Engine/Transmission (1998.5 - 2002) Lack of throttle, possible VP44. Any advice...

[Underdog67]

I have a 2002 24V H. O. 6 speed, about 150 miles ago the 1688 code flashed up. The truck drives fine untilyou try to go past 3/8s throttle, then it's just a mule w/ hardly any acceleration. I cleared the code and it hasn't come back. The original owner had the injection pump replaced at about 60K at the dealer, the truck now has 119K. I'm hoping someone can tell me it's not the injection pump, from what I've read when the pump goes out it goes dead and doesn't limp along like mine is.

 

[Mishkaya]

I hate to say it, but it's most likely the VP44 that is about to go out again. It could be the APPS that is giving you trouble, but odds of that are pretty slim. Have you tried an APPS reset, to see if that helps your condition. If not, you should start saving for a new injection pump I'm afraid... :{

 

[Joseph Donnelly]

A “dead pedal” can mean the VP44 pump is bad, or the Accelerator Pedal Position Sensor (APPS) is bad. In your case, Code 1688 means “Internal fuel injection pump controller failure. ” Thus, the VP44 is indicated as the culprit. Codes are summarized in TDR Issue 55, p. 96. See TDR Issue 51, p. 96 for procedures and photos to help you change the VP-44 injection pump.

 

[Mishkaya]

Forgot to add: you don't indicate that you have a fuel pressure gauge installed on your truck. If you don't, you should get one ASAP. It could simply be that your lift pump is no longer working in which case your VP44 is being starved for fuel and you will kill it in short order driving it this way. I have known a few that were able to get away with simply installing an aftermarket lift pump, although the lack of fuel will always shorten the life of the injection pump. Welcome to TDR by the way.

 

[Underdog67]

Ya I tried the APPS and nothing changed. I was about 90% sure that it was the Inj. pump but just wanted to see if there was possibly another problem before I went out and bought a big dollar pump and be really ****** if that didn't cure it. I'm definitely going to put on a fuel gauge, I was also thinking of just doing a lift pump first since I was going to do one with the inj. pump.

 

[Mishkaya]

Ya I tried the APPS and nothing changed. I was about 90% sure that it was the Inj. pump but just wanted to see if there was possibly another problem before I went out and bought a big dollar pump and be really ****** if that didn't cure it. I'm definitely going to put on a fuel gauge, I was also thinking of just doing a lift pump first since I was going to do one with the inj. pump.

I would suggest an aftermarket lift pump over an OEM lift pump as they are about as unreliable as can be. A little more money up front, but usually good savings long term. If you can find someone with a simple test gauge to check your fuel pressure, you should do that. I would not recommend driving the truck if the lift pump is out. Another simple way to check is to loosen the fuel line at the VP44 inlet, and have someone bump the starter (without starting the truck). The lift pump should run for about 15 seconds. If you don't have any fuel flow, or very little, your lift pump needs replaced.

 

[Underdog67]

I was planning on going w/ a FASS lift pump. No sure if I should go w/ a 95 or 150gpm, I have a TST Power Max. Also, weighing the fact that I'm going to have to smog it next year so I don't want things getting to pumped up. Thanks for the info BTW, I'm going to try out what you said about testing the lift pump-so glad I finally became a member, what you spend on fees saves you way more on parts and time.

 

[Mishkaya]

I was planning on going w/ a FASS lift pump. No sure if I should go w/ a 95 or 150gpm, I have a TST Power Max. Also, weighing the fact that I'm going to have to smog it next year so I don't want things getting to pumped up. Thanks for the info BTW, I'm going to try out what you said about testing the lift pump-so glad I finally became a member, what you spend on fees saves you way more on parts and time.

If you don't plan on going for high HP, a 95 will be plenty sufficient. I have an Airdog 100 gph on my truck, and it managed to dyno over 600hp. Good luck.