Audi 80 V6 Help

[Matt86]

So I've had this car for a bit over a year now, and I've slowly worked out all the kinks and issues with it.

Car in question is a '94 Audi 80 V6 2.6 (ABC Engine) - Same as the early A4's, A6's, VW Passat's which had the 2.6 engine.

Right now I'm down to the last one essentially.

Basically whenever the car is cold started (that is the engine is cold) it will run really rough, as if it's stalling or misfiring until it warms up (about 50-60c) going by the temperature gauge on the dash.

I do get a check engine light too but that dissapears really soon after starting. I have a feeling this is unrelated though, not sure.

Things that have been done/tried

• G62 Sensor Replaced
• Oxygen Sensors Replaced
• Cleaned the crankcase hose breathers (if that's what they are?)
• Changed the Spark Plugs
• Connecting a computer and clearing codes/viewing codes - No errors came up supposedly!

One thing I haven't checked yet and don't know how to check is the injectors.

Any input is appreciated!

Cheers
-Matt

[jgribben]

Hey Matt. Really no expert and will probably be off but just wondering if you have tried it. My cars fuel pressure drops overnight so I have to turn the ingnition on and off 3 times without starting the car to build the pressure up then start it on the 4th. Seems to work ok for now (I thought my injectors were stuffed too). But if you do that and it makes the start better at least you'll know its to do with the fueling then go from there.

As I said before though no expert and never worked on that specific engine so could be well off the mark with what is wrong.

Plenty of mechanics on here though sure someone with chime in soon

[gldgti]

Sounds like it might not be fuelling enough when cold. When the engine is really cold, the intake runners/head is cold enough that fuel will condense on the walls of the inlet/ports before it gets past the valves - hence petrol engines typically run very rich at cold start to ensure enough fuel is actually in the air going into the cylinder.

I'm not familiar with that engine though so no idea really apart from what you have already replaced what could be the problem. I guess potentially a fuel supply problem might cause it, but you would be seeing other issues too like a lack of power. Is this the case?

[Matt86]

Sounds like it might not be fuelling enough when cold. When the engine is really cold, the intake runners/head is cold enough that fuel will condense on the walls of the inlet/ports before it gets past the valves - hence petrol engines typically run very rich at cold start to ensure enough fuel is actually in the air going into the cylinder.

I'm not familiar with that engine though so no idea really apart from what you have already replaced what could be the problem. I guess potentially a fuel supply problem might cause it, but you would be seeing other issues too like a lack of power. Is this the case?

Well thanks for the input, I haven't really tested for power when it's cold as that's a bad to run the engine hard when cold..
But when it's warm it can still go fast... Not posting how fast I've been in it but it's close to the original spec of the engine..
(210kp/h)...

Hey Matt. Really no expert and will probably be off but just wondering if you have tried it. My cars fuel pressure drops overnight so I have to turn the ingnition on and off 3 times without starting the car to build the pressure up then start it on the 4th. Seems to work ok for now (I thought my injectors were stuffed too). But if you do that and it makes the start better at least you'll know its to do with the fueling then go from there.

As I said before though no expert and never worked on that specific engine so could be well off the mark with what is wrong.

Plenty of mechanics on here though sure someone with chime in soon

Thanks for the input! I've literally checked everything I can think of.. Next bet is replacing the fuel filter maybe, I'm thinking that maybe it can't get the flow it needs when it's cold or something?

[gldgti]

Actually I didn't mean when cold, I meant when warm. If it has plenty of power, the fuel supply is probably just fine. In that case its most likely a problem restricted to open loop mode for the ECU.
Check if it cold starts any different with the coolant temp sensors disconnected.

[Matt86]

Actually I didn't mean when cold, I meant when warm. If it has plenty of power, the fuel supply is probably just fine. In that case its most likely a problem restricted to open loop mode for the ECU.
Check if it cold starts any different with the coolant temp sensors disconnected.

I recently replaced that so it shouldn't make an issue surely?

I actually ran it this morning cold start obviously and well..

It only does it when it's in park, Neutral or Drive make it stop.
While moving though i do get the constant stall and continue however.

It's rather odd, had a few people look at it (1 mechanic/Audi guy) and they all have no idea what it is. I've literally replaced everything that people have thought it was so far.

[gldgti]

I realise you replaced the sensor but that doesn't rule out an issue related to open loop/ closed loop mode. Its worth trying, and doesn't cost a thing.

[Jmac]

Hey Matt. Really no expert and will probably be off but just wondering if you have tried it. My cars fuel pressure drops overnight so I have to turn the ingnition on and off 3 times without starting the car to build the pressure up then start it on the 4th. Seems to work ok for now (I thought my injectors were stuffed too). But if you do that and it makes the start better at least you'll know its to do with the fueling then go from there.

As I said before though no expert and never worked on that specific engine so could be well off the mark with what is wrong.

Plenty of mechanics on here though sure someone with chime in soon

Wonder who showed you that trick It could have carbon build up, id try some Fuel x through it, you can buy a bottle at bursons. Also does the engine fast idel when cold?? it could have a throttle body issue, need a clean and reset. There is a few things that can be checked there. At least you can say its only cold so all hot running problems can be ruled out.
Cheers
Jmac
ps ABC is a bomb proof motor

[Matt86]

I realise you replaced the sensor but that doesn't rule out an issue related to open loop/ closed loop mode. Its worth trying, and doesn't cost a thing.

Yeah that's true I suppose, sorry I actually overlooked that completely.

Wonder who showed you that trick It could have carbon build up, id try some Fuel x through it, you can buy a bottle at bursons. Also does the engine fast idel when cold?? it could have a throttle body issue, need a clean and reset. There is a few things that can be checked there. At least you can say its only cold so all hot running problems can be ruled out.
Cheers
Jmac
ps ABC is a bomb proof motor

What's Fuel x / Any alternatives you could suggest as well?

By fast idle you mean high idle, say over 1,200RPM? Yeah it does, when it warms up it drops to the 900ish mark.

The throttle body looks kind of hard to get to.. I was told to try cleaning that by my local(ish) Audi wrecker/mate too.

Just going to do it the same as the hoses by using degreaser and then washing it with water a few times.

Good to know that she's bomb proof! :p

Thanks for all the help so far guys!

[gldgti]

It only does it when it's in park, Neutral or Drive make it stop.
While moving though i do get the constant stall and continue however..

...this..... perhaps this is a vacuum leak issue related to the brake booster? The reason i suggest this is because when you start the car in park, your foot will probably be off the brake. When you change to N/D, you have to have your foot on the brake, and likewise when you try and move off you release the brake and from your description it sounds like you have the problem then too. If theres a crack in the booster diaphragm or something similar, that leaks when your foot is not on the brake but for some reason doesnt (or leaks less) when your foot is on the brake, it may account for the strange behavior.
I suppose to test its probably pretty easy, disconnect vacuum to the booster and block it so you are sure theres no leaks, then see if the issue is still there or not. Obviously I would suggest you dont actually drive anywhere though!

Just a thought.

[Matt86]

...this..... perhaps this is a vacuum leak issue related to the brake booster? The reason i suggest this is because when you start the car in park, your foot will probably be off the brake. When you change to N/D, you have to have your foot on the brake, and likewise when you try and move off you release the brake and from your description it sounds like you have the problem then too. If theres a crack in the booster diaphragm or something similar, that leaks when your foot is not on the brake but for some reason doesnt (or leaks less) when your foot is on the brake, it may account for the strange behavior.
I suppose to test its probably pretty easy, disconnect vacuum to the booster and block it so you are sure theres no leaks, then see if the issue is still there or not. Obviously I would suggest you dont actually drive anywhere though!

Just a thought.

Hmmm, I may look at this once I've cleaned out the throttle body and tried the other more simple things.

How does one go about disconnecting the brake booster anyway? I absolutely have no clue.

[Matt86]

Hmmm, I may look at this once I've cleaned out the throttle body and tried the other more simple things.

How does one go about disconnecting the brake booster anyway? I absolutely have no clue.

I shall take a video tomorrow morning if I remember to.

I'll put it on youtube tomorrow evening when I get back from Archery!

So I'm more bored then what I thought I would be... Gonna go for a quick drive to get some footage.
I figure it'll be easier to see the dash lit up now anyway.

Here we go, harder then what you think to drive with a phone in one hand!

As you can see putting it in gear makes it rev to around 1,500RPM and then it sort of "seeks" or stalls when I take my foot off the throttle.

Once it warms up however.. (Notice the temperature gauge)

It still does the "seeking" think when it's started to get warm but it's less and less jumpy the warmer it gets, stopping altogether at ~90c.

EDIT: Just realized I missed the main part! Doh' must have turned the recording off...

I'll grab that bit tomorrow before I leave. You can still get an understanding from those two videos to an extent.

[gldgti]

its quite regular.... interesting

[Matt86]

its quite regular.... interesting

It's still fine to drive.. It's been like that for a bit over a year now.

Unfortunately it's the only car I have so I can't set it aside to work on it/look at it for too long.

[jgribben]

Wonder who showed you that trick It could have carbon build up, id try some Fuel x through it, you can buy a bottle at bursons. Also does the engine fast idel when cold?? it could have a throttle body issue, need a clean and reset. There is a few things that can be checked there. At least you can say its only cold so all hot running problems can be ruled out.
Cheers
Jmac
ps ABC is a bomb proof motor

Haha it was good advice I'm just sharing around the knowledge. All credit to you.