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dap930 dap930 is offline
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Join Date: Dec 2011
Location: Virginia Beach, VA
Posts: 324
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John,

You said when trying to start hot engine you had to crank and crank. If the engine will not catch, then I think you need more cranking pulses for that temperature range. Or is it vapor lock from sitting? Is your fuel pressure being maintained for 20 minutes after shutdown? If it is catching but just won't take off, then ASE needs increased and ASE taper may need to be increased. WUE should be tapered down to 100 (no enrichment) at a CLT where the engine will run without stumbling from cold start, so it does not have an effect on hot starts

One thing you can do help with tuning ASE taper in Tuner Studio is to change the Y-axis from engine cycles to seconds (0.1 sec increments: i.e. 600=60sec). Note that when it is changed to seconds the graph label still says cycles.

I used increased ASE taper time to cure my engine rough running hot start issues. You can have ASE going on for longer periods of time at higher CLT temps than when the engine in cold. You can also use O2 correction at idle to keep AFR's where you want them but usually after the engine is warmed up. Of course for start up, the O2 sensor does not start reading until the controller boots up.

Another thing you can do is to run the car at normal operating temperatures then run a datalog(set O2 correction authority to 0% to not effect idle) with the car sitting, idling for a period of time to monitor the AFR as the IAT increases. IF the AFR starts to lean out, you adjust the MAT correction curve in that temperature range to keep the AFR in range. This will give you an idea of how far off the MAT correction curve is off for your installation. The MAT correction curve is supposed to follow the Ideal Gas Law. Many people running MS2 & MS3 have found it too aggressive, leaning the AFR too much with increasing temperatures. I think it varies depending on the installation. This adjustment will help with heat soaked engine starts and less ASE taper may be needed. Note that changing the MAT correction curve at temperatures seen while under boost will affect the AFR in those areas as well.

Are you using the Idle VE and Idle Advance tables to tune the engine idle?
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-Dennis
1977 930 Slant, MS3 EFI, Carrera intake, Twin plug, Powerhaus headers, Magnaflow muffler, Garretson intercooler, GTX3071R
Old 07-05-2017, 01:17 PM
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