Odd wiring / ecu fault

Rapidresto · Posted: Fri Apr 29, 2011 9:16 am Post subject: Odd wiring / ecu fault

Hello folks!

Back to playing with the Ghia again, it's been a while and i'm going to start to track down some of the running faults, but first i've got to get it started properly.

2.2 92 legacy, no lambda, self converted loom.

Anyway, it's been running and starting no problem for a while and only recently has been munching starter motors.

I've now traced the starter problem to the cold start circuit. The engine started fine, and the 12v feed from the switch was off, and the cold start circuit was also off.

After a couple of minutes running and a quick trip up the road and back (engine was now warm), the starter engaged causing a lovely noise!

Turned the engine off and as soon as i turned the ignition on the starter turned over.

Long story short it turns out that the cold start circuit is live and feeding 12v back to the starter motor.

Snipping the wire from the ecu to the starter stops this issue and the engine starts normally (although the ignition light on the dash now stays on?).

Any idea why this would happen? I'm at the point of swapping out the ECU and loom for another that I have.

I've also picked up another known good engine that i could swap in or at least use for parts!

Oh and i've got no diagnostics circuit it would seem

so pulling off fault codes is going to be difficult.

ElusiveStranger · Posted: Sat Apr 30, 2011 1:36 am Post subject:

Wood for trees?

Starter motor should only be switched from the IGN. That sends the 12V to the ECU.

The 12v feed from the IGN is key controlled not ECU controlled - there's NO way the ECU can power a starter

Are you running a setup with a dodgy starter bush?

I don't doubt your diagnosis but it's a bit .....
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Rapidresto · Posted: Sat Apr 30, 2011 7:08 am Post subject:

Its strange but true, when the engine is running the cold start wire that usually runs from the ecu to the starter (to provide the ecu with the signal that the starter has been turned on and off) was live.

I'd checked that the ign wasn't staying on (i've already swapped out the switch in case that was dodgy) and when i pull both wires (ign and cold start) off the back of the starter motor it was the cold start one that was live and not the ign when the engine was running.

This 12v signal coming from the ecu was enough to flick the solenoid on the starter.

Essentially my question should be why the hell is the ecu sending a 12v signal down the cold start wire and why is the ignition light staying on now!

I'm suspecting damage to the loom or ecu fault as its a problem that has occured whilst i've been using the car.

ElusiveStranger · Posted: Sat Apr 30, 2011 10:46 am Post subject:

Curious!

Maybe put in a blocking diode on the starter to ecu wire
_________________
The advice you receive on here is worth the paper it's written on.
Your experiences are worth shed loads to others, including the f'ups - live and learn.
Wouldn't YOU rather learn by someone else's mistakes? So would they.

'78 Bay, 2 litre 091 box, EJ20 NA & the ashtray's on the 'right' side.
I don't lean forward for hills any more Grin

Bugger, missed out on "Live fast, die young"

Rapidresto · Posted: Sat Apr 30, 2011 11:04 am Post subject:

Rapidresto · Posted: Sat Apr 30, 2011 5:17 pm Post subject:

ok i've done a good bit of playing today.

First up i've got diagnostics running which threw up a faulty injector code, traced that to a duff wire in the engine loom so swapped that out for one off the spare engine. That'll explain the dissapointing power levels, it felt like it was only running on 3 because it was!

anyway, with that sorted i'm still getting the problem with the ignition light staying on? Never used to happen.

oh and my tacho has suddenly stopped working, checked all the wiring to that and it seems ok?

no fault codes now other than a series of 5 long pulses (ie code 50) but i can't find anything to correspond to a code 50?

Have tried swapping the ecu i have and it didn't make any difference.

EDIT

turns out the ignition on, tacho not working was nothing more subaru related than a dodgy connection on the ghia fusebox, all working now!

Still need to know what 5 long pulses on the fault codes means?

Cheers
John

ElusiveStranger · Posted: Sun May 01, 2011 9:49 pm Post subject:

@ the wiring.

I've looked but I can't find a 50 code
_________________
The advice you receive on here is worth the paper it's written on.
Your experiences are worth shed loads to others, including the f'ups - live and learn.
Wouldn't YOU rather learn by someone else's mistakes? So would they.

'78 Bay, 2 litre 091 box, EJ20 NA & the ashtray's on the 'right' side.
I don't lean forward for hills any more Grin

Bugger, missed out on "Live fast, die young"

rjes · Posted: Sun May 22, 2011 11:31 am Post subject:

As you have found other wiring faults, the most likely cause of the cold start circuit backfeeding the starter, if that is definitely the cause, is another wiring fault. A short between something at 12V and the cold start wire. As Elusive says, there is no way the ECU can feed 12V to the starter.

Another option is that the stater engaging when it shouldn't is due to another intermittant fault which had nothing to do with the engine management. Faulty ignition switches can cause this, as can wiring problems.

In my experience the majority of VW's from the 70's suffer from regular electrical problems unless they have been rewired to a high standard by now. Often the spade connectors have lost their grip on whatever thay are plugged on to.
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