why loss of power

Reply Subscribe

Page 2 of 2

Thread Tools

#11

01-08-2007, 12:55 AM

bob h

Senior Board Member

Join Date: Oct 2006

Location: Nb

Posts: 752

Quote:

Originally Posted by yurkym

I appreciate the responses, but she is still at the shop . We are going to get her on Monday. The shop did replace the sensor and all the fuel lines were fine. So we'll let you know>
Thank you

it doesn't make any sense whatsoever that the fuel lines could be causing this problem.

__________________
Bob H

#12

01-08-2007, 01:35 AM

bob h

Senior Board Member

Join Date: Oct 2006

Location: Nb

Posts: 752

Quote:

Originally Posted by Splitshifter

Quote:

Originally Posted by marylandkw

I had this problem a few years back, was interment at first and then became steady after about 300 miles (I was going to limp home but had to goto the dealer) Turned out to be a speed sensor on the back of the transmission. If I remember correctly, and I seldom do, the motor goes into a protect kinda mode when it can't sense all the things it wants too.

I will second that.

Had that happen a few years ago on a Mack.

Speed sensor on trans output shaft failed. Speedo registered zero MPH, engine was totally devoid of power.

I would assume that without a MPH signal, the ECM thinks the truck isn't going anywhere, and wont allow the engine to receive full fuel.

Replaced the speed sensor and all was well.

it's irrelevant to know this, but; the ecm is still aware that the truck is moving, even without the vss. it simply has lost a parameter that allows the engine to operate efficiently. this is a programmable parameter in most ecms, meaning that it can be disabled.

__________________
Bob H

#13

01-08-2007, 04:49 AM

marylandkw

Senior Board Member

Join Date: Sep 2005

Location: Maryland

Posts: 731

Bob, just out of morbid curiosity, How does the ECM know I am moving without the VSS?

I sat here and thought about it and I can't figure it out. I am not saying you are wrong, I am saying I am slow :lol:

__________________
Paranoia is nothing more than the pathological habit of paying close attention.
All ideas in this communication are sole property of the voices in my head. (C) 2006, "The Voices" (TM)

#14

01-08-2007, 10:43 AM

bob h

Senior Board Member

Join Date: Oct 2006

Location: Nb

Posts: 752

Quote:

Originally Posted by marylandkw

hmmmmmm, there's a question i've never been asked

i'm only gonna attempt to turn the lights on ...

when you press the accelerator pedal down, the ecm sees this as "fuel demand"; if you push the pedal all the way to the floor, this is seen as 100% fuel demand.

if a truck is unloaded, 100% fuel demand will take the engine from 700 to 1600 rpms in X seconds. if the same vehicle is fully loaded, it will require Y seconds (longer than X) to get to 1600 rpm with 100% fuel demand... ...this is (sort of) how the ecm calculates engine load...,

and the vehicle must be moving to load the engine ....... ........ ....... ........ right?!?

now, if that same vehicle is sitting still in neutral, and you push the accelerator pedal all the way down (100% fuel demand), how long will it take for the engine rpm to reach 1600? ... much quicker than the loaded vehicle at 100% demand, correct?

this would only be one basic strategy, i'm sure there's more.

__________________
Bob H

#15

01-13-2007, 08:59 AM

yurkym

Rookie

Thread Starter

Join Date: Apr 2006

Posts: 18

Thank you Thank you Thank you....one and all. It was the speed sensor. And she is up and running.
Sorry I took so long to thank you all but we picked her up Monday morning and just got home with her today. We changed out the fuel lines because they were lookong old...we try to do as much preventitive maintance as possibble.
Again "love you guys"