Stage II distributor advance

[CFI]

Does anyone know if a Stage II engine uses distributor advance at idle? Dave McKeen and I are trying to track down a weird problem I’m encountering with his new idle ECU.

[DMC5180]

Does anyone know if a Stage II engine uses distributor advance at idle? Dave McKeen and I are trying to track down a weird problem I’m encountering with his new idle ECU.

I have Stage II and Daves ECU. I haven’t noticed anything abnormal from when it was just Stage I. I think Base timing on Stage II is about 16-17 BTDC. I do run my Idle at 850 ish. I’d have the check the DIP settings to verify that though. What is the issue you are having?

[CFI]

I have Stage II and Daves ECU. I haven’t noticed anything abnormal from when it was just Stage I. I think Base timing on Stage II is about 16-17 BTDC. I do run my Idle at 850 ish. I’d have the check the DIP settings to verify that though. What is the issue you are having?

For the record, I confirmed yesterday while performing some tests that there is no vacuum advance at idle on a Stage II.

As far as Dave’s ECU: when installed as directed (idle switch screw backed out, diode bypassed) the engine will hunt between 1,100 and 1,500 while coasting to a stop. It will do this 5 or 6 times then slowly go to the correct setting. It also does this when shifted into park or neutral after driving. I was able to (mostly) solve this by reconnecting the diode and adjusting the idle screw so the switch was activated when my foot is off the accelerator pedal. It still hunts but now it’s one quick jump to 1,500 and that’s it.

However, with the AC bump line installed and AC on, the idle hunt comes back. If I coast and the RPMs slow to 1,100 the hunt begins. If I shift into park or neutral after driving, the hunt begins. It seems to me that the hunt is caused by the activation of the idle control motor. IIRC his ECU turns the motor off at 1,500, and turns it back on at selected RPM idle plus 300 (which would be 1,100 with my current settings).

Today I will test a different “delay” setting and possibly a new curb speed setting. I’m currently running idle at 800 with a 100 bump with AC on, delay of 10. Stock idle was within factory specs with the original ECU, with no hunting whatsoever. If I put the old ECU back in, everything works normally.

[DMC5180]

For the record, I confirmed yesterday while performing some tests that there is no vacuum advance at idle on a Stage II.

As far as Dave’s ECU: when installed as directed (idle switch screw backed out, diode bypassed) the engine will hunt between 1,100 and 1,500 while coasting to a stop. It will do this 5 or 6 times then slowly go to the correct setting. It also does this when shifted into park or neutral after driving. I was able to (mostly) solve this by reconnecting the diode and adjusting the idle screw so the switch was activated when my foot is off the accelerator pedal. It still hunts but now it’s one quick jump to 1,500 and that’s it.

However, with the AC bump line installed and AC on, the idle hunt comes back. If I coast and the RPMs slow to 1,100 the hunt begins. If I shift into park or neutral after driving, the hunt begins. It seems to me that the hunt is caused by the activation of the idle control motor. IIRC his ECU turns the motor off at 1,500, and turns it back on at selected RPM idle plus 300 (which would be 1,100 with my current settings).

Today I will test a different “delay” setting and possibly a new curb speed setting. I’m currently running idle at 800 with a 100 bump with AC on, delay of 10. Stock idle was within factory specs with the original ECU, with no hunting whatsoever. If I put the old ECU back in, everything works normally.

Okay, mine will hunt a little maybe 2 pulses and settles. I don’t think it gets to 1500 though. More like 1200 then 1000 then idle rpm stable. I’m not running the A/C bump rpm. I’ll check my dip settings This Friday and get back to you. I’m away from home till then.

[David T]

AFAIK the Stage II uses the same standard distributor as an original stock motor. Same mechanical and vacuum advance systems where there is no vacuum or mechanical advance at idle. The base timing is not 13 degrees (stock) but I don't have any spec on what it should be. To verify that there is no vacuum advance at idle, measure the timing at idle with the vacuum line connected and then disconnected. Then you can measure the advance as per M:01:04. The Stage II should idle a bit faster than 775. One way to figure out what the base timing should be is to set it at 10 and then take it out for a ride and see if it pings under load (going up a hill). Keep advancing it till you get pinging and then back off 2-3 degrees. Use the highest octane fuel you can get. A Stage II will have a "lopey" idle due to the lower manifold vacuum because of the larger valve overlap. That's why you will need a slightly higher idle so you don't get a large stumble when you accelerate off idle.

[CFI]

Upping the delay to 16 has helped tremendously. I’m finally at a point where the idle behaves most of the time. At any rate, I’m able to load the electrical system at idle and still see at least 13 volts, if not slightly higher. And that’s what I was looking for, so I’m happy.

[CFI]

I’m not running the A/C bump rpm.

The AC bump is awesome. 100 RPMs makes a big difference.

[David T]

At idle the alternator does not spin fast enough to charge the battery. The design is that the battery is sized large enough to handle the load for the short time the car would actually be idling. Once above idle the alternator would then charge the battery.

[DMC5180]

Upping the delay to 16 has helped tremendously. I’m finally at a point where the idle behaves most of the time. At any rate, I’m able to load the electrical system at idle and still see at least 13 volts, if not slightly higher. And that’s what I was looking for, so I’m happy.

Hmm, I didn’t think the Delay went that high. But it’s been years since I played with the settings.

[CFI]

At idle the alternator does not spin fast enough to charge the battery. The design is that the battery is sized large enough to handle the load for the short time the car would actually be idling. Once above idle the alternator would then charge the battery.

Agreed. The reason for wanting a higher idle RPM was my 6 year old battery decided it had had enough one day and the engine stalled after many minutes of bumper to bumper traffic with AC on high. I replaced the battery but ideally I’d like to not go through that again. I’m also considering a more powerful alternator, one of those that advertises high amps even at idle.