I'm writing this for a friend that I helped over the weekend.
The car is a '97 LT1 with OBDI PCM and Edit which was bought used with only one file that was allegedly tuned to the following application.
Car has ported heads/intake, GM847 cam, Hooker LT headers, no cats, stock 24# injectors, ported MAF.
Took it to the dyno to get tuned on Friday. Make a baseline run and find out it's running extremely lean. Fuel pressure stayed constant at 40psi but when a WOT run was made it would go to 30psi. We changed the pump to a Holley 255. The pressure then would stay at 40psi during WOT. We figured we found our culprit.
Take the car back to the dyno yesterday. Made a baseline. Car made good power to work with and was between 12:1 and 13:1 with it getting a bit rich on the upper rpm range. Tuner makes some changes to the fuel (not specific on what since I'm just clueless when it comes to Edit).
We make another run and the car was right back running about 17:1.
After that NO MATTER what changes were made (including adding about 60% duty cycle) the car would run lean. It's as if the PCM just would not respond to any change whatsoever. We went back to the original "customized" calibration and did another pass yet came up with the exact same lean results.
We did not start off with the stock calibration. As said the Edit software was bought used with one file that was somewhat "customized" for this application using no dyno and no wide band.
So.. with this being said thoughts were tossed around as to why car is running lean. It was said the Edit file could be corrupt, but that wouldn't explain why the car made a good run with the original "customized" file and then run lean for all runs that followed including going back to the original "customized" file. It was mentioned the FPR (which is stock) could be bad. Of course, none of us watched the pressure for the first good run. For all runs after the pressure remained at 40psi.
I'm reading the controversy on ported MAF's and am now wondering if this could be an issue. Not sure if the MAF tables were even looked at. Again.. how would we get a good run before anything was done?
Injectors... they are the original stockers with about 100K on them. Yet again.. good baseline run. Bad runs thereafter. Not sure if injectors would be to blame?
Any thoughts/ideas would be appreciated.

 

Compare what you have with a stock file so at least you know what has been changed. Are you making changes to the PE tables? That's were you need to go to work on you lean at WOT. That is as long as you fuel constant is set correctly.

 

what is the duty cycle on the injectors at max rpm?
I would think the stock 24# would not be able to
suppourt the fuel needs of the 847.

 

I hit 103% DC with 24lb injectors on my 224/230. Upgraded to 30lb and it maxes about 80 DC now.

 

Thanks for the replies.
I don't think the injectors were maxing out because of the good baseline run we had. However we are going to go with 30#'s as soon as the problem is solved.
The only program we have is the one that was sold to with Edit. We have nothing to compare it to.
Speaking of solving the problem, I have a very sneaking suspicion the file is corrupt. I found out today the PCM was constantly in open loop. The learn function is disabled (can't turn it back on for some reason). We were able to get the PCM to go into closed loop but now it's always in closed loop even at WOT. I think it's time to just reflash the PCM and start fresh.

 

The only thing I can say is you were probably in OPEN LOOP durring the other runs or vise versa, making changes in the PE table will do nothing to the A/F in OPEN LOOP. The first run was probably in closed loop, those two can be FAR off. Again PE table only makes changes to closed loop.

matt.

 

PORTED MAF is causing problems. Changing the MAF tables for a ported MAF does NOT fix this issue.

Put a stock ( descreened is ok ) MAF on and return your MAF tables to STOCK, then make sure your injector constants and offsets are entered correctly as well as the engine displacment values.

THEN start your tuning, you will find you will only need to adjust your PE tables and SPARK curves to get your AFR in line and pick up some Horse Power.

Below is what my car did with the PORTED MAF on the dyno....take a look at that Air Fuel Ratio line.

click for picture http://www.tripintaz.com/pic/dyno1.jpg

once the STOCK MAF and TABLES went back on the AFR line was horizontal startign at 12.4 afr and ending up at 11.9 afr at 7000 RPM. And yes, I intentionally left it a touch on the rich side.

 

Are you sure about that? WOT is kinda like open loop... Its open loop mode during closed loop is how I see it so PE changes should be reflected no matter what.

 

The car does not enter open loop mode at WOT, It enteres power enrichment mode which IGNORES the 02 feedback ( just like open loop does )

In OPEN LOOP mode the PE tables are ignored as well as the 02 sensors.

 

All good info. Thanks again!
Yes I will be telling this clown to get a stock MAF put back on before any more tuning will take place.
I cannot remember if any of those pulls were during power enrichment mode. We were more paying attention to knock since the car was running so lean.
I'll ask and find out.

 

If you use a scanner you will still see PE mode becomming enabled when you hammer the gas in Open loop, but the PE table is still ignored all together, you can have "-40" in the PE table & have the same AFR on the dyno as "+40" in the PE table.

matt.

 

If you are making changes in the software and the car is not responding, that strongly implies a mechanical/electrical problem (a la the fuel pump) and not programming.

Rich

 

changes made = not responding can also be open loop, if changes are in PE I repeat.

 

We did the following:
I don't believe PE was engaging when we were logging our WOT runs until we were able to get the car in closed loop. Not only that but we are seeing 23mph instead of the 17mpg after the changes were made. Still not sure why we are still seeing "Learn Disabled". Maybe it takes much longer to engage? I dunno....
The PCM will be reflashed by a GM dealer and we are going to start over.
All replies have been greatly appreciated!!!