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Thread: My 1% TPS bug analysis & thoughts.

  1. #1

    Default My 1% TPS bug analysis & thoughts.

    For those that don't know, the TPS showing 1% at idle/stopped is actually NOT OK. I assumed it was harmless, but I learned from a Holley tech that it will cause problems as the EFI won't act like it's idling. That's why the issues with the Snipers TPS sensor being faulty is actually something you need to address if you have the problem. There are a few of contributing factors on why you would get a 1% TPS at idle:
    • The strength and geometry of additional return spring.
    • The actual geometry of your throttle cable linkage and the angle it connects to the throttle (and gravity just pulling it open).
    • Faulty TPS sensor.
    • The handhelds display rounding.

    So here are my thoughts on that.

    Throttle Return Springs
    The first thing you do to check if your TPS is faulty, is try different throttle return springs configurations (you need to run an additional spring and cannot rely solely on the spring within the Holley throttle).

    There are several mounting points and configurations available, however, I prefer a light pedal feel, so I have a somewhat light spring attached applying minimal leverage.

    It seems the preferred configuration of the return spring I use isn't strong enough and can result is a 1% TPS at idle SOME of the time. (it will actually flicker back and fourth between 0% and 1%).

    I have since moved it to another location, that makes the spring much stronger, resulting in a 0% TPS reading, however now my gas pedal feels like I'm trying to crush a can under my foot. This is NOT ideal, so hopefully there is another option. which leads me to the TPS sensor.

    The Handheld Display's (In)-accuracy

    I setup my TPS gauge on the handheld to be "yellow caution" @ 0%, and "Normal" @ 1% (You CANNOT set the display to show normal at 0% and caution at 1%, but I won't get into that here).

    I set it up this way to let me easily see if I'm having any TPS issues. If I'm stopped, and my TPS sensor isn't showing YELLOW, then somethings wrong.

    HOWEVER, there are finer values between 0% and 1%, and the gauge, understandably, rounds the decimal.

    SO I would sometimes get a digital value of 1% TPS display, but then still the sensor would still show it as the same YELLOW as if it were 0%.
    This means the TPS sensor is probably @ 0.6% - so the displayed value is being rounded differently then the warning settings - Hopefully a Holley Tech can chime in here.

    The TPS sensor adjustability.

    If you look at the TPS sensor, it actually has some adjustable room on the 2 bolts that mount it.
    I'm wondering if I mount the TPS sensor rotated a little bit, it will result in a better 0% reading.

  2. #2

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    Watching. I have the same thing happening. I too figured it was harmless and was ignoring it.

  3. #3

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    I ended up adding another spring for the time being, so my throttle is stiff, but snaps to 0% TPS.

  4. #4

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    Good to know. I very often see that my TPS is at 1%. What exactly, is the issue caused by this? I haven't had any ill effects. It idles right at my set RPM & AFR.
    1985 Ford Bronco. 300 (305) ci inline 6. 9.1:1 compression, P&P head with enlarged valves, high flow exhaust. 32" BFG A/T tires. 5 speed ZF5 manual transmission with 3.55 rear end. Holley 550-850 2300 Sniper EFI.

  5. #5

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    The TPS auto-calibrates when you turn on the ignition, so adjusting the position will only work until the next time you cycle the ignition switch. What you can do:
    Add a throttle return spring going forward from the throttle linkage.
    Make sure the throttle plates are exactly centered in the bores. Easy but time consuming.
    Make sure your throttle cable moves very freely. If it binds at all, it won't allow the throttle to seat 100%.

    I also added just a touch more "slack" in the primary to secondary linkage, allowing the primaries to start opening before I hit the resistance of the secondary spring. I think it was just straightening the linkage a touch. Kind of a Band-Aid, but did help a little when running the extra return spring. Progressive linkage modification helps the pedal effort a lot. It just didn't happen to work well on my setup for some reason. Maybe it will with my new manifold.

  6. #6

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    I also had this problem crop up literally overnight. The TPS would not return to zero unless I lightly tapped the throttle or let off the throttle abruptly. Over the course of several days I searched for every conceivable mechanical malfunction that could cause this to occur, didn't discover anything, and replacing the TPS had no effect. As an experiment I reset the IAC to 2% and went for a drive of about 20 minutes and with screwdriver in hand, I readjusted the IAC to 6-8% and didn't turn off the ignition, so no TPS Autoset. I proceeded to drive for another 10 minutes or so, and the TPS returned to zero each and every time I let off the throttle. I believe this eliminated anything mechanical that would cause this issue. I stopped for fuel and when I got back on the road the issue resumed.

    I called Holley Tech and explained all the troubleshooting I'd done and the consensus of two Techs and their Supervisor was a bad ECU. So I sent the unit to Holley and the ECU was replaced along with the TPS. The unit is now on its way back to me. Scorecard for this unit since I've installed it: Two ECUs, one TPS, one CTS, and one IAC motor. I must say though, this unit is way out of warranty and Holley is stepping up to fix the problem, and I've never had an issue with any of the Techs with whom I've spoken, they have all been cordial and helpful.

  7. #7
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    22,750

    Default

    Is there a throttle return spring installed? When this happens, can you physically move the throttle shaft back to 0% TPS Position by hand?
    Read "Important Note" at center of page 23: http://documents.holley.com/techlibrary_199r11259.pdf (Holley Sniper EFI Help Manual - EFI Software, Tuning & Datalogging)
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  8. #8

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    Of course I had a return spring installed, and tried a super strong one as well with no change. I believe that would fall into the category of "everything conceivable". As would physically moving the throttle arm. If the issue was mechanical, Holley wouldn't be replacing the ECU.

  9. #9
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    22,750

    Default

    OK, I wish you the best results.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

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