RPM Pulse/Spike after/during shift

[SDWA]

Ok, anyone else experienced this:

I get a slight "pulse" or "spike" in engine RPM's right after, or during upshifts when lightly accelerating (pedal doesn't change position, no more than 2200 rpm before shift) on level streets, during 1-2, 2-3 and sometimes 3-4 shifts.

This doesn't happen all the time, but is pretty easy to duplicate if needed (need to find right street to do it on)

I'm thinking this a software issue, or there is some type of slipping in the tranny, i.e. two solenoids are open at once, or who knows what?

It's headed for the dealer the first week of June for the steering rattle, just thought I'd see if anyone else had experienced this...

Thanks!

Scott

[ 05-23-2003: Message edited by: SDWA ]</p>

[ndamico]

my buddy's truck did it and the problem disappeared when he changed his fuel filter (which was overdue)..

[mdadgar]

My truck does that occasionally. Seems to happen most often when cold.

It's exactly like the throttle-blip during a heel&toe downshift. Except I've got an Allison. smile.gif

- Mark

[Kent Tuttle]

I also have it, mostly at cold and light throttle. In fact when it is warm I haven't noticed it lately. Of coarse with it warm the Juice is kicked in and well you guys know what that is all about :D

[SDWA]

Well, it's not the fuel filter, I change that every 10K and it's been there even right after a change. I do notice it most after startup; not necessarily cold, but in the first 10 minutes or so.

At least I'm not the only one that has it... maybe the dealer will know more; or, maybe not.

Scott

[1822]

My 02 does tke same thing under very light throttle such as slow moving traffic. Did it from the very begining and have since changed exhaust and added a Smart Box E and it stil does it. I had a 98 6.5 which also blipped the throttle the same way. There does not seem to be any increase in forward motion when it happens though. Be interested to see what the dealer says about it.

[DmaxMaverick]

Sounds like shift event de-fueling. Normal. Should only be noticeable before engine gets up to temp under light pedal. Search the Duramax forum. It's come up a few times over the last couple years.

[SDWA]

The so-called "event de-fueling" from what I could find here sounds more like a DROP in RPM's, not an increase. Listening to it again today 4 times, being a non-allison mechanic, I'd bet there's two solenoids overlapping in the open position (?), and a resulting "slip" of the tranny. It acts just like my original transmission (which was replaced...) did when there was a valve sticking - an increase in RPM's but no associated "go" with it and no "jerkiness" in the return to applied power when the valve un-sticked (technical term).


Scott

[ 05-26-2003: Message edited by: SDWA ]</p>

[a64pilot]

SDWA,
I believe you are right, Mine does it too, I don't think it hurts anything though as this slip is under very light throttle only and I don't there is much stress and therefore very little wear associated with this slip.

[SHOPMAN426]

SDWA,
I too have had this problem since the get go. I figured it had to do with the fact that I just started the truck and things haven't warmed up and settled down. I also have the steering rattle but haven't taken it in. I guess I should get off my lazy butt and take it in.

SHOPMAN426.

Mike. tongue.gif

[zsqure]

I've got this problem also,sounds exactly like a throttle blip during a manual transmission shift. I am out of warranty and will continue to "drive it until it breaks."
Has anyone experienced this? Cruise on, speed at 65 (stock tire size) 2 or 3 hours into a trip and the engine will "burp" or "cough" just once and everything will be fine the rest of the trip. I got it, it's the air bubbles in the fuel line trick right? :D :D :D

[SDWA]

Well, it's not "normal", at least according to GM... Mechanic drove around with the Tech II hooked up and recorded a few of the incidents, then back at the shop plotted them out on the PC screen (which, BTW, is too cool of a feature/tool)...

Seems the ECM was commanding an abrupt increase in fuel pressure from the FRP for some reason. Showed up like a mountain on the screen, very obvious, very different from the other shifts.

No one could figure out why! TAC recommended replacement of the Fuel Pressure Regulator (not the entire fuel injector pump - I thought these were serviced as one unit?) and the problem is still there...

All software revisions are of the most recent versions... No codes were stored.

Scott

[DMAXTODD]

My 01 did it,my 02 does it...must be normal right...?

[Waypoint3D]

Interesting...I've had an '83 Z28 Camaro w/CrossFire Injection(gas),'92 Z71 4x4 Throttle Body Injection(gas), '99 AMG Hummer HMCO 6.5L and now '02 GMC 4x4 D/A. Every one of them has shown this behavior intermittently. Kinda like a throttle blip during a quick double clutch upshift...never thought anything about it, since it didn't cause a problem for me.

However...the '97 Dodge 3500 dually 12v Cummins, '97 Ford F250HD Powerstroke and '02 Excursion..never exhibited this behavior. :confused:

[afp]

Mine used to do it also, and had a mild lopey idle after starting to warm up to about 185 degrees. The ECM reflash at the dealer fixed all that for me.

Blaine