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Hey All, so ever since I've had my 04 Z06 it's exhibited a bucking when at the lightest of throttle.
I've not looked at fuel trims but I have a BT OBD2 adapter and several apps on my ph. I think I could try to watch them as it does this.
1. It's inconsistent in intensity but it almost always happens.
2. Some days its slightly noticeable and other days its very annoying.
3. Speed and gear doesn't seem to matter. But its most noticeable up in 4-5-6 gears
4. This only happens at the very lightest of throttle input.
- Like your going down a slight incline but the car is not coasting. Needing just the slightest amount of throttle to keep speed.
- It will happen with cruise on or off.
- Steady speed 40+ mph is most noticeable. But.. 15mph in 2nd gear will do it too.
- Decent headwind or going uphill where it needs a little throttle and it DOESN'T happen.
5. Engine temp: It seems to mostly NOT happen when the engine is cold. Definitely happens after the engine is fully warmed up. BUT.. not always true.
6. The engine never ever dies or even acts like its loosing power. It's at those extremely light throttle inputs where it seems to have a on/off feeling and causes the whole drivetrain to buck.
It feels to me like the fuel is being shut off & on. It's got that hard on / off feeling.
As far as a vacuum leak is concerned see what your fuel trims look like at idle...anything over 10% you should worry about...if over 10% raise the RPM to around 3000 RPM and hold it there for a few minutes...if you have a vacuum leak the fuel trims will decrease...the long terms may take a little while !!
Hey All, so ever since I've had my 04 Z06 it's exhibited a bucking when at the lightest of throttle.
I've not looked at fuel trims but I have a BT OBD2 adapter and several apps on my ph. I think I could try to watch them as it does this.
1. It's inconsistent in intensity but it almost always happens.
2. Some days its slightly noticeable and other days its very annoying.
3. Speed and gear doesn't seem to matter. But its most noticeable up in 4-5-6 gears
4. This only happens at the very lightest of throttle input.
- Like your going down a slight incline but the car is not coasting. Needing just the slightest amount of throttle to keep speed.
- It will happen with cruise on or off.
- Steady speed 40+ mph is most noticeable. But.. 15mph in 2nd gear will do it too.
- Decent headwind or going uphill where it needs a little throttle and it DOESN'T happen.
5. Engine temp: It seems to mostly NOT happen when the engine is cold. Definitely happens after the engine is fully warmed up. BUT.. not always true.
6. The engine never ever dies or even acts like its loosing power. It's at those extremely light throttle inputs where it seems to have a on/off feeling and causes the whole drivetrain to buck.
It feels to me like the fuel is being shut off & on. It's got that hard on / off feeling.
The engine feels like the fuel (or ignition) is shut off / on / off / on ect.... and all the slack in the drivetrain goes from unloaded / loaded / unloaded / loaded ect....
It only happens at the ever so slightest of throttle. Like cresting a hill or going down the slightest of a grade where you need only a hair of throttle to keep speed. Decelerating and accelerating are perfectly fine as is all other running and starting situations.
From my time tuning fords with SCT proracer, I could have made it feel this way by setting the fuel cut (for MPG improvement) to happen only milliseconds after throttle reduction. Where as the factory tune has something like a 2000ms delay after throttle close before fuel cut. So there is a part of me that knows it could possibly be the tuner trying to maximize MPG. Just maybe set a little too quick. (in my tunes I'd set the delay around 400ms)
On the other hand its severity is NOT consistent. Which makes me think it might be a mechanical thing like a small vacuum leak. But I have no other symptoms of a vacuum leak.
Kinda hoping someone might have seen the same phenomena and can tell of their experience.
Last edited by wydopnthrtl; Mar 22, 2020 at 01:52 PM.
I sent the PCM to ECS for a mail order tune and after about 500 miles in differing conditions and temperatures it now runs perfectly.
(Doug asked me to clean the MAF which I had already done.. but I did again anyway (it still looked new))
So in this case it seems my problem was the tune that was on the car.
Last edited by wydopnthrtl; Jun 4, 2020 at 06:09 AM.
Glad you got it fixed. I was going to say that it sounded like a tune issue to me.
Doug didn't explain what it was. So all I can draw from is my Ford tuning experience where you turn fuel off upon throttle close. Felt to me like was set way to sensitive and had no time delay. I donno.. could have been something else.
I was on a road trip and it started doing this again and there was a big off / on steady cruising at 70mph. Biggest I've ever experienced... it was like shutting the key off / on. Check engine light popped on and stayed on. Car run ok though. Checked the DTC and it was a MAF malfunction. I've cleaned it several times and it looks ok to me. Installed a new GM MAF and it ran perfectly for about 30 miles. It's now back to 95% ok but every once in a while still bucking.
I think my next two tasks are to check for a vacuum leak and maybe try to data log the fuel trims and MAF.
What was the DTC ??…these MAF sensors don’t operate by magic so you will have to address the MAF wiring…could be a bad connection at the sensor…it’s 3 wires and it’s a 12 volt supply, signal, and a body ground…if you can find a DIAGNOSTIC shop (not a Joes Auto Repair) they will use a scope plugged into these wires while the car is going down the road and see what’s happening !!
You need to report the MAF readings along with the long and short term fuel trims. Also it wouldn't hurt to see what the O2 sensors are doing since you have headers. I would talk to ECS since they did a tune for you and see if they have any suggestions. I think this kind of bucking is usually do to a lean surging while the throttle is almost closed but not really closed.
You need to report the MAF readings along with the long and short term fuel trims. Also it wouldn't hurt to see what the O2 sensors are doing since you have headers. I would talk to ECS since they did a tune for you and see if they have any suggestions. I think this kind of bucking is usually do to a lean surging while the throttle is almost closed but not really closed.
Yep this is exactly what I'm thinking. I have a license of SCT that I used tuning fords but it doesn't do me any good. I'm thinking of getting two licenses of HPT and just do it myself. (I have another car I'd like to tweak some things on)
My thought... since it was perfect for 30 minutes after the new MAF (w/batt disconnect) this is a learned condition. I also just got a smoke machine that helps finds leaks.. so I'll give it a try over the yr end break. At least I could rule that out and gain some experience using it.
C5 diag... I lost my notes which one it was. (3 months ago) As I recall it was MAF though. When I first got the tune, I asked ECS about this and he suspected I had a dirty MAF. But I had properly cleaned it.
When this failure happened w/the MAF 3mos ago, I just decided to get a new one.
As-is it is a bit better than before. But in certain weather conditions it'll buck at the slightest throttle opening. And I mean its right there at like 1-2% opening. Just a hair off fully closed. Always stays running and runs clean everywhere else.
Last edited by wydopnthrtl; Dec 16, 2021 at 12:30 PM.
This bucking could also be a TPS signal dropping out…I’d check the sensor terminals for fretting and also a terminal tension check could be done..make sure the terminals look aligned !!..you can get this kit cheap on Amazon…good to have !!
…a scope is best to look for this fault…a voltmeter refresh rate is just too slow to pick up the voltage dropping out…a scope can see millions of voltage samples over a millisecond !!
This bucking could also be a TPS signal dropping out…I’d check the sensor terminals for fretting and also a terminal tension check could be done..make sure the terminals look aligned !!..you can get this kit cheap on Amazon…good to have !!…a scope is best to look for this fault…a voltmeter refresh rate is just too slow to pick up the voltage dropping out…a scope can see millions of voltage samples over a millisecond !!
Will do. Is there a DIY'er type of scope that doesn't cost too much?
Will do. Is there a DIY'er type of scope that doesn't cost too much?
There are some pretty cheap oscilloscopes on Amazon. The one listed below first connects to a laptop and you use the supplied software to display the waveforms. The second one is a stand alone. I would get one of them and see how it works. Should be good for automotive signals, I don't believe that they are really 100mhz scopes fully functioning scopes. If they don't work for you, you can just return it to Amazon.
Engine bucking - need advice
