After installing the Superchip, when taking off from a barely rolling start, there is a slight hesitation which makes the engine rev slightly then the tranny catches and she takes off with a hard jerk. Kind of like popping the clutch, but this is an auto trans. Funny thing is, it takes off completly normal if you come to a COMPLETE stop. Only does it if barely rolling. If I remove the Superchip, the jerk is gone. Comes back with the Superchip installed. Had the rearend rebuilt a year ago (at the dealer, under extended warranty) due to bad bearings. It had a terrible growl. Is this common or rare? U-joints seem ok, but maybe they are the culprit. It only does it with the Superchip in place.
Any ideas?
Thanks!!

 

Hi cjmf150,

Well, that isn't really possible to properly diagnose here, it could be just about anything.............

Sounds like you are giving it more than just a little bit of throttle to make it do that - something that isn't good for any vehicle, but especially not an older high-mileage truck.

On an older truck like that, it could already have any number of problems that don't show up with the "weaker" stock program, but that surface once you have a performance calibration installed and you start hitting the throttle after all the slop is in the driveline - which happens when the truck is rolling at any speed but no throttle is being applied - then when throttle is suddenly applied, all that slop is taken up at once, and you get that bang! This is why you just don't do that, it's never a good idea to suddenly take up driveline slop like that - it's not a normal driving situation. If it were doing that only at very light throttle, that would happen both with and without the chip.

It could simply be the normal relearn cycle you go thru any time you disconnect a battery or change the PCM's program - for the first 500-2000 miles (this is talked about in the vehicle's owners manual) after you interrupt power to the PCM or change it's program, you can have symptoms with idle speed & idle quality, or things like the transmission's internal line pressure taking some time to settle back into it's normal routine, etc. You go thru both the basic relearn cycle as well as the adaptive strategy adjustments begin again from scratch any time you disconnect the battery or change the program.

Or, it could be that you've got a well-worn transmission (valve body, shift solenoids, etc.) that just can't tolerate any changes at this point in it's life - being a 1997, that tranny is at least 7 years old, and probably has a lot of miles on it as well. That vehicle was built during a period of time when there were some valve body and shift solenoid problems in those transmissions, which can easily cause those kinds of symptoms - at first only with a performance chip installed, then later on even in stock condition - I've experienced that myself in a vehicle from that same period of time that only had 30K miles on it's tranny, and the shift solenoids, which weren't old and didn't have high miles on them were just shot - they were a very weak design, and got updated numerous times throughout the 1990's and into 2000. Once I replaced them, I never had another problem with the tranny - and I went on to install a shift kit at a high level and pound on it pretty hard.

We've got plenty of people who install chips at 50K miles, or 80K miles, etc. (though I do not recommend taking any older vehicle with higher than 100K miles and start hot-rodding it), and who virtually never have any problems.

It may well be just a matter of driveline slop being taken up suddenly, and most likely that is what's happening - even with with engine gaining some rpms, that could easily be perfectly natural, and just the torque converter "stalling" (slipping, actually) and allowing the engine to gain rpms - that's how it multiplies torque. Now if it''s actually staying in Neutral long enough to allow the engine to gain several thousand rpms, then you've got a *transmission* problem - maybe it's only showing a symptom with a chip installed, but if that is what it's doing, then it's just a matter of time before it does that under other conditions, too.

There are all kinds of possibilities, but the bottom line is this cannot be diagnosed here - it's going to take some troubleshooting by someone who really knows what they're doing (and who knows these vehicles well) to actually determine the real culprit here. A lot of mechanics love to point their fingers at performance chips and say that's the problem automatically, citing the fact that it only happens with the chip installed, instead of actually doing proper troubleshooting - and there have certainly been some really poor powertrain programs sold in chips over the years, which have legitimately caused some mechanics some problems. But not the Superchip - as you can see, there is no track record of that here, and there are 6 years of posts here with no such pattern. But there are plenty of transmission problems in bone-stock vehicles that get reported here in other sections of this web site - more the older the vehicle gets.

You've got one of 3 basic choices (as I see it, I should more accurately say!) - either stop driving it like that, where you are deliberately applying significant throttle after coasting at no throttle at a very low speed like that - or have someone that really knows what they're doing *properly* diagnose the vehicle - or remove the Superchip and hope for the best.