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Cobalt ss goes dead rich on letting go of throttle after re tune

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Good morning,

I was working with a buddy of mine to tune my newly turboed cobalt ss.

The car is a 2005 and has the lsj motor from the factory, it was factory supercharged and we pulled the supercharger off and went turbo.

After the swap it ran fine (afrs were good and no knock and it made some powerful to the ground) even before a tune, we went ahead and decided we were going to go e85.

We installed a new dw310 fuel pump and a set of used 79lb/790cc injectors.

Now here is the tricky part, because we are using hptuners to tune, and the cars maf can only read so much we had to do some scalling. On top of that the computer in the car can only read up to a 60lb injector so we needed to scale for that as well.

After all was said and done under normal driving conditions and wot pulls the car ran great And afrs were great And so was the timing, and we had no knock.

But there is an issue under letting go of the throttle, the car for a slight second goes lean like it should, but then dead rich below 10's.

Now also to note, when letting go of the throttle while in any gear going downhill the afrs seem to go up to 10.8/11 but that may be because the fuel that's being dumped is just sitting in the exhaust.

Now the thing is, the hptuners software allows me to see the direct fuel cut off and it's set to on (which is supposed to essentially close the injectors under letting go of the throttle, but it's not working from what I gather).

So I'm essentially trying to diagnose what is going on here, if there is an issue with my tune and tables down low causing this issue when I depress the throttle or does anyone think that the one of the injectors is staying open and dumping fuel on deceleration.

Also to note if I go to neutral after the car sweeps fuel tables and rpms jump up and down till the car balances itself out. I really feel like this is all more of a scaling issue then an injector issue but I'd like to hear people's thoughts.

Also this is my first ever post so please bare with me

Thank you

Also to note it stays dead rich upon deceleration I feel like I didn't explain that well enough.

Does your ecu KNOW it should do overrun fuelcut?

Or put in another way is your tps calibrated and is the voltage low enough on closed throttle to actually trigger overrun fuelcut?

I just re edited my post it meant to say dead rich on deceleration and letting go of the throttle. And the computer has its own calibration settings for tip in enrichment that I cannot change on initial throttle as well. The direct fuel cut off I can change though so I'm unsure as to what the issue is as I have this set to be on upon deceleration or letting go of the throttle.

Does the rich condition continue through the overrun or deceleration, or is it a momentary spike?

Scaled tunes in my experience are a complete pain in the arse. The trouble is that once you scale the load input you need to address EVERY table that has airflow as a load axis and adjust it accordingly. There are so many tables in the ECU that it's very easy to overlook just a single table and hence introduce some issues that can often be tricky to find.

What is your commanded AFR doing, and more importantly does it match your expectations? What are your fuel trims looking like in closed loop? You may find some hints here as to what is going on. Even without decel operational I wouldn't expect the AFR to be as rich as you suggest.

Also I forgot to respond to what you said. Yes it is automatically calibrated.

To Wesley, yes the car continues the rich spike throughout deceleration.

Commanded afr seems great, under wot and normal driving. Tables read great And the car makes very good power to the ground on minimal timing and a very smooth fuel delivery

Also Andre and everyone, I will do my best to grab an excel sheet this week of the pulls and driving we did so you all can see it. Maybe there is something dumb that I'm missing.

Well I'm dumb and I think I figured out what I did wrong. I remembered I have a blow through maf set up and I placed the blow off valve between the maf and throttle body like a dummy. I'm going to relocate it the opposite way in the grand scheme of things. I think that will clear up my issue.

What your saying would make sense but I would still expect the ECU know the throttle is closed and shut off the injectors. I've always avoided using blow through MAF set ups, if a customer of mine is going to that extent they should really go standalone and ditch the MAF IMO.

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