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Thread: AFR Spikes/IAC

  1. #11

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    I should rephrase, it stalls it from the 2000-3000 RPM, back down to idle, not killing the engine. The IAC is definitely stuck at the Hold Position when this happens even though the TPS reflects zero. Occasionally, if I blip the throttle that will get the ramp down to start, but that's not done with any consistency at all.

  2. #12
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    Maybe this is an electrical interference issue. Ensure the spark plug wires (or any other high voltage wiring) aren't too close to the IAC motor/wiring. The IAC motor is easily susceptible to this, and I've dealt with it causing strange occurrences (from helping others).
    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

  3. #13

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    I'll check that tonight. I just drove from one side of base to the other, and each time I play with the IAC settings I can get it to duplicate and follow suit. I lowered my IAC Hold to 20%, and set the ramp to 1200, and left it at 200 for return to idle. If I adjust the ramp to a lower RPM, it just holds sooner and for a longer period of time. If I adjust the IAC Hold to a higher percentage, then it revs quite a bit higher due to the increase in air, and if I mess with the control all kinds of weird stuff happens. What is throwing me for a loop is exactly what the other person posted and the stinking manual, they're significantly different in how they explain it vice what you said. However, up until September it wasn't a problem, and I had not changed my settings. I'm thinking about trying an IAC just to give me peace of mind as well, but it's super strange that I can get it to do it at varying times based on the IAC settings. So I'll check the grounds & spark plug wires tonight, but the only thing even close are my wires going to the coil, but I used shielded wires for those. Another weird thing is that I cannot get the car to steadily hold an RPM level anywhere within the ramp, unless I lower my IAC percentage. (I.E. I can't hold 1500 RPM steady, unless I lower the IAC or the ramp RPM to below that area, any other time it will kind of bounce around in that area.)

  4. #14

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    I noticed on mine that I couldn't hold a steady RPM below 2000, because Closed Loop was over compensating. It could be a number of things such as Acceleration Enrichment not tuned right or Base Fuel Table not fully Learned yet. Steady driving in that lower RPM range helped straighten out some of those things. As Danny said, it could also be electrical interference. Nothing looked out of place in the datalogs to me, but it's always good to double check. For the IAC settings, your IAC Hold % will be at whatever the engine wants. When the engine is at operating temp, I would temporarily change the idle RPM to the 750 RPM, plus the 1200 RPM and see what the IAC shows. Then set the IAC Hold to 5% below that number.
    Last edited by SatherCS; 01-07-2018 at 12:49 AM.

  5. #15
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    Try decreasing your IAC Hold Position. An IAC Hold Position that's too high causes strange things to happen.
    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

  6. #16

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    I'm pretty confused on what your saying about changing my RPM and then adjusting my IAC. As soon as the engine comes off idle, it goes to whatever IAC Hold Position I program in. So the number I would subtract from would be the number I load in. Maybe I'm missing something there though.

    Danny my IAC Hold Position has been anywhere from 20-25 and no higher, I could go lower, but I've been basing my settings off that little chart you post.

    I got the spacer in & installed. Took it out for a cruise and it was still doing the hold. So today I decided to clean the crap out of the TB. It was beyond filthy and really needed to be cleaned, I was really surprised how nasty it was for such a short time. I pulled out the IAC & MAP sensor and cleaned those as well. The spacer made it so I had to readjust the IAC at idle, so I went ahead and redid all that and noticed that I couldn't get the TPS to show zero even if I backed the idle off a little after the TPS Autoset. So I went to adjust the TPS sensor and it was a little loose. Not sure if it was moving at all, but it was loose. So I reset it properly and tightened it back down and took her driving. The spacer and setting the IAC to around 10% at hot idle made it quite a bit more smooth. I was highly impressed there. I also didn't have the usual hang up, but it was nearly 70 today, so I won't know for sure until it's colder, as that seems to be the only time it occurs. It's set to rain the next couple days, so I'll find out later in the week. I don't like taking the Mustang out in the rain if I don't have to. I have a Custom setting in my Closed Loop Advanced Control that Holley sent me, but I've been considering using one of the 1-5 Advanced Control settings and seeing how it goes.

  7. #17

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    You can tell the ECU what RPM you want it to idle at, and it will automatically adjust the IAC so that the engine will hold that RPM. Right now your Target Idle Speed is set to 750 RPM when the engine is warm, which is fine no problem there. You also have your idle ramp set to start 1200 RPM above idle speed. This means that when you let off the throttle and push in the clutch, and the RPM is above 1950 RPM, it will keep the IAC at the IAC Hold Position number. Right now your IAC Hold Position number is causing the RPM to stay at 2000-3000 RPM, which means that the IAC will never ramp down because it is above 1950 RPM. An easy way to determine what the IAC Hold Position number should be, is to go on the handheld and change the Target Idle Speed RPM to 1950 RPM. The computer will automatically adjust the IAC so that it will idle at 1950 RPM. After you give it some time to settle down look at what the IAC number says, subtract 5 from that number and use that for your IAC Hold Position number. Then set your idle RPM target back to 750. Change the hot engine idle speed to 1950 and see where the IAC sits at. Then change your IAC Hold Position to 5 lower than that. Also, I took a picture of the setting I was talking about. Hope it turns out OK:
    Click image for larger version. 

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  8. #18

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    Ah, there we go. I kind of assumed that's what you meant, but hadn't had an opportunity to play with it yet. I was thinking I would lower it to 1000 RPM and try that, so I'll shoot for around 1750 for the ramp down. The book has quite a few different numbers & recommendations, so that didn't help with the confusion.

  9. #19

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    Quote Originally Posted by Danny Cabral View Post
    Maybe this is an electrical interference issue. Ensure the spark plug wires (or any other high voltage wiring) aren't too close to the IAC motor/wiring. The IAC motor is easily susceptible to this, and I've dealt with it causing strange occurrences (from helping others).
    Danny, do you have recommendations on what to check for with regards to interference? Holley seems to think that's my issue as well, and I'm not quite sure what else to do. If I have to move my wiring for the coil, I will, but I'd rather not. My coil is wired with the MSD shielded magnetic pickup harness and seemed to work great for months; now I'm not sure that isn't my issue. My spark plug wires are about six inches from anything, so I'm not sure that's the issue. Is there some way for me to shield the IAC itself or maybe it's wires up to a point? I'm kind of at a loss for this issue, and it's so intermittent that's nearly impossible to reasonably troubleshoot.

  10. #20
    Join Date
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    Connecticut
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    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

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