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Thread: Slight Bogging Down (Lag) After Accelerating from Stop

  1. #1
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    Slight Bogging Down (Lag) After Accelerating from Stop

    I got my car to a dyno shop a couple of days ago. The car runs better but I think I need to do some tweaks. One issue the dyno shop couldn't quite eliminate was a slight lag when pressing the gas pedal from a stop. I have an automatic and there is the tendency to bog down briefly when pressing the gas pedal after a stop. I don't have a TPS. Has anyone with an automatic been able to overcome that?
    Shannon

  2. #2
    Senior Member AdmiralSenn's Avatar
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    I had the same issue on my manual, and never solved it until I added a TPS. You could try playing with the vacuum line coming off the manifold, I've seen people recommend any of a slight restriction, an accumulator/chamber, or a check valve. None of those worked for me.

    Could also try bumping up your low end ignition advance slightly if you're running spark control. I noticed it didn't seem to happen to me as much when I advanced the distributor.
    Aka Adam S, aka Adam Wright
    1981 DMC-12 #3416, mothballed in preparation for motor swap
    2006 Volvo S60R

  3. #3
    EFI'd Member dn010's Avatar
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    I had to adjust acceleration enrichment & timing (if you're using a MS ECU) otherwise I had a huge pause after hitting the pedal until the engine responded from a stop. However, I too have a manual transmission and TPS.
    Last edited by dn010; 10-08-2015 at 03:57 PM.
    -----Dan B.

  4. #4
    Back to the Omnipresent! Spittybug's Avatar
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    Shannon, without the TPS you are relying on the vacuum signal to tell the MS unit that you are accelerating. That has a delay on it since the vacuum must "travel" (backwards I know) to the MS unit via the hose and then be detected. No way around the physics of that other than to make the hose as short as possible. The electrics of a TPS are virtually instantaneous in comparison. I suppose it might be possible to use the stock microswitch in some way, but the more reliable way would be to use a modern car's pedal-based TPS system. I know little to nothing about them, but IIRC, Dave M. posted something about them once upon a time. Worth looking into......

    Ian sent me his MS tune after he dyno'd and I'm digesting it. I also drove his car and the acceleration is nice. I suspect changes to my timing curve and acceleration enhancement are in order.
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  5. #5
    EFI'd Member dn010's Avatar
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    It must be a potentiometer based TPS to use with the MS unit that will read the travel of the throttle throughout the entire range closed to full.

    I tried to use a switched based (stock Volvo Bertone 780 TPS) and it did not work for me, the manual even states not to use a switch based TPS unfortunately I read this after the fact. I guess it only tells the ECU when the throttle is closed and wide open and does not tell you what percentage the throttle is open.

    I am now using a newer Bosch potentiometer type TPS that are found in a wide variety of cars.

    Cheers,
    Dan B.
    Last edited by dn010; 10-09-2015 at 10:17 AM.
    -----Dan B.

  6. #6
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    Quote Originally Posted by dn010 View Post
    It must be a potentiometer based TPS to use with the MS unit that will read the travel of the throttle throughout the entire range closed to full.

    I tried to use a switched based (stock Volvo Bertone 780 TPS) and it did not work for me, the manual even states not to use a switch based TPS unfortunately I read this after the fact. I guess it only tells the ECU when the throttle is closed and wide open and does not tell you what percentage the throttle is open.

    I am now using a newer Bosch potentiometer type TPS that are found in a wide variety of cars.

    Cheers,
    Dan B.
    Is this working with Megasquirt? Where and how did you install it?
    Shannon

  7. #7
    EFI'd Member dn010's Avatar
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    Yes, I'm running a potentiometer based TPS with my MS and it has been working fine. The TPS I'm using is Bosch #0-280-122-001. I'm guessing you've got the stock D motor converted to EFI, if that is the case you'll need to find a way to make the TPS work either by using the throttle spool or perhaps somehow using the butterfly assembly

    I'm running the Volvo Bertone variation of the B280F engine with the EFI manifold etc - If you have the same setup, here is additional information. If not, you can skip this part:
    On this motor, I have the TPS mounted where the old, stock TPS was mounted on this engine - attached to the butterfly assembly. It isn't a simple swap to install the new TPS, the old one has the butterfly valve rod hole in the center between the mounting holes and the new one has the hole offset. To make this work the original bracket must come off and be modified along with the brass butterfly rod to be shortened (length wise) and cut in half (width wise) to fit in the new TPS hole.

    Quote Originally Posted by lazabby View Post
    Is this working with Megasquirt? Where and how did you install it?
    -----Dan B.

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