Poor throttle response noticed in emergency

truckguy82 · July 5, 2016

So I've been driving my truck for about 45 days now, never really thought the throttle response everybody complains about was a big deal.

So over the weekend as I was on the highway, traffic came to a stop and I noticed the car behind me braking far later than it should. So I mash the gas pedal and pull off to the shoulder. I avoided the accident, but...

It seemed like it took forever for the truck to start moving, something I really didn't notice until I had a car hurdling towards me

I noticed throttle response was complained about frequently on here and something that is improved with a tune.

Just wondering if anybody knew of a reason why GM would have a throttle delay? It's an obvious downside and I can't imagine it's a plus for drive-ability in anyone's mind, so I wonder if it intentional to protect a component of the car?

Maybe WOT in v4 mode is bad for the motor and the delay gives the engine time to switch from v4 to v8? Just throwing it out there and wondering if anybody has figured out why there is such a significant delay in throttle response.

silveradoz7113 · July 5, 2016

Most likely because these engines are "tuned" to maximum efficiency and to meet ridiculous emissions standards. GM is tweaking every last bit of economy out of these engines, not performance. My '13 is the same way.

KARNUT · July 5, 2016

If you were at a complete stop it's possible your tires were spinning when you nailed it and traction control took over killing the power. Any time I felt power drop, sure enough the light was blinking.

DanMan_S · July 6, 2016

Most likely because these engines are "tuned" to maximum efficiency and to meet ridiculous emissions standards. GM is tweaking every last bit of economy out of these engines, not performance. My '13 is the same way.

And the solution is stupidly simple because GM only needs to use a drive mode selector like in the Corvette/Camaro that lets you tune between sport, tow, eco, snow, etc, etc.

Heck, Ford has this in varying degrees in the F150's; sport mode in the regular trucks, full mode select in the Raptor.

muddkatt · July 6, 2016

The main reason for the slow throttle response is the drive train warranty according to everything I have read. By opening the throttle body butterfly very slowly, it prevents "shock" to the transmission, transfer case (if you have a 4x4) drive shaft and the differential(s). I saw a video and it took about 2 seconds for the butterfly valve to open to 100% with the factory tune. On the old mechanical systems it was instant, and with a tune on a drive by wire system it only takes milliseconds.

Trust me when I say I HATE the throttle response on the 2015. I bought the truck to have a dependable truck with a warranty, but I am seriously considering having the truck tuned so that it drives like it should. I tried the accelerator shimming due to flex and it made no difference on my truck. I found that the first full inch of pedal travel when the truck is in park only gains 500 rpms. Add that to a 2 second delay to WOT and launches in a panic situation is down right scary and dangerous. It might be good at the GM proving ground, but in real city traffic it sucks.

Asells · July 6, 2016

I suggest a tune for sure. I was was hesitant on getting one for the possible voided warranty if something went wrong. I definitely dont regret it. Ever since I put the tune on the throttle has really woken up. I have the diablo intune with just the 87 octane tune with firm shift and also bumped up the throttle boost abit, also disabled afm. Been thinking about getting a custom tune from diablew aswell.

truckguy82 · July 7, 2016

The main reason for the slow throttle response is the drive train warranty according to everything I have read. By opening the throttle body butterfly very slowly, it prevents "shock" to the transmission, transfer case (if you have a 4x4) drive shaft and the differential(s). I saw a video and it took about 2 seconds for the butterfly valve to open to 100% with the factory tune. On the old mechanical systems it was instant, and with a tune on a drive by wire system it only takes milliseconds.

Trust me when I say I HATE the throttle response on the 2015. I bought the truck to have a dependable truck with a warranty, but I am seriously considering having the truck tuned so that it drives like it should. I tried the accelerator shimming due to flex and it made no difference on my truck. I found that the first full inch of pedal travel when the truck is in park only gains 500 rpms. Add that to a 2 second delay to WOT and launches in a panic situation is down right scary and dangerous. It might be good at the GM proving ground, but in real city traffic it sucks.

My concern is that it has something to do with AFM, like maybe it's not good for the v4 to v8 switchover process if the vehicle is at WOT.

I think there is a good way to find an answer to this solution

One of us needs to research the lt1 engines and find out if they have the same delay. They have the exact same motor with the AFM, and I doubt a throttle delay is going to fly in a sports car. If they don't have this delay, then it sounds like you're correct and it's simply to save the drive-train.

muddkatt · July 7, 2016

My concern is that it has something to do with AFM, like maybe it's not good for the v4 to v8 switchover process if the vehicle is at WOT.

It will not swap from V8 to V4 at WOT and if the truck is standing still at idle it is in the V8 mode already. The only way to get it in the V4 mode is to be in motion and pretty much either burp the throttle or easy off of it so that you are coasting then barely apply the throttle. If it was an old school engine, I would say it swaps back and forth due to the vacuum that is either high or low. I am sure it is electronically monitored with a load of sensors now.

truckguy82 · July 7, 2016

It will not swap from V8 to V4 at WOT and if the truck is standing still at idle it is in the V8 mode already. The only way to get it in the V4 mode is to be in motion and pretty much either burp the throttle or easy off of it so that you are coasting then barely apply the throttle. If it was an old school engine, I would say it swaps back and forth due to the vacuum that is either high or low. I am sure it is electronically monitored with a load of sensors now.

I meant if you are cruising on the highway in V4 and then mash the gas pedal. I was thinking the throttle delay could possibly be there to allow the engine some time to switch from v4 to v8.

If the throttle response is faster than the AFM, you could theoretically be under full load in 4 cylinders and during the switch over process.

I have limited knowledge of how the AFM actually operates though.

DanMan_S · July 7, 2016

I meant if you are cruising on the highway in V4 and then mash the gas pedal. I was thinking the throttle delay could possibly be there to allow the engine some time to switch from v4 to v8.

If the throttle response is faster than the AFM, you could theoretically be under full load in 4 cylinders and during the switch over process.

I have limited knowledge of how the AFM actually operates though.

No, it's entirely for emissions/economy. The engine & drivetrain really don't care what the AFM is doing. There is a programmed lag before the engine is allowed to go into open loop fueling (dumping fuel into the engine and ignoring the O2 sensors). This is one of the first things that an ECU tune eliminates.

truckguy82 · July 7, 2016

No, it's entirely for emissions/economy. The engine & drivetrain really don't care what the AFM is doing. There is a programmed lag before the engine is allowed to go into open loop fueling (dumping fuel into the engine and ignoring the O2 sensors). This is one of the first things that an ECU tune eliminates.

This is what I don't understand, why wouldn't the engine care what AFM is doing. I mean AFM deactivates 4 cylinders? there has to be some sort of mechanical change to the engine otherwise the 4 "dead" cylinders would be engine braking.

Also is WOT closed loop? (haven't tuned anything since obd1 lol)

muddkatt · July 7, 2016

I meant if you are cruising on the highway in V4 and then mash the gas pedal. I was thinking the throttle delay could possibly be there to allow the engine some time to switch from v4 to v8.

If the throttle response is faster than the AFM, you could theoretically be under full load in 4 cylinders and during the switch over process.

I have limited knowledge of how the AFM actually operates though.

Got it...

What you described in your first post, and what I tried to describe sounds the same to me. If we are at a dead stop it will be in the V8 mode and if we stomp the accelerator pedal it takes a couple of seconds before we are TRULY at WOT.

The factory tune should allow WOT to take milliseconds if the truck is not moving. Hell, it already has traction control and stabilitrak so it should only govern back enough to keep from spinning the tires.

muddkatt · July 7, 2016

WOT - Wide Open Throttle, it should have nothing to do with being in open or closed loop.....there might be some minor adjustments to the fuel mixture but the damn butterfly valve on the throttle body should go from closed to wide open almost instantly.

truckguy82 · July 7, 2016

WOT - Wide Open Throttle, it should have nothing to do with being in open or closed loop.....there might be some minor adjustments to the fuel mixture but the damn butterfly valve on the throttle body should go from closed to wide open almost instantly.

Well that we can all agree it. We also know that GM did this intentionally.

The question is, did GM do it to protect the drivetrain, or protect the engine because it's an engine that has cylinder deactivation

DanMan_S · July 7, 2016

WOT - Wide Open Throttle, it should have nothing to do with being in open or closed loop.....there might be some minor adjustments to the fuel mixture but the damn butterfly valve on the throttle body should go from closed to wide open almost instantly.

The problem is that it isn't like that at all. The throttle body will be open, but the engine won't do the corresponding fueling immediately. You can actually see it on the dyno charts for the engine when you do a full throttle pull. The fueling and what the throttle body are doing are tuned seperately. This is why there is such a huge benefit to getting an ECU tune, as a large part is fixing the fuel to match the air flow itself.

This is what I don't understand, why wouldn't the engine care what AFM is doing. I mean AFM deactivates 4 cylinders? there has to be some sort of mechanical change to the engine otherwise the 4 "dead" cylinders would be engine braking.

Also is WOT closed loop? (haven't tuned anything since obd1 lol)

Yes, there is a mechanical change as the lifters are collapsable using oil pressure, but other than that, it can move from V8 to V4 mode nearly instantaneously without the rest of the drivetrain caring what it's doing.

Normal driving is closed loop (fuel is adjusted based on O2 sensors), WOT goes into open loop and starts dumping fuel in once the right parameters are met (typically the PE delay).