Fuel trim way off. Too lean on both banks Touareg 3.2 V6 - Club Touareg Forums
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post #1 of 50 Old 02-25-2019 Thread Starter
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Question Fuel trim way off. Too lean on both banks Touareg 3.2 V6

I'm having a problem with my Touareg (v6 3.2 year 2003).

Check engine light comes up and car is very lean.

Fault codes are the ones for both banks lean at idle and after a while also both banks lean under load.

Fuel trim values > +25% on both banks when i use my scan tool.

First the short fuel trim and after a short while also the long +25% for both banks.

What garage and i already did:

- Vacuum leaks check (smoke test) found a little hole and changed that line.
Did not help. Codes came back.

- Exhaust had a big leak on the front side. Is also fixed by garage. Codes still come back.

- MAF is tested by the garage well within normal operating range.

- The breather valve (PCV valve) was sucking in air also at idle. I also changed that for a new one now works fine but did not fix my trim values that are still the same.

- All other values (o2 sensors, lamda) look good to me. A friend of mine has the same car. Volt values etc look exactly the same. (except for the fuel trim values. his stay near 0 long and short mine shoot up to +25%).

I think the only thing is left for me to check is the Fuel pump (filter). I think that is where the problem is.

The reason i suspect the fuel pump is because when my fuel tank is almost empty (please refuel light comes on) from that moment on the long fuel trim values are returning to normal. (between -5% / +5%)
And if i reset the check engine light the fuel trim values stay between -5 and +5.

I'm guessing that when the refuel light goes on the second fuel pump kicks in and helps the main fuel pump. >> i know know for sure it does. When fuel tank is empty both fuel pump are working. I did some testing and i can hear them both working. When more than 1/4 fuel in fuel tank than the second pump shuts off after 30 seconds after starting up the car

Anyone had this issue before and would this be a dirty fuel filter? Or do you think the main pump is just (half)dead?

Car holds in when refueling and tank is full. stutters until i give it allot of gas than drives ok (but not great) and the fuel trim values are way off +25% on both banks again.
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post #2 of 50 Old 02-25-2019
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Other leads:
Evaps system (n80)
Fuel cap
Sorry to have hijacked your other thread
Do you have vcds. You need a vcds autscan to see if you have other codes.
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post #3 of 50 Old 02-25-2019 Thread Starter
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Evaps system (n80) = PCV value right? i Changed that one for a new one.

Yep i hope a can do VCDS autoscan soon...
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post #4 of 50 Old 02-25-2019
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Nope. Evap is a different setup. The valve is on the passenger side. You can remove and check it.
Here is a link to have some info:

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Quote:
Originally Posted by TRespect View Post
Nope. Evap is a different setup. The valve is on the passenger side. You can remove and check it.
Here is a link to have some info:

https://youtu.be/4IWzZzZb6B8
Did you read through my whole story? i cannot imagine it can be anything different than the fuel system. because i only get the lean condition if 1 pump is working. When both pumps are active no issues.

i think we are talking about the same thing no.. ? it is on the passenger side yes.

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post #6 of 50 Old 02-25-2019
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Remove and check it before getting a new one as it's a bit expensive and you don't want to be changing parts for the sake of changing parts.

Remove it, use a 12v source to test if it clicks and blocks air if you blow through it. It's number 21 in the diagram, located right behind the throttle body.

You really nead vcds and log the same data on both your touareg and your friend's touareg and compare.
You need to do advanced measuring block logging. Let me know when you get vcds and I will show you how.

You need to do an additional check of all the vacuum system.
Use a carburetor cleaner check.
Check the throttle body is sealed correctly by spraying carburetor cleaner and see if engine revs up.
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Quote:
Originally Posted by TRespect View Post
Remove and check it before getting a new one as it's a bit expensive and you don't want to be changing parts for the sake of changing parts.

Remove it, use a 12v source to test if it clicks and blocks air if you blow through it. It's number 21 in the diagram, located right behind the throttle body.

You really nead vcds and log the same data on both your touareg and your friend's touareg and compare.
You need to do advanced measuring block logging. Let me know when you get vcds and I will show you how.

You need to do an additional check of all the vacuum system.
Use a carburetor cleaner check.
Check the throttle body is sealed correctly by spraying carburetor cleaner and see if engine revs up.
Thanks

You need to do an additional check of all the vacuum system.
Use a carburetor cleaner check.
Check the throttle body is sealed correctly by spraying carburetor cleaner and see if engine revs >> allready did these test and after this also a smoke test on the whole intake systeem >> no leaks
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post #8 of 50 Old 02-25-2019
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Quote:
Originally Posted by mmlinx View Post
Did you read through my whole story? i cannot imagine it can be anything different than the fuel system. because i only get the lean condition if 1 pump is working. When both pumps are active no issues.

i think we are talking about the same thing no.. ? it is on the passenger side yes.
the n80 is not the pcv. the n80 is located somewhere behind the pcv.

Then replacing the pump might solve it. At least you will know for sure and if not go on with the troubleshooting.
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post #9 of 50 Old 02-25-2019
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If you think it is the fuel system, why not check to see if the pumps are in spec?

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post #10 of 50 Old 02-25-2019 Thread Starter
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Quote:
Originally Posted by nickyt View Post
If you think it is the fuel system, why not check to see if the pumps are in spec?

https://www.youtube.com/watch?v=ZVBaH2jsPg4
Yep i also saw that vid. But i dont have that fancy fuel pressure equipment
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fuel pump failure , fuel pump filter , fuel trim , lean condition

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