Is this Normal?

[OleBlackyLBZ]

So I have noticed this for a long time and just assumed it was normal, now I'm not so sure. But when I'm accelerating hard on my bigger tunes and I hit a little bump like say where road meets bridge or something like that, anything that's enough to bounce the truck a little, the truck stops pulling as hard for a couple seconds. It is most definitely not the tires spinning but I can't figure out what is going on. Is it normal? I read somewhere a bump like that could activate the brakes and unlock the converter for a couple seconds but I held the pedal up with my foot while accelerating and that didn't seem to change anything. I'm really thinking bumps is just causing the converter to unlock somehow under a load...

 

[2004LB7]

does it do it on cruise control? are you 100% sure you're not lifting up at all on the throttle during the bump?

 

[OleBlackyLBZ]

Cruise is fine, it's not under nearly enough load to do it then. Throttle burried on a 550+ hp tune it does it, but only when I hit a hard bump. It's like it pops out of gear for a second or two.

 

[2004LB7]

cruise should act the same for the same load and speed. I would look hard at a loose harness connector or ground connection

 

[N2BRK]

Every dmax I've driven does the same thing. I recall George telling me it's normal.

 

[2004LB7]

haven't had this happen to any of mine

 

[N2BRK]

George asked me if I ever felt it and then laughed and said it's normal.

 

[2004LB7]

I'm going to guess the brake pedal gets shaken to the point of activating the brake switch. if you can see a bump in the road coming up, put your foot under the brake pedal and hold it up and see if it still does it

 

[NC-smokinlmm]

Normal... Expansion joints make my 16 do it. Even when it was stock.

 

[1FastBrick]

I was wondering if it was a fueling issue like if it sucked air or something.

 

[dndj]

I'll toss out a theory. It could be the speed limiter. LB7 stock is 98mph I think.

At 60mph, with 33" tires, you're getting 10.5 tire rotations per second, or about 1 tire revolution in 1/10 of a second. Under acceleration, a sharp bump could cause the tire pop off the pavement for a half or whole revolution and you wouldn't even feel it spin. However it would be fast enough for the ECM speed limiter to kick in.

 

[darkness]

Get a log of a pull and see if you can spot it.

 

[NC-smokinlmm]

It's the conveter unlocking.

 

[OleBlackyLBZ]

does it do it on cruise control? are you 100% sure you're not lifting up at all on the throttle during the bump?

There is no acceleration with cruise control on therefore it does not do it then. You have to have the pedal on the floor during acceleration for this to happen. Specifically racing

 

[OleBlackyLBZ]

Every dmax I've driven does the same thing. I recall George telling me it's normal.

It's the conveter unlocking.

Thanks, I knew it had always done it and there were never any codes so I thought it might be normal.

 

[Chevy1925]

if the converter was unlocking, you would feel the re-lock or an "extra gear". to confirm it, log the TCM and watch the TCC slip. if you see anything over 0 when you hit the bump, then you can say its the converter. if not, its something else causing it.

you ought to be logging this and looking at the ecm and tcm. monitor fuel MM3 and see if for what ever reason it is dropping under wot over the bump. it could be something as simple as a torque table that was missed.

in all the trucks ive been in, they have never done this. the bump either causes no difference, wheel spin or blown up c2 hub.

 

[OleBlackyLBZ]

if the converter was unlocking, you would feel the re-lock or an "extra gear". to confirm it, log the TCM and watch the TCC slip. if you see anything over 0 when you hit the bump, then you can say its the converter. if not, its something else causing it.

you ought to be logging this and looking at the ecm and tcm. monitor fuel MM3 and see if for what ever reason it is dropping under wot over the bump. it could be something as simple as a torque table that was missed.

in all the trucks ive been in, they have never done this. the bump either causes no difference, wheel spin or blown up c2 hub.

Thanks, I don't have a way to log but I will try to figure something out. May just wait until I go back up to Mark's and let him look at it.

 

[Chevy1925]

No autocal or anything?

 

[OleBlackyLBZ]

I do have an Autocal. But I talked with Mark wal ago and he said it's normal, the tcm unlocks the converter as a failsafe when it sees the wheel speed jump suddenly.

 

[OleBlackyLBZ]

I'll toss out a theory. It could be the speed limiter. LB7 stock is 98mph I think.

At 60mph, with 33" tires, you're getting 10.5 tire rotations per second, or about 1 tire revolution in 1/10 of a second. Under acceleration, a sharp bump could cause the tire pop off the pavement for a half or whole revolution and you wouldn't even feel it spin. However it would be fast enough for the ECM speed limiter to kick in.

I didn't think the tires were spinning and I don't think they are enough to feel anything, but apparently you are right.