Grandsport with: supercharger, downpipes, methanol spray, catch can, HP Tuners, MAF tune

I've had a long series of issues with my car and it would almost take a book to tell you the story. Most of the problems originated from a poorly installed catch can (but let's not get side-tracked). All problems have been fixed and the car was tuned a dyno. No check engine lights and everything is perfect except for one thing...

This problem has been noticeable for more than a year while a lot of the other issues were happening, and while they have all been resolved, this one has stuck around. If you accelerate hard, the car runs strong. No issues. The problem I'm about to describe can come and go, but it's most noticeable after a strong pull in first and then shift to second, and then light-to-medium acceleration. When I apply maybe 20-25% pedal, the car has a very slight power stumble or loss (it's not running "normal" at the pedal position - pedal is at 25%, but power is 18%). I leave the pedal at the same position and wait, in about 2 seconds the power loss disappears, and the car accelerates slightly to catch up to the pedal position. At this point it's running great and you can do whatever you want with the pedal until you shift into third. This then repeats itself. The difference between normal power and this power loss is sometimes enough to scratch a tire when the power comes back to normal. It's actually safer to drive the car a little hard because you have predictable power at a heavier pedal position.

I don't think a tuner will see this on a dyno because they're using wide open throttle. Is this a fuel delivery issue? Spark? Remember, no check engine lights. Please give me some ideas to start tracking down. Thanks for your help.

 

I’d be scoping your TPS and APP sensors looking for any dropouts on the signal wires !!

 

I'm not ruling anything out at this point, but I think you might be saying that because I didn't give a completely accurate description of the problem. It's not that the pedal position is inaccurate, I can feel that the car is not running "normal." When it's in the power loss scenario, it's like the car is running on 7.5 cylinders. It's not smooth. Then after a few seconds something clears up and the car is normal. It's this change from power loss to normal that causes a slight lurch. If I shift into a gear and just go for 75% throttle or more, there's no issue. It's only apparent when I'm at 25% throttle. I think that's why my original description of the issue had so much to do with pedal position. Also, the problem clears itself in a few seconds without me changing the pedal position.

 

You need to log the car with HP tuners an see what's going on , what is the commanded pedal , what is the throttle blade angle , there are many parameters in the tune that could cause this

 

If you can “graph” some data PIDS with a scan tool you can graph RPM, vehicle speed, O2 sensors, fuel trims, TPS, APP, MAF…in addition to these PIDS having a scope to look at fuel injector and coil pack current ramps would rule these 2 items out…may be more cost effective to take the car to a diagnostic shop that uses all this equipment to quickly identify your issue…can get expensive shot gunning parts !!…also good idea to check for any DTC’s that may give you guidance.

 

My thoughts too.

 

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My only issue is that dealerships fall WAY short in diagnostics !!…I’ve seen it multiple times on this Forum from members…dealerships only use scopes (Picoscope) for instance to diagnose only NVH issues…99% of dealer techs I’ve spoken to over the years don’t even use a scope…a scope is ESSENTIAL to diagnose cars these days.

 

Did I miss something , nowhere in the post does this guy say that the work was done at a dealership .....This is a heavly modified GS with a supercharger that was on a Dyno and is tuned

Dave

 

I know this wasn’t done at a dealership but Chevy Customer Service contacted him about having a dealership do the work and fix his car…I replied to this customer service that their dealerships are CLUELESS when it comes to diagnosing their cars…I don’t care whether a car has a supercharger or turbocharger on it…diagnostics is diagnostics !!

 

Thanks guys. I will try to do some logging and see what I can find. I'm new to the HP Tuners and I know how to operate the basics, but understanding what all the numbers mean is a whole 'other language.

Yeah, this has nothing to do with a dealership. I think it shows how clueless they are to even reply to this thread and suggest I come see them. No dealership would know anything about diagnosing this car and likely wouldn't even attempt it once someone who knew what they were talking about got involved. I appreciate the effort, but that was misplaced.

I'll try some logging and see what I can come up with. Thanks.

 

LOL take it to the dealer comment from Chevy. Please DO NOT do this.

To the OP, if the car is mechanically sound, my first guess would be that the tune needs adjusting. It could be a simple as Driver Demand needs to be calibrated better in that area or it could need some Virtual Torque and VVE changes to fix. This kind of issue is common with "MAF only" tunes on cars that are heavily modified, as they do not address the transient fueling correctly.


Make sure you log the correct Torque and Airflow PID's and the issue may be obvious to an experienced tuner. Many of us are over on HPTuners forum. You may find some assistance over there in the Gen V section.

 

Thanks so much. I'll attempt to get the right things recorded and I'll check out the Generator V section.

 

Ok. I've posted in the GEN V section of HP Tuners and uploaded a scanner file. You can see the thread here. Please feel free to respond here or there. Thanks for any help.

 

If Sultan is willing to help you over there, let him. He knows what he is doing.

 

Sultan helped and I think my problem might be solved. More driving is required to know for sure. I don't know if I'm getting all of the power I should our not, but at least the car drives so much smoother. He said something about torque mgmt and timing. I wish I could tell you more, but from my short test drive I can tell you that's it's much better.