I changed my lift pump about two weeks ago and the vp44 today truck has no power now 2nd gear has a little but 3,4 and 5 have none it takes forever to get speed built up in any gear. Before vp change it have dead pedal for a few seconds if i slowed down and then pick back up. Now i have nothing. The pump came from sheid diesel and have heard they do good work. I do not have a fuel preassure gauge yet but will this week, i did the volume test on lift pump and was good. The truck has 248,000 miles on it and i am the original owner so i know history of truck. Please help this is my work truck and fixed fast. This is a 98.5 24 valve with a 5 speed. Thanks in advance. Dave

 

Have you tried to reset the APPS yet?
Accelerator Pedal Position Sensor

instructions here:
https://www.dieseltruckresource.com/...n&onlynewfaq=1

 

things I would like to know..... how much boost, and what codes if any.

 

I have tryed the apps reset and it did not help. I do not have a boost gauge(will this week). I cleared codes after repairs and drove truck about 15 miles and it is not showing any codes. Thanks Dave

 

Might be a silly question (excuse me if it is) but what's the condition of the fuel filter?

 

How about the fuel lines? Ever replaced? Common problem.

 

The filter was changed at same time lift pump was and seems to be putting out plenty of diesel. It was not a stupid question either, i should have mentioned this. I have not changed the fuel lines. The problem has went from bad to terrible after vp change. I cleaned vp terminals and did not help. Could it be the apps, it is the original with 248,000 on it. But the apps throws acode doesn't it. Thanks Dave

 

Might be the APPS.
I know mine was giving me a dead pedal, but I'd get a Check Engine Light when it happened.

You can only pull codes with a DRB or ScanTool on the 98.5 through '99 model years.

 

Since you are not reporting codes associated with your symptoms of continuing lack of power I would do the following:

Check the APPS for erratic or low voltage output. The APPS is a linear variable potentiometer that controls the signal voltage to the ECM that enables the ECM to tell the VP44 injection pump how to set the angle of the regulator plate for the delivery valve. All your power settings start here. It craps, and then the entire system goes south. A weak or dirty APPS may not set a code, but can really lower power to the point that you are only making 30% or less of the available engine power. My experience is that about half the shade tree guys change their VP44 and transfer pump when the problem is a dirty APPS.

If the APPS is good to go, then check the MAP sensor. It is a good idea to pull and clean it after a few years of operation. Check the terminals, any corrosion on the MAP terminals will result in the ECM thinking that the manifold pressure is low and not signaling the VP44 to open up the fuel flow. That gives the same result as driving with a Valet switch on. This is another source of guys frequently changing pumps when the pumps are just fine.

If the MAP is good, then check the IAT. It is a good idea to pull it and clean it too. Also, make sure there is no corrosion on any of the terminals. The IAT generally does not result in low power of the levels you report, but failure most often results in lousy fuel economy and drivability problems with a cold engine.

You should install a fuel pressure gauge to read the delivery pressure to the injection pump. My experience with OEM transfer pumps has not been good, about 1 out of every 5 purchased seems to come with a factory defect of either a stuck bypass valve or defective pressure switch. There is pretty poor quality control on these parts from whichever third world factory builds them, and it is real frustrating to install new only to find you have 5 psi when done.

 

Well i have more problems now. I put a volt meter on the apps(orange wire with blue stripe at ecm) had .15, so i tryed to adjust it acording the instructions on one of the post using the meter. the apps said .506 volts i could only get mine up to .48. So i tryed that and truck would not start at all, cel came on so i got a122. I figured it was because i adjusted it so cleared it. Then i put it back to .15 hoping it would start, it will not. I now have 336 and 122(ckp and apps). i have enough money in this between the vp and lp, i just would rather fix it my self than give the dealer the money to fix this. If anybody has any ideas about this please help, i need this truck running asap. Thanks for the help so for. Dave

 

Well today i changed the ckp and apps cleared codes and went for i drive, still no power. The truck barely pulls itself. It also seems to be loosing its prime. I checked codes and am not getting anything. Please help Dave

 

bump !!!!!!

 

Sorry to hear of your troubles!

In reading thru, I expected to see the APPS fix clear the problems, but.....

Did you clean the MAP sensor?

I would double-check the fuel lines for air leaks - you said you appeared to be losing prime - AND get a FP reading ASAP, pre- and post-filter, and double ck all connections from the tank to the IP.

Does it idle okay? These things need only air and fuel to make power, so if you walk completely thru the fuel delivery system, including the IAT and MAP sensors, without finding any problems, you may take a look at the boost system, see if the turbo is spinning freely and you are making boost to the manifold.

Keep us posted!

 

Seems it may be a bad vp 44. I'm sending it back today. Has anybody else had problems with a new pump. I'll keep you posted. Thanks for all the help Dave

 

Truck is finally fixed. Scheids exchanged the pump and overnighted me a new one( Great Service, I highly Recomend Them). Installed it and alot better performance, but still low power. So i hooked my E-Z back up and it took of slow and then kicked in. So i decided to unhook the boost sensor plug and ran great. Cleaned the boost sensor hooked it back up and it ran better than new. I noticed tonight that somebody suggested the boost sensor(i just Missed it before, i guess because i was at the end of my rope). I have noticed from searching for a cure for my problem that several people had the same problem, But did not let anybody know what cured the problem. I hope this helps some people( low power check Boost sensor). I would like to thank everybody that tryed to help me on this problem. Again Thanks Dave