DTC fault codes 28, 29

I have the following DTC fault codes showing on my 2002 L322 V8:

28 Additive mixture adaptation, Bank 1, control limit reached
29 Additive mixture adaptation, Bank 2, control limit reached

I have erratic idle and sometimes cut out when engine is cold.

When faults are cleared I have to drive 5/6 miles before they come back?

Is the MAF sensor the best starting point?

Thanks

MAF is usualy pretty good on these things....

Check for PCV valve or manifold gasket leaks....also check condition of the Lambda sensors too....

I posted a few days ago on a thread some information on the adaptive and multiplicative fuel trims and what they mean....search of this. here is a link to the PDF

http://www.landyzone.co.uk/lz/attac...blems-bmw_e39_oxygen_sensor_and_fuel-trim.pdf

Reaching an upper or lower limit of fuel trim can indicate either an induction air leak or fueling issue...depending on which limit is reached depends on where to look first!

Can't remember of the top of my head, but additive is idle and multiplicative is fast running or is it the other way round...anywho, search for the PDF file and go from there!

Thanks Saint V8, vert helpful.

Any idea why it takes 5/6 miles for the faults to return?

I now have fault 98 showing 'Tank ventilation valve solenoid valve' in addition to the above??

Forgot to mention, car has LPG system fitted.

I always turn the gas off before sorting these issues out. get it running right on FRESH petrol, then when you know that is fine, try it on gas. If it plays up then you know it's a gas issue.

If the fuel tank vent valve is stuck open that will introduce a vacuum leak on the inlet side and cause it to run weak. Blank the pipe off and clear the codes and carry out a road test - you now know that a 6 mile r/t will bring the codes back, so if you manage 9 or 10 miles without the codes returning - that is your fault.

The adaptive codes take a few miles to show, because when you clear the fault codes the ECU is reset to 'base' settings, then as you drive it the ECU will be adjusting the fuel trim to attempt to get the O2 (lambda) sensor reading into the limits that it wants to see. When it can't manage that, it gives up and throws the codes up and puts the MIL on.

Don't necessarily blame any sensors here - they could be correctly reporting a fault. Can you see what the O2 sensor voltages are? if you can, can you make them move by unplugging an air pipe to make it run weak, or spray a bit of carb cleaner up the intake to make it run rich - do the readings chnage accordingly? id so the O2 sensors are working, its unlikely both would die together anyway.

MAFs normally read low as they age, but most get changed unnecessarily due to 'fit and hope', rather than working through a logical test process and properly diagnosing the fault.

Thanks for that N5Fav.

I have just got a Bearmach HawkEye which has Tank Vent. Valve actuator facility. I will try that and see what response I get.

Will update later...

I'm sure I read recently on here that it's only NAS L322s that have tank vent valves.....is this correct? If it is why am I getting this fault? Think it was Saint.V8 who posted this info?

Ive had "issues" with my cel. Ended up changing the maf as it had a non genuine one fitted and it sorted it finally. But I also changed, pcv valve and breather pipes, 4 x 02 sensors and fixed an air leak on the inlet pipe where it connects to the inlet manifold, it wasn't seating properly at the bottom, it kept pushing the big O ring out. It still throws a fault every now and then but nothing I worry about. Also on lpg, I just think its what they do!! LOL

kgeddes said:

I'm sure I read recently on here that it's only NAS L322s that have tank vent valves.....is this correct? If it is why am I getting this fault? Think it was Saint.V8 who posted this info?

Click to expand...

Tank Vent Valve is NAS spec vehicles only....mine shows the same

Thanks for replies so far.

Can I ignore DTC 98?

Diagnostic test (HawkEye v 7.0) this morning after 15 mile run on petrol/LPG:

DTC 20 Oxygen sensor heater after catalytic converter Bank 2: signal
DTC 27 Multiplicative mixture adaptation Bank 2 control limit reached
DTC 33 VANOS inlet valve Bank 1
DTC 98 Tank ventilation solenoid valve

On cold start up engine was hesitant with rough idling but fine when warmed up a bit and over to LPG, ran perfectly thereafter.

Previous DTCs 28 and 29 gone?

Any ideas what's going on?

Thanks

I'd try a second hand maf. I got mine from range rover breakers. Think he's on here

Thanks v8hotrodboy, I think I might do that, on eBay for less than £40 new.

Concerned about the VANOS DTC......could a problem with this be screwing up the system?

If the VANOS isn't working properly this could create all sorts of running problems. You can google VANOS on the BMW's and see. So get that checked out properly.

If you can do it, check the resistance (with an OHM meter) on the two grey wires to your after cat oxygen sensors. The grey wires go the heater in the sensor. If the heater isn't working properly the sensor can't get up to temp to give accurate readings.

Personally I wouldn't fit cheap MAF's or cheap oxygen sensors, if they need replacing get Bosch or NGK or similar quality.

Does your diag kit measure air flow through the MAF?

N5Fav said:

If the VANOS isn't working properly this could create all sorts of running problems. You can google VANOS on the BMW's and see. So get that checked out properly.

If you can do it, check the resistance (with an OHM meter) on the two grey wires to your after cat oxygen sensors. The grey wires go the heater in the sensor. If the heater isn't working properly the sensor can't get up to temp to give accurate readings.

Personally I wouldn't fit cheap MAF's or cheap oxygen sensors, if they need replacing get Bosch or NGK or similar quality.

Does your diag kit measure air flow through the MAF?

Click to expand...

I'm very new to the HawkEye. Just checked live data. Shows AIR MASS fluctuating between 16.7 - 17.5 kg/h

Is that ok?

Thanks for your help.

Cheapo MAF's often do not work.

Don't buy a cheap one! Only buy Bosch.

Sound advice forgetting the LPG for the minute. Pull the fuse to de-activate and toot round on petrol for a while. The Motronic ECU will soon trim itself.
Your MAF reading looks OK, at idle, try the following speeds and see if you get about the same - make sure all engine loads are off.
600rpm idle - 17.1 Kg/hr.
2000rpm - 44Kg/hr.
3000rpm - 76Kg/hr.
My thoughts are its the LPG system needs a tune up, maybe no more than a tweak on the vaporiser to up the pressure to allow for a stretched diaphragm.
DONT BUY A CHEAP MAF !!!