GEN7 Basics

[MichBC3]

I have pretty lousy idle quality and a frequent stalling problem when coming to a stop after cruising for a while – unless I double foot the brake and throttle.

I’m only pulling about 16” of vacuum at idle (engine warmed up of course). I have my idle A/F set at 14.55 to 1.0 (closed loop w/wideband feedback). It won’t go any leaner and still idle reliably. The injector duty cycle is only about 1.2%. Perhaps that is not enough pulse duration for the computer to be able to control the injector well?

I believe that my problem might be in the basic throttle blade setup. I followed some Accel setup information and adjusted the throttle blade to make the IAC counts read 5% to 7% bypass air.

On the Minimum IAC Position vs. Coolant Temp. (%) screen, from 80 degrees to 240, the minimum IAC is at 5.1. Out of curiosity, I jacked up the value to about 20. The idle quality improved dramatically and the pulse width went up (into the 2’s I believe). After cruising, the stalling problem seemed to be gone too.

I have read some posts that say that the IAC should be 20% at idle. If that’s where I need to be, then should I change the curve values to 20% or should I open the throttle blade wider to give me those higher counts?

FYI, my (not very radical) cam is roughly 212/206, 0.500 lift and 109 lobe separation. Injectors are high impedance 55s.

Thanks, Bob

 

[KevinB]

I had the same problem this year after a burnout. Car would die coming out of the water box. I opened the tblade a little and reset the tps. It seemed to help. Not sure what the iac % was though..never thought to check.

 

[MichBC3]

What I'm experiencing isn't while doing burnouts, preparing for a racing run - though I imagine it could happen there too.

I can be driving easy from stoplight to stoplight and when I finally get to a full stop (and not double footing the pedals) - the engine often stalls.

According to the Accel manual, the "Minimum IAC Position vs. Coolant Temperature" screen's purpose is to "prevent large speed undershoot upon rapid deceleration".

I think that I need to go from 5% minimum to 20% minimum. I can either adjust the values on that "IAC minimum position" screen - or - open the throttle plates to make the IAC go higher. I'm basically looking for advice on which method that I should use to make the adjustment.

 

[KevinB]

Chris Lyons (turbobuick on here) or Lonnie Diers (quickt on here) are the ones i consult when I'm stuck. Give them both a pm as I don't think they frequent here that often lately. Maybe it will send them an email letting them know they have a message.

 

[MichBC3]

Yes, I hear nothing but crickets chirping... So I may have to PM a few different people directly.

I could have done that in the beginning, but thought that others might have the same question since Accel recommends a 5% to 7% IAC minimum setting, but many on the TurboBuick forum have recommended 20% in other old posts that I've read.

 

[norbs]

I sent you a PM and I;ll find you a link to the idle vid with 95's lb injectors and 224 soild roller cam idle...

 

[MichBC3]

Thanks for the PMs Norb.

 

[norbs]

http://www.youtube.com/watch?v=ka9-fWSQ6Ug

If you want your car to run as above you will need the following components as we talked about.

http://www.turbotweak.com/turbotweak60docs.pdf

http://www.bmotorsports.com/shop/product_info.php/cPath/103_107/products_id/357

http://www.frozenboost.com/

The sale of your "exisiting" set up will provide the cash flow and you will end all your suffering in a hurry I also feel bad about hi-jacking your post but the car just runs too well now I had to post.

 

[turbobuick]

I have pretty lousy idle quality and a frequent stalling problem when coming to a stop after cruising for a while – unless I double foot the brake and throttle.

I’m only pulling about 16” of vacuum at idle (engine warmed up of course). I have my idle A/F set at 14.55 to 1.0 (closed loop w/wideband feedback). It won’t go any leaner and still idle reliably. The injector duty cycle is only about 1.2%. Perhaps that is not enough pulse duration for the computer to be able to control the injector well?

I believe that my problem might be in the basic throttle blade setup. I followed some Accel setup information and adjusted the throttle blade to make the IAC counts read 5% to 7% bypass air.

On the Minimum IAC Position vs. Coolant Temp. (%) screen, from 80 degrees to 240, the minimum IAC is at 5.1. Out of curiosity, I jacked up the value to about 20. The idle quality improved dramatically and the pulse width went up (into the 2’s I believe). After cruising, the stalling problem seemed to be gone too.

I have read some posts that say that the IAC should be 20% at idle. If that’s where I need to be, then should I change the curve values to 20% or should I open the throttle blade wider to give me those higher counts?

FYI, my (not very radical) cam is roughly 212/206, 0.500 lift and 109 lobe separation. Injectors are high impedance 55s.

Thanks, Bob

This is the first I've seen this post and you have not sent me any PM's so I'm not real sure why your hearing crickets.

I would start with setting the target idle AFR to 13.50 and turn off the correction under 2000 rpm then adj your idel VE #'s accordingly. That should get you idling. 14.50 is fine for cruising under load but the car will want to be richer than that at idle especially when transitioning from park to gear. I usually richen it till it stops surging which is what it probably doing in your case. If you are having decel stalling or stumbling you will have to look at your transitional fuel tables which there are a ton of in the Gen 7.

 

[MichBC3]

Hi Chris - I appreciate your interest. No I haven't PM'd anyone except Norb. Norb helped me several times over the past 2 years with several other issues.

Yes, I can richen the idle and it will run better. But if the IAC value is higher, the idle quality improves too - and it doesn't stall on hard de-cel. Do you recommend the 5% to 7% IAC setting at idle or 20% as I've seen in older posts? If the 20% value, should I increase the values on the minimum IAC screen or just turn the screw on the throttle body up until I hit 20% IAC actual?

I've also been looking at the TAU vs. MAP. I think that was over-fueled.

After the snow that we got the other day (plus the Holiday), it could be a few weeks before I can go out and tune again... But thanks for the opinions and brainstorming.

 

[Craig Smith]

There are many factors involved that could make a difference, but ideally you would have the throttle blade set so that you idle at the targeted RPM with a low IAC count. I'm not familiar with increasing the airflow through the IAC at idle becoming a popular tuning strategy, but I wonder if it simply increases the idle speed for people, which of course helps any car to idle. Getting the idle speed lower, the a/f leaner, and the engine running smoother are my goals when tuning, and relying heavily on the IAC motor rather than the throttle body for idle airflow typically makes this more difficult in my experience. I hope you will consider contacting me when you bring it to Michigan and let me have a crack at it.

 

[turbobuick]

Doesn't get much better than an offer to help from Craig he was, IMO, the last tech guy at Accel that knew anything, lol.

 

[MichBC3]

Thanks turbobuick. I plan on looking up Craig in the Spring (probably late April) to give him a shot at tuning it. I agree with his objectives and approach for idle (minimum throttle blade opening, lean A/F). In the meantime, I plan to keep fooling around with the car when conditions permit (like clean, dry roads). I am trying to obtain decent driveability, not into power testing at this time of course. When the car is rolling, I really have no big complaints. It's the transitions that are not very good.

Additional info, just so that everybody knows: I have to pass a VA emissions test on a rolling dyno (15 and 25 mph) in March 2012. I got it to legitimately pass in March of 2010, but it wasn't easy. Took about 10 dyno runs. When I got the CO right, the NOX went up. Then I'd get the NOX down and the CO would go up. Eventually we found the sweet spot. Anyway, to get the (removable) cat converter to work, I shot for 14.7 A/F at 15 and 25 mph.

 

[MichBC3]

Learned something

In some older posts I read that guys were using 20 counts of IAC at idle. I just learned that there are 255 counts total.

In the Accel Gen7 instructions, they say to set the throttle plates for 5% to 8% IAC. Well, that would translate to about 13 to 20 IAC "counts". Roughly equivalent.

So my problem has been that I was confusing "counts" with "percent". Now I've got it straight. I'll set my throttle plate for 5% to 8% at idle, fully warmed up engine of course. Thanks for following along...

Best, Bob

 

[MichBC3]

Say Craig - If I am shooting for 5% to 8% IAC opening at idle using the throttle body screw, should I first configure the Minimum IAC Position vs. Coolant Temperature (%) curve to that same (5% to 8%) value when the engine is fully warmed?

PS - I think you were right about that 20% value - idle rpms were up, so the engine was smoother.. incorrect of course.