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Old 06-24-2008, 04:05 PM   #1
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Default I think i have a faulty injector circuit in my MS

I've spent the last two weeks debugging every little thing in my car and MSI. i think it's down to a faulty injector circuit or bad MS micro controller, i just need to prove it. when i plug the stock ECU back in, everything is dandy. i've confirmed that all the settings and wiring is correct. the only thing left to do is to start probing with my lab equipment from the CPU pins 21 and 22 all the way to the injector outputs.

This is an email i've sent to Matt yesterday:

Hi,
I purchased an MSI V3.0 kit and the typical addons a couple of
weeks ago for a stand alone miata 96 install. it's flashed with the hi
res 10G firmware and i read all the sensors correctly except for the
O2 sensor, but i turned down the O2 correction down to zero so it
shouldn't matter.. i think i have a bad sensor since i tried feeding
the board with a variable 0-1V signal and megatune displays it
correctly. i have downloaded your 96/97 base tune map and have only
modified the JS0 output function to fan relay output (which is what i
have on the board) instead of water injection. i also calibrated the
TPS.

Here is the problem:

i originally had RC 550 injectors and setup the req fuel (5.7) &
cranking PWMs. the car would not start no matter what. i found that if
i changed the req fuel to something ridiculous for the injector size
(15) then that car would catch and idle every 20 tries and have non
existent throttle response. throttle would kill the engine, and if i
feathered it really light then it would struggle to rev and buck. once
the engine got warm i couldn't start it anymore.

after 4 days of painful and time consuming debugging, i swapped the
stock injectors back in and then used your exact 96/97 msq. no luck,
same symptoms. when the car actually starts, i checked timing and it's
correct.within a couple of degrees. i checked each spark plug and i'm
getting spark on all 4 cylinders. i must also be getting fuel since
going crazy rich gets the engine to catch and the couple of times i
got it to idle for a couple of minutes the engine was rough but it
wasn't loping or shaking like it would on two cylinders.

I would appreciate any help you could provide.


He asked me for my MSQ and startup data log. i've also attach to this post in case anyone can shed light on whats happening. he didn't see anything strange in the datalog and asked me to check my wiring.
Attached Files
File Type: zip 96_250.zip (22.4 KB, 28 views)
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Old 06-24-2008, 07:24 PM   #2
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I checked the circuits for both injectors and they're fine. Does anyone know how to emulate the tach signal going into the MS? is it a sine wave? square wave? 0-5V? 0-12V? what is it?
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Old 06-24-2008, 07:55 PM   #3
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It's two square waves. They look basically like this, where CKP is on top, CMP is at bottom:



The upper (CKP) pulse is the primary trigger, one per ignition event or two per crank rev. The lower pulse is a counter reset.

Hath thou not a Stim? This is exactly the sort of thing it's used for.
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Old 06-25-2008, 04:56 PM   #4
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Joe, with the above photo, how would you set up the wheel decoder settings in megatune?

thank you
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Old 06-25-2008, 05:16 PM   #5
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Old 06-25-2008, 06:44 PM   #6
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thanks.......nice kitty
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