craig72

Hey gang,
I'm hoping someone here can help me with this issue. I have an '07 with 122k miles. There is an issue with the car when I attempt moderate to hard acceleration.
I have observed the following behaviors:

• If I hit the gas hard, the engine will suddenly cut out, almost as if it hit the rev limiter or VSC has kicked in.
• The engine does not die, it just appears to go back to idle.
• It is not a miss or stumble. It is a full loss of engine power.
• If I keep my foot on the gas, it will kick in and out, sometimes so suddenly that it will chirp the tires when it re-engages. It will do this until I let off the gas and accelerate more slowly.
• It seems to happen when the car starts to pull hard over 3k rpm.
• It can happen in any gear, as I have tried playing with keeping it in 1st, 2nd, or 3rd, and have observed the same behavior when I hit the gas hard.
• It is not pedal position dependent, as I have observed this at anywhere between half throttle and wide open.
• There are no lights when this occurs. I have held it in this state for almost 20 seconds at times, trying to get a CEL, but nothing happens.
• I have hooked up a TIS tech stream monitor, and there are no problems recorded.
• The car runs and idles perfectly aside from this problem. If I accelerate normally, it will run just fine.

It almost seems like a fuel delivery problem. Could the pump be suspect, not allowing enough fuel during high demand? Any other suggestions to check?
Thanks for any help you can provide.
Craig

mlacomb

I had something similar happen years ago on a Chevy Camaro - full throttle would cause it to stumble and die; which is slightly different than yours. My only take would be to get to a dealer and see if it's either electronic or computer related. You'd think if the fuel pump was not flowing properly, the computer would notice that you're at idle speed and throw a code though...

ESh

I bet it has to do something with throttle by wire.

GCL

iTrader: (1)

Have you had the ECU recently updated to correct for unintended acceleration ( brake override? )

The update will cut out the throttle when it detects both high acceleration and brake application. Perhaps there is a problem with the sensor that detects brake application.

It's dangerous when you can't accelerate when you want.

craig72

Thanks for the feedback.

You know, I thought about the throttle position sensor, but I guess I would expect that if there were a problem with that, it would happen throughout the entire range, not just under heavy acceleration. But I guess it is possible.

I did have the ECU updated for the unintended acceleration problem, but that was years ago. I thought it was only supposed to activate if the engine was at WOT and the brake was being depressed. I could be wrong.

Does anyone have any good suggestions for checking the TPS? If I remember correctly, there was a live data readout in the TIS software. Its possible that even my Lenova scanner will display, as it shows life data as well. Maybe moving the pedal in/out looking for a sudden drop in signal.

I still find it odd that the fuel filter is not more easily accessible. In every other car I have had, it has been an external item that is replaced regularly at 15k miles or so. Has anyone with a higher mileage ES had a fuel delivery problem or had your fuel filter replaced?

Thanks again for the responses.

oldgrump

Just for troubleshooting purposes have you tried disabling the Traction Control and VSC?

craig72

You know, I have not done that. I guess I figured that if those systems were causing the issue that the lights on the dash would come on. But it would be a good data point.

1. Make sure the car is in Park and the parking brake is disengaged before you start the car.
2. Start the engine.

Perform 3-13 within 30 seconds after engine start
3. Engage the parking brake.
4. Fully depress the brake pedal and then release.
5. Fully depress the brake pedal and then release.
6. Disengage the parking brake.
7. Fully depress and hold down the brake pedal.
8. Engage the parking brake, then disengage it (while holding down the brake pedal).
9. Engage the parking brake, then disengage it (while holding down the brake pedal).
10. Release the brake pedal.
11. Engage the parking brake.
12. Fully depress the brake pedal and then release.
13. Fully depress the brake pedal and then release.

I tried this procedure and the slip indicator light came on when I completed it. Does that mean that both the VSC and Traction Control are off?
I have not driven it like this yet, just wanted to be sure the procedure was good.

oldgrump

On the later cars (I've got a 2011) there is a TC button (just to the left of the instrument cluster lights adjustment ****) which is simply just pressed quickly to turn off the TC only, and if you hold the button for about 3 secs. and release it, it turns off both the TC and the VSC. But, the procedure you seem to have to accomplish on your '07 to disable both the TC and VSC does turn the "slip indicator" light ON (as you stated) just as when the TC button on the later cars is used to disable the TC and VSC. I think you can assume that your procedure does in fact disable both the TC and the VSC.......so see what happens when you repeat your acceleration tests now.

jbalian

This might help

http://gregstoo.com/why-does-my-car-...press-the-gas/

craig72

Okay, test is complete. It does not appear to be related to the VSC/Traction control. Behaved exactly the same way with the system disabled. I am going hook up my scanner and see if anything strange is being reported for throttle position when this occurs.

craig72

I hooked up my scanner to monitor live data. There were about 6 different TPS readings. I wrote down the ranges I observed, but do not have the paper with me. However, all seemed to move smoothly through the range as I pressed and released the pedal. My next step is to record the live data as the problem occurs and see what the playback shows me.

GCL

iTrader: (1)

Does the Techstream readings show anything regarding the brake pedal being applied?

If that sensor failed (i.e. showing that the brakes are applied when it really isn't) then that could confuse the "brake override" safety which prevents unintended acceleration when both the brakes and throttle are applied together.

craig72

I'm not sure if it does or not. Right now I'm just using my hand-held scanner, which reports some live data.

I will move on to the Techstream next, as I'm curious if it reports fuel pressure as well.

How do the fuel filters on these cars not need to be changed regularly?

craig72

I just found this info in another thread. My symptoms sure seem to point to a faulty brake indication.
My original thinking was that the car had to be at WOT for this to kick in. Turns out that is not the case. Any tips on diagnosing this one? I'm curious which sensor is being used on the brake pedal.

craig72

So here is an interesting data point. Yesterday while driving home from work, the problem was easily producible, happening with almost every 'sporty' acceleration. After I got off the highway, I needed to fill up b/c I was low on gas (light had just come on). After I filled up, I have noticed that the symptoms are not nearly as bad as they were. On the way home today, it pulled pretty good with no major dropouts, but still getting weak around the 5k rpm mark. I thought I had observed this on my last fill-up as well, but wanted to verify before I brought it up.
I did spend some time looking through Techstream data, and could not for the life of me find any parameter related to brake pedal travel, other than for the light in the back. I think the nanny update runs off of a different sensor, but I could be wrong.