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Thread: AFR Spikes/IAC

  1. #21

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    So here's my current situation. I'm back to the beginning more or less, however, I did a lot of preventative stuff and tried to fix and interference issues. The car will still hang up and will not come down from the hold position but only after hard throttle. It also does seem to have something to do with the weather, but I cannot prove that. The colder it is, the more prone it is. The IAC will also have a very hard time staying stable at idle, i.e. it will fluctuate between 5 to 10/11 and bounce a bit, I can observe it moving while this is happening as well. The more I play with the IAC settings it will change how high it holds, but it's clearly an IAC issue. Since everyone thought it may be a interference issue, I moved my ignition box to the entire other side of the car and in the fender well. The wiring for it is shielded completely, included the tach & signal from the ECU as well as the two wires feeding the coil. They are now no where near the ignition or throttle body harness so it's hard to say there's interference now. Nothing is near the ECU or ECU wiring except for some wires for the A/C system and the radio, but it will do it when the radio is uninstalled as well. So I'm out of interference ideas if that's the case. There are no vacuum or exhaust leaks anywhere, the WBO2 seems to be working, and I have it on the HBX-1 bung. I thought about replacing my coil & CD box just to make sure it isn't anything there, but that seems to be a waste. So now I'm at the point where I think I'll try an IAC and see if it somehow went bad or any other ideas someone may have. Otherwise I'm to the point to where a carb is going back on the car, as I'm not comfortable with my wife driving it as it sits. It's basically a missile when the RPM is stuck at 3-4K, and I don't feel she would know how to make it stop. I do appreciate the help thus far.

  2. #22
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    You could use your Base Timing Table to pull timing out of it when you lift off the throttle. That may help the RPM to drop. Right now, you're giving it full timing on deceleration.

  3. #23
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    My engine returns to idle much better with a few less degrees of timing advance, but then actually idles better with a few more degrees.
    Also, the Idle Spark control (Idle ICF) retards ignition timing a lot during deceleration towards idle. So I added a little more to that area.
    May God's grace bless you in the Lord Jesus Christ.

    '78 BRONCO: 508" stroker, TFS heads, 11:1 comp ratio, Dominator MPFI & DIS, cold air induction, Spal dual 12" fans/aluminum radiator, dual 3" exhaust/Magnaflow mufflers, Moroso vacuum pump, Accusump, engine oil & trans fluid coolers, 100HP progressive dry direct-port NOS, A/C, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, traction bars, 4" Skyjacker lift, 35" mud tires

  4. #24
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    Your IAC closes at 1200 RPM above your idle setting and then the RPM drops. So I would say the IAC is working. Have you tried raising your RPM Above Idle To Start Ramp, above your 1200 RPM setting, and lower your IAC Hold Position? I run my IAC Hold Position at 5%. You could also try taking fuel out of it in that area of the Base Fuel Table.

  5. #25
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    Quote Originally Posted by Danny Cabral View Post
    Also, the Idle Spark control (Idle ICF) retards ignition timing a lot during deceleration towards idle. So I added a little more to that area.
    In his datalog, the timing doesn't retard until it hits the 1200 RPM above ramp down setting. Then it starts to pull timing and the IAC closes and the RPM comes down. If he was to set that setting to 2500 and work his way back to see what works the best.

  6. #26
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    Quote Originally Posted by 81 TransAm View Post
    ...and lower your IAC Hold Position? I run my IAC Hold Position at 5%.
    Yes, some engines don't tolerate a high IAC Hold Position %. I used 10% for a long time.
    May God's grace bless you in the Lord Jesus Christ.

    '78 BRONCO: 508" stroker, TFS heads, 11:1 comp ratio, Dominator MPFI & DIS, cold air induction, Spal dual 12" fans/aluminum radiator, dual 3" exhaust/Magnaflow mufflers, Moroso vacuum pump, Accusump, engine oil & trans fluid coolers, 100HP progressive dry direct-port NOS, A/C, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, traction bars, 4" Skyjacker lift, 35" mud tires

  7. #27

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    Quote Originally Posted by 81 TransAm View Post
    Your IAC closes at 1200 RPM above your idle setting and then the RPM drops. So I would say the IAC is working. Have you tried raising your RPM Above Idle To Start Ramp, above your 1200 RPM setting, and lower your IAC Hold Position? I run my IAC Hold Position at 5%. You could also try taking fuel out of it in that area of the Base Fuel Table.
    Yes, I have raised it, I've been upwards of over 2000 RPM above idle. However, I haven't lowered the IAC down below 23 or so in quite some time, so I'll try that. I'm confused as crap as to why it worked great for months at 1200, 30%, 1.5 second & 200 RPM, but now it won't. I was also going to try 250 RPM for the resume because I remember that working a little better last time I drove it, but this last run I didn't take the laptop, so I couldn't play with that setting.

    You're wanting me to set my above idle to 2500? That is a lot higher than I've ever set it before, not opposed to trying it, just haven't seen it that high.

    I can play with it, I used Danny's setup as a guide when I did my timing and adjusted the degrees to match what my engine likes. I know that's not what is causing it to hang completely, but I'm open to see it run better all around regardless.

  8. #28
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    Quote Originally Posted by sr1032 View Post
    You're wanting me to set my above idle to 2500? That is a lot higher than I've ever set it before, not opposed to trying it, just haven't seen it that high.
    You never know what will work on your engine until you try it.

  9. #29

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    At this point, I’ll just set it to 10% and then unplug it, so it can’t hang anymore! LOL. I’ll try a few things later on and report back.

  10. #30
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    Don't unplug it with the ECU turned on. I have heard that is not good for the ECU. Maybe Danny can enlighten us to whether this is true or not.

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