Fuel Trim Fault Codes

[Bigfella70]

Hi there,

Got an intermittent issue with the following fault codes showing up. Car runs fine, decent fuel and a Cataclean treatment have been used…….which actually cleared the management light at one stage.

Seems to trigger the engine management light at tickover more than when running under load.

Thinking maybe an air leak on the induction side.

Any tips or suggestions most welcome!

 

[AntStark]

Yes air leak most likely

 

[Bigfella70]

Thanks! any ideas on where to start looking / how to trace potential leaks on the M54 engine……

 

[AntStark]

Usual suspects are the flexible boots from the MAF to the throttle body, they split at the concertinas. Any of the pipes that come off those as well. There are little rubber bungs on the back of the intake manifold (near the bulk head) that split and fall off. If you have the secondary air pump (front left clump of plastic) there are a load of vac hoses that come of that and go round the back of the engine. My leak was from the rocker cover gasket failing. Also the PCV system can crack. To be honest I would get someone to smoke test it for you, saves you throwing unnecessary money at the issues
…or make your own ! https://zroadster.org/threads/i-did-a-thing.67817/

 

[Bigfella70]

Thanks for the advice, will update on findings!

 

[Bigfella70]

Apologies, however I have a long overdue update for this thread!

Stripped the intake hoses, DISA valve and idle control valve off for a check and clean up.

Found a very slight split in the upper intake hose where it connected to a plastic elbow. Also the 3.5 mm vacuum hose had seen better days.

Additionally the DISA valve isn’t holding any vacuum, and doesn’t actuate when 12 volts is applied to the terminals with a power probe. Hence new parts ordered and awaited. Hopefully this will see an end of the intermittent engine management light appearing. The car seems to have been running fine but from what I’ve read there may be a perceptible improvement in performance with a new DISA fitted……

Update and photos to follow once the new bits are fitted hopefully this weekend…….

 

[Bigfella70]

So, replacement DISA valve fitted, along with new Febi intake hoses. Also established that the MAF sensor was damaged and not functioning correctly hence that was replaced also.

The car drives and performs very well, however………the engine management light still popped up after a day or so. Showing fuel trim codes.

The car seems to be running perfectly however next move will be a smoke test and possibly change both oxygen sensors. I’m sure that I’ll track down the cause and get it sorted soon!

 

[Peter1450]

Good luck with the fault finding, try not to drop any nuts n bolts, you’ll spend hours in the gravel trying to locate them

 

[Zola3]

Hi bigfella70,

Just wondering how you've got on with your issues. I have similar issues on my 2.2.
For years (literally) INPA has reported a MAF sensor error (i.e. a number of errors thrown each journey). No dash errors until recently (fuel trim bank 1 in excess).
Car runs fine. However replaced cracked main boot and sourced a second hand Siemens MAF (new unit is stooopid money and I'm not interested in cheap after market ones).
Reassembled everything and..... it's exactly the same. Like yourself, I suspect air leak(s) somewhere causing unpredictable maf readings etc.
I used a creator reader while driving and looking at the data stream graph the fuel trim bank 1 adjustment was varying between 0.0% and 15%.

Bloody infuriating task. Still, these cars are approaching exceeding a quarter of a century

 

[NZ00Z3]

Hi Zola3

A smoke test is the best way of finding the vacuum leaks in your engine. Read: https://www.e46fanatics.com/threads/how-to-smoke-test.1261077/

 

[Zola3]

Hey NZ00Z3,

Yeh it's looking that way. Any tips on a cheap home made variant?

 

[colb]

Home made smoke tester I made is in this thread page 2 I think

ZedShed (Midlands).

Spot the difference. Tony.

zroadster.org

 

[Bigfella70]

Hi Zola3, I replaced the disa valve having tested it and found to be faulty. Whilst I was at it I made my own smoke machine similar to the above and carried out a test. No sign of air leaks. I returned the supposed “Febi” oem quality intake hoses as they were far too soft and squashed down when connected to the MAF, restricting airflow.

Another thing worth looking at is the two pre cat oxygen sensors. If they’re faulty then that would likely trigger the engine management light. I’d recommend getting a garage to do a smoke test or make your own the go from there and consider the oxygen sensors as next port of call.

Good luck and please keep us updated on findings….

 

[colb]

Always worth looking at the pre cat sensors in live data on a good scanner to see what they are doing. With engine running and up to temp when viewed in graph form they should be seen to produce a rising and falling volt range indicating they are working. In the event of their heater circuits being faulty that would/should set a code to indicate the fault with that part of the sensor. These sensors can get lazy with age which would be indicated by slow movement of the wave form as it rises and falls over the voltage range. If any require replacement go for oem brand like Bosch dont cheap out on these.

 

[Zola3]

Thanks colb, yeh I did watch the graphs of those sensors on the "creator" (indeed all the air/flow mixture stats - they all seem seem to behaving ). The only one that shows such a large variance is the fuel trim bank data, which is consistent with the ECL - though I never saw it reach the 20% threshold.

 

[Zola3]

Thanks for replying bigfella70 and congrats on nailing the prob. I had read about the DISA valve often causing an issue. I will readdress the issue when time allows and hopefully provide a successful summary.