Engine double shifts sometimes when flooring gas pedal

Ariel Guerra

Original poster
Member
Jul 11, 2012
17
Maybe this is related to my other problem but this happened a couple of times when I raced the truck in attempts to clear out the injectors.

When I floored the pedal it kicked into overdrive and then did so again with just as hard a jerk as the first time. It freaked me out, though it did accelerate at the normal increased pace it always has. When I tried it again on the same drive it didn't do it.

I checked the transmission fluid and it's full. It doesn't do this when I push the pedal halfway down to get the truck moving faster than the gradual pace.

Any ideas on this one. Could it be spark plugs or coil pack? Something else? I forgot why I hate having an older vehicle, everything pops up all of a sudden. :mad:
 

Bartonmd

Member
Nov 20, 2011
545
I certainly hope you were on the salt flats or somewhere else legal (or more importantly, safe) if it went into overdrive (4th gear) at WOT. I think that's something like 126mph on my computer settings, IIRC?

Mike
 

Ariel Guerra

Original poster
Member
Jul 11, 2012
17
Bartonmd said:
I certainly hope you were on the salt flats or somewhere else legal (or more importantly, safe) if it went into overdrive (4th gear) at WOT. I think that's something like 126mph on my computer settings, IIRC?

Mike

I hope my sarcasm meter is correct right now. :rotfl:

Actually I think I posted this wrong.

It's not that it double shifts, per se, more like it downshifts then hesitates, then downshifts again. Like it had a break in what it was doing.

I so wish I spoke mechanic, sorry guys. :frown:
 

Bartonmd

Member
Nov 20, 2011
545
Ariel Guerra said:
I hope my sarcasm meter is correct right now. :rotfl:

Actually I think I posted this wrong.

It's not that it double shifts, per se, more like it downshifts then hesitates, then downshifts again. Like it had a break in what it was doing.

I so wish I spoke mechanic, sorry guys. :frown:

No, I was completely serious. Overdrive is 4th gear in this transmission (5th in some, 5th and 6th in some, just 6th in some, etc.). Overdrive just means that the output shaft of the transmission is going faster than the input shaft.

If you were talking about downshifting, you did post it wrong.

Are you sure it didn't just downshift to 3rd, then decide it wanted 2nd right after that?

Mike
 

Ariel Guerra

Original poster
Member
Jul 11, 2012
17
Bartonmd said:
No, I was completely serious. Overdrive is 4th gear in this transmission (5th in some, 5th and 6th in some, just 6th in some, etc.). Overdrive just means that the output shaft of the transmission is going faster than the input shaft.

If you were talking about downshifting, you did post it wrong.

Are you sure it didn't just downshift to 3rd, then decide it wanted 2nd right after that?

Mike


Good question, but I really don't know. All I know is I did this on two seperate occassions at the 50 mph mark and had same result. I did it at that mark because that's where I was getting the heistation/stumble when I gradually increased speed so I thought by stomping on the gas it would eliminate that if there was some gunk clugging the injectors.
 

ScarabEpic22

Member
Nov 20, 2011
728
Thats the factory GM transmission calibration right there. Both of my TBs did it before I tuned them, now if I punch it they drop straight into the correct gear. No downshift, hesitate, then downshift again. Its the PCM/TCM having to perform the table lookup for the values, the stock GM settings are all over the place. When you tune it, the PCM/TCM doesnt have to think/worry about the upshift/downshift points crossing like they do in the stock calibration.

And heads up, punching it isnt going to do jack ____ for cleaning the injectors. Either run a few bottles of Techron through the tank or pull them and have them cleaned.
 

Ariel Guerra

Original poster
Member
Jul 11, 2012
17
ScarabEpic22 said:
Thats the factory GM transmission calibration right there. Both of my TBs did it before I tuned them, now if I punch it they drop straight into the correct gear. No downshift, hesitate, then downshift again. Its the PCM/TCM having to perform the table lookup for the values, the stock GM settings are all over the place. When you tune it, the PCM/TCM doesnt have to think/worry about the upshift/downshift points crossing like they do in the stock calibration.

And heads up, punching it isnt going to do jack ____ for cleaning the injectors. Either run a few bottles of Techron through the tank or pull them and have them cleaned.

Ok so I need to change the spark plugs then? That's what you mean by "tune" right? sorry all I know is "tune-up"?
 

Wooluf1952

Member
Nov 20, 2011
2,663
Milwaukee, Wisconsin
Ariel Guerra said:
Ok so I need to change the spark plugs then? That's what you mean by "tune" right? sorry all I know is "tune-up"?

The "tune" we refer to is changing the specs of the PCM (the computer for the engine & trans). As Bartonmd said, try a bottle or two of injector cleaner before changing plugs. The cleaner most referred to here is Chevron Techron.

It really would help if you would fill in the truck info at the left.

Depending on your mileage, it may be time for plugs and O2 sensors.

I just read your other thread. At 198k miles you could be ready for your second set of plugs and O2 sensors.
 

ScarabEpic22

Member
Nov 20, 2011
728
What he said, time for plugs and O2 sensors, plus check the operating temp with a scanner (the dash is worthless). If you havent had the cat replaced yet, it's probably due as well.

Sorry I was referring to a PCM tune, not a tune-up. Changes the fueling, spark, VVT, trans shift points, firmness, etc. There are literally 0 downsides to a tune, better power, smoother, transmission actually knows what it's doing vs thinking all the time, and usually better mpg.
 

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