Fast & GM 3 Bar MAP sensor

[DOHC Vobra]

Shane,
Thanks for your reply... you and chuck must be long lost twins or something, he sent me an email with almost the exact same list of things! LOL!

Anyway, First, I probably should have clarified, this is not a Wide Band option FAST, I'm using a DIY wb to monitor AFR, so theoretically, none of the closed loop stuff should apply to me, right?

Chuck agrees, I need more timing, and as you both said, I think this will help with idle.

I've never messed with the timing trim table, but will definitely mess with that... as you said, it may help with the fan situation.

I'm guessing that the correction limits etc. won't make any difference since I don't have the wb option.

Thanks again Shane!

Best,
Justin

Originally posted by 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.

 

[NoSlix]

Anytime, Justin. Timing trim is easy. Set the far right to 7 and ramp down to the left to 0. You'll end up left to right at 0, 1, 2, 3, 4 , 5, 6, 7 with a smooth line going up.

 

[Craig Smith]

Even easier than that. Set the right side to seven, highlight the whole thing, and hit "I" for interpolate. It will fill in a straight line between the beginning and ending points.

 

[Pro Stock John]

Justin we are running the same setup, 3 bar map from a TTA and a FAST BtoB on my 98 LS1 Formula and after tweaking it idles fine.

PSJ

 

[DOHC Vobra]

Thanks John, good to know that my sensor is at least compatible.

Just wanted to let you guys know that I haven't been able to get to the car yet (single dad + no babysitter = busy me!). But hope to this weekend. I'll definitely post results once I have things figured out! Again, thanks to everyone for all of your help.

Justin

 

[DOHC Vobra]

Okay guys,
Using all of your input, I've tried the following few things this weekend:

1) Fixed problems with my fuel pressure...now stable! (Haven't checked under boost yet, but works well in vaccuum)

2) Bypassed my MSD DIS-4. It decided to crap out while I was testing...classic MSD... GRRRR! Funny thing, car seems to idle much smoother with the MSD out of the loop.

2) Changed the MAP noise parameter to 10, didn't seem to make any appreciable difference to the driveability of the car. A/F stayed about the same as with the default setting.

3) Changed the timing at idle. Increased from my default of 25deg to 30 and 35 deg. Idle quality got much worse, car went quite a bit leaner as I advanced the timing. Reducing timing down to 20deg actually seemed to help...odd. I noticed that going much leaner than about 13.2:1 causes the car to make lots of "popping" noises in the exhaust... Car seems to like to idle best at about 12.5:1. Also, increasing the timing raised the idle RPM... I guess I'd need to close down the throttle follower a bit to lower it again???

4) Used a .gct file that Chuck sent me for another 3bar Cobra. (Changed the injector size to my 65lb injectors). The car fired up and idled while cold, but started to go way lean as enrichment approached 0 (coolant temp vs. enrichment). Funny, but the rest of the table looks VERY similar to my table... (the numbers around his idle were much lower than mine, but off idle quickly approached my VE numbers)

This all makes me wonder... why would my car have such huge ve numbers? Any ideas what mechanical or electrical problems could cause such problems?

I put the 2bar sensor back on and switched back to my 2bar .gct just to make sure that the car was still okay. The car ran great again with the 2bar and 2bar program, so I'm guessing that mechanically things might be okay.

Thanks Guys!
Justin

 

[DOHC Vobra]

One more observation guys... My brother is setting up a FAST car with 150lb injectors, he noticed that in order to get the VE numbers to be reasonable, the injector offset needed to be changed (in his case, 2ms)... anybody think that I may need to change the injector offset in my case? I'm using Holley 65lb low-impedance injectors, currently using the standard 1ms offset.

Justin