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Thread: Strange Timing/Idle Problem

  1. #1

    Default Strange Timing/Idle Problem

    I got my Sniper TBI and Dual Sync Distributor installed and have been driving it for two weeks now. The engine is running great, but I noticed a strange problem. I set my timing (twice) while my engine was over 170° according to the handheld. While warm & sitting, my idle speed is around 750, which is what I set it at. My IAC sits at 5% and timing is at 15°, all good. Here's the problem, every now and then while driving when I come to a stop and put it back in park, my idle sticks at 850-1000, the IAC drops to 0, and my timing is sitting at 7° instead of the selected 15° at idle.

    While reading this forum, I saw a post from Danny saying someone's throttle blades might be open too far. Today I adjusted the blades closed a little more and brought my IAC count to 9. After sitting great for about five minutes, something strange happened. The CTS temp on the handheld hit 188° and my idle raised, the IAC hit 0 and the timing dropped to 7°. I thought for some reason "warm" maybe meant 188° instead of 160° as Holley states. I readjusted my idle with the engine idling at 190° and drove the truck. All went well for a while but once again I stopped, put it in park and the idle was high, timing at 7° and IAC at 0.

    So here are the things I have tried/checked:
    -Looked at the idle curve and there are no spikes at a given temp.
    -Used the troubleshooting advice for "will not return to idle" using the red highlighted posts.
    -Lowered IAC Hold Position from 30 to 24 in increments of 2.
    -Manually made sure throttle was closing.
    -Prayed to the car gods.

    *I should have mentioned, at any time when this stuff starts, restarting the engine resolves the problem.*

  2. #2

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    Pic #1 is good idle, pic #2 is bad idle:
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    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Last edited by N.Paul; 05-30-2017 at 07:19 PM.

  3. #3
    Join Date
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    Default

    Quote Originally Posted by N.Paul View Post
    Here's the problem, every now and then while driving when I come to a stop and put it back in park, my idle sticks at 850-1000, the IAC drops to 0, and my timing is sitting at 7° instead of the selected 15° at idle.
    That's the Idle Spark control varying the ignition timing to stabilize/control the idle RPM.
    http://documents.holley.com/199r11031r.pdf (Holley Sniper EFI Instruction Manual - "Idle Spark", Page 31)
    https://forums.holley.com/showthread...-Idle-Solution! (Sniper EFI High Idle 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

  4. #4

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    The second day I started the truck, I took out the -40°F dip in the idle curve. That post which leads to the fuel injection page is good, I have probably read it about 20 times now over the past week or so, but it's not helping my situation.

    I see for sure how the Idle Spark control is trying to drop the idle down to compensate for the IAC already being zeroed, but why is the idle randomly raising is the question? Sometimes I can drive it for 30 minutes and it's fine while sometimes it randomly raises, requiring a restart.

  5. #5
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    Quote Originally Posted by N.Paul View Post
    ...but why is the idle randomly raising is the question?
    I don't know. Is the IAC Hold being activated? What's the TPS Position when this happens? Are you using a throttle return spring (LINK)? Secondary throttle blades sticking open?
    IAC Control/Ramp Down parameter settings? Also, if you'd like to eliminate the IAC valve as a problem, temporarily block off the IAC air inlet port with a strong piece of tape.

    I'd have to see your Config File and a short datalog of this occurrence for us to analyze.
    Also, review the datalog and inform us of exactly where in the datalog (time/seconds) the problem occurs.
    Global Files & Datalogs must be linked to a document hosting website such as Dropbox.com. Someone will analyze it & offer advice.

    Adjust the idle speed screw to the achieve the hot Target Idle Speed RPM setting.
    http://documents.holley.com/199r11193.pdf (Holley Sniper EFI Quick Start Manual - "Target Idle Speed", Page 8)
    http://documents.holley.com/199r11031r.pdf (Holley Sniper EFI Instruction Manual - "Idle Speed", Page 30 & 31)
    http://documents.holley.com/199r11193.pdf (Holley Sniper EFI Quick Start Manual - "Idle Setting/Throttle Plate Setting", Page 11)

    Quote Originally Posted by Holley Sniper EFI Quick Start Manual
    IDLE SETTING/THROTTLE PLATE SETTING
    Once the engine is up to operating temperature, the idle speed can be set to what was configured in the Wizard.
    To do this, open up the Initial Startup gauge screen that was used in section 17.0. With the vehicle in neutral,
    adjust the idle screw until the IAC Position reads between 2 and 10%. While adjusting the screw if the TPS
    Position reads begins to read higher than 0% cycling the ignition switch will recalibrate the TPS back to zero.
    NOTE: Do not attempt to set the target idle speed and IAC position until the engine is above 160°F!
    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. #6

    Default

    What about engine load? Drive vs Park, A/C on vs A/C off? The IAC base setup should be done with minimum load on the engine, I.E. in neutral, A/C off, headlamps off, anything else that puts load on the engine off. The IAC will then open further to compensate for load. This is exactly the other way round from a carb, where you set the idle in Drive with the high beams on.

    Then there's also an engine sometimes being weird: On my car, I'm seeing a 10% variation in IAC Position under comparable circumstances without any pattern or reason to it. But as the IAC never zeroes out, it does not affect idle behavior.
    Last edited by Dr_Grip; 05-31-2017 at 04:53 AM.

  7. #7
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    Additional Info: http://forums.holley.com/showthread....neral-IAC-Info (General 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

  8. #8

    Default

    IAC Hold is not activated during my problem, as it shows 0. TPS also reads 0. I'm indeed using a standard style carb throttle spring, and I've checked twice to make sure blades are closing.

    When this happens, the vehicle is in park and there is no extra load on the engine, besides electric fans. The electric fans do not change idle characteristics beyond 1% change in IAC, so about 10 RPM. Today I'll try blocking the IAC port while this is occurring, and also do a datalog for both good & bad idle.

  9. #9

    Default

    Interesting comments here, and in the linked thread about the return spring being required. The sniper has a stronger resistance than any Holley carb I ever had. It has return springs on both shafts.

    I was not about to add another return spring to mine. Nor did I read anything in the Sniper or Terminator manual that states one must be purchased separately and installed? The Holley carburetor manuals clearly point out the return spring perch on the linkage (not present on my Sniper), and states this:
    NOTE: Unless replacing an existing Holley carburetor, you may need to purchase spring & perch kit.
    Of course, I have no pedal time on mine yet, but a few times I did depress it, I already thought it was too much effort (and was looking into the adding the leverage extensions bracket). You can see the dual return springs that I haven't seen on any 4bbl:
    Click image for larger version. 

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  10. #10

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    **UPDATE** While warming up just now, I heard the IAC open (huge suction sound from port) and my idle raised. The handheld unit shows 0 counts for IAC. I pulled air the cleaner off and the IAC was indeed open by suction feel on the port. I taped off the IAC air inlet port and idle returned to normal. Restarting the engine resets the position so all is well after that. 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?

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