Strange VE idle issue: Too lean when cold, too rich when warm (FAST)

[carbuff]

Hi guys,

Ok, I'm back with another FAST question. Things are going better, but this one has me a little baffled.

I've been struggling with my cold vs. warm idle VE settings. If I get the car warmed up and set the VE entries to match my desired AFR numbers (about 13.6:1 at IDLE), it idles great with very little O2 correction in closed loop. The VE numbers are in the 45-46 range around the IDLE entries.

After doing this, I turn the car off, let it cool, and restart. Now, when it's cold, it won't idle well at all! It 'hunts' for it's idle point, and the O2 is reading 15.94 (max lean). I have to keep blipping the throttle to help keep it running until it gets a little heat in it. Once it goes closed loop, I see it adding a large amount of fuel which helps. Then, finally, once things warm up, it stabilizes where I had set it previously.

The condition was so bad that I added fuel to the VE tables (up to about 52 around IDLE). Now, when I start it, it will still hunt slightly, but nowhere near as badly. But once the engine warms up, it's pulling about 14.9% fuel to get close to my 13.6 AFR that I requested.

I have experimented with the After Start tables somewhat, but I'm not sure if I'm doing the right things there... I feel like I would rather lower the VE numbers for the hot conditions and work with these tables for Starting. But how much fuel should I add? Or should I be adding to the Warm-Up Enrichment vs. CTS table instead? I haven't experimented much with this table yet...

Anyway, where is the best place to work to 'fix' the problem I'm seeing (too lean when cold).

THANX!
Bryan

 

[bobc455]

You should ignore the O2 sensor when it is cold- although it does have a heater, the numbers can't be taken as gospel until things get "cooking".

The VE #'s should be correct when warm, so tune for that (45-46). When the engine is cold, the mixture should be richer in order to get it to run properly- there is fuel being added by the warm-up enrichment (or at least it should be!). The warm-up enrichment should start fairly high when cold and then dwindle down to zero enrichment at running temperature.

A "hunting" engine idle is often caused by a lean mixture, and when the engine is cold is needs to be extra rich. (Just because they don't make chokes on carb's any more doesn't mean that the principle doesn't still apply!).

-Bob Cunningham
bobc@gnttype.org

 

[carbuff]

Thanx Bob. I discovered that my CTS Correction was WAY low! It was down around 14% at the low temps, and lower as the temps increased. I bumped it up to about 30%, and the cold idle was MUCH improved. I still need to tune on it some in the middle areas (warn start), but the cold start idles great now!

Thanx again!
Bryan