Engine/Transmission (1994 - 1998) RPM limiter on CDN Trucks? Help.

[dmcowboy]

Hello All,

I was at the Central Texas dyno day last Saturday the 10th and put my truck (98, 12 valve, 4x4 dually, auto transmission, ext cab, built for the Canadian market) on the dyno for the first time to find out what kind of HP and torque I was running. I had just picked up the truck from the transmission shop where I had put in an ATS torque converter, TCS input billet, shift kit and valve body. When the tech ran the dyno test he pushed the O/D off button on the gear shift to take it out of O/D then he put the gas to it to run the test. When he hit around 2900 rpm's (just below the red line on the gauge which is 3000 rpm's) the engine stalled out (best way I can describe it) down to around 1900 rpm's, then "caught" again and began revving up to 2900 rpm and stalled out again. At first I wondered if there was a limiter/governor on the truck to prevent blowing the engine but the tech had never encountered this before on any other Dodge with an auto transmission and didn't know what was going on. As a result of the "stalling" he couldn't get a good reading on the dyno test.



Given that I had just done major surgery on the transmission I figured that something was wrong with that. The transmission guys have looked at it again for the last couple of days and have found nothing wrong and have discovered that the truck stalls out at 2900 rpm in 1st and 2nd gear as well, and so they are convinced there is in fact a limiter/governor on the engine.



I have never notice this problem before, but then again I have never ran the rpm's that close to red line either, in or out of O/D.



So does anyone know if there is a limiter/governor on my year Dodge built for the CDN market, and if so how do I get an accurate dyno test done on my truck?

 

[Forrest Nearing]

I don't know of any differences in the engine rating in the Canadian market, but even an american truck shouldn't rev to 2900 stock. you'd be lucky to see much more than 2700 under power w/ a stock truck

 

[dmcowboy]

So do you know how a guy gets an accurate dyno test done on a automatic transmission? It seems strange to me that the tech had never hit 2900 rpm's before and stalled it out on another truck. I wonder if the tech was wrong to try to run the engine past 2900 rpm's during the dyno test.

 

[Forrest Nearing]

if your truck ran to 2900 then "stalled" and "caught" maybe you've got a fuel supply issue?

 

[Bob4x4]

The peak horsepower would be at a lower rpm anyway. How much diesel work does that dyno operator do ?



Bob

 

[Swamp Donkey]

Nothing to do with a Canadian truck. Mine revs to 3500 rpms no problems at all. Even stock it never lost rpm's like you describe.

 

[dmcowboy]

I don't know how much experience the dyno guy has, I think they usually do souped up gas engines (dodge vipers, corvettes, etc).



The transmission shop checked the fuel supply and couldn't find anything, but then again they are a transmission shop so who knows it they know what they are doing on a diesel. They think there is a limiter on the engine.



This is really bugging me.

 

[dmcowboy]

OK, FYI, I got a hold of Barry of NADP in Edmonton Alberta, and he told me that the 12 valve cummins engines do have a governor spring (maybe the 24 valves too I never asked about those) that usually kicks in at around 2700 rpm. This spring over time will stretch a bit so that the governor will kick in at around 2900 rpm, which is where mine is working at. Apparently a person can get governor springs that change the rpm limit to around 3200 rpm's, which if installed, would give a smoother, better driving experince (his word's).



I don't know if the same thing applies for standard transmission dodges, I would have thought so but based on what one of the earlier posts wrote I don't know.



So anyway, if anyone out there tries to do a dyno test of a 12 valve with an automatic transmission and it "stalls out" at somewhere above 2700 rpm's that is what is going on.