Serial Port Problem

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JasonNA
MS/Extra Newbie
Posts: 6
Joined: Sun Feb 17, 2013 4:56 am

Serial Port Problem

Post by JasonNA »

I had my turbo'd NA MX5 off the road for the winter and relocated my megasquirt into the glovebox. When I went to start it for the first time yesterday I was getting no spark and the fuel pump wasn't pumping.

After swearing at it for a while I disconnected and reconnected all the plugs again; the 2 Mazda ones, the middle megasquirt extras one, the serial plug and the vacuum pipe but it still didn't start.

I then reconnected everything except the serial plug and it started straight away but when I pushed the serial plug in again the car just cut out.

Does anyone knows why this would happen?

The car runs as good as it did before I took it off the road but without the serial lead plugged in I can't get the car remapped on my laptop.

Any help appreciated.
SymTech Laboratories
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Re: Serial Port Problem

Post by SymTech Laboratories »

What main board are you using (v2.2 or v3.o/v3.57)? What kind of serial connection do you have (serial port or USB-serial adapter)? What voltage do you measure on the TPS Vref wire when the serial cable is plugged in and the engine dies?
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damon308
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Joined: Tue Nov 17, 2009 7:36 am

Re: Serial Port Problem

Post by damon308 »

JasonNA wrote:I had my turbo'd NA MX5 off the road for the winter and relocated my megasquirt into the glovebox. When I went to start it for the first time yesterday I was getting no spark and the fuel pump wasn't pumping.

After swearing at it for a while I disconnected and reconnected all the plugs again; the 2 Mazda ones, the middle megasquirt extras one, the serial plug and the vacuum pipe but it still didn't start.

I then reconnected everything except the serial plug and it started straight away but when I pushed the serial plug in again the car just cut out.

Does anyone knows why this would happen?

The car runs as good as it did before I took it off the road but without the serial lead plugged in I can't get the car remapped on my laptop.

Any help appreciated.
Hi JasonNA, yes that is a weird problem all I can think of is try another cable ??, so what mods have you done or is yours a PNP as I am in the process of modding a V3 to run std coils and Trigger wheels as per DIY's site, Regards DM
JasonNA
MS/Extra Newbie
Posts: 6
Joined: Sun Feb 17, 2013 4:56 am

Re: Serial Port Problem

Post by JasonNA »

Need to bump this old thread up as I just ignored the problem last time I asked but unfortunately I now need to plug the ECU into the laptop to diagnose an overfueling issue so this problem now needs to be addressed :(
SymTech Laboratories wrote:What main board are you using (v2.2 or v3.o/v3.57)? What kind of serial connection do you have (serial port or USB-serial adapter)? What voltage do you measure on the TPS Vref wire when the serial cable is plugged in and the engine dies?
Not sure what main board it is, is there a way of checking? Its an original MSPNP if thats any help.

The serial connection is USB-serial adapter but I never get as far as plugging it in to the laptop end as it just dies when the round serial plug is plugged into the ECU.

The TPS is a 3-wire on/off sensor but I can't seem to get any 12v readings off of it at any stage, I'm getting the correct levels of resistance when its open and closed though but no voltage. Unless maybe I'm not doing the correct procedure for checking the voltage...
damon308 wrote: Hi JasonNA, yes that is a weird problem all I can think of is try another cable ??, so what mods have you done or is yours a PNP as I am in the process of modding a V3 to run std coils and Trigger wheels as per DIY's site, Regards DM
Not sure if the cable is at fault but I know someone local who just bought a Megasquirt for his build so I might swipe his cable to try. Mine is a PNP for the mk1 MX5.
JasonNA
MS/Extra Newbie
Posts: 6
Joined: Sun Feb 17, 2013 4:56 am

Re: Serial Port Problem

Post by JasonNA »

Got sorted, turns out it was the cable that was at fault, was squeezed between a bolt and the chassis and was being earthed.

All it took was a year to actually go and look! :yeah!:
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