MSPNP Gen 2 blown transistor? 10 amp fuse left in. Does Gen 2 suffer too? - Miata Turbo Forum - Boost cars, acquire cats.

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Old 12-26-2012, 08:27 AM   #1
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Default MSPNP Gen 2 blown transistor? 10 amp fuse left in. Does Gen 2 suffer too?

Hi Guys,

Been reading about the problem caused by leaving the ST IGN (I think thats the name) fuse in - 10 amp one anyway. I read this about the ms pnp gen 1 but I have the same symptoms on my 2nd gen unit.

Starts then stalls straight away. I bridged the FP - GND on the diagnostic port and the fuel pump is running all the time but the car runs now and revs etc.

SO have I done the same thing and damaged the transistor? It didn't mention anything about removing the fuse in the instructions that came with the ECU but I found instructions online after the problem started that did say I needed to remove it. If thats the case, which transistor do I need and are there instructions on replacing it anywhere? I can solder but not brilliantly.

Any ideas?

MSPNP Gen 2 1995 Eunos mx5 1.6L

Cheers, Dan
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Old 12-26-2012, 09:41 AM   #2
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It didn't mention anything about removing the fuse in the instructions that came with the ECU but I found instructions online after the problem started that did say I needed to remove it.

yeah, its step #1 in the installation:

Quote:
Physical Installation

  1. Remove the ST SIGN fuse from the underhood fuse box. You should not put it back in when you finish installation. Do not run the MSPNP with this fuse in place, ever. We've beefed up the Gen 2 MSPNP so it is less likely to be damaged by failing to remove the fuse, but it is not intended to be run like this.
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Old 12-26-2012, 12:42 PM   #3
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Nah, I've removed the fuse now. I meant are there instructions to fix the transistor if thats the cause?

I only found info saying to remove the fuse after searching the symptoms of my problem. The information included in the box with my ecu didn't say anything about removing this fuse and I assumed the problem had been resolved since the 1st gen.
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Old 12-26-2012, 02:19 PM   #4
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It's not really a "problem" with the design, per se. The 1.6 miata harness was never intended to allow the ECU to drive the pump, so DIY came up with a clever workaround. They are back-feeding 12v into the line originally intended to signal the ECU that the starter is running, said line also happening to drive the fuel pump relay directly.

The problem is that the starter is essentially a dead short from the point of view of any reasonably sized transistor. So given the design of the OEM harness, there's really nothing you can design that won't blow up if you neglect to remove that fuse.
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Old 12-26-2012, 02:25 PM   #5
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I dont think you understand what I'm asking.

Which transistor do I need to replace? (I assume that is broken now)

If so, how do I replace it?

Thanks
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Old 12-26-2012, 02:29 PM   #6
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Originally Posted by Joe Perez View Post
So given the design of the OEM harness, there's really nothing you can design that won't blow up if you neglect to remove that fuse.
I know its reinventing the wheel from the point of view of the DIY pnp units but with the FWD BP's I have been wiring the MS fuel pump output to the VAF signal wire at the ECU, then placing a jumper between the Vaf signal wire and the F/P trigger on the VAF connector allowing the MS to control the F/P without the need for the extra transistor mod or removing the ST fuse.

this also has the added benefit of being dummy proof if the end user needs to go back to the stock ecu, as the jumper has to be removed to install the vaf.
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Old 12-26-2012, 02:40 PM   #7
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SO do I need to replace the transistor?

If I do - which? and how?

I don't want to run the car with a paper clip in the diagnostic port as a permanent solution.

I'm not looking to reprogram or modify the ecu in any way. I just want to fix it.
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Old 12-26-2012, 03:10 PM   #8
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You would need to find a PCB layout for the new MSPNP2 unit. I've not seen one so I can't tell you what transistor you may have killed.

After you figure out what transistor you may have killed, you will need to learn how to test a transistor.

Quote:
Originally Posted by Dagger View Post
MSPNP Gen 2 1995 Eunos mx5 1.6L
DIY lists the MSPNP2 94/95 for the US spec 1.8 engine and wiring. Do they sell one specifically for the UK/EU Eunos 1.6 cars? I honestly don't know.

You may need to contact DIYAutoTune directly for this question.
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Old 12-26-2012, 03:59 PM   #9
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Thankyou EO2K for your answer!

I was looking at this thread before: https://www.miataturbo.net/megasquir...-damage-58494/

Someone links to the transistor that the OP needs. I'm wondering if anyone knows if its the same one that I need?

I have emailed DIY auto tune but havent had a reply yet.

Cheers
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Old 12-26-2012, 04:11 PM   #10
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I'd give them a little time. We are all still coming down from the holidays and they may be backed up from holiday purchase tech support emails.
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Old 12-26-2012, 04:32 PM   #11
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Yeah thats what I assumed. Damn Holidays slowing me down lol
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Old 12-26-2012, 10:37 PM   #12
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Quote:
Originally Posted by Dagger View Post
SO do I need to replace the transistor?

If I do - which? and how?
Probably, yes.

The link given was for the first gen MSPnP.

I know that DIY changed the design with the MSPnP2, and as they don't publish the schematics, I can't tell you which one or where to find it. You'll have to wait until they re-open and ask them.
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Old 12-27-2012, 05:34 AM   #13
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Quote:
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Probably, yes.

The link given was for the first gen MSPnP.

I know that DIY changed the design with the MSPnP2, and as they don't publish the schematics, I can't tell you which one or where to find it. You'll have to wait until they re-open and ask them.
I know the link given was for the first gen. That's why I posted it and asked if my issue was similar to the issue in the link I posted.

If you don't know then fair enough and as I've said a couple of times I'll wait for them to re-open.
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Old 12-27-2012, 09:45 AM   #14
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Assume nothing.

The Gen 2 fuel pump output for the MM9093 is designed to shut down if whatever is on the other end draws more than 500 mA. I'd say there is around a 90% chance you didn't kill it, which is a good thing because it's nearly inaccessible.
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Old 12-27-2012, 10:52 AM   #15
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Clever.
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Old 12-27-2012, 11:43 AM   #16
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Thanks Matt.

In that case do you have any insight into how I may use the ecu without the jump in the diagnostic port?
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Old 12-27-2012, 01:12 PM   #17
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Quote:
Originally Posted by Joe Perez View Post
Clever.
I (destructive) tested 3 or 4 different protection circuit designs before we settled with what made it to production. It probably is not 100% failure proof, but it has been tested for 10+ minutes of continuous fault protection with the fuse still in place. This is opposed to the Gen1 circuit which had a little ZTX553 to drive the pump circuit, which works very well so long as the instructions were followed, but would let the smoke out instantly if the ST SIG fuse is left in place.

We have 0 reported failures of our new design to date, with a great many MSPNP Gen2 90-93 systems sold. It uses a larger transistor (TIP125 IIRC) and an overcurrent protection. I suppose it will still eventually fail if given enough abuse / time to do so; there is a polyfuse that will heat up. However it will give the user *more* than enough warning time to realize that there is a problem and hopefully go back to the instructions to find out what is happening. Step #1 in the instructions is to remove the ST SIG fuse.
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Old 12-27-2012, 01:57 PM   #18
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Step #1 in the instructions is to remove the ST SIG fuse.
Thanks for all the info! Just to make it clear - I have removed the fuse already, but this was not included in the IN BOX instructions as I would have expected which is why I did not immediately take it out.

Please don't tell me to remove the fuse any more and please don't tell me that it says to remove it in the instructions as I have explained those 2 points 2 or 3 times already.

Thanks
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Old 12-27-2012, 03:10 PM   #19
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Quote:
Originally Posted by Dagger View Post
Thanks for all the info! Just to make it clear - I have removed the fuse already, but this was not included in the IN BOX instructions as I would have expected which is why I did not immediately take it out.
Please post a photo of the in box instructions, and I'll look into how you could have been sent the wrong instructions.

You can send the ECU back for repairs - it's $75 an hour plus parts - or jump it at the diagnostic port.
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Old 12-27-2012, 03:15 PM   #20
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Quote:
Originally Posted by Matt Cramer View Post
Please post a photo of the in box instructions, and I'll look into how you could have been sent the wrong instructions.

You can send the ECU back for repairs - it's $75 an hour plus parts - or jump it at the diagnostic port.
I've replied via my personal email regarding the query through the DIY auto tune website contact details so please check your non-forum emails. I can't really send it back for repairs as I live in the UK so the postage would be massive. Is there really no other way to 're-set' it as you say it has most likely shut down rather than sustained damage?
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