VCDS Fuel and Misfire Logging Help

[KieranM]

I'm currently getting misfires top end at around 6500rpm and it's getting worse. It got pretty bad the other day and actually registered a misfire fault code on cylinders 1 and 2, it also gave a low fuel rail/system pressure fault code but I have no idea what is causing it.

Does anyone know what blocks to log to check the misfire counts and check the fuel rail pressures and the actual and requested fuel pressures?

[pudding]

I can't remember off hand, but if you click Advanced Measuring Blocks it should pop up a big list of all of them, scroll through and click the relevant ones.  I think you can datalog up to 8 of them if I remember right.

You want to log actual and requested fuel rail pressure, actual and requested boost, requested and actual low pressure fuel pump, lambda regulator and knock regulator.  A couple of other things like intake temp and throttle position might be useful too.

If the HPFP pressure falls below specified and the lambda regulator is pegged out at +25%, you have a fuel deficiency. 

Is it remapped?  KO4 or KO3 engine?

Also, some KO4 engines have weak exhaust valve springs which are known to cause misfires at the top end if the exhaust back pressure is excessive.

[Dan_FR]

Look through here: http://www.ross-tech.com/vag-com/m_blocks/

Misfire is 15 & 16, look at lambda specified and actual(31), lambda correction (01), low pressure fuel side is 103 and 106 from memory, high pressure side is either 230 or 231. Just compare specified to actual. I suspect your low pressure fuel side is struggling to maintain pressure if its a high rpm, you'll see the duty cycle climbing and the actual pressure falling rapidly.

Log full throttle runs from 3ish k rpm through to the rev limit and post the data up here

[KieranM]

It's a ED30 APR Stage 1
Thanks guys, I'll get it logged this weekend and hopefully that will help pinpoint the issue.

[pudding]

APR maps are famed for being pretty aggressive, so the fuel demand they specify is probably beyond what your standard pump can deliver.

Had exactly the same issue with my Stage 1 ED30.  It needed an uprated pump.

[KieranM]

I'm upgrading everything for stage 2+ so I'll be getting an uprated fuel pump very soon along with RFD, RS4 FRV, injectors cleaned and tested and valves cleaned.

I've noticed that it seems to be giving off a fair bit of black smoke when on boost. Did yours also do that?

[pudding]

Mine has a 'custom' map but the only time I've noticed black smoke was when hovering on the edge of boost for a while waiting for an overtake - say 3500rpm in 4th or 5th - and then nailing it.  Got a momentary small puff of black then it clears up, otherwise it's a pretty clean exhaust 

Too much smoke can mean an excessively rich AFR request from the map, poor atomization (bad injector(s)), boost leak, bad MAF or EGT failsafe map shoving loads of fuel in because it thinks the engine is about to go into meltdown.

To be honest, I have yet to see a 100% soot free TFSI exhaust.  I've followed standard GTIs and ED30s and even they throw out a puff of black when you boot it.

I've had turbo engines for years and hardware is rarely instant.  It takes time for the turbo and injectors to react to inputs.  So when you shove your foot down, there's a sudden demand on the injectors, they cram loads of fuel in and if the turbo hasn't quite woken up yet, you'll get a momentary rich condition, nothing to worry about.  Constant plumes of thick black smoke on the other hand, that is a concern!

[KieranM]

I would expect a little bit of soot but this seems to be quite bad, it's not quite derv bad but it's definitely worse than a 'normal' tuned TFSI. I think it may be the injectors but I'll find out when they get tested.

[pudding]

I take it you're getting chunky smoke in the midrange, not at the top where it's misfiring?

Have you done a valve clean yet?   Personally, I would not waste your time or money on cleaning the injectors, just put new ones in when you do a valve job.  The way they fail is nothing to do with them being clogged etc, the pintles inside them wear out and replacement is the only proper way to do it unfortunately.

Does your APR tune allow you to switch to stock?

[KieranM]

No not yet, the valves will be getting cleaned very soon when I do the RFD.

I did a little bit of logging today and looking at the HPFP (block 230) at points the specified value is around 119 and the actual is down at 80ish, then the actual will rise back up again to about 128.

Going by that I take it it's the HPFP that's needing replaced?

[pudding]

Was that big drop in the midrange, 3000rpm ish?  That's why K04s need a pump.  When they thump out 1.7 bar at 3000rpm, the stock pump struggles.

I think the low rail pressure fault code and that data log kind of points in that direction matey 

[KieranM]

The drop in pressure was right near the limiter at around 6000rpm onwards, it also gives of some loud bangs as well.

I changed the pump for another standard one to check if it was knackered but it's not made a difference.

[Dan_FR]

logged low pressure side?