throttle is as smooth as it was when it was stock. I asked seth about this and he told me it is an issue with the height of the springs in most of the spring sets that people purchase.
 
Opinions Vary said:
with the set up I have I doubt anyone would be running a stock fuel system. My lines are all brand new braided lines, no leaks. My DTT Assassin is idling around 20-25 and goes up with RPM.
Click to expand...

That is where mine used to idle. I stretched the spring in the OFV and now see 35psi @ idle. It is much easier to drive. I know the 180 is not that sensitive to fuel pressure, but it's an easy thing to try.

FWIW, I just remembered that I only had one return spring when I first built my P-Pump 24 valve. It ran fine with no issues.
 
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