Injector Fault and Setting Timing

Hi, did a search but couldn't find a thread about the specific issue.

I've an Audi A4 with a 110bhp AFN engine (European model). It has previously been chipped to around 155bhp.

After a blown turbo and getting the car back up and running (no engine damage done, cleaned intake manifold and intercooler and got reconditioned turbo), I was scanning the car for faults with Vag-Com and came up with:

00550 Start of Injection Regulation (Control Difference Intermittent).

After using the instructions on RossTech and here I checked my injection pump timing and found it to be at around 150 (spec about 45-65). After a few tries I got it to just above spec (68) but, while the car is running very smoothly, it will not start any more. To get it to start I've had to put the injection timing back up to 135.

Not sure if this fault code is even for this problem but anyone any info on what the Vag-Com fault may be and also why the car won't start when I put the pump timing in spec? I've a PiperCross air filter, the fuel filter was changed a few weeks ago, and as I say, the intake manifold and intercooler are spotless.

Thanks in advance.

PS. The flywheel is also in perfect condition as I fitted a new clutch and gearbox a couple of weeks ago also.

It sounds as if your N108 timing regulator is not working.

This advances the timing during starts, especially cold starts.

You can tell by recording a measuring block during cold starting. It shows actual and specified start of injection, and N108 duty cycle. During cold starts the Duty cycle should start high and work down to under 10%

Also ensure you are using the proper graph for setting your timing.

Look for a thread by aNut on timing basics recently.

http://forums.tdiclub.com/showthread.php?t=240450&highlight=timing

Make sure you are fully warmed up.

Cheers. Yep warmed up and the setting is hovering around 132-136 for the pump timing. Any lower and the car is struggling to, or won't, start. So I gather if this N108 valve is ok then the car should be starting with the timing back around spec of 65.

A lot of tech stuff in that other thread. Basically do I need to go to Meas Blocks on 004 when starting and if the duty cycle on the valve doesn't go up over 10% while starting then it's faulty? What should it go up to of it is working ok?

Also, where is this valve located physically so I can change it if it's blown?

Thanks again.

You want to look in measuring block4 and see if actual is tracking specified injection. The duty cycle could be as high as 80% when it is really cold, then as it warms up the duty cycle will drop as it lowers the timing to the specified value for a warm engine. It should be below 10%.

If actual and specified start of injection are not tracking together, look at your duty cycle, if it is over 80% or under 3%, then it has hit the end of its control range.

You set the mechanical timing in the Basic settings mode of operation. This turns off the N108 and lets you truly set the mechanical timing without the computer controls interfering.

Thanks. I checked tonight and the actual was not tracking the specified (can't remember the exact values). The duty cycle read 2.8%.
I've left the timing set high on the injection pump to aid the starting but would I need to get this sensor then, as I'd like to get the injection timing back in spec?

Also, I've read in my manual (Haynes) that this sensor contains an outer seal, a sieve, and an inner seal. Could my sieve be blocked up and causing this, or is the low duty cycle value always a sign that the sensor is blown?

Thanks.

Update:

Got a new N108 sensor and fitted it today. It's an absolute nightmare to change this without removing the pump but got it done in the end.
Set my injection timing right on the blue centre line on the Vag-Com graph and the car is starting no problem now, all the readings in measuring block 4 are spot on, and after a good test drive the 00550 Injection Regulation error is not showing up any more. Success.
Thanks for the help.

Congrats. Not many people can do a repair like that.