Engine/Transmission (1998.5 - 2002) surging

[MDSlover]

Truck has 189,000 miles on it, lift pump was changed 1 year ago, cam sensor has been changed, surging has gotten gradually worse - especially when the weather is cold. It's almost like you are giving it throttle and letting off the throttle. At 70 mph, it's fine. No codes.

 

[Moe]

Could you post a sig so we know what you have?

 

[JLandry]

in the mornings especally when its cold between 1500 and 1700 rpm there is asurge after it warms up its not so bad any suggestions

There could be many causes for engine surging.



Has it suddenly started doing this or has this been coming on gradually and getting worse? If suddenly, was anything done to the truck just prior to it starting (maintenance or upgrades)?



Does it do this when the truck is both moving or stationary?



Have you checked for trouble codes?



Have you checked the fuel pressure at the VP44 fuel injection pump inlet? Ideally you should have about 15 psi at idle and never see it fall below 5psi under a load with the throttle wide open.



Do you have any engine performance accessories or programmers we should know about?



How many miles?



Does it have the original lift pump and / or VP44 fuel injection pump?



Which sensors have you replaced (if any)?



Best regards,



John L.

 

[MDSlover]

Truck has 189,000 miles on it, lift pump was changed 1 year ago, cam sensor was changed last week, surging has gradually gotten worse over the past 6 months - especially when the weather is cold. It's almost like you are giving it throttle and letting off the throttle. At 70 mph it's fine - it doesn't surge. No codes

 

[hcole]

OK, do a search on APPS problems. That sounds like your problem.

 

[JLandry]

Well with that many miles, it could be a problem with the APPS (Accelerator Pedal Position Sensor), the VP44 fuel injection pump, or one or more fuel injectors.



First, get a fuel pressure test gauge hooked up at the fuel inlet to the VP44 and verify adequate fuel pressure is present when the surging is occurring. You can pick up fuel pressure test gauges for dirt cheap at places like Harbor Freight Tools or eBay.



If you find the fuel pressure is adequate, then I can post instructions on testing the APPS.



Best regards,



John L.

 

[MDSlover]

this morning i turned key on without running engine pushed throttle to full position let off did that about 5 times and its not surging anymore what could that be how do you check apps

 

[JLandry]

... could that be how do you check apps

No... that's the procedure to teach the ECM what the APPS full range of voltage values are. It's normally done anytime the APPS, ECM, or batteries are disconnected.

I hope that cures your problem, but your TPS (Throttle Position Sensor) could be deteriorating and may be in need of replacement. The TPS is the black plastic rheostat on the side of the APPS assembly (that big cast aluminum bracket with the accelerator linkage / bell crank). You can buy a replacement TPS from Blue Chip Diesel or TDR member Timbo for less than $200. A complete APPS assembly will set you back around $500 or more.

But before you start swapping parts, be sure and test your fuel pressure if you haven't done so already. Low fuel pressure can destroy your VP44 fuel injection pump.

Best regards,

John L.