ABF Cutting Out

If G28 comes up, then you have issues with the wiring to the crank pick up. That would stall the car intermittently.
Ambient temp comes from the IAT. This can be found in the intake duct near the airbox. -40 deg C is the upper limit, which suggests it is disconnected. This has some effects on ignition timing trim.

With two sensors not being seen by the ECU, it could also suggest the loom is pretty brittle.

ABF OE controls usually always work after many thousands of miles. If they do not and your have scanned the car, replaced the suspect sensors then look for symptoms such as brittle looms or corroded connections.
I have run a 'Topran' distributed crank pick up in my MK2 for 40K miles. In my engine it does get buzzed to 7600 rpm frequently! No issues.

 

And the ground point to the block might be worth a look if you havent already as well.

 

Thanks for this. The funny thing is that the car never stalls. The only current symptom is complete non starting intermittently, but when it will start it will run 100% reliably.

 

Thanks mate, will look at this and the loom this afternoon.

 

Brief update on this. Decided to swap the 20 Topran crank sensor for a new one as recommended by rubjonny in another thread. After messing about and getting nowhere again for ages, it fired straight up after fitting the new sensor.

I won't believe for sure it's fixed until it has sat for a day or two, but fingers crossed.

 

Its the sensor... youll be sweet, but check all the looms anyway. And bat, note that these sensors are not just an analog sine wave magnet and coil, they get converted to square pulses, the fail often when up to temp. In one of my posts I mentioned that because its tucked deep and hidden we run around the fault, long live VCDS

Ps... mine was intermittent too and if a Meyle sensor comes by your way, grab it and keep it as a spare. They are a higher quality construction with seals and fully encased.

 

Thanks man. I got a Facet sensor which seem to come well recommended. So far the car still starts every time. Currently having the wiring all checked over by a pro. Also having him fix the inlet air temp sensor which I recon has never worked int he last 4 years+ since I first transplanted the engine!

 

Bat, dont be too alarmed, my findings are that the wiring is quite good in terms of quality. Its more often the connectors and connections that oxidiseor shale with vibration, specially the knock sensors and crank sensor on that bracket on the side of the head. I made a home made box to house mine and i need to revise it, but I no longer use that bracket. Most every mk3 I tried to get parts from at wreckers also had si ilar issues.

I also found the knock sensors were perished and I found those on a more modern audi. So if you ever get the inlet manifold off, take a peek at those too.

In hindsight, if I knew what I know now....

• Remove front end
• Remove intake manifold
• Reinsulate and inspect wiring behind the intake manifold including connectors
• Replace knock sensors
• Replace cps sender
• Replace thermostat
• Replace water pump
• Replace lower connecting radiator pipe
• Replace oil cooler and hoses
• Check and inspect oil temp, pressure sensors and connections
• Replace top radiator flange
• Replace side radiator flange
• Clean, inspect and Rewrap t28 connector
• Inspect and clean up lighting looms.
• Inspect and replace vacuum lines
• Clean isv and connector check, that is vulnerable too
• Check main earth and check grounds, all brown wires

Mainly a whole lot of labour and a few parts, some new, some used and some self made, nothing scarey, just time and effort.

Cheers and enjoy

h

 

Hi
I had similar starting issues as you, random non starter but 100% when it did.
I traced it down to the multi earth-ing point by the steering Colum, which is to the left of the fuse box. It had managed to come lose from its mounting point (not the best design) but then i was messing about in that area while adding other electrical bits and pieces.

Once i secured it everything was back to normal
Hope this helps

Dav

 

Thanks, will check that out too.

 

So it still seems happy. Wiring has all been checked and looks good.

However I am still getting 00523 - Intake Air Temp Sensor (G42) 30-00 - Open or Short to Plus.

Sensor has been changed, and wiring and plug tested. Just to check my sanity, that fault does refer to this sensor right?:


Measuring blocks shows -40c still which I guess is the default non-signal reading. How is this likely to be affecting the running of the engine? It seems spot on, but then I only have presumably the current state to compare to.

 

Just like the alfa romeo problem with the thermostat open, it will assume the air temps are very low and there will be more O2 in the air. It can then richen up, hurt your catalytic converter, combust poorly and cause other grief, so try and get it resolved, it is very important.

Remember that with efi, its the air that is measured in the fuel mix, so get onto it asap before you muddy plugs and other efi systems. As an example, the alfa destined fir my son, has a harmed the catalytic converter and maybe O2 sensors, if i give it wot, the unburnt fuel triggers an engine management problem, because the cat reached its threshold of efficiency. Fortunately my golf abf doesnt measure exhaust.

 

I reckon it has been running like this for 4-5 years and >30k miles. My understanding is that if there is no signal, the ECU will cope to a degree, rather than just assume it's actually -40c, but I could be wrong.

No cat to worry about. Did have to change the lambda probe a year or so ago, but no idea if that is related.

I'm a bit stumped. Guy who I use who knows his stuff has checked it over and reckons the wiring is all good, and I changed the sensor itself. I wonder if it's something silly like the wires are crossed...

 

Rubjonny is the man for all things wired, I can vouch that once Id been through the whole process, the abf runs more efficiently, i get around 600km inner city on a tank of 98 octane. Under 7 Litres per 100km is normal now, open road down to low 6s

 

When you say you've tested the loom, i assume you've tested for continuity between the ECU plug and air temp sensor, which may well still be perfect, that doesn't mean there isn't a short across to another wire. I would untape it and have a look or check for continuity between air temp sensor wires, and other wires close to it...

 

OMG

This is a SEAT loom though, so will those colours still be accurate?

 

I can check mine if need be

 

Thanks guys. Will have a play once the working week is out of the way.

Any tips for tracing the wire colours from the ECU plug? Finding it really tricky to figure out what goes where!