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Thread: TBI Swapped Ford 351M - Hi Idle Issues after in gear

  1. #1
    Carb and Points!
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    TBI Swapped Ford 351M - Hi Idle Issues after in gear

    I did some searching and couldn't find anything like my issue, apologies if I missed something.
    Ok; truck is a Bronco II crawler with a Ford 351M, mild cam, nothing crazy, swapped a GM TBI onto it with a 1227747, running a Moates Ostrich and TunerPro.
    Got VE, AE, PE etc sorted and it works really well except for one issue I admit I can't figure out - any (most) of the time it's been in gear (automatic) and I shift it into park, the idle hangs around 1100 RPM.
    No VSS in it, tried MPH to idle in my tune from 0 to 4 with no difference
    Park sense switch which I can monitor in scanner data and it shows P in park.
    TPS voltage is 0.90 at idle - I've set TPS voltage for idle to 0.94 in my tune thinking the ECM assumes idle at anything under that value
    I've set idle speed in closed loop to 800 - as long as I leave it in park, or don't leave it in gear too long, it will maintain that RPM.
    I've set IAC vs Temp to 1 in the entire table
    Stall Saver isn't occuring (in at 500 and out at 650)
    Retract IAC for voltage drop isn't the issue (scanner data shows ECM voltage above my setpoint in the tune at all times)
    The IAC counts at idle before I pull it into gear are around 20 (RPM at 800) - once It's been sitting in gear for a long enough period of time that the IAC has to compensate to maintain 800 and I put it back in park, the IAC shows approx 70 and the RPM remains at about 1100, and it stays there until I shut it off - so the ECM is commanding this high idle speed. If I shut it down and immediately restart, it will get back into CL pretty quickly (I installed a heated 4 wire O2 from a later model GM to help keep it in CL on the trails) and the idle stabilizes at 800 RPM.
    It seems as if once the ECM raises the IAC count to maintain the desired CL idle speed in gear it can't bring it back down for some reason once put back in park.
    I admit to not knowing how to data log as I'm using a scanner that does that on it's own so I can't post a log...
    If anyone has any thoughts or suggestions, or needs more info, please let me know.

    Thanks in advance - D

  2. #2
    Super Moderator dave w's Avatar
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    Sometimes the IAC adjustment procedure in the attached .pdf will help idle.

    dave w
    Attached Files Attached Files

  3. #3
    Fuel Injected! jim_in_dorris's Avatar
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    Try setti,g your TPS voltage lower, stock GM voltage is .45 volts at idle for a 7747
    Square body stepsides forever!!!

  4. #4
    Carb and Points!
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    Thanks Dave and Jim - I ran the IAC adjustment procedure and also opened up the holes in the TPS so I could adjust it to a final TPS of 0.48 V at idle. I changed the TPS V for idle in the tune to 0.52 V, and set the throttle follower steps to 0 for the time being.
    The first time I started it after the IAC adjustment, IAC counts were at around 18 warmed up and idling at target RPM.
    It seemed to return to idle fine after being in gear, throttled up in Park etc.
    I let it sit for a few hours and tried again - started and idled at target RPM (750) but now the IAC counts were around 35.
    Once I throttled it up to around 2200 in Park, IAC counts went to 54 and stayed there, even when I let off the throttle to idle it - RPM hung around 950.
    Shut it off and restarted it and IAC was again 35 to maintain desired idle speed....
    IAC is a relatively (1 year old) new aftermarket unit.
    I re-did the IAC adjustment procedure with the same results; idle was ok at the time, but hours later IAC counts were high and idle would not come back down to desired.
    Any ideas?

  5. #5
    Super Moderator dave w's Avatar
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    I once read somewhere, don't remember where, that the IAC resets at 35 MPH. It's only here say information that the VSS is needed to reset the IAC.

    Maybe someone else can confirm or deny the VSS is needed to reset the IAC.

    The vast majority of gearhead-efi posts related to idle problems are vehicles without VSS.

    IAC counts in the 10 - 40 range when the engine is fully warmed up is a good target to adjust to.

    dave w

  6. #6
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    park neturel switch? maybe lower temp where it goes closed loop,change iac followers sometimes help if you haven't , one bin I seen had the iac follower at 100 set at 40 helped but mine is std trans
    Last edited by ony; 07-03-2018 at 03:27 AM. Reason: more info

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    Fuel Injected! MQQN28's Avatar
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    Dave
    My system does not run a VSS. It is a customised tune on a delco 808. When it was developed in the mid 90's for the flathead it had a lot striped out including the VSS. I have learned that the first users of these were told when they got the first tune to install A VSS signal.

    I got my system from a person that sat on it for number of years and didn't use it. So when I finally got my going it was on a generic tune and the idle was over 1000rpm. The initial tune was to get the fuelling right for the diff ratio and wheel size. The idle was ignored. A short time later I got a another tune with the idle set to 700 (c4 auto netural). It was only mentioned at the time that economy would be better if a VSS was installed. The tuner decided to change the IAC steps from 256 to 128, I don't know if this is better or worse.

    On reflection the idle seems to be ok, but I have a strange condition that if in neutral and I slowly raise the revs to say 2500 and try and hold it surges low and high. In drive cruising and stoping seems fine.

    I have just this week installed a VSS sender and wired the signal up to the ECM ready to change the data. I'm under the impression that on the Delco 808 that if you hold the revs at around 3000 for 6 sec's it will reset.
    Maybe that's how this works others are different, any way not far away from VSS and more questions.

    MOC
    Last edited by MQQN28; 07-03-2018 at 02:22 PM.
    Ford 28 Roadster Pick Up
    Ford Flathead 51 8BA. Balanced, ported,3/4 cam, Edelbrock 59A heads, C4 trans, 8" diff 3.55 narrowed 40mm /side.
    Fuel injection by Flatattack racing, 60mm Holden TB.
    ECM Delco 1227808 160 baud.

  8. #8
    Carb and Points!
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    Hey Dave; I thought about the lack of VSS a few times - but I have set any tune values to 0 as far as throttle follower steps, MPH to enable Idle or large IAC error etc.
    Not discounting anyone's thoughts, but riddle me this: what it does is - Truck in Park, idling - closed loop, holding desired idle RPM in park (IAC counts around 18 = 750 RPM) - pull it into gear and let the ECU raise IAC counts to get back to desired CL idle RPM (Now prob 34 counts to get back to 750 RPM) I put it back into Park (yes ony - P/N switch works and I can see it change state with my scanner) and then the idle seems to hang at anywhere from 950-1000 RPM - the IAC counts are higher than at desired RPM (usually stay at 34-ish), so the ECU is commanding the new idle speed; since I haven't moved the truck, a VSS signal shouldn't matter - otherwise a stock GM TBI would act the same way if you pulled it into gear, idled for a few seconds sitting still and put it back into park, right?
    I did find a scaler in the tune labelled Min TPS % which was set at 25% - now that I'm at 0.50V TPS at idle that puts me at 10% - I changed the value to 10% and will see what happens tomorrow. Thanks for any and all suggestions so far... I wouldn't give a rats a** about the idle issue if it wasn't for the truck having a doubler transfer case with a redic amount of gear reduction, and my tendency to flop the thing on it's side from time to time on the rocks. A nice predictable low idle would be very nice :)

  9. #9
    Super Moderator dave w's Avatar
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    Quote Originally Posted by Speedyzee View Post
    Hey Dave; I thought about the lack of VSS a few times - but I have set any tune values to 0 as far as throttle follower steps, MPH to enable Idle or large IAC error etc.
    Not discounting anyone's thoughts, but riddle me this: what it does is - Truck in Park, idling - closed loop, holding desired idle RPM in park (IAC counts around 18 = 750 RPM) - pull it into gear and let the ECU raise IAC counts to get back to desired CL idle RPM (Now prob 34 counts to get back to 750 RPM) I put it back into Park (yes ony - P/N switch works and I can see it change state with my scanner) and then the idle seems to hang at anywhere from 950-1000 RPM - the IAC counts are higher than at desired RPM (usually stay at 34-ish), so the ECU is commanding the new idle speed; since I haven't moved the truck, a VSS signal shouldn't matter - otherwise a stock GM TBI would act the same way if you pulled it into gear, idled for a few seconds sitting still and put it back into park, right?
    I did find a scaler in the tune labelled Min TPS % which was set at 25% - now that I'm at 0.50V TPS at idle that puts me at 10% - I changed the value to 10% and will see what happens tomorrow. Thanks for any and all suggestions so far... I wouldn't give a rats a** about the idle issue if it wasn't for the truck having a doubler transfer case with a redic amount of gear reduction, and my tendency to flop the thing on it's side from time to time on the rocks. A nice predictable low idle would be very nice :)
    I'll answer your riddle with a riddle. Why did the spark advance change in your experiment "when the VSS signal shouldn't matter"?

    dave w

  10. #10
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    I haven't used that ecm so this is just a wild guess. Could it be with no vss connected the unknown internal logic thinks when you put it in gear it moves to moving vss logic and stays there until the key is cycled.
    6395, BHDF, 7.4 BBC lightly modded now 6395 BMHM back to BHDF

  11. #11
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    some where if you search this sight there was a man in germany with about the same conversion,can't think of his handle.might find something he learned I think he had this problem too.

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