Engine/Transmission (1998.5 - 2002) Towing Charactoristics - Gas pedal

[curatchko]

Okay, just got back from a long haul from Michigan to Memphis tennessee... . towing about 11000 pounds.



I've noticed something in the accelerator pedal. While towing if I put my foot to the floor in overdrive, the engine loses power. If I ease up on the pedal, probably to about less than 1/2 way down, it picks up power again.



Now my truck is very under powered and I don't know yet if it's fuel pressure, (find that out this week), the rear gear(3. 54), or what... . but I'm only gettin 10 mpg towing, 16 with no trailer flat highway... and so something is up... just not sure yet. 3 months ago I was getting almost 21 highway, and 14-15 towing the same trailer, same load.



But this pedal trait has me puzzled.



Any thoughts?



:{

 

[Shovelhead]

TC unlocking?

 

[Piston Slapper]

Seen it too!

I have noticed this too. Don't have the answer though. Notice it on pulling hills, let up on the throttle a little and she'll pull like a dickens! I suspect something to do with Torque Converter??



Any ideas anybody??

 

[curatchko]

No, the torque converter stays locked. It's engine related... . rpm dive with the power loss...

 

[jsnyder]

Not the auto...

I have noticed this quirk too. If I floor it, it seems that I have slightly less power than if I let up a little on the go-pedal. This is pulling 12k with the NV4500.



Jason

 

[Pull'nOld Iron]

Fuel

I noticed this also with mine last july. I was concerned it could be the fuel pump starving.



Could this be a sign of a lift pump not being able to keep up with

the fuel boost?



Also check your filter. When I got home my filter was blown apart. :--) :--)



I changed the filter after I got back to Mississippi and pulled some loads not nearly as heavy. I haven't seen the same event. Filter? Pump?



Something to check along with LP pressure if you have a gauge. I don't.



I hope this helps

 

[dpope]

Could it be that the MAP sensor is sensing too much boost which is causing a de-fueling situation?... . But, that still doesn't explain the the poor fuel mileage on an empty truck... Oh'well just a guess.

 

[Steve Campbell]

This is a shot in the dark...

There has been a lot written/posted about the IAT sensor in the past 1 1/2 years. As the Turbo increases the pressure through the intercoler and into the intake manifold, it also increases the temperature of the air charge coming in. That "increase in temp" is picked up by the IAT and sent to the ECM. ECM says "Whoa there pardner"... . too much heat, better defuel some to bring the intake temp down to levels I have been programed to accept. The ECM defuels to lower this temperature "crisis".



Do you notice this "problem" more in the summer than the winter? Have you cleaned your IAT lately? Have you considerd moving "it" to the intake horn like Marco did?



Speaking of moving it, I know it reads a lower temp in that location. Lower temp means higher fueling and lower fuel mileage (by about . 5 mpg). Well, if dirty IATs decrease mileage and power more than that, a move to the "cooler" location, over the long haul, might give higher average mileage because it would not get dirty. My logic here (or lack of it) it that the stock location is best if everything is fine. With time in general and the use of exhaust brakes in particular, the IAT becomes dirty and before you know it, you have lost 1/2... 1... ... 2mpg.



Too much rambling, time for some sanity by more knowledgable posters.



P. S. have seen the same symptoms you describe:{

 

[RichB59]

I always

slowly roll on the throttle. It seems as if more throttle before the boost can catch up is counter productive and increases EGT more than it needs to. I can tell by the sound the truck makes when I have to much fuel pouring in. Just my opinion.





LOL RichB

 

[curatchko]

Could it be that simple? That it's just flooding the engine with too much fuel and not enough boost? While this is happening I'm only at about 15-16 psi boost. I can't get the boost to max at 70 with the converter locked... . unless it down shifts.



I'm considering moving the AIT sensor... . anyone done this?

 

[Steve Campbell]

You might do a search for...

IAT sensor cleaned



and



IAT sensor moved



To answer your question, I know Marco did!!

 

[DiTrani]

If you were over fueling the engine you'd see a smoke cloud out back. The whole purpose of switching to the VP44 and it's associated electronics was to never let this condition happen, even though most of you guys undermine that objective routinely ;-).



Have you had the battery disconnected recently? You're supposed to calibrate the ECU for throttle position after removing power to the system. I forget exactly, but I think the first time you key on you slowly run the range of the pedal up and down, then key off. When I had mine disconnection to install cruise it drove funny intil I did this. Not what you describe, but it might be worth a look.

 

[SOOT]

I have noticed the same thing on my truck and my Moms truck since day 1. More so when loaded and climbing a hill. Because it's consistent, I think it is just the nature of the beast.