3116 Cat in Topkick - Diesel Truck Forum - TheDieselGarage.com
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post #1 of 4 (permalink) Old 11-11-2006, 03:29 AM Thread Starter
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3116 Cat in Topkick


I just recently acquired 91 GMC Topkick, with 3116 Cat turbo and a 5 speed.

The engine seems to have a rev limiter and will not approach redline (2900 rpm) until in fifth gear. 1st gear is about 1400 rpm's, 2nd is about 1700 rpm's, 3rd about 2000 rpm's, fourth about 2300 rpm's, and fifth will go up 65 mph, but not beyond unless going down hill (and then just barely). What can be done to increase the rpm range? The tranny doesn't have any wires going to it, so I presume it's linked to the speedometer or speed sensor?

I know the owners manual spell's out that shifting is easier for the tranny's syncro's at low rpm's, that you'll get to top speed quicker shifting at low rpm's, and fuel will be conserved with low rpm's -- but sometimes you need 2800 rpm's in second gear!

Any suggestions would be greatly appreciated. Thanks!

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post #2 of 4 (permalink) Old 11-11-2006, 08:00 AM
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Sounds like a strategy to keep you from overtorqing the transmission. Even in some older 855 cummins they have a torque limiting system to keep you from getting full power in the lower gears to save the transmission and the rest of the drivetrain. I don't know it for sure but that is what it sounds like.

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post #3 of 4 (permalink) Old 11-19-2006, 05:11 PM
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Probably in the ecm programing. I don't know about the cats but for the detroits it's called progressive shift that limits the rpm in the lower gears and also the speed limiter can be set to limit top speed. Should be able to eliminate all that by changing a few parameters in the ecm.

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post #4 of 4 (permalink) Old 11-19-2006, 08:19 PM
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I could be wrong But I thought a 1991 3116 would still be mechanical.

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