OEM MK4 management wiring => Mk1/2/3 harness install FAQ (Now with added dieselness!)

Ah great thanks!

If i combine pin 5 and pin 8 from the t14a to z/1 isnt the load too high?

 

thanks il check that!

 

Jonny, the mk3 a/c pump bolts up the exact same as the mk4 type.

To simplify the swap s&p automotive sell a billet a/c adapter to make the mk2 a/c lines connect up to a mk3 compressor.

Only thing I’ve needed to do there was change the plug over from a mk4 type to a mk3 square plug.

 

Hey mate, followed this guide for my Mk3 conversion and have run into an issue that prevents it from running.

The car will start fine and start to idle but then stall out within ~10 seconds, the only ways to make the car stay alive is to unplug the throttle body or using starter fluid. Since the car will run on starter fluid that leads me to think that it's an injector firing issue

There's no fault codes on VCDS

So far I have tried/confirmed
- tried different tb, no change
- replaced fuel pump + filter + regulator
- confirmed fuel pressure at rail with mechanical guage
- replaced crank sensor, no change
- tried starting with maf unplugged, no change
- tried starting with map unplugged, no change
- tried capping all vacuum ports (brake booster, fuel reg, dv and pcv), no change
- confirmed ecu pins 1&2 have ground
- checked all grounds while cranking/running
- when the cars does idle it's making around 18-20hg of vacuum which suggest no vacuum leaks

Keen to hear what you think, thanks

 

Hi thanks for this write up.. I’m building a harness for a non VAG car using the mk4 1.8t as a donor drivetrain and harness. I’m a little stumped on the ac.. I’m looking for the idle up/ rpm bump up pin out. At this time I don’t plan to use the mk4 fan module etc. Can you advise on which wire(s) for rpm bump? Thanks!

 

Thank you sir! Will update my results.

 

How has everyone wired up there radiator fans when using the alloy radiator and aftermarket fans?

3pin 2speed fans oem off mk2 gti 8v with air conditioning

I’ve spit the grounds to feed both aftermarket fans
Then connected on one both red/back and red white wire to the power fees for 1x fan and the red black only for the other.

I’ve jumped the terminals to the coolant temp sensor in the radiator and they manually turn work when you jump low and high speed however put a new sensor into some boiling water and the fans don’t turn on at all.

Both fuses on fusebox positions #19 and 13 are ok

I’ve got the after run temp sensor off the mk2 installed also.

If I cycle the ac fans they turn on. Just not when getting up to temp

 

Hi Guys,
First of all I just want to say thanks so much for everyone that’s put time and effort into this thread. Especially Rubjonny.

I am currently doing my BAM loom and the engine is to be run on a rwd gearbox without the tt dials. I thought I had everything figured out although after hours of research in these threads I’m currently worried about the ecu not seeing signal from the VSS causing a low rev limit.

Has anyone managed to work around this?
I know there is a mk2 escort running on a rx8 gearbox using oem management so it must be possible somehow.
Any info is much appreciated.

 

Thanks for the reply,
The engine is going into a Volvo, using a rx8 gearbox. Does the vss change the map even if you’re not using limiting power in certain gears?

 

Hi @rubjonny first all the best in the new year.

I'm in a loop of bad luck lately and I would appreciate if you or anyone else could give me some useful advice on my current problem with 1.8T mk3. Ok so I did a swap ( AGU, DBC ) as per your guide and everything worked flawlessly for the last 6 months. I'm gonna try and explain everything as short as possible with all of the important details that could help to resolving the issue.

2 weeks ago or so, my RPM needle suddenly started to jump around on its own, it would bounce back and forth randomly and than it would work like normal for a bit than again madness of randomly jumping around. I thought nothing of it as day before it was really heavy rainstorm so I thought maybe water got somewhere and is fucking up reading of the gauge. Shortly after needle bouncing was paired with oil light flashing and buzzing. So first thing I checked is oil level, which was good, than I checked wires to oil pressure switches which commonly get broken from high temps but they are good as well. Ok never mind, I don't have time for that now so I let it be, it is mk3 after all.

Fast forward last week, I came back from work, everything fine while driving, as I said motor has been ultra good since the swap, pull in my parking space, put it in neutral to let oil cool down a bit before turning it off and suddenly it starts idling really bad ( my gut feeling said that its working on 3 cylinders only ). I shut it off, try to start it, cranks but no start. I let it cool down a bit, came hour later turned on like nothing happened, idled good, I let it warm up a bit and took it for a spin. 20 meters later starts stuttering, I need to keep gas pedal down to keep it alive. It did manage to shut off while I was parking, I barely managed to start it and it just started smoking like crazy from exhaust, everything smelled like petrol so I assumed either bad spark plugs or injectors over fueling.

I connected it to read fault codes: Cylinder 2 injector shorted to GND, intermittent. Pulled off cyl. 2 injector plug, both pins are grounded. My first thought w as there is something wrong with wiring since it goes through T14 plug to ECU. Disconnected everything and pulled out whole loom to check if something is shorting out but everything is fine, not even plug pins are corroded ( btw this is the best loom condition vise I've seen, especially regarding injector and coil wiring ). After plugging back everything in cranks but no start, RPM gauge and oil light still doing its own thing ( dk if this is connected to the issue but yeah ).

Next thing I did was pulled out ignition coils and spark plugs. Valve cover gasket is pretty bad since its leaking oil into cyl. 2, and sparkplugs are not great either ( I knew this and was planning on changing gasket and spark plugs ). I cleaned everything, checked if I have spark, yes, good blue spark. I checked if I have fuel, yes ( spark plugs get wet after cranking as well ), I even checked if its in good condition and flammable, yes. Tried few different fuel relays. Put everything back together, still cranks but wont start.

Now I need your opinion on what could be the cause and not to spend all my money on things that wont solve the issue.
Timing jumped a tooth and not igniting at right moment? Bad knock sensor? Bad ignition module? Cam position sensor?

Sorry for the long ass post.

 

G1/5 is grounded to ground ring under the dash, and it worked properly last 6 months so I doubt its that. Faulty cluster could be cuz it started to act weird days before car stopped working. Where does it get RPM signal from on 1.8T engine? Oil light flashing I assume its due to incorrect RPM reading and now car not being able to build the oil pressure up since it just cranks.

No, that was my next thing to do, and will see if a friend has spare ignition module to rule that in as well. I assume its one of above mentioned sensors that's faulty just need to rule out one by one.
By looking at other people posts on forums for similar situation, lot of them changed almost everything to get it to work and didn't quite get what actually was faulty.

 

Update,
so my friend has mk3 1.8t AGU as well working perfectly so we used his car as a part tester for my shitbox. Firstly we tried his ignition amp, no difference. Than we connected it again to scan codes, now it showed "Injector shorted to GND" on all 4 cylinders, which we expected because fuel smell was really hard after trying to start it. Next we removed coils and plugs, disconnected injectors so that they not fire, to crank it to empty all excess fuel from cylinders and oh geez, we surely didn't expect approx. 3-4l ( yes liters ) of fuel just shooting straight out from cylinders all over us. So we swapped over his fuel rail with injectors to test if mine are done, but same thing. Both his and mine injectors have really good spray pattern but they are just over fueling, and we found out that cyl. 2 injector ( which was originally only code we had ) is spilling fuel already after key is just in ignition on position which is weird. Now for some reason we haven't tried his ECU on my car but my ECU on his car and his car fired up straight up without any hesitation or problems.
Next thing was to tackle wiring to recheck everything regarding T10a plug since its him who delivers power to injectors and coils. This is how it is connected to mk3 fusebox:
- Pin1 -> G2/10
- Pin2 -> G2/4
- Pin3 -> G1/11
- Pin4 -> G2/3
- Pin5 -> Z/1 ( 10A fused )
- Pin6 -> Z/1
- Pin7 -> Battery GND
- Pin8 -> ECU relay pin 87
- Pin9 -> Battery GND
So since injectors are getting short to GND code, I immediately checked Pin5 and Pin7 and they are shorted. I unplugged everything from fusebox and they weren't shorted anymore. So by elimination method I plugged back one by one plug until I got it shorted again, and ofc it was the last one, which is the M plug aka fuel tank wiring harness. Since it was late we left all of it there to continue tomorrow ( battery was disconnected ). Does this give any more insight to what could the cause be?

EDIT: he just called me while I'm writing the post that car is running ( roughly, but runs ) with all 4 injector plugs disconnected, and without hose from IC to throttle body ( weird cuz it never could idle without IC connected ), he connected his ECU ( 100% working ) this time.