Archived 24v engine swap engine won't rev

[dcamilleri]

I have just finished my 2001 24v dodge cummins into a 1985 suburban. Engine starts and runs great. When driving engine will not rev over about 1800 rpms then computer pulls the fuel. Could this be a problem with the VSS? I did not hook up the wires for the VSS because I was told I didn't need them. Any Ideas?

 

[Alan Reagan]

I'll bet it needs the VSS. Otherwise, it will think it's revving, without putting power to the rear wheels. If you knew what the VSS signal was, you could probably put in a zener diode to simulate that it is OK and it would work just fine.

 

[Todd T]

almost a definate. the pump will defuel or govern fuel based off of a few parameters. the VSS is one of them. i cant say for sure. with a Chrysler ECM on the cummins there is an exchange of info between the ECM and PCM. i had a switch on my VSSbetween the PCM to the ECM and it still ran. but i noticed i could kill the engine if i left the circuit open and drop the clutch. if i turned the switch back to normal you could hardly kill the engine even with the brake. "idle validation" i believe it was called. actually that is how a few vendors get around the speed limiter. I'll bet you are looking at a need for it becuase other sensory input like maybe tach signal are missing too. did you use the Dodge ECM? or a Cummins one? do you have a dodge truck PCM hooked up too?



you should probably talk to a vendor like TST for some more info or maybe Joe D. for some help.

 

[dcamilleri]

I am not running the Dodge pcm, only the engine ecm. I am not utilizing the tach signal or the vss signal. Throttle response seems normal except for the lack of rpms. Power seems normal except that I can not stay into it long enough to make anything happen because I hit the rev limit. As I was looking through fault code information,P084 says tampering has been detected on the vehicle speed circuit pins 8 and 18 of the oem harness, effect: engine speed limited to Max engine speed without vss. While I have not retrieved any codes this seems logical, but I don't know.

 

[ToolManTimTaylor]

VSS should throw a p0500 (God I know that one too well0 At highway sped I lost the VSS for a seccond and the Vp44 cut fuel alltogether had to restart.

 

[ToolManTimTaylor]

BTW maybe for what it's worth throw NTIMADTR a Pm or email as he finished a Sick dually 95 suburban CTD 01 swap.

 

[Todd T]

i think that is going to be your problem. the DODGE ECM and yes i said ECM, was versioned only for the dodge application. it needs to have or see input from the dodge PCM as well. as it would it it were in a dodge truck. you really have two options. hook up a dodge PCM with the tach and VSS signals feeding the ecm. or the better option is go with a cummins ECM on your engine so you can run it in stand alone mode. if you shop right you should be able to by a 275 horse ecm directly form Cummins. plus you could get even more uprates from cummins that way. (if they would turn their head on the emissions issue. )



more pluses would be; PTO inputs that actually work, and high idler inputs that could be used.

 

[Todd T]

you also have the can bus to think about. I dont know what all is shared between the two over that.



the cummins ECM is probably the easier and cleaner way to go. how much of the harness do you have? do you have the part that runs over to the PCM? could you just power, ground and plug one in? or have you butchered that? <-- no offense

 

[dcamilleri]

I still have the oem dodge plugs to the ecm but they have been cut off. I know several other people that are running similar setups without vss or pcm and are not having any problems. However at least two of them are 99 model engines. I am trying to track down a cable driven vss but so far I do not know what pulse width I need or if it uses sine or square wave. If I could find out what the signal is I could probably duplicate it.

 

[dcamilleri]

I just got off of the phone with TST and their tech gave me what could be the best answer yet. He said that others that have done conversions with automatic engines have had the same problem and that I need to get the ECM reflashed to the manual trans version. I hope this does it. He also said that the vss only controls top speed on standard output engines and top speed plus cruise on H. O. engines. Thank you TST. I will post the results after the reflashing.

 

[MCummings]

Penny for your thoughts,,,,



Dollar if you flash me...

 

[dcamilleri]

The beast is fixed! Yesterday I made a trip to Cummins Rocky Mtn. in Billings, MT and asked them to reflash my ECM to a manual trans application. That sounds easier than it is. There were over six different programs and they are not distinguished. The first one we tried had the same results as my original program, would not rev past 1900 rmps. The tech was thinking something else was wrong, but I promped him to down load another program and bingo! 3600 rpms, 50 feet of impressive suburban burn out in the parking lot! Thanks TST for the info and thanks to Cummins tech Dave Moody, he is a heck of a hand.

 

[barbwire]

Dave Moody

dcamilleri

Hey, I met dave the last time I was in Billings. I will have to agree with you, I think he knows his stuff. I am going to try to set up an appointment with him to work on my rig, the next time I'm in Billings.