Hello,

I am working on tuning a 1996 LT4 with a Pro-Charger. Want to use Speed Density with a 2BAR MAP. I currently have the car running with the 2BAR MAP. But I have an issue with the Short and Long trims. They will not kick in during closed loop with a 2BAR MAP. I am currently running in the 700-2000RPM range as I tune this car.

I change the map back to 1BAR and magically the trims kicked in...

2BAR
Scanner says 23kpa with at idle - Barometer says 55.35kpa >>> 0 trims

1BAR
Scanner says 31kpa with at idle - Barometer says 103.69 kpa >> trims kick in

What am I missing? What triggers the trims to kick in? I am using JET DST software.

 

It's been awhile since I changed to my 2bar turbo setup so I don't recall the exact parameters that might keep it out of closed loop. When I did the conversion I adjusted every MAP based threshold to account for the 2 bar sensor. My car has been running well and in closed loop for years with the 2bar SD tune.

 

I have never tuned / played with the JST Software for the 1996 model,. but taking a stab at this for you:

Under Fuel Tables - Look for "Long Term Fuel Trim MAP Cell Boundaries" your current values may be too low. Check to see if your MAP values are relevant since you went to 2 Bar.
May also want to check your values in "Long Term Fuel Trim RPM Cell Boundaries" to see if they will be adequate to meet your driving ranges

 

There must be some sort of low baro scalar that prevents the PCM from going into closed loop if the atmospheric pressure is below a certain threshold. You might have to look around in other definition files to find it, that is if they even exist or if JET is capable of that?

FWIW, I successfully tuned my car on the OBD1 computer with 2 bar MAP, speed density, and open loop only. I had to jump between definition files EE, EEX, and various versions of EEXtra to get all of the baro stuff right. Closed loop always made it run like crap though.

 

For Speed Density Mode:
Under SWITCHES: Calibration Options: you need to enable "speed Density Mode.

 

Yes- the SD constant is enabled.

I did a hack to set the baro at 5v/100kpa on startup by jumpering the 5v signal to the map signal wire.

Then let the 2bar map take over once started. So logging shows the bara at 100kpa and the current map at 21kpa/0.58-0.62 volts.

No trims.

Hack 2. I now used a pot to run the car at idle. The same process set the baro at 100kpa on startup, now moved to a potentiometer. Set the voltage at .05v - no trims - moved to 1.18-1.2- trims started... KPA 32.

So there is a threshold on when trims will start. My question. How in the world do you adjust this boundary? I tried to 1/2 the following table with no luck?

BLM Cell MAP Boundaries

Boundary MAP (Kpa)
Low 37
Mid 57
High 77


Am I wasting my time? Should I just tune in idle somehow and then only work trims when they hit. Is this the sacrifice for using a 2BAR on a 96 Vette. I am limited resolution on idle with no closed-loop trims. I can control timing and fuel on boost.

Is there some sort of circuit available to scale the range I am looking for. 1-5volts from 18kpi to 12lbs of boost.

 

I believe your current setting of "BLM Update Enable MAP 20 kPa" is too high for Idle, since you halved your MAP for 2 BAR SD Mode.
Try decreasing this value to 5 Kpa

 

That's probably screwing with things, but I'd imagine there would be some BLM activity as it's not under 20kpa all the time. Definitely reduce it all the way, but I'd look around more in the OBD2 tune.

In OBD1, I did see 2 parameters in EEXtra I didn't notice before, BLM Enable - Min MAP and Min MAP to Update BLM. They were set at 15 and 20kpa respectively.

 

That sounds like the root cause of this issue... I just sent a note to JET to see if I can gain access to this parameter. "BLM Enable - Min MAP "

Line 6739: <title>26F0 BLM Enable - Min MAP</title>

Currently, it must be set in the 30-35kpa or 1.1-1.2volt area. That is the only time I can get trims.... I tested this by leveraging a potentiometer vs the MAP sensor.


Here is a dump of a stock LT4 tune: https://github.com/lpfrnk/96vette/bl...6_lt4_mod2.txt

 

Seems to me that this is only occurring at Idle. If it's really a pressing issue for you then force it in Open Loop and tune the VE in that MAP /Rpm region
You can run Open Loop by increasing the "VE Min. Cool. Temp. for Closed Loop 33.5 Deg C" setting to a high value like anything over 150. Please note that this will put you in fulltime Open Loop with no fuel correction so your VE Table will have to be completely looked over.

 

Open loop may be the way to go... I just don't understand.... my car will starts fine.... runs for ~2-3min... then will go into closed loop..... I see no trims but then goes rich... ~11.5-12AFR..... I can toy with the VE tables all day long but can't control the AFR in closed loop.

I thought by getting control over the trims at idle I can see what is happening but, it appears that will not happen. I am told that the
BLM Update Enable MAP 10 kPa
is the correct flag.

Here is an example log...

https://docs.google.com/spreadsheets...it?usp=sharing

Will try to stay in open loop to see if I can get more control.

 

I can't see your log because you don't have link sharing enabled.
Is the 11.5-12 AFR only at idle and other high vac situations? Could be that the min inj pulsewidth isn't low enough, you'd see the pulsewidth bottom out in the logs. I've had no ill effects with running my Deka 80's down to 1.1ish according to the logs.
Otherwise, the rich condition might be coming from a fault somewhere else. Issues with the knock circuit can cause this so I'd look over all low octane and emissions related stuff and make sure it's not interfering.

I kept my car in open loop because I was constantly fighting idle surges and the occasional surge with part throttle. My cammed motor wasn't too happy at stoich with the added drag of the D1, it wanted more fuel as far as I could tell. I tried a few patches to force OL @ 0% TPS which helped the idle surge, but part throttle was still crappy due to the computer constantly chasing stoich. I'll revisit CL in the future once I figure out what the O2 Swing Voltage bytes correlate to, I'll be able to richen it that way.

 

I changed the sharing.... you have a very interesting note.... let me try to reduce the pw floor.....Thanks

 

Have you set the BLM Update Enable MAP to 5 Kpa ( not 10 Kpa)

 

I believe your issue of not be able to get Idle to go into Closed Loop correction may be caused by the following:

Your current setting of “Closed Loop Idle Enable Vehicle Speed =0.9 MPH” (should be set to 0 MPH)

Your current setting of “BLM Update Enable Map = 17 Kpa” should be adequate enough as per your Data Log but setting it to 5Kpa will probably be better.

These settings should provide you with proper Closed Loop Idle Fueling Control. If not I have another method we can try to implement to resolve your Idle Fueling issue.

Also, according to your Data Log I can also provide you much better BLM Cell ( MAP & RPM) Boundary settings if you like. ( They will provide you much more Fuel Correction Resolution )

 

I would do as FrankieD is saying and drop the BLM Update MAP down. I see it's listed as 20kpa in the LT4 tune you posted, and you're hovering at 21-20kpa in the log by the time you hit closed loop. There should be activity, but there could be some sort of hysteresis affecting it, so I'd reduce that further.

Just to make sure, did you account for the offset of the 2bar sensor when scaling the VE tables? It's not as simple as halving the MAP values, see the table here:
http://www.ltxtech.com/forums/showth...-speed-density

I looked at your log and see the injector pulsewidths are pretty much static at 1.8ms as if you've hit the pw floor and no change as it warms up. Looking at the LT4 tune, I see the min pw around idle is around 1.4ms and the voltage offset is about 427us at 13.6v voltage. Adding the two together would explain the 1.8ms, so I'd subtract 700us out of the whole Base Pulsewidth vs. RPM table and see how your injectors handle it. I'd also zero out the End of Injection Target Offset vs. Baro table while you're in there, it could be screwing with your fueling at different Baro values. If Baro were to update mid drive, it could throw all of your fueling out of whack.

Also, are you sure that the wideband script in your log is correct? I'm assuming you're using the AC pressure sensor for logging. My AEM wideband logs AFR from 10-20:1 as a 0-5v signal, so the equation is a simple y = 2x + 10. The wideband script in the log looks like it goes from 7-20:1 AFR which is odd. If it's actually scaled like my AEM, the motor may be leaner than the log suggests.