8.1 funny revs?

zorrro · June 11, 2004

On my way home today I thought I noticed some pappy exhaust notes. In park I took a quick stab at the accelerater peddle and then another. I expected the truck to go vroom, vroom! Instead it went vroom, pluuuuuuuuuh and when I did it again vroom, pluuuuuuuuuuuh. I don't let the truck rev-up very high the tach never gets to 4,000 rpm. It seems to do ths every time you take two quick stabs at the gas peddle. My exhaust leak was just extra noise I wasn't used to from the chil'n opening up the rear windows.

I this normal, the pluuuuuuuuuuuh thing? You can hold the gas peddle down to floor on the second stab and the engine never gains any rpm (stays near idle with a loud sucking noise). Other than that, it seems to run down the road just fine................Help?

snoman · June 11, 2004

If that is a 2001 or newer it is a drive by wire unit (gas pedal is not mechnically linked to throttle plates) Engine responces to gas pedal input are detemined by the ECM, not your directly. Given limited data you supplied I cannot even offer a guess at this moment.

8100HD · June 11, 2004

Well, since your truck has to be atleast a 2001, since you have the 8.1......Welcome to the wonderful world of GM electronics and the dreaded torque management...seems that GM engineers thought they had to babysit us with this motor and control throttle input through the ECM.....get yourself a custom tune to help correct this problem.

zorrro · June 12, 2004

Thanks for your responses. Sorry about not giving much input. The specs are in my SIG at the bottom of the post. I think you have the choice of seeing the SIG or not. You guys must have chosen the not?

Here it is. The truck is a 2001 8.1, Allison, 2500HD, 85,000mi, 4:10 gears, stock size tires and no modifications.

It sounds to me like nothing is wrong with the truck. The ECM is just slower or programmed against consecutive rapid stabs at the pedal. I will look at the drive by wire set-up in the morning make sure it has that. Yes, the pedal has a detached from the motor feel to it, like most modern rigs.

Those tuners look more and more appealing...............Zorrro

snoman · June 12, 2004

Those tuners look more and more appealing...............Zorrro

They could really wake that beast up! A 8.1 with 4.10's is a serious towing machine.

Chev8.1 · June 16, 2004

Try hold the gas pedal down to the floor in park or neutral. Does not go any high than 3000 rpms. Kinda sucks when a guy is trying to sound off. This is for when 8.1 used in work truck chassis(6500) allison has a pto output, instead of cruise, you can set the engine to idle to 3000 rpms. Personally I like the ECT, nice when mudding, no bouncing off rev limiter, just keeps peg at 4650rpms. Also I if you try when stuck to rock the truck, like a guy would in old truck. you have to be below a certain rpm and mph to shift the trans when doing this there is no phuuuahhhh, its zing, zing,zing. Then you have to wait 10 or so seconds for it to shift.

Hope this helps, some more info on different situtions for yah.

zorrro · June 16, 2004

Thanks, makes good sense now. This is exactly what's going on.

I have a question for you chevy8.1. This PTO option, that's why the trucks have that 3,000RPM limiter (mines's about 2,500) in neutral and park? How can I use this? Where's the button to run this speed? Just tape the peddle to the floor and hope nobody slips it into gear? lol. I have a PTO wench but didn't realize I could use it with this truck.

8100HD · June 16, 2004

As far as I remember you cannot use the PTO from the tranny....it is only available for use with cab/chassis models as the floor pans are different....2500HD's/3500's have a block off plate...I know that alot of Diesel guys are hooking up a high idle set-up, but thats all you can use.