Rpm Rise And Drop @ 40mph?

BNSF · November 11, 2010

2008 Silverado Crew Cab 5.3L 4 Spd.

When driving at a constant speed on a flat terrain (with or with out cruise on) once in a while the truck will start lurching with a 200RPM drop, and then a 200RPM rise from the original RPM at that speed. I can't figure out what the hell is going on. Keeps doing it till I release the gas or press the gas to raise the RPMs.

Is it possible that the computer might be out of whack for the shift points? and increases RPM to shift?

Any help is possible.

Had someone tell me that it is totally normal with those trucks. Find it hard to believe.

On a side note, does anyone know if Chevy offered Vinyl seats for trucks other than the WTs? My pleather seats look some much different than others soft leather seats. Don't know what the heck they are.

Bowler807 · November 11, 2010

I believe what you are experiencing is what I did before my Black Bear tune.

My truck would shift into the V4 mode, and the engine didn't have enough torque at the low RPM to keep it engaged. Just a slight change would cause it to shift back to V8 mode and at the same time unlock the torque converter.

This was very apparent at about 40 to 45 mph. Higher and lower it was not nearly as noticable. After the Black Bear tune, my engine has more torque across the entire RPM band and will hold in the V4 mode longer without being overly sensitive.

It's annoying, but it is nothing to worry about.

SouthCo · November 11, 2010

I haven't experienced this. What speed are you traveling and where are the rpm's?

I think you could get vinyl on trucks other than the w/t with code 9S1 but thought that was for fleet vehicles. Cloth was a free option. That's from looking up specs on 2008 from the web so take it with a grain of salt.

joe04 · November 11, 2010

I haven't experienced this. What speed are you traveling and where are the rpm's?

I think you could get vinyl on trucks other than the w/t with code 9S1 but thought that was for fleet vehicles. Cloth was a free option. That's from looking up specs on 2008 from the web so take it with a grain of salt.

BNSF, I just picked up my 07 Classic last week with exact same complaint. Dealer kept truck for 3 days, Tech II saw the RPM change, but with no code, just keep driving it. News is that now, even at 50 I'm noticing it, as well as mileage falling off a bit.

Throttle position sensor possible? Anyone else?

Blacktop · November 11, 2010

the rpm's raise slightly when the afm kicks in to v4 mode, and drop silghtly when going into v8 mode. if have the dic you can switch it to instant fuel economy and it will tell you when it switches over and it should match the rpm change.

Trav_13 · November 11, 2010

the rpm's raise slightly when the afm kicks in to v4 mode, and drop silghtly when going into v8 mode. if have the dic you can switch it to instant fuel economy and it will tell you when it switches over and it should match the rpm change.

Maybe Justin can chime in here and help on this one....I am experiencing a similar issue with mine....he had mentioned something about DCFO....which I think stands for Deceleration Fuel Cut Off....which I think is something in the programming....he is currently tweaking my 2009 to adjust for this. Mine is kinda in the area you described as far as speed and such, and I even noticed it out on the highway a few weeks ago when traveling down some hills, etc....it just kinda the slightest jerk and a increase or drop in the RPM's...

Bottom Line get the Blackbear tune and turn the V4 mode off and you will be much happier.

joe04 · November 12, 2010

the rpm's raise slightly when the afm kicks in to v4 mode, and drop silghtly when going into v8 mode. if have the dic you can switch it to instant fuel economy and it will tell you when it switches over and it should match the rpm change.

Note that mine does not have afm, it's an 07 classic. same symptons......

music · November 12, 2010

Neither of my 4L60 trucks have done this, so I'm going to say "not normal". It sounds like the TC is locking and then unlocking. If so, something isn't right, as it should stay locked until more power is needed, at which time it unlocks (bumping up a few hundred rpm). If that isn't enough power, it then downshifts to 3rd.

dlewis1111 · November 12, 2010

2008 Silverado Crew Cab 5.3L 4 Spd.

When driving at a constant speed on a flat terrain (with or with out cruise on) once in a while the truck will start lurching with a 200RPM drop, and then a 200RPM rise from the original RPM at that speed. I can't figure out what the hell is going on. Keeps doing it till I release the gas or press the gas to raise the RPMs.

Is it possible that the computer might be out of whack for the shift points? and increases RPM to shift?

Any help is possible.

Had someone tell me that it is totally normal with those trucks. Find it hard to believe.

On a side note, does anyone know if Chevy offered Vinyl seats for trucks other than the WTs? My pleather seats look some much different than others soft leather seats. Don't know what the heck they are.

Your title says it happens at 40 mph. I think that your truck is in between choosing whether or not to lock up the torque converter and it is just cycling back and forth. Does it only happen at 40, or at higher speeds too?

BNSF · November 12, 2010

Nope, just happens in the 40MPh range. Noticed at 38 and as high as maybe 42. When it does start jumping up and down, it's a constant up and down finishing a cycle in about 1 sec. Absolutely annoying.

Info about Black Bear Tune please. THx

joutlaw · November 12, 2010

Mine does this at 55mph - 57mph and I am blackbear tuned. Justin said he could fix it, but I'd have to send the PCM back or might just got Autocal.

It's quite annoying and I'm afraid I'm going to tear something up on my truck.

Specs:

2004 Siverado Z71

5.3L/4L60-E

3.73s

265/75/R16

Hunt1 · November 13, 2010

This is definately a TC engagement issue, and depending on how finnicky our owner is, it may be normal operation.

BNSF · June 14, 2012

Well, not a TC issue. Put in a new one and still the same crap. Put up with this crap for almost two years. Dealer says there is no issue and no codes. I dunno what to think. I'd did a tranny swap since I had the damn thing out.

00Silverado4x4 · June 14, 2012

Personally, not a tech specialists, but sounds like TC "programming" issue. Sounds like the computer is not sure if the TC should be locked or unlocked as that would be the perfect speed to go either way. Have you by chanced a flash or reprogram or whatever it's called to reinput stock programming into the whichever computer controls the TC.

BNSF · June 27, 2012

Well, new tranny, new torque converter, fuel injection cleaning, new throttle body, flashed the computer that controls the tranny/shift points/torque converter......... and you guessed it...... SAME SHIT.

My next option is an insurance claim....... after I torch the truck.

I'm about ready to pull my hair out.