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How to diagnose a hesitation on throttle transition

Jeff Hare

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My subaru has a hesitation when you first apply the throttle and when you let go of the throttle.  Happens in every gear, even with no load ie free revving.  It is worse when cold.  It also happened on the factory ecu before I changed to Link and has been there ever since I bought the car.  I have a very experienced tuner and he has tried everything he knows of with only a minor improvement.  Therefore I dont believe it is in the tune but something physical.

I have started running logs to troubleshoot why this is occuring.  I have ruled out the throttle position sensor as the sensor voltage looks good and seems to respond quickly and accurately to changes in the throttle.

What I have found is that there is a dip in the fuel injector pulse width when this hesitation is felt.  I have attached a graphical representation of the logs showing what I have found.

What I am missing is the next step, how do I work out what is telling the ecu to have this dip in the amount of fuel causing the hesitation?

Thanks, Jeff


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  • 1 year later...

Thanks Simon, i am working on getting the logs.

In the meantime, I noticed that my ecu is configured to use a V7-9 Map sensor.  The map sensor is Subaru part number: 22627-AA170.  The version numbers on the Link ecus confuse me.  I notice there are 3 choices for a Subaru map sensor: V1-6, V7-9 or V10.  Can you tell me if I have the right Link ecu setting for the above subaru map sensor part number?

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Hi Jeff,

When using the correct MAP sensor the calibration the MAP reading with key on engine off should be pretty close to your local barometric pressure (BAP).

You can see the ECUs current MAP and BAP reading by looking at the General tab of the Runtime Values Window (F12 key to open).

Once you have the correct calibration selected you can use the MAP calibration function to get the MAP and BAP matching exactly.


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