Audi Cabriolet 2.6 Stalling after 2-3 seconds

Jaco Mostert · 13-04-20, 01:48 PM

Good day everyone,

I've got a 1996 Cabriolet 2.6 which starts up perfectly, runs for 2-3 seconds and stalls.

TLDR - I think it is the immobilizer or ECU

Things that might help:
- The engine starts up perfectly almost every time, the just dies after a few seconds.
- I replaced the head gaskets recently and the car drove perfectly after that.
- The car does not drive too often, but I try and start it up at least once every 2 weeks.
- The problem started only when the engine was hot, but now it does not matter.
- Using VCDS (Vag com) to check there are no fault codes, but I can't connect to the engine module. I could do this previously.
- I need to replace the air-con pump as the clutch is not engaging.
- I sat on the rear lid for the top fixing the rear window.
- The car ran perfectly last week.
- The car has a battery cut of switch, which I use.
- The car has a problem with the battery draining quickly (within a week or 2 if left connected.) The battery is still good as it is fairly new.
- The key is worn, but the light in the dash goes out when turning the key.

What I've tried so far:
- Checked the fuel pressure regulator (seems to be working.)
- Checked the cam sensor (when I disconnect it the car doesn't start at all.)
- The fuel pump primes perfectly and the relay seems to be working.
- All the fuses look good.
- Found the ECU (behind the glove box), unplugged the connectors and put them back. (It seems like someone has fiddled here previously, but I've had the car for 4 years now.)

What I suspect:
- I've had problems on my A6 2.6 before with the fuel pressure regulator, cam sensor and crank sensor before and the symptoms were different so I don't think it is those.
- I think it has something to do with the immobilizer or the ECU, but I'm not sure how to confirm this. (My biggest indicator is the engine module not being available.)

VCDS/Vag com

Thursday,09,April,2020,12:56:36:40899
VCDS -- Windows Based VAG/VAS Emulator Running on Windows 10 x64
VCDS Version: 19.6.2.0 (x64)
Data version: 20190930 DS308.0
www.Ross-Tech.com

Mileage: Repair Order: Cabriolet

--------------------------------------------------------------------------------
--------------------------------------------------------------------------------

Chassis Type: 8G - Audi Cabrio B4 (1992 > 2000)
Scan: 25 01 02 03 08 15 26 35

-------------------------------------------------------------------------------
Address 02: Auto Trans Labels: 01N-927-733.lbl
Part No: 01N 927 733 AP
Component: AG4 Getriebe 01N 2850
Coding: 00000
Shop #: WSC 00000
VCID: 7F0BBB767D62BFB7DE-095C

No fault code found.

-------------------------------------------------------------------------------
Address 03: ABS Brakes Labels: 4A0-907-379.lbl
Part No: 4A0 907 379 A
Component: Bremsen-Elektronik
Shop #: BB 33837
VCID: 295F452ED366E107D0-4AE6

No fault code found.

-------------------------------------------------------------------------------
Address 08: Auto HVAC Labels: 4A0-919-579.lbl
Part No: 4A0 919 579 F
Component: Stg. Klimak. 6-Zyl. D07
VCID: 3363A74601AAABD76A-2012

1 Fault Found:
00532 - Supply Voltage B+
07-00 - Signal too Low

-------------------------------------------------------------------------------
Address 15: Airbags Labels: 8A0-959-655.lbl
Part No: 8A0 959 655 B
Component: Airbag V AUDI D00
Coding: 00766
Shop #: WSC 01670
VCID: 326DA242FEB0A2DF61-5120

No fault code found.

-------------------------------------------------------------------------------
Address 26: Auto Roof Labels: 8G0-959-255.lbl
Part No: 8G0 959 255
VCID: 72ED62423E30E2DFA1-4B32

No fault code found.

End-------------------------(Elapsed Time: 01:42)--------------------------

steveb · 13-04-20, 05:53 PM

Does yours have the K jet injection ? not sure what was fitted to the them.

It sounds like the cold start injector is working , which starts the car but the fuel pump is not running afterwards to keep the car running

Of course if it's not k jet this will be no help at all :-)

Jaco Mostert · 13-04-20, 10:04 PM

Thanks for the reply.

It has electronic fuel injection with only 6 injectors. It's a 12v V6 (https://www.12v.org/engine/index.php?section=fe)

I'll have another look at the fueling system tomorrow. I also suspect a loose or worn wire somewhere that might also cause this problem, but so far could not find anything.

rangerovering · 14-04-20, 08:42 AM

Hi,

Does this have the flashing red triangle on the dash for the immobilizer? On my 1994 saloon fuse 19 disables the immob might work for you? If so and it is like my car the immobilizer is part of the central locking pump which may be faulty.

Worth a try!

Jaco Mostert · 15-04-20, 05:45 PM

Thanks, rangerovering, on my side removing the fuse, seems not to do anything. I'm not sure if it should stop the central locking from working, but that still works fine even without the fuse.

The orange light below is the immobilizer light that flashes when I turn the key. (Stays on when I use another key that the car does not recognize.)

When using the right key the light flashes once and goes out. The other lights usually go out after I've started the car. (It also seems that the roof is sorted out. That light used to stay on and I had to unlatch and relatch the roof and it would go out.)

Maybe my problem has nothing to do with the immobilizer and it is working perfectly. From what I've read on VCDS not connecting to the engine and immobilizer module, it seems that there might be something interfering with the K-line. I'll unplug the radio and have a look if there is anything funny there just in case. These cars came with aftermarket radios here and the previous owner fitted an original Audi Gamma CC radio.

I also still need to check the fuel pump and filter properly.

Fuse description according to the owner's manual.

mikes2 · 16-04-20, 07:56 AM

On the 2.6, the ecu can cause the non communication issue

Jaco Mostert · 16-04-20, 07:10 PM

Thanks, Mike. I'm also starting to think the ECU is bad. I've got an A6 with the same engine, but I'm skeptical about borrowing it's ECU since I don't want to damage it if there is another issue somewhere. What has me confused is I can read most of the modules in VCDS. Only the immobilizer and engine modules are not available. In my mind, it also makes sense that if the ECU is damaged the car should not start at all, yet it starts up perfectly, runs beautifully for 2 to 3 seconds and then just dies.

I've read somewhere that the immobilizer works with the central locking pump, so I'll try and have a look at that, maybe there is a connection there that got damaged.

So far just by visual inspection, the connections to the ECU and all the wires in the fuse box look good. If all else fails, I'll start looking for a good ECU specialist or maybe try and take the car to Audi.

Jaco Mostert · 17-04-20, 02:49 PM

I might have found my problem. I think I found the immobilizer or something, but it seems there have been some modifications. Maybe it was bypassed? It also looks aftermarket

An overview

This purple wire has a short piece of blue (with a red stripe) wire on that goes from the box to nowhere

One blue wire from the box is plugged into this plug that goes somewhere into the car.

The radio has a connection without a plug. I assume this is supposed to power the antenna to boost the signal or something as it is a fixed antenna.

tractor Dave · 17-04-20, 05:08 PM

That's more likely the feed for a powered antenna that was once fitted.
Immobilser wires will more likely be under the dash and cut into the ignition plus other circuits.. It's a case of finding it and tracing back all the connections. Took me a few hours to find all mine and cut it all out/make good where they had cut in.

Jaco Mostert · 17-04-20, 05:40 PM

Thanks, tractor Dave.

I plugged the red connector into my antenna for what it's worth. It sounded like the signal on the radio was better, but it could just be in my mind. The speakers are badly worn anyway.

The box turned out to a very old tracking unit. It was only using power from the car. The other clear connector supplies 12v. Thus this should have no effect on my problem. Hopefully, my battery lasts a little longer now. While I was testing there, I checked the earth on the body and that still looks fine.

On a side note, I need to fill up the reservoir on the pump for the roof. I'll also take some more pictures while the trim is removed. Maybe it will help someone else in the future.

I also went ahead and got proper manuals from erwin.audi.com and the immobilizer is indeed under the dash. I see it can apparently disable the ECU via a W-wire, so I hope this whole problem is just a loose wire or something there.

Rebuilding the engine is a lot better than electrical fault finding.

13-04-20, 05:53 PM	#2
steveb Senior Member Classic Audi Club Member Join Date: Jul 2008 Location: West Berkshire Posts: 1,155	Does yours have the K jet injection ? not sure what was fitted to the them. It sounds like the cold start injector is working , which starts the car but the fuel pump is not running afterwards to keep the car running Of course if it's not k jet this will be no help at all :-) __________________ [FONT] '76 Leyland Princess 2200 HLS '79 Scirocco storm '84 WR '89 coupe quattro '01 A2 1.4 TDI SE '14 A3 1.4 TFSI COD [/color][/size][/font]

16-04-20, 07:56 AM	#6
mikes2 4 ring whore! Classic Audi Club Member Join Date: Nov 2007 Location: Polmont Posts: 2,617	On the 2.6, the ecu can cause the non communication issue __________________ 1991 90 quattro 20v sport 1991 90 quattro

13-04-20, 10:04 PM	#3
Jaco Mostert Grown up member Join Date: Dec 2013 Location: South-Africa, Hartbeespoort Posts: 49	Thanks for the reply. It has electronic fuel injection with only 6 injectors. It's a 12v V6 (https://www.12v.org/engine/index.php?section=fe) I'll have another look at the fueling system tomorrow. I also suspect a loose or worn wire somewhere that might also cause this problem, but so far could not find anything.

14-04-20, 08:42 AM	#4
rangerovering Grown up member Join Date: Aug 2016 Location: Kinross Posts: 174	Hi, Does this have the flashing red triangle on the dash for the immobilizer? On my 1994 saloon fuse 19 disables the immob might work for you? If so and it is like my car the immobilizer is part of the central locking pump which may be faulty. Worth a try!

15-04-20, 05:45 PM	#5
Jaco Mostert Grown up member Join Date: Dec 2013 Location: South-Africa, Hartbeespoort Posts: 49	Thanks, rangerovering, on my side removing the fuse, seems not to do anything. I'm not sure if it should stop the central locking from working, but that still works fine even without the fuse. The orange light below is the immobilizer light that flashes when I turn the key. (Stays on when I use another key that the car does not recognize.) When using the right key the light flashes once and goes out. The other lights usually go out after I've started the car. (It also seems that the roof is sorted out. That light used to stay on and I had to unlatch and relatch the roof and it would go out.) Maybe my problem has nothing to do with the immobilizer and it is working perfectly. From what I've read on VCDS not connecting to the engine and immobilizer module, it seems that there might be something interfering with the K-line. I'll unplug the radio and have a look if there is anything funny there just in case. These cars came with aftermarket radios here and the previous owner fitted an original Audi Gamma CC radio. I also still need to check the fuel pump and filter properly. Fuse description according to the owner's manual.

16-04-20, 07:10 PM	#7
Jaco Mostert Grown up member Join Date: Dec 2013 Location: South-Africa, Hartbeespoort Posts: 49	Thanks, Mike. I'm also starting to think the ECU is bad. I've got an A6 with the same engine, but I'm skeptical about borrowing it's ECU since I don't want to damage it if there is another issue somewhere. What has me confused is I can read most of the modules in VCDS. Only the immobilizer and engine modules are not available. In my mind, it also makes sense that if the ECU is damaged the car should not start at all, yet it starts up perfectly, runs beautifully for 2 to 3 seconds and then just dies. I've read somewhere that the immobilizer works with the central locking pump, so I'll try and have a look at that, maybe there is a connection there that got damaged. So far just by visual inspection, the connections to the ECU and all the wires in the fuse box look good. If all else fails, I'll start looking for a good ECU specialist or maybe try and take the car to Audi.

17-04-20, 02:49 PM	#8
Jaco Mostert Grown up member Join Date: Dec 2013 Location: South-Africa, Hartbeespoort Posts: 49	I might have found my problem. I think I found the immobilizer or something, but it seems there have been some modifications. Maybe it was bypassed? It also looks aftermarket An overview This purple wire has a short piece of blue (with a red stripe) wire on that goes from the box to nowhere One blue wire from the box is plugged into this plug that goes somewhere into the car. The radio has a connection without a plug. I assume this is supposed to power the antenna to boost the signal or something as it is a fixed antenna.

17-04-20, 05:08 PM	#9
tractor Dave Senior Member Classic Audi Club Member Join Date: Apr 2018 Location: Wales Posts: 1,174	That's more likely the feed for a powered antenna that was once fitted. Immobilser wires will more likely be under the dash and cut into the ignition plus other circuits.. It's a case of finding it and tracing back all the connections. Took me a few hours to find all mine and cut it all out/make good where they had cut in.

17-04-20, 05:40 PM	#10
Jaco Mostert Grown up member Join Date: Dec 2013 Location: South-Africa, Hartbeespoort Posts: 49	Thanks, tractor Dave. I plugged the red connector into my antenna for what it's worth. It sounded like the signal on the radio was better, but it could just be in my mind. The speakers are badly worn anyway. The box turned out to a very old tracking unit. It was only using power from the car. The other clear connector supplies 12v. Thus this should have no effect on my problem. Hopefully, my battery lasts a little longer now. While I was testing there, I checked the earth on the body and that still looks fine. On a side note, I need to fill up the reservoir on the pump for the roof. I'll also take some more pictures while the trim is removed. Maybe it will help someone else in the future. I also went ahead and got proper manuals from erwin.audi.com and the immobilizer is indeed under the dash. I see it can apparently disable the ECU via a W-wire, so I hope this whole problem is just a loose wire or something there. Rebuilding the engine is a lot better than electrical fault finding.