Engine Running Lean

Post by **Joshie** » Thu Jun 19, 2003 11:16 am

Part of the enjoyment of driving in France was spoilt by an intermittent fault code number 17538 - "Long term fuel trim mult. bank2 system too lean"

This fault causes the car to go into limp mode and had to be reset on the fly. Problem is that I cannot conect to VAG Com when the engine is running more than 1000 RPM so it was a case of dipping the clutch while the ECU was reset.

Questions are:

- has anyone encountered this probelm before? (car at AmD at the mo so should be sorted this time tomorrow)
- has annyone had any problems logging on the VAG-COM Engine Controller module "on the fly"?

Post by **toasty** » Thu Jun 19, 2003 11:43 am

I get a similar but opposite error.

Regularly see:
Long Term Fuel Trim Add.FuelBank2 System too Rich " 17547
Long Term Fuel Trim Add.FuelBank1 System too Rich " 17545

Doesn't cause any running errors (I guess running rich is less dangerous than running lean?) But when deleted reappears within a week or so.

My guess for my error is a air leak past the MAF so the mixture is slightly rich. I suppose by the same reasoning yours could be a fuel leak or fuel deficit (perhaps a bigger fuel pump or pressure regulator)

As for connecting to VAG com at high engine speeds, I've never tried it, sorry [img]images/graemlins/frown.gif[/img]

Mine's in for a service in a month or two, and now that I have the Audi warranty I'm going to have them look at it [img]images/graemlins/smile.gif[/img]

Post by **Joshie** » Thu Jun 19, 2003 3:03 pm

AmD felt that it could be a faulty Lambda probe which have an average life of around 60K mls. If so then the problem is not really there - just a spurious reading telling the ECU there is a problem.

Interesting that you have experienced the reflection of this problem Dan.

Post by **s2driver** » Thu Jun 19, 2003 5:35 pm

Surprised that the lambda sensor reacts quick enough to use it as ECU feedback on your engine on full chat. If I remember correctly, RS2 tuners do not use Lamda over 380 bhp for WOT fuelling. Think they just use it for steady state fuelling feedback to get it through emissions. Am probably wrong though!! Corrections please!

Lee

Post by **Joshie** » Thu Jun 19, 2003 6:39 pm

Hi Lee,

Couldn't get over to AmD this afternoon to collect my car but I was told that it had a split turbo hose. I am wondering if this may have caused the DTC mentioned? Power should be up as a result though [img]images/graemlins/jump3.gif[/img]

I'll keep you posted.

Post by **Dippy** » Fri Jun 20, 2003 12:56 pm

Ian,

In theory a split hose would cause it to run rich: The ECU uses the MAF to measure the air coming into the engine and so sets the amount of fuel added. If some air is being lost, the ECU won't know, and just add a bit more fuel than is needed.

From what I know (which is half of bugger-all), running lean is dangerous as the exhaust/turbos get too hot - hence limp mode. Part of the reason for running an engine a bit richer (what AmD did for me after my Miltek cats were fitted) is that the fuel has a cooling effect on the intake.

Post by **Joshie** » Fri Jun 20, 2003 4:39 pm

Well Dave you may know half of bugger all but that's not a bad diagnosis.

The F pipe was indeed split and was replaced. I collected the car from AmD and off I went. 10 miles later the car was in limp mode again as I turned it around and headed back to AmD.

Fault diagnosed as, you guessed it, a faulty air meter. One on order now should be fitted by the end of next week.

Performance is much better than before due to the pipe and the air meter is an intermittent fault so only in limp mode periodically.

Post by **Dippy** » Mon Jun 23, 2003 12:37 pm

If it was the F-pipe then air would have been leaking in, not out! This is the pipe which feeds vacuum to the DVs.

I would have expected you to have noticed this as the DVs should not have been opening properly and you would have experienced surging and possible turbo stall.

However if extra air is being sucked into the engine through the split, then indeed it would run lean. However as it's only a narrow bore pipe, there wouldn't be that much air. So the explanation that your MAF is faulty makes sense.

Is this a new RS4 MAF or is it the one you cleaned a while back?

Post by **Joshie** » Mon Jun 23, 2003 3:02 pm

Hi Dave,

The car was running inconsistently and occasionally developed "limp mode" without registering any specific DTC (No DTC or DTC not recognised). I believe that this was a result of the F-pipe. The MAF problem causes a spacific code of lean mixture.

It is, as far as I know, the original MAF which I cleaned about 15K miles ago. The replacement will be an S4 MAF until I get round to chaging the intake for RS4 airbox etc. I am wondering if cleaning it will helpn this time [img]images/graemlins/idea.gif[/img]

Post by **Nige_RS4** » Mon Jun 23, 2003 3:07 pm

Joshie, try this link for help on cleaning your MAF.

Nige. [img]images/graemlins/thumbs.gif[/img]

Post by **Joshie** » Mon Jun 23, 2003 7:08 pm

Thanks for the link Nige [img]images/graemlins/thumbs.gif[/img]. The last paragraph got me wondering how much AmD will charge for a replacement. I have just contacted Martyn at VAG parts since they are a piece of cake to fit - it would make good sense to DIY
[img]images/graemlins/clap.gif[/img]

Post by **wazza** » Tue Jun 24, 2003 10:46 am

Easy to fit. [img]images/graemlins/smile.gif[/img]
£246 from a dealer, but there are a couple of versions for the S4 [img]images/graemlins/thumb.gif[/img]

Post by **Joshie** » Tue Jun 24, 2003 11:18 am

Thanks Paul - I'll keep you posted [img]images/graemlins/beerchug.gif[/img]

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