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Old 04-16-2008, 03:17 PM   #1
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Default Odd MS no start issue - resolved

I'm posting this because it might help someone in the future.

I began having starting issues and misfire issues with the MS a couple months ago. I assumed it was due to wiring issues because I did have some bad splices at the CAS and the ECU from old piggybacks. Those wiring issues were resolved and the car would then run fine on the stock ECU, but would not run on the MS at all.

I went to DIY autotune and they replaced the processor in the MS, and the car still would not start. The whole time I was thinking that the issue HAD to be the MS, because on the stock ECU the car ran fine. Matt from DIY fully scoped out my MSPNP unit and could not find any problem with it at all.

so for "***** and giggles" I replaced the CAS sensor... and the car started right up. WTF? Why would a CAS work fine with a stock ECU and not the MS? Must be an odd failure mode.

I'll be giving the old CAS to Jerry, and when he gets around to it he will put it on the scope to see what happens.

So it is possible for a CAS to fail in a manner that it works fine with the stock ECU, but not at all with a megasquirt. Something that NB folks planning to get a used NA CAS may want to be aware of.
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Old 04-16-2008, 04:14 PM   #2
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So you have an NB and put an NA CAS on your head?
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Old 04-16-2008, 04:28 PM   #3
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So you have an NB and put an NA CAS on your head?
No. I have an NA. But, if you were squirting an NB it is possible to get a NA CAS that ran fine on a stock ECU but has failed in a manner that the megasquirt wont work for it.
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Old 04-17-2008, 09:30 PM   #4
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I have had similar problems with my MSPNP MM9495.
I will change my CAS this weekend and see if that fixes it.

Matt reckons that Mazda's engineering boffins have encoded the ECU with a way to bypass the CAS signal if it degrades.
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Old 04-17-2008, 10:05 PM   #5
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I have had similar problems with my MSPNP MM9495.
I will change my CAS this weekend and see if that fixes it.
Is that you Andy? If not, I'm lending another Aussie MM9495 owner a CAS this weekend!
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Old 04-18-2008, 01:03 AM   #6
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Originally Posted by OZMX-5 View Post
Matt reckons that Mazda's engineering boffins have encoded the ECU with a way to bypass the CAS signal if it degrades.
the stock ecu is far more forgiving of what it will accept from the CAS than the megasquirt, that is for sure!
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Old 04-18-2008, 09:56 AM   #7
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We've also noticed that sometimes the stock ECU will have no trouble with piggyback timing devices that can cause trouble with the Megasquirt. Now that we have an example of a "borderline" CAS, we can see if we can duplicate the problem and look for solutions.
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Old 04-18-2008, 10:19 AM   #8
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Originally Posted by Matt Cramer View Post
We've also noticed that sometimes the stock ECU will have no trouble with piggyback timing devices that can cause trouble with the Megasquirt.
Indeed this was the case with my car. Stock ecu ran fine with the MSD box intercepting CAS signal. Had no spark with MS.
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Old 04-19-2008, 08:09 PM   #9
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Saboteur, yup, this me
A million thanks for installing the LC-1 this weekend.

Matt, you have PM
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Old 04-20-2008, 08:24 PM   #10
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Indeed this was the case with my car. Stock ecu ran fine with the MSD box intercepting CAS signal. Had no spark with MS.
Seems that I recall the same issue back in the day of people trying to use a JnS knock sensor on other ECU's as well.
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Old 04-21-2008, 06:53 PM   #11
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Stealth97, could you please send me a PM with your email address?
I would like to swap and compare datalog files with you in order to ascertain if we have the same problems.

I tried to send you a PM but this forum will not let me unless I have more than 15 posts.

Thanks

Andrew
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Old 04-21-2008, 06:57 PM   #12
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mx5tuner at gmail.com
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