Discovered an issue tuning w/ boost

[TGP37]

AFR never were on target until first boost no matter how fine a tune. It was consistent every time.

Now I realized there is a pcm table for atmospheric pressure. It reads the MAP sensor before the engine kicks over and marks this as ambient pressure. It is 97 kPa where I am and when logging the barometric sensor, [PID.2340], it remains at 97 kPa until I hit boost. Apparently the boost is pushing the MAP sensor right up to 104 kPa. Not a problem when using a MAF sensor but it adjusts the fueling. The PCM doesn't know it's boosted so the pressure must be the atmospheric pressure. It will rise to 104 kPa and stay there until shutdown.

Now the manifold kPa can bounce around all day below 97 kPa and the baro variable remains at 97. But hit 102 kPa manifold pressure in WOT once and the baro stays at 102 kPa.

So if your tuning a turbo with a 1bar map (using a MAF), only use data when the baro sensor, [PID.2340]>103.


This way the AFR will be off a bit at first, but will be spot on after the first spool up.


This anomaly was persistent for a while. Finally found the gremlin responsible.

The image below describes what I am posting up. This is just one instance I have a pic for. I've seen consistently the same effect. It almost appears a voltage issue but is just coincidental in that image.

Baroinstance.jpg

[robertisaar]

barometric update function.

there are setting to adjust when it's possible to update the value, but if they're unlocked or not in whatever tuning programs, i couldn't say.

if possible, set the max RPM to a little under the lowest RPM where you can possibly get into boost.

[AleroB888]

How would a fast-acting check valve on the MAP sensor affect it?

[TGP37]

barometric update function.

there are setting to adjust when it's possible to update the value, but if they're unlocked or not in whatever tuning programs, i couldn't say.

if possible, set the max RPM to a little under the lowest RPM where you can possibly get into boost.

barometric update function......good to know the name of the gremlin

even if I tune under the boost threshold via rpm limiting, whatever I tune will be off after the 1st boost. It seems the entire fueling calculation is effected by the barometric value (which makes sense). We just have to ignore any data logged while baro is >103 kPa.........or calculate the difference of 6 kPa and adjust the data accordingly.

How would a fast-acting check valve on the MAP sensor affect it?

Not sure, it would definitely be worth a try. Can you post a link to a site which sells them?

The issue isn't too bad and I can live with it knowing how it works. The good side of this is the fueling gets a little bit richer when entering boost for the first time since start up. So it's manageable until I can fix it. I just have to tune for a 104kPa value for now.

Next time a friend comes down with his DHP I plan to fix it. I do believe there is a setting that allows a default baro value versus a learned value.

--------------------------------------------------------------------------------------------------------------------------
Hope this post helps someone tuning their turbo like me trying to find out why the AFR was adjusting so much part way in driving around.

[Z26-T]

So does this not work then? Installing a diode on a 2bar and running it?

http://60degreev6.com/forum/showthread.php/39051-0-6psi-lt-48hrs/page3?highlight=bar+map

^^ Post #30

[robertisaar]

barometric update function......good to know the name of the gremlin

even if I tune under the boost threshold via rpm limiting, whatever I tune will be off after the 1st boost. It seems the entire fueling calculation is effected by the barometric value (which makes sense). We just have to ignore any data logged while baro is >103 kPa.........or calculate the difference of 6 kPa and adjust the data accordingly.

think of it this way: if you disable the baro update at any time boost is possible, you'll always have the actual, real baro value stored in the PCM, since it will update in the time period while near WOT, but not at a high enough RPM to generate positive manifold pressure.

[timg]

The L36 guys who tried to use 2 and 3 bar MAP sensors found that same issue. The NA PCM didn't expect it and did exactly what you said, it replaced the baro value with the highest value seen by the MAP sensor can caused poor running. IIRC, a few tried swapping in some of the L67 code to fix the problem and it may have worked. I wish the old DHP forums were still around, because there was a ton of great info on there about this and other issues.

Tim

[unchained01]

dhp forum is still around its just very slow site and still alot of valuable knowledge there

[TGP37]

I found tuning the PCM with data after the Baro shot up made the problem manageable. The car idles a little lean until 1st boost, I consider it a fuel saving mode lol. But still, I plan to fix it soon.

If I can get a hold of a BIN file of my pcm id, I can fix that problem. I wonder if the DHP software can be calibrate to use the HPTuner cable. I have all the data needed to connect to it through ubuntu. VID/PID, serial, addresses. Maybe decompiling DHP and inject the proper data for it to use the HPT cable.

Interestingly, the HP Tuners firmware plays a sneaky game. The cable switches modes to hide a part of the firmware. I got past that using FTDI drivers for the FT2322D.

So I have the data to interface with the USB hptuner box/cable. It would be great to use DHP via the hptuner cable......hehe