Rich At Idle Only

Blown85Z

New Member
Joined
May 29, 2001
I have my system doing pretty well. Just one prob. I idle in the 50VE area. As soon as I come off idle I have to jump the VE into the mid 60's. That makes for a not so smooth transition. Right now I have the idle numbers high and let the O2 correct it so I can pull out smoothly. My idle TPS is set right. The way it is right now my O2 is at -10 or so at idle and then it straightens out off of idle. Any suggestions?
 
Idel

Go to open loop and adjust your off idel and idle , then return to colsed loop
 
Blown85Z-

A bit more information would be helpful. What are your target A/F #'s? What is the "not so smooth" transition that you're worried about- does the engine stumble? How big of a cam are you running?

A VE of 50 or so at idle wouldn't bother me if it's a cammed-up motor, and VE's in the mid 60's might be fine for normal driving around...

If you could explain the problem better, we could offer some more insight.

-Bob Cunningham
bobc@gnttype.org
 
Thanks for the help! Here is where I'm at right now: idle AF is 13.5, VE is set at 57 and has a correction of -10. The next group of cells over jump to upper 60's and the correction factor goes to zero. The numbers go up like I would expect from there so the rest of the VE is normal and peaks at 85. I had to jump the AF in the next cell over from idle to 12.2 to eliminate a tip in stumble. The rest of the AF table is fairly normal for my set up. The injectors are 36lb. and I'm running a fairly mild cam in a 383 with a blower. The way things are right now I consider the driveability excellent. It pulls out great and the logs look good. I just don't like seeing that much correction at idle. Am I being to picky :eek:
 
13.5 A/F seems okay for idle.

57 seems high for idle, but if it corrects -10% then you should be around 50, which doesn't seem too bad.

What if you drop the VE at idle back to 50 and then increase the AE enrichment? (I'd use the AE enrichment vs. TPS) Would that eliminate some of the stumble?

85 seems low for a peak VE value on a blown motor, I would think you'd be over 100, even if you only run 6 lbs boost.

-Bob Cunningham
bobc@gnttype.org
 
My AE vs TPS is already very high in that area. I also have the AE Map decay #'s very low so the AE tapers off slowly. This made the biggest improvement with the stumble, but richening the AF in that area eliminated it completely. One thing I failed to mention was that this all started after I replaced the intake gasket over the winter. I made no other mods. I also had to drop my hole VE table down about 10% after that. Reason is unknown. There are no vacuum leaks and all else seems fine. Timing is the same and so is the TB. Till I can up with some funds to upgrade the blower I'm stuck running @ 5PSI max. I had higher VE's back when I was using 30lb injectors but they were real close to going static.
 
You should be able to tune the stumble out with the AE fuel vs. TPS rate of change AND the AE fuel vs. MAP rate of change. In the VE table, I would work to minimize the O2 correction without worrying about the stumble, and after that is set, work on the stumble with the AE fuel tables. On light tip-in, the rate of change is very slow, so look at the graph towards the left side of the screen. I usually start it right at 0 and then ramp it up rather steeply, and start to level it off around the pulsewidth value you observe at an idle. Look at the demo calibration file that came with your C-Com disk for a model to go by.

Hope this helps.
 
Originally posted by Blown85Z
I have my system doing pretty well. Just one prob. I idle in the 50VE area. As soon as I come off idle I have to jump the VE into the mid 60's. That makes for a not so smooth transition. Right now I have the idle numbers high and let the O2 correct it so I can pull out smoothly. My idle TPS is set right. The way it is right now my O2 is at -10 or so at idle and then it straightens out off of idle. Any suggestions?

Try pulling some timing out as you transistion off idle to WOT.
When the VE gets too far off, you might be trying to cover a timing problem. Too often guys get hung up in this more timing is good, mind set. If your running an auto, below the stall speed of the converter you hardly need any advance.
 
I'll check that when I get home tonight and see where I have those set Craig, but I'm pretty sure they are already in that area.

Bruce, I had the timing all over the place yesterday. All it effected was the responsiveness.
Thanks!
 
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