MK1 Golf Motronic ECU Wiring

Check your main ECU earth's as well, brown on ECU 35 pop it to battery

rubjonny said

Check your main ECU earth's as well, brown on ECU 35 pop it to battery

You are just another well grounded fellow.  

I hate VW's and Grounds…. But having good grounds on a VW is a well grounded and usually good running car.

I thought Lucas was bad, until I met Bosch and VW.
         

as we say over here, very 'down to earth'

Ok so I've checked all the ground wires I can find inside and in the engine bay including connections onto the block and alternator etc and from what i can tell these all appear fine to me.

All the wires from the fusebox to the headlight loom, fuel pump and dash loom are all connected and again all look fine to me.

I've got 2 brown wires from the ECU straight to the battery. I've also attached the brown/red wire from the ECU to the battery as you thought this might be another earth (I have tried disconnecting this wire btw and it made no difference to my current issue)

The battery is knackered though so all the 'testing' I am doing is whilst I have a battery charger attached, whether this makes a difference I have no idea!? 🤷‍♂️

I have found an odd connector hanging beneath the steering column with 2 wires (brown and brown/yellow) however I cant find anything that this should be plugged into, any ideas?

I feel I've reached my limit on this and don't want to keep wasting your time, which I really appreciate! So I'm going to admit defeat and call in an auto Electrician, I'm sure the issue is most likely very minor and stupid but I'm just getting nowhere fast here.

I'll post an update once I get it sorted.

Thanks again for all your help so far! 👌👍

Brown/red what ECU pin?

2 pin most likely choke warning light

Get battery charged first, that could definitely cause your issue

Tbh I'm not sure what ECU pin the brown/red wire comes from, it's just nestled in with all the others wires coming out of the Motronic ECU that are all contained within the plastic sleeve.

I did wonder as to whether I should connect the carbon cannister wiring (brown plus Green/yellow) to anything? Factory these were connected to the ISV and cold start via the common black/white wire between all of them, just clutching at straws here I guess though 🤷‍♂️

Ah choke warning would make sense as the car was originally 1100cc, now all the choke parts etc has been removed so there wouldn't be anywhere for it to connect to

Yep I've ordered another battery as the first one got lost in the post apparently 🤦‍♂️

cant see a brown/red on my diagram, use a multimeter on all the pins till you find it

dont need either of the carbon canister system plugs the ecu doesnt care, made several looms and just cut it out entirely no problem

let us know how it goes

So I've done a bit of research and found this:

Factory immobiliser - ICE 'n' Secure - The Corrado Forum

Full credit goes to 'vw rule' on the-corrado.net

It lists all the pins and wire colours from the Motronic ECU so I'm going to check through every wire (thankfully less than 35) to be sure I've connected everything to where it needs to be

From a quick first glance I believe there's more earths from/to the ECU to connect to the fusebox than I've currently got - are there any obvious / easy to connect to earths on the fusebox that would be the better ones to use?

I've also now got a shiny new battery to hook up and see what difference that will make……..just need to find the spare time to do it now!

his list isn't quite right, missed off the throttle switches, lambda and incorrectly lists speed sensor as earth

1 - gry/wht - diagnostics K-line
2 - blu/wht - vehicle speed signal (no need to worry about this)
3 - pur/wht - coolant temp sensor pin 1
4 - red/wht - DPR pin 1
5 - brn/blu - DPR pin 2
6 - gry - knock sensor 2 (G66) pin 1
7 - pur - lambda probe
8 - blu - knock sensor 2 pin 2
 \- yel - knock sensor 1 pin 2
9 - blu/yel - EGR sensor (california models)
11 - grn - coil pin 2
12 - red/yel - G1/3, fuel relay earth trigger
13 - yel/blk - fault lamp
14 - blk - G1/4, ignition live feed shared with coil
15 - gry/yel - carbon canister freq. valve pin 2
16 - blk/red - cold start valve pin 2
17 - wht - ISV pin 1
18 - brn/yel - earth to battery, shared with coil, carbon canister on/off valve & lambda probe heater
19 - red - Y/2, permanent live
20 - brn/blk - earth, only for automatic models
21 - red/blk - distributor pin 3/+
22 - yel - diagnostics L-line
23 - gry/grn - airflow potentiometer pin 2
24 - wht - knock sensor 1 pin 1
25 - grn/blu - G1/12, low amp rev counter signal for late clocks
26 - gry/red - airflow potentiometer pin 1
27 - grn - ignition timing sensor pin 2 (on #1 spark plug lead)
28 - wht/red - throttle switch unit pin 1 (idle switch)
29 - red - ignition timing sensor pin 1 (on #1 spark plug lead)
30 - grn/wht - distributor pin 2/0
31 - yel/red - T5/4, only for automatic models
32 - yel/pur - throttle switch unit pin 3 (WOT switch)
33 - grn/red - T2n/1, aircon(?)
34 - brn/red - G1/6, earth
  \- red/blu - T5/1, only for automatic models
35 - brn - common sensor earth to rocker cover, shared with knock sensors, coolant temp sensor, throttle switches,  airflow potentopmeter, ignition timing sensor, distributor

Ah ok, nice one, cheers for the accurate list of pins, I'm going to go through each wire to make sure everything is where it should be, cheers

So I have another corrado loom, unbutchered, and the only difference I can see is where the common black/white wire connecting the cold start injector, ISV and carbon cannister converge into 2 wires, one of the wires (black/white) splits off and goes to a multi connector, other wires here include yellow/red, green/black, yellow, red/white and blue/black

Back to where the 4 black/white wires converge the other wire, now solid black, runs to a 3 pin connector which also includes white/blue and brown wires - I dont appear to have this connector on my loom. Any ideas what this is for?

Spidermonkey84 said

So I have another corrado loom, unbutchered, and the only difference I can see is where the common black/white wire connecting the cold start injector, ISV and carbon cannister converge into 2 wires, one of the wires (black/white) splits off and goes to a multi connector, other wires here include yellow/red, green/black, yellow, red/white and blue/black

Back to where the 4 black/white wires converge the other wire, now solid black, runs to a 3 pin connector which also includes white/blue and brown wires - I dont appear to have this connector on my loom. Any ideas what this is for?

Is this the engine harness mate

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speedometer

So, I finally managed to get back to the car, fitted a new battery and the relays are no longer going nuts which is good however the car still won't start. Dash lights come on, fuel pump primes just no crank, not even a click from the starter motor.

I’m beginning to believe I’ve either mis-wired or completely missed a connection I should have made, excluding all the standard ECU to sensor connections I have spliced in the following:
 

• ECU (pin 19) red wire to MK1 golf fusebox (P-Spade)
• ECU (pin 12) red/yellow wire to MK1 golf fusebox (pin D13) for fuel pump which is working
• ECU (pin 14) black wire to coil (terminal 15)
• ECU (pin 11) green wire to coil (terminal 1)
• ECU to ignition control unit green; black; brown - then blue wire to coil (terminal 1); red wire to coil (terminal 15)
• ECU (pin 17) white wire to ISV then black/white wire to MK1 golf fusebox G spade nr. 5
• ECU (pin 16) red/black wire to cold start (5^th injector) then black/white wire to MK1 golf fusebox G spade nr. 5
• ECU (pin 34) brown/red wire to battery negative terminal
• Lambda sensor red/white wire to MK1 golf fusebox (pin E14)
• 2 x brown wires from ECU to battery negative terminal

6 nr. unused wires, these are:

• ECU (pin 15) yellow/green wire to carbon cannistor
• ECU (pin unknown) brown wire to carbon cannistor
• ECU (pin 2) blue/white wire to speed sensor
• ECU (pin 22) yellow wire to diagnostics L-line
• ECU (pin 25) green/blue wire to G1-12 Rev Counter
• ECU (pin 1) grey/white wire to diagnostics K-line

Have I missed something? Do I need to connect any other wires to the started motor / coil other than the standard MK1 loom?

All the grounds I can find / know about look good.

If there’s no other wiring connections to do then I think the only other options I have are to check / replace:
 

• Ignition switch
• Ignition control module
• Coil
• Starter motor

Failing all the above, I’m at a loss!?

ok starter wire is powered direct from ignition switch regardless of ecu wiring, jump startewr with 12v direct first to make sure it actually works. if so, unplug ignition switch and loop a wire between the red and red/black. if it cranks, replace ignition switch. if not, check wiring between

Ok so I've just put a direct feed from the battery + to the spade terminal (ignition live) and theres nothing……so I'm hoping replacing the starter (which ironically is about the only thing I haven't replaced on this bloomin' car!) will solve the starting/cranking issue.

I've been so focused on it being a wiring issue I've overlooked this simple check, going to kick myself if that's what the issue was……watch this space…….

Ok so bit of an update, finally managed to fit new starter motor and she now cranks, I've got a spark and fuel at the metering head and cold start (5th) injector but she won't start!

From past experience I reckon the timing belt might have slipped a tooth, or else I've got issues with the distributor……….any other ideas greatly appreciated!?

Managed to book some time in to look at it in daylight hours tomorrow morning, hoping I'll find the issue then…………..🤞

Spidermonkey84 said

Ok so bit of an update, finally managed to fit new starter motor and she now cranks, I've got a spark and fuel at the metering head and cold start (5th) injector but she won't start!

From past experience I reckon the timing belt might have slipped a tooth, or else I've got issues with the distributor……….any other ideas greatly appreciated!?

Managed to book some time in to look at it in daylight hours tomorrow morning, hoping I'll find the issue then…………..

You would still think it would at least make an effort at one tooth or even two out mate is the cold start injector actually spraying

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Good shout nicci21paul, checked 5th injector and it's working fine, timing is spot on, spark is good however found that the metering head isn't delivering fuel to the other 4 injectors.

Put a power probe on 5th injector to get a constant fuel feed and did get her to cough into life if only very briefly but there was life nonetheless! 👍

In the process though the new starter has fried itself, the saying 'buy cheap buy twice' has unfortunately being proven right again! 🤦‍♂️

So, another starter has been ordered, also luckily found a second hand metering head off ebay…….so close now

have you got fuel at the warm regulator