ISM Throttle Response

[LindyT]

I haven't had this coach long and this could be normal, but I'm curious about throttle response times. From a standstill, there is approximately a 2 second delay from the time the throttle is pressed until it seems like the turbo spools up and speed begins to gain. There doesn't seem to be a power issue once moving and minimal, if any black smoke.

My old ISC had a bit of lag, but I don't recall it being like this.

Any thoughts or is this par for the course for the ISM?


Thanks!


Forgot to add: boost pressure under load averages 29-34psi.

[racer0624]

I've heard, though not confirmed, that the turbo was changed for the '09 product year to one that spools up faster than the '05 Essex we used to have. I can tell a little improvment but not much. It takes a bit of umph to get 41k pounds plus towed vehicle going.
My boost pressure is in the same area as yours.

[Doc Mark]

Same problem with ours. I've just learned to live with it.

[Chickadee]

Yup, our 08 EX (4502), 500 ISM, exhibits the same "delay" but as John (racer0624) pointed out, there alot of weight to get rollin!! Steve

[LindyT]

Thanks guys! I feel a bit better... it's concerning at first when you're leaving a green light -- there's a 2 second feeling of panic that you may be stuck in an intersection, then all of a sudden - it launches. Ha!

I'll mentally file this as "working as intended."

[Ann n Gene]

I have the same lag on my 07 T.S. Alante NOW, BUT did not until I took it to cummins to get an abs warning light checked out and fixed. I suspect it was a software "upgrade" with something to do with emissions that ended up derating the engine some. But thats just me, maybe nothing and all in my head. just my experience. Gene

[RustyJC]

Blame it on our emission regulations.

The problem is that, if the engine fueled immediately as you pressed the accelerator, you'd get a big puff of black soot (partially burned fuel) at takeoff, just like diesel engines have done for 100 years. To eliminate the soot, modern electronically-controlled diesels increase fueling only as air (boost) becomes available to ensure complete combustion. In other words, the fueling rate tracks along with the boost pressure - as boost increases, fuel rate increases.

My Cummins has a "box" and bigger injectors (347 hp and 762 ft-lb torque at the rear wheels; roughly equivalent to 400 bhp/900 ft-lb torque at the flywheel), and it responds to the accelerator RIGHT NOW, but at the cost of a healthy (pun intended) puff of soot. To avoid the soot, I have to ease into the accelerator gently, allowing the boost to come up before I add more fuel - the same thing the EPA-compliant ECM software is doing on a stock computer-controlled Cummins.

Rusty

[a k]

Cummins limit the fuel so you don't over torque the axle rating. That's why it's slow off the line and you can't get top boost in first gear.