ecu problem???
 

hi hoping for some help

car is v4 sti ra with an esl daughterboard

it was driving fine before i parked it up but i did have a similar problem before but i thought i had cured it thinking it was an earth problem but now its back with a vengeance.

havent started my car for a while so went out today and tried to start it.

it turned over but not started, then iturned ignition off and then on and it let out an almighty backfire sounded like it was from the engine bay, it did this again but this time it sounded like it was from the exhaust.

i can hear the ignition relay flickering as was my cel light but now it doesnt even come on at all, now and again it flickers with the ignition as do the relays. tried to play with the wires to find out if it was a dodgy one but couldnt really find anything. ive changed the ignition relay if its the brown one in the middle of the other 2 metal relays. ive checked the feed in pinouts to the ecu and the live out to ignition relay they are live.

a bit stuck at the mo

steve

ps when i was turning it over there was a delay between turning the key and it turning over. it clicked like it does wih a flat battery and then a second or 2 later turned over

Sounds like you may have dropped a cell. Put a multimeter across your battery terminals and see what the voltage is.

It's very unlikely to be the ECU but I'm happy to do a full systems check on it FoC to rule it out.

The starter motor runs straight off the switch, although the ECU does sense the starter signal, it does not control the starter, so this symptom does not sound like an ECU problem (although you may have more than one problem, of course!)

It does sound like a problem in the electrical system, but there is a lot to chase down there. It could be a relay problem or a ground / power feed issue. It could also be immobiliser related if you have an aftermarket immobiliser.

Can you confirm if B136 pin 11 is at between 10 and 13 volts with the ignition ON and the engine OFF. B136 pin 11 is one of the two innermost pins of the 22-pin connector, the one nearest the top of the ecu.

Thanx for the replies

I am going to get a new battery tomorrow.

Pin 11 lit a bulb, the cat pissed on my multimeter and fried it. I will get a new one, it does feel like an earth issue to me but will try new battery first. Btw which relay is the ignition and why is there 3 not 2,I know one is the fuel pump relay
Cheers steve

Attached to the bulkhead harness (assuming that is what you mean?) there can be up to four relays, depending on the fitted options, the main relay (6-pin relay, brown connector), the fuel pump relay (4-pin, green connector), front fog light relay (4-pin, black connector) and horn relay (3-pin, black connector).

The ECU gets +12 volts direct from the ignition switch on B136 pin 11, the light suggests this is good, the ECU +12 volt power supply comes from the main relay. Power for the CEL comes from fuse no. 15 in the main fuse box.

Since you've checked most of these and they sound okay, it feels more like an earth problem. Have you checked the main ECU earth at the back of the engine?

Wow you have the knowledge.lol
I did clean the earths before but it has sat in my garage a while so I will recheck that main earth. I was going to check the earths from the ecu ,the ones actually coming from a pinout.I know there is at least one.

I'll try and do this tomorrow but got alot on,many many thanks you've been very helpful.

had a quick look today

i got a new battery, still the same though ,ive tried using jump leads as earths, one from the earth terminal on the battery( with the earth lead connected) to the body and one from the earth on the ecu to body aswell.

now the relay is clicking like mad with the ignition ,seems to be more regular than before where it didnt do anything then started clicking then stopped. now everytime i put the ignition on that relay clicks like mad. sometimes the cel flickers but most of the time it doesnt come on.

i`m wondering if its a damp relay or something but because i had a similar problem before i`m guessing its come back and i fluked a temporary cure. bloody weather is not helping , the light in my garage blew up today and tripped the rcd in the house.
good job i`m alot more patient than i used to be

Hmm, good to eliminate the battery as a possible source, very annoying though (typical electrical problem!). Do you know which relay is clicking? Is it the main relay (6-pin one)?

Certainly a faulty relay is possible, interesting that changing the earth seemed to have an effect.

i know mate ,hate electrical faults. i`m presuming its the main relay tbh because of the cel flickering sometimes.
ive found when the electrics are doing something really strange and inconsistent its usually an earth problem.

ive seen wiring diagrams for other imprezas but not mine where i could trace each pinout and where it goes to ,tells you the wire colour aswell, if i had that for mine i would have a chance of finding the fault.
i think its the new battery rather than the earth making it more consistent clicking wise.
i`ll sleep on it and get a multimeter tomorrow.

The main relay provides power to the ECU, but if the ECU has a consistent +12volts at it then the main relay is doing its job. It is possible the clicking relay is the fuel pump relay. The CEL gets +12 volts through the ignition switch, not via the relay, but it earths through the ECU.

There is a wiring diagram floating around for the 1998 euro impreza GT, which is close although not identical to yours, should be close enough for wire colours etc. to be correct. I'll see if I can remember where it is located.

right ok i did get confused by what does control unit power supply mean as in pins 1 and 2 on b136, i originally thought that was the power in and the pin 11 was an output to the relay.

so pin 11 gives the cpu power via ignition and 1,2 gives the cpu power aswell via the main relay??? is that right. if that is right are there 2 separate circuits in the cpu as in high and low current.

i was thinking about the ignition switch tbh, i am going to go earth hunting today with a multimeter.

i am more confused tbh though. i thought the cel was more of a sign that the ecu was on as such and as you stated the fuel relay could be the one thats clicking because of recieving an intermitent signal from the ecu (if the cel is flickering).thats what lead me to think earth problem.

ive aslo seen pin137/24 - ignition earth, pin 137/14 -power supply earth (so thats main relay???) and pin 136/12 - control system earth (ecu???)

Sorry, I may not have been too clear.

Pins 1 and 2 of b136 provide power to run the ECU. These come from the main relay.

Pin 11 is an input to the ECU from the ignition switch. It is needed for the ECU to operate correctly, but is not the main power input.

If you have a good ground on B136 pins 12 and 13 (with the ECU plugged in) and B137 pin 24 then you should be okay. The ignition system has its own separate earth which is isolated internally in the ECU to prevent electrical noise getting into the more sensitive circuits, but I don't think that would cause the behaviour you are seeing.

If the power and grounds to these pins are good and consistent, even while it is clicking, it might be worth taking Andy up on his offer to check the ECU. (NB while the ignition is off, check the grounds using the ohms range, while the ignition is on, check the grounds using the volts range - you may know this already but thought I'd mention it just in case!)

didnt have much time today but its not the three relays that is clicking, its another one which is higher up and behind the clocks facing down.

i`m sure a friend of mine mentioned a problem with something in the clocks which stopped his car running, took him forever to find it. i`ll ring him and find out.

just started mine up and fro last 3 times the engine check light comes on very briefly and flashes 3 times but u have to be quick to catch it, changed oil friday but car is running perfect idle sweet no noises, ( is this a warning! ) mmmmm???? hope u get yours sorted stedee, heart goes out to u its a horrible thing when the scoob is unwell.

you need to do this mate

http://www.jollygreenmonster.com/ecu.asp.htm

mine is coming along think i`m getting to the bottom of it now. not using it at the mo anyway

dont suppose anyone knows if this was solved, i have a very similar fault but with apexi PFC ecu

The ECU was fried lol

thanks for replying, fingers xd im not in the same boat , as just did the above recommendations and im not getting power on pin 2.

Sorry to drag up an old thread but I having the same issue on my new simtek ecu on 2004 wrx
but it’s intermittent I can drive it fine for a week one one day it will do all this then it’s fine