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Thread: AFR Spikes/IAC

  1. #31

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    Oh, I wasn’t quite serious. I’ll try and get it right first! But that's a good question, as I have done it in the past while troubleshooting.

  2. #32
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    Quote Originally Posted by 81 TransAm View Post
    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.
    It doesn't damage the ECU, but you can't just unplug the IAC motor connector. Depending on the IAC Position at the time you disconnect the IAC motor, it may be somewhere in the open position. I'd temporarily block off the IAC air inlet port (with a piece of tape), and verify the engine will idle/return to idle well. This will also confirm if the IAC valve is causing the high idle problem. Lots of additional information in the first several paragraphs of the link below:
    http://forums.holley.com/showthread....neral-IAC-Info (IAC Information - Read "IAC NOTES")
    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. #33

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    Covering it up with tape will get it to return to idle. I'll play with the IAC settings. What's weird is how it was normal in the summer, but starting in the fall/winter it's crappy. January was really warm here for some reason, so it stopped doing it, and now that it's cold again, she's doing it all over, that's the only part that throws me off. But let me try raising the hold over 2K, as well as lowering the IAC Hold Position down quite a bit and I'll report back.

    Well now, this took another twist that I have no idea how to fix. What I always found odd was how it would hold up at roughly the same RPM no matter what I set the IAC to, and it did so again today. I've gone ahead and attached the datalog I took showing how it went down before I found what I think is the problem. At first I had the air cleaner on and could get it to do it every single time I would full throttle the car. If I would stop real quick, jump out so I could see what was going on. As soon as I touched the air cleaner and started to unbolt it the car would start the ramp down, pretty weird I thought. So I taped up the IAC again to verify and drove around with no air cleaner, I didn't really hammer on it like I usually did so it didn't do it, but then I got to thinking, why was it every time I touched the car it would stop. I also remembered how in the past, if I was able to get out and put my finger over the IAC, it would drop down and then kick back up. As well as if I blipped the throttle every now and then it would stop, all with no consistency of course, that would be too easy. So I took the tape off and drove off, this time I had the IAC at like 3, 2000 RPM (2500 is not possible by the way, out of limits), etc., and it still held strong at 3000, but showed zero on the IAC which was also weird as that shouldn't ever happen right? But when I stuck my finger over the IAC there was no suction, so it was actually at zero and that did nothing to stop the high idle. Then I noticed that the secondary blades were open and I watched them all the sudden snap back and the car ramped down. Wondering, I drove around again and got it to duplicate, but after I manually moved the secondaries they seemed to not bind up anymore. Finally I got it to do it again and was able to get a picture, you'll see the secondary is quite a bit off from the link bar and just holding steady so now I have no idea how to fix that. I did notice the lower I set the IAC Hold Position the quicker it would start to ramp down, it's almost like the suction from the IAC helps hold the secondary blades open. So now the real question, how do I fix this or should I send the throttle body in to Holley for a look? No, it's absolutely not hitting anything on the intake and there's not physically noticeable about it, and when the car isn't running it doesn't seem to have any binding. It only happens when I full throttle the car as well, if I part throttle all the way to 6K it won't do it, only when I really get on that throttle. Super strange, thoughts?
    https://www.dropbox.com/s/vbk8zx965z8z6pu/IAC.dl?dl=0
    Click image for larger version. 

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  4. #34

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    Maybe the air is forcing the plates open at higher RPM. You might try winding the secondary spring up one or two more turns.

  5. #35
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    Quote Originally Posted by sr1032 View Post
    Then I noticed that the secondary blades were open and I watched them all the sudden snap back and the car ramped down. Wondering, I drove around again and got it to duplicate, but after I manually moved the secondaries they seemed to not bind up anymore. Finally I got it to do it again and was able to get a picture, you'll see the secondary is quite a bit off from the link bar and just holding steady so now I have no idea how to fix that. I did notice the lower I set the IAC Hold Position the quicker it would start to ramp down, it's almost like the suction from the IAC helps hold the secondary blades open. So now the real question, how do I fix this or should I send the throttle body in to Holley for a look? No, it's absolutely not hitting anything on the intake and there's not physically noticeable about it, and when the car isn't running it doesn't seem to have any binding. It only happens when I full throttle the car as well, if I part throttle all the way to 6K it won't do it, only when I really get on that throttle. Super strange, thoughts?
    This is usually caused by one of the secondary throttle blades rubbing in the bore:
    https://forums.holley.com/showthread...8709#post68709 (Related Forum Thread)
    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. #36

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    I went ahead and put penetrating oil on the secondary shaft and will let it sit. I tried to coil the spring one more time, but of course it snapped off and I was in a hurry to head to work, so I'll pull the throttle body off tonight and put the spring back on. I found a lot of threads about needing to do that, makes me think it's not a very good design. Part of me wants to put an external spring on it, but I'll rock this tighter and see what happens.

    I readjusted the spring one turn and boy that made a difference in how it closed, so much so that I had to completely redo my IAC/idle settings. I’ll take her out for a spin tomorrow, but I had a question from probably reading too damn much. I adjusted my idle and am curious if I’m doing it wrong. Basically I covered my IAC with tape, removed the link bar, took my primary & secondary adjustment screws all the way out, so they were both closed and then turned them both in equally until the car would idle around 50 RPM below my target. I then removed the tape from the IAC, and reinstalled the link bar and had an IAC of around 5. The reason I'm confused is a lot of the readings seem to imply to set the idle only using the idle speed and not adjusting the secondary which seems odd to me if all the injectors are firing. Wouldn’t you want the primary & secondary letting air in? Either way I’m way more confident that my hanging idle will be good to go tomorrow, can’t wait to check it out! I appreciate all the help thus far, these nagging gripes sure can be frustrating!

  7. #37
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    Quote Originally Posted by sr1032 View Post
    The reason I'm confused is a lot of the readings seem to imply to set the idle only using the idle speed and not adjusting the secondary which seems odd to me if all the injectors are firing. Wouldn’t you want the primary & secondary letting air in?
    Yes, Terminator TBI users may need to also adjust the secondary shaft screw (LINK), so the throttle blades are equally open. However, the final adjustment is performed with the idle speed screw only.
    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

  8. #38

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    Well for anyone who may have this problem in the future, it was definitely the spring on the secondary shaft. I kinda feel like an idiot right now that chased his tail for over four months, for something as simple as a spring that just wasn't tight enough. Oh well, she's back to her happy self. This EFI is probably the best, most frustrating experience of my life! LOL. I feel like I need to log all the issues I had from start to finish! Anyway, just wanted to close the loop.
    Last edited by sr1032; 03-06-2018 at 10:14 PM.

  9. #39
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    Location
    Connecticut
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    Thanks for the update. I'm glad that resolved the problem.
    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

  10. #40

    Default Return To Idle

    My problem is the RPM dips while returning to idle. Sometimes it dips enough that the engine dies. It happens at low RPM or when it sees a (small) load change, such as shifting from Neutral to Drive or Reverse. It is most pronounced when cold, but even happens once warmed up. The car has a 347 with a 220° cam (FRPP E303) and an automatic transmission with a tight (stock) converter. It has a relatively smooth idle with about 10 inHg of vacuum.

    I've attached both a datalog and my Global File. At time 66 seconds, I shifted from Neutral to Reverse and the engine almost died. At time 240 seconds, I was driving slowly down a road, did a quick stop & again, the engine almost died. Each time, the Left AFR (my only WBO2 sensor) spikes to 20:1 and then recovers. For that matter, does the AFR readings look right? It's spiking frequently and this run was a slow drive around a couple residential blocks (with an automatic transmission).
    CAT - 2018-03-01 - Return to Idle Problem.zip

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