PW regularly drop to zero for 1/4 sec

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JamesBroChill42
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PW regularly drop to zero for 1/4 sec

Post by JamesBroChill42 »

Hi, I've got a 93 Nissan 240sx running full fuel & Ignition on a MSII 3.57 board. I've been running this setup for about two years now with little trouble. This entire time though I've had this strange RPM drop at idle. I thought it would go away as I tuned the car but it has not. From what I can see on my logs the PW is dropping to zero for about a quarter of a second and then returning to normal. The temperature of the engine only causes this to happen less frequently. My idle control is a cracked throttle plate and is fairly stable aside from this issue.
In the log file you can see the TPS reading -.03%, this is an error on MSDroids part it seems, and to show that it has no effect on the problem i bumped the throttle up to 1%.

Does anyone have any ideas as to what might be causing this?

-James
pit_celica
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Re: PW regularly drop to zero for 1/4 sec

Post by pit_celica »

I see that something is trigerring a fuel cut (status3 = 1), but I can't see what could trigger it. Based on your msq, it's not overrun fuel cut because the RPM is too low. And you do not have any other fuel cut options enabled (flat shift, launch control, overboost, etc).

Maybe someone else can chime in. My suggestion would be to reload the msq just to make sure everything is as it should. Maybe reload the firmware.

Sam
jsmcortina
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Re: PW regularly drop to zero for 1/4 sec

Post by jsmcortina »

It certainly shouldn't be over-run fuel cut, but it sure behaves like it.

Turn over-run OFF and see if this behaviour continues. When you do re-enable over-run your "MAP less than" setting needs to be a lot lower. You are idling at 24kPa, but your over-run setting is 40kPa, that's no good. Try 18kPa.

James
I can repair or upgrade Megasquirts in UK. http://www.jamesmurrayengineering.co.uk

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JamesBroChill42
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Re: PW regularly drop to zero for 1/4 sec

Post by JamesBroChill42 »

I just finished a warm up cycle with the fuel cut turned off. There were no random dips at all. :yeah!: I'm about to do a 400+ mile journey so I'll keep and eye out to see if the dips come back.
I was curious why you said I should pick 18KPa for the fuel cut trigger? I agree 40Kpa is too high, I didn't realize I had it that high. :oops: My question stems from the fact that the engine almost never hits 18KPa.

-James
jsmcortina
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Re: PW regularly drop to zero for 1/4 sec

Post by jsmcortina »

JamesBroChill42 wrote:My question stems from the fact that the engine almost never hits 18KPa.
That's rather the idea. How often do you want the fuel to cut??? It should only be cutting in over-run situations, not normal driving.

Take a datalog of driving and then releasing the throttle at say 2000RPM and then coast down to 1000RPM. (Clutch engaged.) See what MAP readings you get.

James
I can repair or upgrade Megasquirts in UK. http://www.jamesmurrayengineering.co.uk

My Success story: http://www.msextra.com/forums/viewtopic ... 04&t=34277
MSEXTRA documentation at: http://www.msextra.com/doc/index.html
New users, please read the "Forum Help Page".
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