Fast & GM 3 Bar MAP sensor

[DOHC Vobra]

I'm wondering if anyone out there has used a GM 3 bar map sensor with a FAST system. I recently switched from my 2 bar sensor that came with my FAST to a 3 bar sensor purchased from GM. It's the one that was used on the Turbo TA's, GM Part number 12223861 (old part number 16040749). The connector had to be very slightly modified to use.

When I connected it to the FAST all appeared to be well, 99-100kpa with the engine off, and about 29 at idle (the same as what my 2 bar reads).

Now, tuning this thing is a whole other deal. I've had lots of problems getting the car to run correctly now that I'm using the 3-bar. I made a table that VERY closely mapped the 2 bar values into the 3 bar table. The car fired up VERY rich, and stumbled a whole lot.

First, I'm wondering, maybe that MAP sensor is incompatible. Second, are there some huge changes that are required when switching from a 2 to 3 bar sensor?

Any help is greatly appreciated!

Justin

 

[Chuck Leeper]

3 bar??

Did you go to the setup for fuel parameters and change the sensor value from 2 to 3??

 

[DOHC Vobra]

heh... Good point Chuck, I probably should have mentioned that! But yes, I did change the software to a 3 bar map.

Justin

 

[Syclone Dude]

as I understand it, that sensor (89 turbo Ta) is the only 3bar ms in existance (correct me if I'm wrong) and I also beleive that they only used it for the boost guage not the ecu.

there might be some after market (made in china type stuff) folks making it now but that's still just a copy of the turbo ta MS

just my .02 worth
BigAl...

 

[Chuck Leeper]

????

Originally posted by Syclone Dude
as I understand it, that sensor (89 turbo Ta) is the only 3bar ms in existance (correct me if I'm wrong) and I also beleive that they only used it for the boost guage not the ecu.

there might be some after market (made in china type stuff) folks making it now but that's still just a copy of the turbo ta MS

just my .02 worth
BigAl...

That's the map used on most all the aftermkt ecu's and data logging devices I am aware of .. Are you suggesting that because it was on the TTA for the boost ga, that it's not what should be used w/ the FAST system???

It's a Delco/GM part.

I think the problem w/ the Vobra is the VE map and such is written using the cell values of what was used w/ the 2 bar map..

 

[DOHC Vobra]

Chuck,
Are you saying that the VE numbers change based on the type of map sensor that is used? I was assuming that a ve of xx at a map value of yy would always be xx, regardless of the map sensor being used... ie, at a map of 50kpa, my VE was 80, it should still be 80 @ 50kpa, right???

Justin

 

[NoSlix]

By going to the 3 bar, though, you've lowered the resolution vertically. With a 2 bar sensor, you have 0, 20, 33, 45, 59, etc. With a 3 bar you have 1, 21, 40, 60, 79, etc. The numbers aren't the same. Fast keeps the same VE #'s in each cell when you change from 2 to 3 bar sensors, though, even though the mass airflow in Kpa has changed. You must retune the map. In addition, since the mass airflow reference #'s are farther apart, there are bigger areas between the individual cell #'s. This means you might have to move a cell value up or down to compensate for the fueling needs of the area between the cell above or below.

 

[Chuck Leeper]

Yep!

Originally posted by NoSlix
By going to the 3 bar, though, you've lowered the resolution vertically. With a 2 bar sensor, you have 0, 20, 33, 45, 59, etc. With a 3 bar you have 1, 21, 40, 60, 79, etc. The numbers aren't the same. Fast keeps the same VE #'s in each cell when you change from 2 to 3 bar sensors, though, even though the mass airflow in Kpa has changed. You must retune the map. In addition, since the mass airflow reference #'s are farther apart, there are bigger areas between the individual cell #'s. This means you might have to move a cell value up or down to compensate for the fueling needs of the area between the cell above or below.

Shane, Thanx....
Have a great holiday season!!

 

[DOHC Vobra]

Okay guys, here's the screen dump of my maps, as you can see, I've tried to map the fuel table into the new 3 bar map...


Whaddya think?

2bar

3bar

Justin

 

[NoSlix]

Interesting.....those are really high ve #'s at idle. Usually we have em down around 40 or so.

 

[DOHC Vobra]

Shane,
I agree that they seemed high when I first set them, I end up with about a 2.0ms pulse according to the dashboard. The car idles at about 11.5:1 with those numbers, and if I try to go much lower, the idle is pretty erratic.

I'm wondering if there's something else that's really wrong here...

Justin

 

[Chuck Leeper]

Some ??'s

What injectors are you using?
What is the base fuel pressure?
Where is the map sensor plumbed into the system??
Can you send us the entire .GCT program??

 

[DOHC Vobra]

Uh oh...now you guys have me worried!

Here's a link to my .GCT for anyone interested in checking it out... I'd definitely appreciate any feedback.

http://users.adelphia.net/~justinluton/images/3bar.gct

Chuck, to answer your questions:

Injectors are 65lb holley, low imp.
Base fuel pressure is about 40psi with vacuum disconnected.
The map sensor is plumbed into a now unused vacuum connector that comes off of the top of the intake manifold (and seems to be getting a decent vacuum signal).

The car doesn't like to idle nicely (especially when the fan turns on) below 11.6 - 11.7. Where are you guys typically tuning idle A/F wise?

Thanks Guys!

Justin

 

[Chuck Leeper]

Huh??

you are reporting:
The car doesn't like to idle nicely (especially when the fan turns on) below 11.6 - 11.7. Where are you guys typically tuning idle A/F wise?

Sounds to me like a low voltage problem, if the fans are loading the system so much as to cause the alt to drag the engine rpm down.

What is Alt output at idle and when the fans are on?? Check at the alt and at the battery.

 

[DOHC Vobra]

Chuck,
Definitely a good guess... FAST is reporting the battery voltage to be around 13.6-13.7 at idle, it's a new battery and I'm running a 130amp alternator. The fan pulls some pretty massive current when it first starts, the car is okay after the fan has started, it's just that transition from stopped to started.

Justin

 

[Craig Smith]

Give this a shot for me, if you would be so kind:

Go into the "MAP AE Parameters" section and turn the "dMAP noise threshold" setting up to 10 or so. This is a lot higher than you should ever need to have it but it will answer a question that I have.

What this setting does is make the ECU ignore changes in manifold pressure before applying "AE vs. MAP rate of change" fuel. If you have a noisy MAP signal at idle, it's not hard or uncommon to have the tuneup reflect some amount of AE vs. MAP fuel that's always being applied without you knowing it. So if you jam the threshold way past the point where this could be a factor and the car cleans up, you are on to something.

Also, expect your throttle response to suffer as part of this test. But this is only a test. (had this been an actual emergency... )

If you get a chance to try this, please let us know what happens.

 

[DOHC Vobra]

Craig,
I'll definitely give that a shot... don't know if it's helpfull or not, but I have noticed that the MAP enrichment seems to not be doing anything at all with my current setup, if I take off from a stop (big change in map), I never see the map enrichment value on the dashboard read anything other than zero. Does this sound like a problem?


BTW, just wanted to say that you guys are great! Thanks so much for all of the help that everyone has offered!

Justin

 

[Craig Smith]

That really isn't a problem. It is happening, but the manner in which this additional fueling is applied is such that it is difficult to monitor in the same way that the other sensors are monitored. If you log the pulsewidth (BPW sensor), you will likely see that the pulsewidth will increase as manifold pressure goes up.

 

[NoSlix]

Justin,

Some things jump out at me about your program.

1. You don't have enough timing at the idle cells in my opinion. I usually bump this up to 30 or so. This in itself will lean the idle mixture out.

2. No timing trim at idle- timing trim helps to stabilize the idle much like the factory ecm does by adding or taking out timing based on how far away from your programmed idle it's running at a given time. Timing trim will help with the fan turn on.

3. closed loop parameters-
a. you don't have the wideband enabled(this may be by your design)
b. even if it was enabled you're turning it on at 7350 and turning it off at 7350 making it innefective
c. min operating temp for closed loop is too low
d. delays are too long
e. gain is too much
f. step is too much


4. Correction limits- you've got some neg numbers in the + side and + in the negative side


I'd be happy to send you an example of how I generally set these up, if you'd like. Others might set them up differently.

 

[DOHC Vobra]

Ahhh...I see... Okay, I'll try the "noise threshold" thing tonight and let you know how it goes!


Justin