NR04

I've been having warm start problems and my dealer won't perform any troubleshooting procedures because there are no error codes. My last visit with them was very unpleasant because they refused to do a residual fuel pressure test to elimniate the leaky fuel component as a possible problem.

Then I noticed that I can monitor fuel rail pressure with Vag-Com and decided to log the pressure after the engine has been shut off (reading the residual fuel pressure). However, the pressure reading is in Kpa and when I convert it over to psi, it's way too high. Here is an example of my log:

6:50pm 3,500 kpa
7:15pm 2,500 kpa
7:50pm 500 kpa

My question is that should I divide the above numbers by 10? 3,500 kpa is 500 psi. I think it makes more sense that psi should be 50. Also, anyone know if the above drop in fuel pressure is normal or outside the spec? I live in Socal and the weather has been quite hot lately and the warm start issue is more prevalent under the hot conditions. Thanks for your input.

Andy@Ross-Tech

Year/make/model/engine? Which measuring group?

NR04

Oops, here it is:

2006 A6 3.2L

Not sure which measuring group... with the version I have I chose "Mode 1 Read Data" and selected "Fuel Rail Pressure" from the dropdown menu.

diagnosticator1

AFAIK, pressure units for measuring blocks is almost always in millibars. Lets see, from your info, 3500 millibar converts to ~50.7 psig, 2500 mBar ....> ~36.3 psig, 500 mBar ...> ~7.3 psig. How do the above values compare to spec?

diagnosticator1

thats 3000 to 7000 mbar.

From label file 06E-910-559-BKH.

NR04

I was checking it with Mode read data and the value actually says kpa but in (relative) mode.

diagnosticator1

The fuel pressure in the fuel rail is approx 35 Bar. The pressure before the high pressure pump is approx 6 Bar.

The residual pressure is specified as at least 3.75 Bar, pre high pressure pump, after 10 min.

Note that 3500 kPa = 35 Bar, 2500 kPa = 25 Bar, etc.

NR04

Looks like my residual pressure is within the spec and is not the cause for my warm starting issue.

diagnosticator1

Yeah, 5 Bar after an hour is good.