S300 in P72, Prelude OBD1 H22A - Just Blown The ECU

Masta_Cutz · Post by **Masta_Cutz** » Thu Apr 30, 2009 10:33 am

Guys,

finally was able to chip the virgin P72 last night.

Everything was going well, here's what we did;

Installed S300 track connections,
Cut J12 (which was a little resistor),
Installed J1 jumper,
Installed chip,
Replaced C14 capacitor,
R54 was not on the board so it was not replaced.

Everything looked good and today I hooked up the ECU. Initially I started the engine without the laptop attached, engine started and S300 status light lit up.

Engine was a bit rough but I hooked up the laptop, started a new map and chose the Prelude H22A basemap.

Engine was running for around 10 minutes as I was looking through the engine status and still a bit rough. I went to the injector page and could see it was set up 450cc, I adjusted the size to 330cc (but it turns out I have 345cc peak & hold) and then uploaded the settings, the engine immediately smoothed out.

I then adjusted idle speed from 1000rpm to 850rpm, uploaded settings and everything seemed ok.

Next I revved the engine a couple of times to approximately 3000-4000rpm and with a few seconds my ECU was smoking like a mofo... I killed the engine immediately.

I have checked the S300 with my P28 and it appears to be undamaged, and have also checked the car with it's standard P13 and it appears to be fine.

Upon closer inspection of the board it appears transistor Q34 & resistor R77 have been damaged... the main damage is to Q34.

Does anyone have any idea why this might happen? I followed all the steps and the only fault I did was to enter 330cc injectors instead of 345cc but could that cause the board to burn out?

I'm hoping I can rescue the board and replace the parts but there is one thing confusing me...

On my P28 (which came direct from Phearable.net) J12 has NOT been cut. Is there a reason why this might be? and could I have damaged my board by cutting it?

Really hope someone has some answers!

Thanks

Post by **Spunkster** » Thu Apr 30, 2009 11:57 am

You have the IAT sensor plug and the purge plug swapped in the engine bay and that is what damaged the ECU. Depending on what damage it did to the ECU you may still be able to use it, but it may also have burned other tracks and you may need to replace the ECU.

Masta_Cutz · Post by **Masta_Cutz** » Thu Apr 30, 2009 4:22 pm

Spunkster, anychance you could give me some more details as to why this has happened?

I haven't swapped over any engine bay plugs (didn't know you could) and my P13/P28+S300 worked fine and didn't burn out.

I'm a little confused and i'd really appreciate the help :S

Post by **Spunkster** » Thu Apr 30, 2009 5:18 pm

I'm sorry, Q34 is related to the secondary runners. You have probably supplied 12 volts to a grounded output. Check to see how the IAB control is setup on your vehicle.

http://www.hondata.com/techwiringgsr.html

Masta_Cutz · Post by **Masta_Cutz** » Fri May 01, 2009 12:23 pm

Spunkstar, I'm running a 94 JDM Prelude, H22A and AFAIK the secondary runners are setup as standard.

So I'm guessing when I was running the P28+S300 secondary IAB support was not there therefore the butterfly didn't open therefore the board didn't get fried.

Wish I had known about this before I had a chargrilled P72 sitting in my lap :(

Any chance of some details as to which components are in the IAB circuits within the ECU?

At least then I would be able to test the individual components to make sure I can run the ECU again.

Thanks

Masta_Cutz · Post by **Masta_Cutz** » Sun May 03, 2009 2:07 pm

Spunkster, any ideas on them details for the IAB circuits?

just so i can get a fair idea of where the damage occured.

Masta_Cutz · Post by **Masta_Cutz** » Sun May 03, 2009 5:42 pm

OK, well lets just say i *can* get this ECU working properly again...and replace my IAB vacuum unit at the same time.

If I was to hook everything back up and simply tell SManager to "invert IAB output" would that solve the whole problem of exploding ECU's or do I need to do further work??

Really want to get this sorted as I'm due to have it Dyno'd in the next week!

Ideally I just need to confirm part number for Q34, rating for resistor R77 and fingers crossed I can replace the parts and get it re-fitted.

Really appreciate the help guys.

Post by **Spunkster** » Mon May 04, 2009 11:49 am

No, inverting will not solve the problem. You need to use a relay or something to go from using a positively powered IAB to a grounded IAB.

Masta_Cutz · Post by **Masta_Cutz** » Mon May 04, 2009 12:57 pm

Aaah ok, thanks man.

Well judging by the Prelude circuit diagrams the IAB is supplied permenant live from the battery when the ignition is on, so the current P13 ECU is supplying ground.

If I simply disconnect the IAB 12v live and earth it instead that should solve the melting ECU issue methinks?

Am I right or still being dense?

Sorry to sound like a typical noob but frying 1 ECU was bad enough, don't want to do it again.

Still really need to know the component details of the P72's Q34, need to get the parts ordered!

I've included a pic, please take a look :)

Post by **Spunkster** » Mon May 04, 2009 1:58 pm

http://www.xenocron.com/install/OBD1-IABs.htm

Masta_Cutz · Post by **Masta_Cutz** » Mon May 04, 2009 2:24 pm

Spukster, I'm already aware of the Xenocron IAB conversion, if I get nowhere repairing the P72 I'll be using my P28 and converting it to IAB support.

My main question still is... what is this transistor?

if i can get a spec of the part, or where it's still available I'll be sorted.

I just need to get these few questions answered, I've been told this is the place to get them answered but as of yet I'm not getting very far :(

Post by **Spunkster** » Mon May 04, 2009 3:02 pm

Sorry, but I don't have the specs on the part.

Masta_Cutz · Post by **Masta_Cutz** » Mon May 04, 2009 3:04 pm

ok thanks for the reply i'll check elsewhere.

Masta_Cutz · Post by **Masta_Cutz** » Mon May 04, 2009 7:14 pm

Just incase anyone is searching for a replacement D1780 for Q31/Q34 on a P28/P72 board...

I've managed to find the technical data sheet, should make it easier to locate a suitable replacement. Enjoy!

http://pdf1.alldatasheet.com/datasheet- ... D1780.html

I'm quite impressed how quick I found that :lol: