Vehicle: 2000 C5 Corvette
Engine: LS1, stock cubic inch
Tuning Software: HP Tuners

So I gave my car over to a tuning shop the other day to have it tuned for the new camshaft. He put it on the dyno and started getting his baseline numbers with SD Tuning. When we started making pulls with the car we saw that it goes lean from 4500 rpm and up. The tuner would find the appropriate cells and add fuel and then make another pull. We were monitoring the AFR using (3) Wide Bands....one in the car, and two more running directly to the laptops. As we made changes and made the subsequent pull, the AFR wouldn't change a bit, and we were adding 15%-25% fuel to see what happens at times. We repeated this over and over and yielded no changes at all. When we started looking at the INJ Duty Cycle, the more fuel we added the lower the % was. So maybe we would start with 53% on the first pull then add fuel and on the next pull it would show 28%. That makes no sense because if we are commanding more fuel, the injector duty % should increase and the AFR should also change.

To verify and diagnose, we did a few things:
- Checked all grounds to make sure we didn't have an electrical issue going on
- Looked for vacuum leaks to make sure that we aren't introducing air from somewhere
- Swapped out my 42# injectors for 60# injectors to see if it was a fueling problem
- Checked the fuel rail for psi and made sure it was constant
- Went thru the HP Tuners settings to make sure that we didn't enable or disable something that may make a difference

None of those things worked. It was like someone is talking but nobody is listening, meaning that we were commanding more fuel thru the tune but the car was ignoring us. I don't see it being the PCM or the driver simply because the changes down low would take effect but up top we had nothing. As a sidenote, the 99-00 PCM's don't respond well to the Write Calibration Only option, so we would Write Entire. Every 99-00 I've seen in person doesn't respond to the Write Calibration option well, typically the gauges go blank for a while.

So aside from realizing that my car is having emotional issues... I am unsure of what else to look for that would be causing this issue. The shop that my car is at is looking over it again to make sure there aren't any vacuum leaks or grounding issues just to be on the safe side. We know for a fact that it isn't an issue with the fuel system, we have plenty of pump, injector, etc to handle this moderate build.

Any other advice?

 

If he "added" fuel and the injector duty cycle went down it sounds like he subtracted fuel by accident. Does this tuner know what he's doing? Was the tune updated with new injector data for the new fuel injectors and if its in SD mode was the MAF disabled?

 

We quadruple checked that as well, we actually added fuel. That is what is confusing us.... there is no reason for the inj duty % to change in the wrong direction. And yes, we adjusted for the new injectors right away.

 

Defective ECU??

 

I thought of that too, but if it was defective then it wouldn't be taking the changes anywhere at all...but it is. The lower RPM range responds to the commands from HP Tuners with no issue, it's the upper RPM's. I think I am going to find a bone stock tune from the repository and upload that and start from zero and see if that helps. Also going to use a smoker machine and see if I can find a vacuum leak somewhere.

 

"Defective" can be all sorts of things. It doesn't have to be all or nothing. Something is not allowing it to tune the upper RPM. You don't think some form of defect can do that?

 

I literally went through this exact scenario with a friend. It was a 2001 f bomb and wouldn't take fuel no matter what. Even to the point of 150 VE values.

He had some minor mechanical stuff going on, found a catch can issue, etc. even replaced map sensor. Found he had different injectors that what he was told he bought, and even correcting injectors didn't fix it.

What actually fixed it? Custom 1-bar SD OS AND total maf delete. Just failing the maf did not help. It was acting like a 99 does when you forget to update the secondary table. The idea was that the custom OS would rewrite the code path, and it got it working.

Edit -- Standard is with maf deleted entirely did not fix it either. Like I said it was like when you tune a 99 and forget to change the secondary VE table. But the 01 does not have the secondary table.

I am starting to suspect a major bug in V4 HPTuners.

 

You mean a 98? Almost all 99+ dont have a backup VE.

 

No I meant 99. Mine is a 99 and has the backup table. All the 99s I have run into have the secondary. The 00s I have done have only had the primary.

 

 

huh...weird. here's an oem 99 tune.

 

 

Idk. Maybe it is a mid year ECU update? But either way, I had never seen a report of what grip and I were seeing except when the tuner forgets to update the secondary table -- except no secondary table. So with no information, we sorta had to figure it out for ourselves.

We thought the OS might be corrupted which is why we tried the SD OS. But now, this is another incident of the same thing, so I'm starting to wonder if V4 has issues.

 

Someone miss labeled that, its a 2002 tune, That OS is only 2002. Prime example why using tunes from the internet are a gamble, even "stock" tunes.

 

Ive every stock stick and auto tune from 99 to 02 and that was listed as the 99. I can check again when I get to my PC.

 

I get my stock tunes from GM using SPS so I know they are 100% stock and correct for that VIN. The downside to the online tune deals is anyone can upload anything and say its whatever they want. A 12212156 OS is a 2002 only OS thats why there isnt a back up VE. A 99 camaro will have a 09373372 or 09360361 OS and a backup VE. A 2000 camaro will have back up VE also and OS 09381344.

 

Most if my tunes are pulled from cars. I suppose it's possible someone had it flashed to an 02 prior to me getting the car.

 

Yeah that 2156 OS is an 02 unified OS

 

We have done that alot of times over the years, the 02 OS is just a better starting point and its also easy to segment swaps or custom os with.

 

I did on my personal car also. At the time for the rolling idle tables. But I found the car ran better on the 02 OS especially after doing the SD OS.