Throttle pedal not working on 2000 Mack RD688s

[mgmdump]

This is my first time posting on this site and I am very hopeful that someone can help me. What I have going on here is a 2000 mack rd688s where the gas pedal operates backwards.....kinda? what happens is the truck starts just like normal and then after about 1 minute the truck revs up to about 900-1000 rpm and stays there. however you can get the truck to idle but that is only if you are pushing on the gas pedal and there is a time delay of about 3 seconds before you notice any response from hitting the pedal. Now i know im going to get the usual "replace the pedal" well that has already been done. i have 3 other known good pedals here that i hooked up to it and i have gotten the same exact response from all of them. what I am hoping is that someone knows of a special sensor or something along those lines that would cause this to happen. This is the first mack truck that we have in this company so if you can be detailed with the information that you can provide me that would be great. thank you very much in advance.

[staxx]

Have you changed the ecu if you have swaped module or programed it some of the software calls for throttle calibration afterwards if calibrating does not fix check to see if your low coolant sensor is leaking coolant into harness and if it is check to make sure it has not got to the engine module yet also check to make sure vehical module connections are clean and dry with module wiring facing down .

[rsb502]

sounds like a pedal calibration, or wiring harness failure issue, is the pedal harness pinched anywhere, or has it gotten hot or melted on the way to the ecu? Syaxx is the man on those engines he has probably fixed more of em than I have seen.

[rsb502]

oops, staxx not syaxx! ha!

[JumperAndSon]

Yep. I'm lost when it comes to 4 strokes, especially those fancy new-fangled electronic controlled ones. But as 84superdog said, my man staxx can take care of business very well in that field

Ben

[Lmackattack]

its a known issue with the electronic pedals on all makes of Trucks. they can go bad and not send the right signal.

[mgmdump]

Is there a quick and easy way to check or recalibrate the settings without a scanner? we had the truck scanned once and it was determined that the pedal was the culprit but obviously after replacing it we found out it wasnt the problem. where are these other modules located at? I have not seen any other issues under the hood and the majority of the wiring still seems to be in great condition (unlike our sterlings that have been hacked). if you would like you can email me back and forth i should be able to respond quicker that way. dank@mgmdump.com

[mgmdump]

problem solved!!!! it was the j3 connector on the computer near the firewall on the passenger side floor. the 3 prongs vertically 2nd row from the right were to blame. cleaned up those 3 prongs and it is working better than ever. gained lot of responsiveness from doing that.

[staxx]

Make sure the module is mounted with plugs facing down so water will not get in ,

[theakerstwo]

Sounds like some eletric is leaking out of something and getting mixed with the conutor switch and its trying to run backwards.

[NewMoney]

 I had this same problem too.  For me it was a short in the wires, the red wire connected to the throttle.  Depending on how I wiggled the wire the throttle would work or not. When it didn't work the engine idle went from 700 to 1000 rpm and stayed there, the throttle wouldn't respond, and the electrical malfunction light came on.  

An electrician tested the connectors to figure which wire it was that wasn't sending a signal, spliced it and repaired it with wire connectors. I guess over time the wire wore got damaged from vibration and the like.  It was a dyi job if I had an electrical tester and knew to probe like he did. I know now going forward. I hope this helps.