DirtyDaveW

Since I'm working on my SD tune for my LT1 turbo charged engine, I'm constantly searching for information about the correlation of 1 bar vs 2 bar when directing Spark, DFCO and fuel. I came across this article yesterday and thought I'd put it here. I *could* have just put the guys link but we all know that at times, a great resource can disappear from the 'net when the author deletes his stuff or moves on, etc. So, the attribution goes to GM MAP sensor identification information 1 bar 2 bar 3 bar

But just in case his page, info disappears, here's stuff I've cut n' pasted..

The Identifying marks on the 1, 2 and 3 bar sensors and where to look for them...


From Robbies site...
The logic module uses the manifold absolute pressure (MAP) sensor to determine the absolute pressure (not the relative to atmospheric pressure) of the air inside the intake manifold and the atmosphere (barometric pressure).
This information is used to determine the density of the air entering the combustion chamber (in conjunction with the IAT(Intake Air temperature) sensor), which is used when calculating the proper air/fuel mixture for the engine, especially at WOT since the system is not in closed-loop at this time.
It is also used to help adjust the IAC(Idle Air Control) motor during idle.

It uses a silicon wafer that is thinner in the center (0.001") than around the edges (0.045"), which causes it to act as a diaphram.
It is mounted with a perfect vacuum beneath the chip so that the air pressure from the other side flexes the chip.
This flexing causes a change in resistance and the circuitry inside the sensor converts this to a voltage ranging from 0.02V to 4.94V when the output is pulled up towards 5V by the ECM(Electronic control module).


1 Bar MAP sensors are used on NA(naturally asperated) vehicles.
2 Bar MAP Sensors are used on forced induction vehicles(Turbo & Supercharged). They can measure up to 2x the apmospheric pressure(29.4psi), so that means it can measure up to 14.7psi boost(the atmosphere is 14.7psi + 14.7psi from the turbo/supercharger).
3 Bar MAP sensors can measure up to 44.1psi, which translates to 29.7psi boost from a Turbo/supercharger.

They all share a common pinout, although the connector keying may be different:
Pin A -- Ground
Pin B -- Sensor output
Pin C -- +5 volts



Places to order MAP Sensors
You can order them direct from:
Summit Racing
PN# MSD-2313 3bar MAP
PN# MSD-2312 2bar MAP
PN# MSD-2311 1bar MAP

or

GM Parts Direct: Your direct source for Genuine GM Parts
PN# 12223861 3bar MAP
PN# 16040609 2bar MAP
PN# 16137039 1bar MAP



Voltage vs Pressure readouts on the 2 bar...


Self titled here...


More text from Robbie above the following chart...
GM 1bar, 2bar, 3bar
1 PSI = 2.036" of Mercury (HG)
1" mercury = 0.4911541 PSI
Formula for the GM 3 Bar MAP sensor is (V*8.94)-14.53
I have no idea why it's 14.53 and not 14.696, [rounds up to 14.7] but it works out on GM's chart every time. It is possible that Detroit is slightly above sea level, and you can use 12.11 in the formula for 1 mile above sea level.




Hope this helps some of you that are on the hunt for the right tune on your forced induction application.
Thanks,
Dave

Kevin Blown 95 TA

That's good info Dave - Thanks for posting. I have a chart like that which I made myself some years back to get my wideband aux box to log the boost with a voltage input from the 2 bar sensor, and it works real well. I used a mityvac to simulate boost and measured the sensor output on several levels and it correlated with the charts I found later. I'm sure that info will be helpful to any guys just getting the boost on their engines.

DirtyDaveW

My latest effort (2 bar SD tune #29, whew..) is great! I've been to 16psi with it, trimming out any knock retard as I encountered it. Trimming fuel via the VE Tables and it's damn near perfect. I cut and pasted the Spark Advance, MAP and RPM from my 1 bar MAF tune to a spreadsheet, highlighted it with Yellow, then cut n pasted my 2 bar SD tunes Spark Advance, MAP and RPM to the same columns, leaving them uncolored/highlighted. I then sorted the 3 columns by RPM, then MAP, and finally Advance. I had excluded the rows for 0%TPS and zero MPH. In every situation, I had a LOT more spark advance throughout the RPM range till Max Boost. The result is a smooth acceleration in traffic, crisp acceleration when getting aggressive and huge grin production when flooring it. I have to drive 250 miles each way in my travel to/from my job site. I drove it tonight on the freeways with the cruise control set on at 75mph, during which, the Wide band typically shows 14.2. Gas mileage seems to be better too.
I got 25 miles per gallon on the freeway going 75 MPH in sixth. I didn't play around with any cars so I was a good citizen this time
The only thing this is still 'off' is the DFCO settings when in cruise control at 65 and below and I start going down a decline. It bucks very noticably till it figures out it's decelerating. Now, with foot pressure (non-cruise control) it's fine.

Kevin Blown 95 TA

I found DFCO hard to get right, too, especially on the interstate on a long downhill grade or taking an exit under certain conditions for example. Partly because the difference in KPA the cam makes throwing off the settings. I remember when it was stock and had a tight converter, I always had to brake even from a slow idle cruise with my foot off the gas. So at least it isn't like that any more. I think I could get it better, but I got tired of dicking with it.

DirtyDaveW

Kevin - I found a site/forum that was talking about this same DFCO and the guy recommended zeroing out the DFCO vs TPS vs RPM. I did it this morning and, although I haven't replicated the long drive on cruise control yet, it IS greatly improved. I'll keep assessing it in the next couple of days. I drive back home (249 miles) tomorrow afternoon.
Here's the link to the thread... Tuning DFCO on the LT1? - LS1TECH

Kevin Blown 95 TA

Thanks - let me know how it turns out. I probably won't get around to trying anything new until next year.

DirtyDaveW

Will do. I drove home tonight and it was a lot better. Not perfect, but better. Now to work on the KPA enable/disable for DFCO.

David94TA

Thanks for the info. Very helpful!

DirtyDaveW

Thought I'd update this thread since I'd started it....
Events:

• I've had successes in some areas and issues in others. Some, if not most, were caused by something totally unrelated to the SD tune but, not knowing that, I ASSUMED it was related.
• One such unrelated thing was the one ground for the driver%u2019s side bank of LS1 coils (I have the LTCC conversion) was making marginal connection so that was causing misses, fake 'rich' conditions, etc and I kept trying to tune it out (changing VE, spark, etc) but to no successful effect (since it was that ground wire, not the tune)
• Just minutes before I found the ground wire issue, I hit a pothole that jarred the last turn off the nut/bolt holding the ground wire so the car instantly started running on just the passenger sides 4 cylinders. Thinking it was a poor connect but mistakenly deciding it was my Acceleronics box, I unplugged it while it was running (amazingly, the engine was STILL able to idle, albeit roughly, on 4 cylinders!). This was a bad idea because with the power applied, it must have had a surge when I plugged it back in, because it fried the Acceleronics box.
• Since the 95# injectors are low impedance and with the box now cooked, I bought a set of used 60# Mototrons so I could drive the car and sent the box off to get it repaired.
• To keep things simple, I took out the 2 bar sensor, put in the 1 bar and put the MAF tune back on.
• Over the next several days, I tried modifying the tune, switching from 2 bar SD to 1 Bar MAF and tweaking this and that. This was over the course of a couple of weekends and just an hour here and another hour there. In other words, no real continuity, which can lend itself to moments were you go, "Did I finish what I was doing last time? And if I didn't, what the hell was left undone?"
• At any rate, at one point last weekend, I put in a MAF tune and took her for a drive. WOW! It pulled hard as could be! The wide band, while showing a tad lean at idle (as opposed to the usual 12.x and 13.x I'm used to seeing unfortunately), was spot on at anything above Idle and perfect in the 10.x at WOT/Peak boost (12 psi for now). It was absolutely awesome. I had been data master logging it this time and came back to the house and 'exported' the log to excel. Imagine my surprise when I looked at the 'absolute BAROMETER KPA', saw it was 50, meaning I had my 1 bar MAF tune running with the 2 bar MAP sensor. I thought, how the hell did that work? While the spark was too advanced beyond 50KPA, the fuel was fantastic. And... Unlike the SD tune, I didn't have the injector constant halved. I had the 60# Mototrons spec's at 60. Mind blown....
• Knowing that the spark was too aggressive in this configuration but loving the power, I compressed the spark tables that were in 20 - 100 into 20 - 50, then just repeated the column that was in 100kpa in columns 55 on up. A test drive proved it was now perfect.
• Given 2 bar SD has to have the injector halved, I was stunned to find the Open loop MAF tune was fine with the actual injector size.
• I can now drive with the car in 5th gear, cruise control set to 30mph and there's no bucking and the wide band says 14.x I can drive on the freeway at 65 using cruise control and the wide band says 14.x. When I go to full boost(12 psi for the moment, normal for me is 15, with forays into the 18/19) the wide band says 10.x and the car is flying.

So for the time being, I'm sticking with 2 bar MAF. I still have my DFCO, Spark tables and Dookies "barometer reset" in this tune from the SD tune but all the fuel aspects are from my original mail order PCM4less turbo tune. The thing that everyone complained about for the original MAF tune was that all the fuel and spark retardation were coming in as soon as the MAF maxed out. With the 2 bar sensor, it waits till the KPA actually rises to the 55 kpa and above (boost) before moving spark back to the 2x advance levels.

Alex94TAGT

Perhaps not terribly surprising, when you think about it.

Recall that the primary reason why the values are halved in 2-bar SD-mode is to attain more headroom in the VE tables. Our VE tables do not allow values in excess of 100% -- which is a problem, considering that forced induction or "boost" constitutes volumetric efficiencies greater than 100%, by definition.

Presumably, the reason you can use the actual injector constant in 2-bar MAF-mode without any fueling problems is because the VE tables aren't primarily used in MAF-mode. SD-mode is heavily dependent on the VE tables (which relies on MAP as an axis variable), whereas the MAF-calibration tables are not reliant on MAP at all -- only frequency and grams/sec. PE uses RPM/TPS/CLT, so the 2-bar MAP wouldn't affect that either. Ignition tables would still be dependent on the MAP however, as you indicated.

Potential problem: MAF mode still uses VE sporadically (during rapid changes in throttle), and your VE tables likely aren't scaled correctly for boost -- might cause some transitional fueling errors. More importantly, in the rare event that your PCM decides to revert back to SD mode (MAF failure), it might leave you stranded -- at least, it might suddenly go very lean when you enter boost.

DirtyDaveW

Alex,
Thanks for the reminders. I'll put my SD 2bar tunes VE tables in place. I used to know, but had forgotten, that when the MAF is in use the VE tables are not typically used.

As far as the MAF failing and reverting to SD, I keep my 1 bar MAP sensor in the car.

I'm sure that if people looked in my car, they'd be surprised to see the 'spare parts' and tools I typically carry.

• Rolls of 12 ga electrical wire
• Box of various electrical connectors, wire strippers and wire crimpers.
• 30 amp relays
• spare serpentine belt
• Noid light
• Multimeter
• 166 piece tool box with metric/sae sockets, ratchets of 1/4, 3/8, 1/2 drives and combo wrenches
• Test wires

I've thought about adding a spare electric water pump too.

Alex94TAGT

Sounds like you've got a nice survival kit there. Luck favors the prepared.

As for the tune, I don't personally see any reason why you can't leave things as they are -- sounds like it's running well, which is the important thing. I only mentioned potential problems so that you're prepared for any surprises, which you are.

It's fun trying to phrase things properly when our tunes are full of lies. I'm continually playing with the the tune as well, and I'm far from a tuning expert. Just wish we had real-time tuning capabilities.

DirtyDaveW

Amen, on the real time. I like the concept of the MAF translater which, according to Bob Bailey, can be manipulated while the engine is running. If you could just drive and, say the wide band said you're too rich/lean, you move a slider bar in the software and it's instantly corrected. Not only that, but it loads it into the PCM when you click a 'save' button. I guess that's what Megasquirt does but, having to have two systems running parallel is not comforting for those like me that have the worst luck.

DirtyDaveW

I'm attempting the SD tune stuff again. Gettting really close to a great tune.

Dinesh_H

I have been running a 2-bar map tune for about a year now. I connected my wideband to the A/C pressure sensor input. Using Greg Banish's video as a guide, I then was able to run a histogram with Tunerpro RT. I logged AFR from the wideband vs. MAP and adjusted the VE table accordingly.

If anyone is interested I can share the files that I used.