Engine/Transmission (1998.5 - 2002) Unusual Dead Pedal Condition

[grichards]

This winter I decided to keep my truck out of the Ohio salt and stored it in the barn. I started the truck a couple of times and warmed everything up to operating temperature and cycled the air conditioner as well. About 2 weeks ago I decided the salt was gone for the summer and took the truck out for a spin. Immediately a drivability issue (dead pedal) occurred. I have no turbo boost below 1500 rpm. Above 1500 rpm all is normal, and boost climbs quickly to 22 psi. Above 1500 rpm the truck runs really strong like it normally does. (In neutral, the engine rpm's rise quickly when the go pedal is pressed.) When the rpm's drop below 1500, the dead pedal condition returns and will not clear under any condition apart from increasing the rpm's. Fuel pressure (post filter) is 12 at idle and never drops below 9 psi at WOT. I searched many threads here and could not find a set of circumstances matching mine, but suspected a frozen waste gate. I took the truck to the dealer for diagnosis/confirmation by their diesel tech. Without revealing my suspicions, the tech came back with waste gate seized and told me a new turbo was required for $2400 and change! The truck has 78K miles and has the original VP-44 and turbo; additionally the check engine light is off and no engine codes are posted. Up to now I have had an independent mechanic replace: the turbo with a reman Holset HX35 (stock), air filter and lift pump (thinking the fuel volume might be low although the pressure is good). The drivability has not changed at all - same dead pedal issue. Any ideas?

 

[Nigel]

I had a bad boost fooler years ago that had similar symptoms. Mash the peddle and no power till about 1800 and then full power and the back tires would light up. No boost fooler then look at the Map sensor.

Nigel

 

[JR]

Any programmers?

Standard or auto?

 

[grichards]

This post was my first after viewing/reading for 14 years. I have really been educated by all of the knowledge shared on this site. This situation is really the first issue I have had with the truck. For some reason my truck profile did not append to my note. Here's that info: 2001.5 Ram 2500 4X4 QC Long Bed; HO 6 Spd, 3.55 Limited Slip; All stock with stock lift pump moved to frame rail near tank. SPA digital boost and EGT; Westach Fuel Pressure; Gauges on A-pillar; Source Automotive Track Bar and Steering Stabilizer.

I have no programmers; the engine is pure stock. I appreciate any and all suggestions.

Gary

 

[JR]

OK, no fuel programmers, can't be transmission related since you have a standard and its not a fuel supply issue since you've got verified lift pump pressure to the VP. There are only a few items that could cause dead pedal, a bad APPS, a bad MAP sensor, or a bad VP. MAP sensors rarely fail, the early APPS sensors as well as the soldering in the FPCM in the early VP44's were pretty flaky at best. If both are still original it's a real good chance one or the other are bad. Sometimes neither will initially show a code when intermittently failing.

Not sure how handy you are with diagnosing but Blue Chips website has the best diagnostic write ups for the VP trucks of anywhere I've ever seen. If you have the time and are diligent you should be able to find your problem. The whole thing is a good read but the dead pedal section has the info your after.

http://www.bluechipdiesel.com/vp44diagnostichelp.html

It's pretty difficult diagnosing a truck with no codes. Have you tried a good scanner or are you going by the codes in the odometer window? Might try to find someone with a good Snap On or a DRB that can do live data.

 

[Bob4x4]

I have had MANY map/boost sensors fail with out setting a dtc on VP trucks,it will react like your description-sluggish till about 2k rpm then normal above that rpm.Simple to verify install a mechanical boost gauge and test drive with a scanner monitoring the boost seen by the ecm,If they do not match you have found your problem

 

[grichards]

I just replaced the MAP sensor, and the dead pedal condition is completely GONE! The truck runs like new again. Big thanks to all for your help. Regards, Gary.

 

[JR]

Good guess! The link I posted above shows how to "fix" a bad MAP sensor. IF the sensor is at fault (good supply voltage but lower than required signal voltage) it works well. Either way, glad you got it fixed.

Spring finally seems to be here in NE Ohio! Lots of rain and just enough sun to make the grass grow an inch an hour :-laf