I know some of the GM GENIII PCM's have an enrichment ramp in rate table.. unfortunately my P01 does not have that table.

@HPTUNERS, it would be a really nice feature to have. I'm getting close to selling all my HPT stuff to get a holley EFI or Something similar for the following reasons.


I've been struggling with lean tip in for months now, I've done extensive trial and error testing without any real results. (Not good ones atleast)

So, during fast throttle changes the VCM scanner is showing that its entering PE and commanding the right target AFR's like I'm asking it to do. Unfortunately I stay in the 14.0+ range from the time It starts commanding PE to 95kpa..

at 95 kpa regardless of RPM it all of a sudden drops straight from 14.0+ lean to .5+ rich bellow my command for a second. From there on to 205kpa it is on target and starts to actually pull. Trainsient power response is terrible until the car is into boost a lb or two beacuse of this lean condition.

The car;

car is a 1999 C5, forged 347ci with a Turbo cam and rear mount twin turbos. (Only 3 degrees of overlap on the cam)

2 bar OS. Car is driven daily in OLSD with STFT on.

My fuel system is 1:1 boost referenced.

I've already confirmed all my injector data is good and the tune is set up right for the 1:1 regulator.


My attempts to un-F%!k this issue so far..

extensively tuned the VE table, even adding quite a bit to the trainsient KPA areas between normal cruising values and the 95kpa mark. Adding to the point where numbers were much higher in the 70-90 range than they were at 95kpa. Didn't fix the issue.

All my PE delay tables are set to 0, the TPS and Map enable are verry low, i've even put the car into full time open loop and I'm still getting the same lean spike with fast throttle openings / positive map changes.

I then thought that adjusting tables in the trainsient fueling tab was going to be where I'd have some luck, not the case. I spent countless hours adding to the fuel to wall impact factor table and impact factor gain table and while I did see results, they were not good ones.

The last attempt I made was adding to the injector offset vs volts vs kpa table in the MAP range where I see the lean spike. (Just above cruising 55kpa all the way to 80kpa. That also did not help at all.

Anyone else ever dealt with an issue like this?
were you able to fix the issue or did you end up swapping PCM's / go to a standalone?

last note, fuel pressure is good. Even if it wasn't, the way I was raping my tables I should have seen atleast some improvement in tip in. There was none.

 

At risk of sounding like I am on HP Tuners forum, post a tune file at least, preferably a log, with lots of data being logged.


And there should be no raping going on.

 

Post a tune file. If your delay is set to 0, it shouldn't be. 0.01 is fine, but not zero.

 

Taking a shot in the dark here, since we can't see the tune or log, but what are your injectors doing during this time? Are they maxing out their limits set in the data tables? I have to cut mine down so far to correct an opposite problem. I had rich decel, which was really bad, and showed numbers as far down as -20, -25, so on.... This is also not good as it can lead to other problems, but certainly not as bad as what you're describing.

The fix ended up being chopping the minimum injector pulse down starting by the percentage shown in the tune, however, this ended up being far greater than the numbers showed, due to sensor inaccuracies at that wide of an error. So having a look at your short pulse adder, and minimum injector pulse, and default injector pulse (I just make the last two match and it seems to work fine). Just tune the areas affected obviously, but for a lean spike I don't know if it will help. Certainly does for rich spikes when the VE is asking for 5% on decel cells. As in set to 5. Not changing that much lol. Clearly its in the data at that point. I even shot the **** with one of the dudes at injector connection, and he agreed with changing the data to correct the issue. In my opinion, if the data isn't working, then it needs to be tweaked, so at that point it's fair game to do some adjusting.

What size are the injectors anyway? Are you out of injector perhaps? Has this always been a problem?

 

Can you explain this? I’ve not heard this mentioned before. I set that to 0 and have no delay entering PE mode.

I’d like to see the tune file as well.

 

0 can cause weird things when you're on the edge, since it wants to (instantly) switch in and out of pe mode. An inperceivable delay (.01) prevents this.

 

He has the same post over on the Corvette forum.

Reading his post, he states that the scanner is showing it goes into PE as commanded. Yet the reported AFR is lagging. And he can feel that in the cars performance.

As Chopper Doc mentioned, a log file would show what the injectors are doing for pulsewidth during this transition.

 

Could also be the fuel pump too. What is the fuel pressure doing through this transition? If it’s a stock pump, then that’s your problem right there. More shots in the dark. Lookout down range.... but I guess he’s not interested in responding now?

 

Seeing as how that ramp rate table does nothing on the Gen3 car calibrations it doesn't matter that you don't have access, it's also why it's not defined in the editor for your OS. I've tuned more Gen3 SD setups over the years than I can possibly count and I've never had that issue and without a file and a datalog posted it's pure speculation.

BTW hopefully you aren't using the Boost Enrichment PE tables as your main PE adder because I could tell you exactly what you are doing wrong.

 

Injectors are fine. Well within an acceptable PW.

I found a file that has the ramp in rate table and I licensed it file from the repository. File is for a stock 2002 C5 Corvette with the same transmission and controller that's in my 1999 C5. (P01 ECU / T56 trans)

I'm going to transfer all my data over to this 2002 file, do the 2 bar OS modification to it then write entire to my 1999 C5.

After that I'll add the rest of my data (VE and BE values)
As far as VATS goes, the re-learn process seams pretty simple.

That will give me the ramp in rate table and should fix my issue.

HopefulHopthe write entire dosent brick my $h!t..

Quite a few guys on the HPT forum said that they've done it without any issues so that gives me hope.

If all else fails and it bricks it I guess it'll just be a good excuse to go with a stand alone. (Looking at the Holley Dominator)

 

Technically any write to a PCM can potentially brick it, it just doesn’t say that on the write screen. It still would be nice to see this file, as this could be something simple. If you feel this is the way forward, then I get it, as it gives you hope. Been there, and I’ve also been let down only to discover my mistakes later. Not saying that’s your case, I’m just saying.

I’m also curious how this is OLSD with STFT on. So it’s Open loop closed loop at the same time? I might be splitting hairs with that line, but technically STFT’s are what is defined as “closed loop” as the PCM adjusts to hit a target based on airmass model, whether that comes from MAF or VE it’s quite irrelevant. O2’s on and correcting = closed loop.

 

Also I would be looking at the fuel pressure during the transition. You could be getting a dip causing the lean spike. Large injectors can make up for the drop in pressure, but it’s really hard to spot in the log. Best way is the good old rail pressure gauge. I’d definitely take a look at this to see if the pump is doing it’s job. Sometimes it’s the little things that get overlooked. Still a shot in the dark, but never assume anything without seeing data.

 

Fuel pressure is good, verified through data log. My pressure sensor is right on the rail.

Voltage is fine, also verified through the log, no drop.

Idle is closed loop with STFT but my PE enable is set verry low so majority of the time I'm in OL. I did it this way to see if already being in OL when stabbing the throttle would make any difference in my tip in. It did not.

I've tried so many different things and checked so many others that at this point I'm convinced it is the lack of a PE ramp in rate table in my current OS.

I'm going to do the write entire some time next week with the 2002 vet file and hope for the best. If it all works out like I think it will I'll gain that ramp in rate table and some better resolution in my spark timing tables.