Rev-Hang/Lurching/Accelerating Issues 2014 M/T

[Stefan de Wet 0]

No problem guys, glad I can help. Sometime it's very difficult to help someone over the phone or over messages especially if you cannot be there at the vehicle it self but what ever I can do to help, I will be glad to do so.

If there is any other problems you guys have related to any GM vehicle which I'm familiar with please ask and I'll se what I can do. I don't know everything and no one does, but it helps to talk about problems and a slightest idea might lead to a solution.

Have fun driving!!

[grsupra 0]

*Update*

My wife met with the GM rep and the service mgr. from the dealership we bought the car from today. The GM rep and service mgr. took the car out. When they returned, they said they re-created the problem, but only slightly. So they wanted to ride along with my wife driving and observe. She felt the car lurch while going down a hill so she put the clutch in to show them what it was doing, and the rpms held at 3000 rpm's for about 5 seconds. Long enough that she asked the rep three times "do you see it?" After returning to the dealership, he told my wife that there is nothing wrong with the car. "It has an anti-stall feature built into the car so that you can drive at 6 mph in 5th gear and it won't stall."

So they issue is still unresolved. At this point I would like to add, that my wife felt the GM rep was very rude, and "scolding" like she was an idiot who knew nothing about cars or how to drive. "Why would you put the clutch in when you entered the turn that day?" My wife said, "Because the car was pushing me through the turn even with brake applied". His comment, "you shouldn't do that, you put yourself in a dangerous situation". Ummm, what put her in a dangerous situation is the car accelerating through a turn!

To recap:

1). Replaced Knock sensor

2). Wife isn't used to little pedals...hits brake and accelerator at same time. They could tell from smudges on the side of the pedal (lol)

3). It's ok because it doesn't throw a CEL. Don't come back until it does.

4). You aren't taking your foot off the gas when the clutch is in.

5). Can't recreate problem.

6). This car is designed that you have to downshift as you come to a stop every time. Even in a panic situation.

7). The car is designed with an anti-stall feature in case you drive at 6 mph in 5th gear.

Seems to me that 6 and 7 are contradictory.

It is also telling to me that no one else on this forum has said "oh, yeah my car does that because ...." If this is a design feature somehow, it seems strange that we would be the only ones to notice it.

The GM rep waved his arms and asked "What do you want me to do?" She told him she just wanted what she paid for (meaning a new vehicle w/out these problems that aren't getting fixed).

Gotta love not only being able to get the car fixed, but then to be scolded by the person who is supposed to be helping you. Customer service at it's finest.

[Greg_E 211]

Wow, I guess I won't have mine checked. The best place to demonstrate this is coasting in gear down a hill where you can feel the car no longer decelerating and it is unnerving at the least. I haven't had this happen where I was getting pushed through a corner yet, but it might just be a matter of time.

I'm going to try the anti-stall feature on the way home and see what happens, I don't believe this is a feature and certainly not a good safety item.

[austex04 48]

Like I said, when it results in a accident, you need to contact a attorney, and attempt to sue both the dealer, and GM. I see another Spark appearing on a used Toyota lot soon.

[Stefan de Wet 0]

Hi guys, just a quick one, most of the GM vehicles have got a PULLAWAY assist function that is sophisticated ECM software, but I'll explain everything as soon as I get back. but I agree tht something is wrong with that M300 vehicle!! just damn frustrating that I cant be there to diagnose myself!!

Please hang on, I'll explain soon!

Enjoy guys!!

[grsupra 0]

Cool. I am very interested to hear what you have to say!

[Stefan de Wet 0]

Hi grsupra. On your model M300 Spark you have a CPPS - Clutch Pedal Position Sensor. The basic principle of operation is as follow, the ECM uses various inputs to carry out various outputs. So what happens is the ECM detects through the CPPS that you are releasing the clutch intention to pull away (keep in mind that the brake pedal is released and the hand brake is off and the engine is running) then at +- 30% clutch engagement the ECM will increase the engine speed by means of commanding the ETC/TAC (electronic throttle control / throttle actuator control) to "open more" as a result of engine speed increase of +- 50 - 100 RPM, this is enough to support the driver (and the engine) to pull away without the engine to stall and if engine speed increases above +- 1000RPM the "pull away assist" is not in action any more (the ECM disables the function by means of not commanding the ETC/TAC anymore other than just the normal intended throttle input from the driver). so here is a easy way to test this theory (if your M300 ECM software calibration contains this feature) start the engine, hand brake off, depress clutch pedal (do not select a gear - you''ll se why) release brake pedal and slowly release the clutch pedal, listen to the engine sound/speed, at +- 30% clutch pedal release the engine speed should increase by 50 - 100RPM. If not, well then your Spark most probably does not have the feature in its software, but it should have. And this is called Pull away assist.

So regarding what the GM rep told you about anti stall feature is true though.

Now, I thought about the problem you experience with your M300, a knock sensor will not cause this problem. Honestly, I think there might be a software or configuration problem on your vehicle that might cause the issue you experience. If your wife drive the engine at 1000RPM or below in 2nd, 3rd or 4th gear, the ECM might sense a "coming stall or jerk condition" and might try to compensate or avoid the stall and thereof as a result increase the engine speed. But if you intentionally drive the vehicle in this way and your problem is not recreated by your self, I doubt that it then is the Pull away assist anti stall that is causing the problem.

ECM (or any Control Module / system) reprogramming and calibration is one of my specialties and maybe your problem might be resolved if something is actually done to your M300 and not just by driving until the vehicle do the problem. As I said, I really want to be there and diagnose myself but I'm in South Africa, so that aint gonna happen soon.

Let me know what you and your Wife gets sorted out and please let me know what your M300 VIN number is, then I'll have a look whether there is revised ECM software for your vehicle that might resolve your issue.

Happy driving and please ENJOY YOUR SPARK M300!!!!!!!!!!

[Greg_E 211]

I did a little test the other day to see what I would find and I might have some suggestions.

If I left the car in gear and used the brakes to slow to under 1000 rpm, the car did indeed start to push to the point where I was concerned the brakes might not stop it. I'm pretty sure if I pushed on the brakes hard enough it would stall but I didn't want to test this theory. So I am able to reproduce this problem in this RPM range (example a slow 90 degree corner). And this tends to support what you were told and the post above about stall control. So my only other question would be, is this happening at rpms that are higher than 1500?

I'm afraid the only suggestion I can make is to use a lower gear when turning a corner, and put the clutch in sooner if the corner is going to be a really slow turn. I don't run my car at lower than 1500 to 1800 rpm because I've found it is not happy. That stupid shift light only has an up arrow and I've found evidence that it will light when it really wants to be in a lower (numerical) gear, my general rule is to run at or above 2000 rpm in any gear and so far my fuel mileage tends to agree that I'm still very economical. This also includes turning corners which often means I am riding the clutch or coasting around corners in the city because shifting into first while moving is not smooth.

All that said, I would see if you can get the dealer or the "specialist" to agree to flash the computers in that car and see if things improve, that would be cheap enough to where they might do this just to get you off their backs.

Wish we had more people who are trained to service this car posting here, sure is nice that Stefan is posting. That's a hint to the corporate Chevy/GM people that read these posts, it goes a long way to better marketing if people can have access to someone knowledgeable with the product because it gives people a feeling of security and they are more likely to buy the product! Or maybe this is too much common sense and that's the reason they won't do it.

[psquare75 35]

5th gear and 1000 RPM doesn't sound like a good idea in any vehicle.

[grsupra 0]

Thanks Stefan and Greg for your imput and help.

Whatever happened to the day you could just get in your car and just drive it? Why should you have to drive it a certain way so some un-needed sub system doesn't kick in? I think that,like has been suggested, one of these processes is not performing as designed and causing the issues. Do we really need an anti-stall feature for some one who wants to drive 5 mph in 5th gear? Instead they should be referred to somewhere offering driving lessons.

They way the dealer AND GM reps have handled us only makes it more aggravating.

Stefan I will pm you the vin number. Right now the Mrs. is at work.

So far, it has been Impossible to enjoy this car.

Edited October 5, 2013 by grsupra

[Stefan de Wet 0]

I understand that enjoying is not part of driving if you have problems with your new vehicle and I respect that, I just hope that GM over there is able to resolve your issue before they loose a valid customer!! The pull away assist is a driveability feature but also has its positive workout on the vehicle. If any engine is under load below a certain RPM, the server vibration and labour might cause damage to mechanical parts over time and especially when the engine is labouring at say 400RPM the engine oil pressure is so low at that time that the bearings might be damaged because the force of combustion onto the piston and the big end bearings is still the same!

The pull away assist feature is not active at engine speeds above 1500RPM so any sudden unwanted acceleration above 1500RPM is a concern.

Let me know what you get done with your local dealer and then we'll take it from there!

[grsupra 0]

After my wife's experience with the GM rep and the Service Manager, I don't think there is anything else they will do, since the GM rep pronounced that there "is nothing wrong with your car". Which basically means, "Get Bent". So the ball is in my court.

I buy new vehicles because they are warrantied, and there is no mystery as to their condition, or worry if they were maintained or abused. I understand things can go wrong...a bad solder here, a defective part there. What I don't understand is how they can say there is nothing wrong after re-creating and witnessing the issue.

I appreciate your help, Stefan, and respect your knowledge and skill. Unfortunately, the GM employees that I am dealing with are your polar opposite.

[Greg_E 211]

I would still ask them if they would be willing to try one more thing and reflash all the computers or at least the one that deals with the fuel systems.

[Greg_E 211]

I did a test last night and I'm not sure I like the results... In fifth gear the car will go 20 miles per hour on level roads with foot off the gas until it hits something. The engine is not happy doing this and I shifted down into second to accelerate back up to speed, but it does tell me that making a 90 degree corner in fifth gear is not something you should be doing.

[grsupra 0]

Scary, isn't it. Today while stopped at a light, with the clutch in, the engine rev'd to fuel cut until it shut down. Just like before they replaced the knock sensor. Tues my wife has to take it to Pgh for an expert to drive it. Only this expert is working for us, not GM

[Greg_E 211]

Mine is starting to slow down less when I'm coasting in gear, pretty sure it is being commanded to add fuel and air ever if the RPM is up around 3000. On many bigger hills I can see this happening on the instantaneous mileage setting because it will show 99mpg when the car is under engine braking, and 72 when I feel it pick up again. It's getting really annoying.

[grsupra 0]

I'm sorry you seem to be feeling some of the same issues we have. I still believe it is a system malfunctioning, and not just the design. The "pull-away" program is something I don't see the need for, and I have come to believe it is buggy and causes these problems on my wifes car.

[NoSprak 17]

This is somewhat "normal" on newer cars.

When cold, the engine needs to run fast (yes, that's bad for a cold engine) to heat the catalyst up quicker. The quicker the catalyst can heat up on cold start, the longer it lives. So, because of that, they have to run a pig rich engine at 2000+RPM when cold and dump a bunch of raw gas in the catalyst.

It's asinine. Also the reason I can not put an intake or exhaust on my Focus. I live on a hill and often coast down in neutral (manual trans). By the time I hit the stop light at the bottom, my car is idling at 3000RPM. Same thing when I start it on a cold morning - it idles at 2500RPM for a few minutes.

The rev hanging is because of two things. The first - mentioned above ... it's going to idle faster when cold to dump raw fuel in the catalyst to heat it up.

Second is, the EPA doesn't want the engine drawing a vacuum quickly. If the throttle is able to snap shut (as it should be able to ) it will draw vacuum quickly, but the engine will still be injecting fuel .. .this causes high NOX emissions.

[psquare75 35]

the fuel injector pulse is tied to throttle position AND RPM.. This isn't a carburetor.

[grsupra 0]

The car does it when it's completely warmed up. And like I mentioned, will rev-max and shut off too.

[NoSprak 17]

the fuel injector pulse is tied to throttle position AND RPM.. This isn't a carburetor.

I agree - but that's what the EPA says and why they make the throttle hang.

Edited October 18, 2013 by NoSprak

[grsupra 0]

To those who tried to help...a sincere thank you.

To GM who monitors this site, and won't stand behind or fix their products, or even acknowledge them...this is the last GM vehicle I will ever buy, not because of the unresolved issues, but because of your poor customer service, and dis-interest in resolving these issues.

[psquare75 35]

I do downshift to slow down and often don't touch the brakes.. I figured 1.2l of engine has A LOT less rotating inertia than a 7.5l V8, lol.

[dzimmerman911 0]

I took my 2014 Spark with 150 miles and knock sensor issue back to dealer to give it back. It's infotainment screen intermittently goes blank also.

[bensemailis 10]

awe, thats too bad. I would have liked to have known your build date.