No smell, smooth idle, it's awesome!!

I almost have the tune right where I want it- BLMs hover around 126-132 at all operating conditions. I believe the timing is optimized (per a previous thread of mine).

The only thing is, for some reason now, during open loop (hot or cold) the engine wants to die if I let my foot off the gas (especially if I go from Park to drive/reverse). I've tried various AFR's at open loop, but it doesn't help. I've also tried OEM open loop fueling values from AUJP, ANHT, $DA3, $EE, but again no effect. I don't have this problem in closed loop; the idle is nice and steady. Any ideas?

 

Are you using a P/N switch?? Is your idle speed too low to begin with? How much advance are you using at idle, and idle with load?

 

I am using a P/N switch. THough, I should look at the scanner and verify that it's functioning properly. Good thought..

Idle speed is 650 rpm in gear, 750 out of gear. I doubt I would have any problem with that??

Idle speed advance is about 35° BTDC in gear and in Park.

 

WOW, that's an awfully high idle spark! While mine may be FUBAR'ed, I'm seeing low to mid twenties idle spark.....

 

agreed. the 406 in my 71 (240/248 @ 0.050 solid roller, ~10.4:1 CR and fastburns) idles great at 20* timing. (It's currently set up with NO vacuum advance, the mechanical advance starts coming in around 1500 and is all done around 3200, where it hits a total timing of 32-34*). It's running carb/HEI dist right now, though. 30+ seems quite high and may be causing false AFR readings on a WBo2 etc.

since the motor is mild, it would probably be worth making a chip with 20-24* idle timing and retuning idle VE cells and just see what happens. If it doesn't work out you can revert back to what you have now.

 

Ok then... I'll try ~20° and see what happens.

One other thing... the scanner is sensing about 13.2 battery volts at idle. Probing the back of the alternator shows about 13.5 volts. I'd attribute the difference to the margin of error between the scanner and the multi-meter. However, aren't alternators supposed to be putting out closer to 14.5 volts? Could the ECM be doing something screwy based on a lower voltage?

 

how's the voltage off idle? 13.2 sounds a tad low, but if you're still using an "era correct" alternator... well, they weren't so great around idle. the stock style alternator on my 71 gains about 3/4v between idle and 2000rpm.

 

I'm using a 105 amp alternator from a thirdgen Camaro. I ditched my old '71 alternator a long time ago... Although my new one is from Autozone (maybe that's a problem in and of itself?).

What voltage do you guys get with yours

 

from a napa NEW (non rebuilt) alternator at about a 900rpm idle:

14.4 - 14.5v

it's rock solid at that voltage regardless of RPM.

I'm not using any underdrive pullies, and that's at minimal load - no brake lights, no headlights, no ac, no radio, all electrical systems off.

oh, and an optima spiral cell battery.

 

This is where I'm also measuring. However, if I have my lights on, fans, etc, the voltage can drop to about 12.9. I've never had a problem with the car not starting, so the battery is definitely being charged. My only question is, what does the ECM do? Is it expecting to see 14+ volts?

 

There's tables in the ECU to try to compensate for battery voltage problems. There's a PW offset vs Vbatt table. It's supposed to compensate for slower opening injectors. But, I wouldn't worry at all about <1V causing measurable differences to the performance.

Maybe those years of bad grounding have been taking their toll on the alternator.

 

There is an injector pulsewidth vs. voltage table. it compensates the injector pulsewidth slightly for differences in voltage, i.e. the pulsewidth will be slightly longer at lower voltage because the lower voltage can't open the injector as fast.

other than that, i'm not aware of any differences due to voltage until you get well below 12v.

 

Well, I put the timing down to about 22° BTDC. Didn't make any difference. I think what I'm going to do is clean out the IAC. Maybe there's some gunk keeping it from operating properly.

 

Make sure it's actually moving, too. The data logging only shows what it was directed to do by the ECM. There is no feedback that it actually went to the correct position. I chased that problem a while until I realized it wasn't moving.....

 

Now that's interesting! I'll have to check that one out...

I believe if you jumper the ALDL into diagnostic mode you can here the stepper motor running, correct?

 

I've not been able to, but then again, I wear two hearing aids and still can't hear Schitz.....