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Thread: Strange Timing/Idle Problem

  1. #11
    Join Date
    Dec 2009
    Location
    Connecticut
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    19,262

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    Quote Originally Posted by N.Paul View Post
    I taped off the IAC air inlet port and idle returned to normal.
    Thanks for confirming this. This means it's not a vacuum leak.

    I've determined that the IAC is losing its position for some reason. This happened to me before on a TBI truck, and a faulty IAC valve was the culprit. Any thoughts here?
    I believe the IAC motor is losing its position, but I'm not convinced it's defective.
    This seems like an electrical interference issue to me. Ensure the spark plug wires (or any other high voltage wiring) aren't too close to the IAC motor/wiring.
    https://forums.holley.com/showthread...PWM-IAC-Wiring (Read "Initial Baseline Idle Speed Screw Setting" & "Sniper EFI Idle Setting/Throttle Blade Setting")
    http://www.youtube.com/watch?v=s3R8whD3ZWg (Wideband O2 Sensor Test) Key-on/engine-off. Also, the sensor heater will time out, so you'll need to work fast.
    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

  2. #12

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    I just looked at the wiring and found the loomed main harness was touching the top of a spark plug boot on the distributor. Can there really be that much RFI coming off a wire to cause this? I'll drive more later, but just a quick drive around the neighborhood looked promising.

  3. #13
    Join Date
    Dec 2009
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    Connecticut
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    Quote Originally Posted by N.Paul View Post
    Can there really be that much RFI coming off a wire to cause this?
    Yes, it's happened before.
    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. #14

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    Quote Originally Posted by N.Paul View Post
    I just looked at the wiring and found the loomed main harness was touching the top of a spark plug boot on the distributor. Can there really be that much RFI coming off a wire to cause this? I'll drive more later, but just a quick drive around the neighborhood looked promising.
    I'm curious if the issue has been resolved? I'm having the same thing happen. I've done all the same checks up to taping off the IAC, because I haven't had it happen to me while it was parked in the shop. One difference with mine is the Sniper is not doing the timing control yet. This didn't pop up until after I'd put a little more than 100 miles on the truck.

    I have my target idle set to 600 RPM. I start the truck and everything is idling as expected. Head down the road and about 10 minutes into the drive, there's a stop sign and when I stop the idle is about 800 RPM. Continue the remaining 10 minutes of the commute, and go through the drive through to get breakfast, and idle is around 800 RPM but the truck is running fine.

    Parked the truck and in park the idle jumps up to nearly 1100 RPM. Put it back in drive and the idle falls to around 800 RPM. I note that because normally the idle will hold 600 RPM whether I'm in park or drive. I kept the truck running and checked the primary & secondary linkage and all is good. TPS reads 0% on the handheld as does the IAC. Fuel pressure is good at just under 60 psi. In my case, I don't see any places where there is contact or close proximity to a plug wire, but I need to take a closer look to verify. After I restarted the truck it was idling back around 600 RPM like it should. Drove another 5 to 10 minutes in town and idle stayed at the target 600 RPM.

  5. #15
    Join Date
    Sep 2015
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    Palm Bay, FL
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    Quote Originally Posted by MrK5 View Post
    I kept the truck running and checked the primary and secondary linkage and all is good. TPS reads 0% on the handheld as does the IAC. Fuel pressure is good at just under 60psi. In my case I don't see any places where there is contact or close proximity to a plug wire but I need to take a closer look to verify.
    Well, clearly the increased idle is being caused by something beyond the Sniper's ability to control. With the throttle plates closed and the IAC at zero, it's doing everything it can to slow the idle speed.

    If you find yourself again in this situation, you could put your thumb over the IAC vent to ensure that it's not faulty, but I expect it is fully closed as indicated. That means you are getting an air leak from someplace else. Second possibility is that the timing has changed.
    Chris Myer
    800-880-0960 x654
    chris@EFISystemPro.com

    Check our www.EFISystemPro.com website for live stock status on
    all Holley items, including the full line of Holley HyperSpark Distributors!

  6. #16

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    OK, it's been a few days of driving with no issues. The main power harness was barely making contact with a plug wire boot and causing interference. Thanks again Danny!

  7. #17
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    19,262

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    You're welcome, I'm glad you found 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

  8. #18

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    Quote Originally Posted by MrK5 View Post
    I'm curious if the issue has been resolved? I'm having the same thing happen. I've done all the same checks up to taping off the IAC, because I haven't had it happen to me while it was parked in the shop. One difference with mine is the Sniper is not doing the timing control yet. This didn't pop up until after I'd put a little more than 100 miles on the truck.

    I have my target idle set to 600 RPM. I start the truck and everything is idling as expected. Head down the road and about 10 minutes into the drive, there's a stop sign and when I stop the idle is about 800 RPM. Continue the remaining 10 minutes of the commute, and go through the drive through to get breakfast, and idle is around 800 RPM but the truck is running fine.

    Parked the truck and in park the idle jumps up to nearly 1100 RPM. Put it back in drive and the idle falls to around 800 RPM. I note that because normally the idle will hold 600 RPM whether I'm in park or drive. I kept the truck running and checked the primary & secondary linkage and all is good. TPS reads 0% on the handheld as does the IAC. Fuel pressure is good at just under 60 psi. In my case, I don't see any places where there is contact or close proximity to a plug wire, but I need to take a closer look to verify. After I restarted the truck it was idling back around 600 RPM like it should. Drove another 5 to 10 minutes in town and idle stayed at the target 600 RPM.
    It appears my problem may have been solved by adding a throttle return spring. I felt like the throttle was pretty stiff out of the box, and I had added an extension to gain some mechanical advantage. The pedal feel was great with the extension, so I was loathe to add a spring. I dug through my pile of return springs and installed the lightest spring I had. After a couple of commutes the idle has been staying where I want it. I'll report back if anything changes for me.

  9. #19

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    Quote Originally Posted by cmyer View Post
    Well, clearly the increased idle is being caused by something beyond the Sniper's ability to control. With the throttle plates closed and the IAC at zero, it's doing everything it can to slow the idle speed.

    If you find yourself again in this situation, you could put your thumb over the IAC vent to ensure that it's not faulty, but I expect it is fully closed as indicated. That means you are getting an air leak from someplace else. Second possibility is that the timing has changed.
    I spoke too soon. On the drive home today the idle jumped up again. This time I pulled the air cleaner and stuck my thumb over the IAC port and it was sucking hard. Soon as it was covered, the idle dropped down. I can't see any plug wired touching any Sniper wiring.




  10. #20
    Join Date
    Sep 2015
    Location
    Palm Bay, FL
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    164

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    I probably wouldn't jump to suspecting RFI just yet, although that may be a possibility.

    As soon as the idle jumps to 800 RPM (when the target idle is set at 600 RPM), we know something is wrong. And if the IAC is open at all then we don't need to really consider vacuum leaks at this point. This sounds suspiciously like the idle air control issue, that occurs when the -40°F setting of the idle speed curve is lower than the -20 degree setting. I go into this in some detail here.

    If this isn't an that particular idle speed setting, then I'd need a little more data. What is your specific IAC setting when this happens? If it is 30 then it sounds like you may be stuck at the IAC Parked Position, and you can safely lower that 5 points or so and try again. Let us know what you find.
    Chris Myer
    800-880-0960 x654
    chris@EFISystemPro.com

    Check our www.EFISystemPro.com website for live stock status on
    all Holley items, including the full line of Holley HyperSpark Distributors!

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