I am currently experiencing intermittent misfire/juddering issues on my 2.0TDI (BKD engine). The car juddered and died one night last week. The AA were called out and suspected a sticking EGR valve, but he could'nt find any codes. Revved the car a few times and took it for a run - all ok again !

I have a vag-com kit, so scanned the car the following evening and got:

17036 - Sensor Reference Voltage B: Too Low

P0652 - 000 - -

According to ross-tech, this points towards a MAP sensor ?

I didn't clear the code as the car was going into the dealer for a service the next day.

Mentioned the breakdown/AA theory when dropped off at the dealer. They wouldn't accept the code I had and said it would need to go on their diagnostic system.

Collected the car that evening, no codes were found by the dealer, but they checked the EGR operation. Said to be ok... The only thing they could point towards was a blocked fuel filter, which was replaced in the service.

Drove the car home (150miles) where it was fine for the first 30 miles, then started to miss/judder when using light throttle.

Scanned the car again, no codes !

Ever since the breakdown last week the car has intermittentally juddered/missed and ran rough at idle.

I plugged my vag-com in today to read specified v's actual MAF sensor readings. With the engine on, idling, I opened the measuring block (003) to find:

RPM Mass/Air Mass/Air Duty Cycle %

819 245 425 96.5

Once the throttle is depressed both values were the almost identical:

1911 255 245 36.7

When I left the engine to idle again for a couple of minutes, the values return to what were originally observed. I've read the the EGR system is disabled after two minutes, so that might explain the change in the duty cycle, but should the MAss/Air value's show different values ?

I'm assuming that the layout on vag-com is Specified MASS, Actual MASS ?

After running a few tests, its looks like the EGR and MAF are functioning as they should, however this didn't stop the car breaking down again tonight. This time it seems more consistent. starts, revs, but dies as soon as any load is applied.

The car was recovered to Pulman, where hopefully the root cause can be found :-(

Any help is much appreciated...

Just a quick thought, but i've heard people recommend unplugging the MAF sensor to try and determine if this is the cause of a fault.

I cant say it would work though as i've never had to try it yet.

When the MAF goes AWOL the loss of power is usually pretty much constant and not a 'misfire'. You could try disconnecting the MAF I suppose. There is always the possibility of a poor connection somewhere. If you think the EGR valve is OK then start to suspect an injector fault (not unknown on this engine!) and in due course you might find a misfire code comes up....

If they can't find it, suggest they check all the hoses to the airbox for splits and disconnections, unplugging the MAF does only one thing, throws up the dashboard light, as said when they go, they cause the turbo to cut out resulting in no power, a misfire and judder suggests a cam or crank sensor if the engine has them.

Well the diagnosis results are in !

No fault codes logged, so an "indepth diagnosis" done to try and find out why it judders/missfires and sometime cuts out altogether !

Whey said there is oil in the fuel system... a little strange as I though diesel was oil based ?

Anyways, to correct it they are going to replaced the tandem pump and the fuel pump too since it been contaminated..

Hopefully this will fix things, Diagnosis makes sense when reading this from an Audi forum.

http://www.audi-sport.net/vb/showthread.php?p=851078

Well, got my car back on Monday night after having the tandem and fuel pump replaced. Car went very well for a day, then started playing up a little bit last night with the odd misfire,judder,stutter call it what you want.

Started the car first thing this morning again and it went ok for the first few minutes, then had a few coughs once into third at fairly low revs/light throttle. Cleared again, then decided to cut the power for a split second while pulling out of a roundabout 5 miles later !

Back to the garage again for further diagnosis. :-(

On 03/12/2009 at 11:51, swil00 said:

Well, got my car back on Monday night after having the tandem and fuel pump replaced. Car went very well for a day, then started playing up a little bit last night with the odd misfire,judder,stutter call it what you want.

Started the car first thing this morning again and it went ok for the first few minutes, then had a few coughs once into third at fairly low revs/light throttle. Cleared again, then decided to cut the power for a split second while pulling out of a roundabout 5 miles later !

Back to the garage again for further diagnosis. :-(

 

This sounds like a common wiring fault in the 5 volt signal system going from the engine ecu to various components on engine ie maf sensor ,g28 engine speed sensor ,g40 cam sensor etc .common problem areas are under the battery or in loom running across in front of the engine to the various components.

17036 - Sensor Reference Voltage B: Too Low

P0652 - 000 - -this code occurs when the 5 volt system goes to ground ie by wires rubbing through or corroding within the wiring loom ie the signal wire touches somewhere on the engine causing earth short or more than one wire corroded through inside the loom touching each other and causing same short to earth , can be awkward to find and may require scope to show 5 volt ref signal dropping out when wires are moved around ie back pin a 5 volt ref signal say g28 etc and see if the volts dropped to 0 when wires moved around and take time to check thouroughly