Quick Diagnosis for VW/Audi GDI fuel pumps
One of the most common issues with VW/Audi GDI, or all GDI would be your P310B LOW FUEL RAIL PRESSURE code. This code, for those not familiar with the system can throw you through a loop. There have been many high pressure fuel pumps replaced multiple times, only to have the same code return.
What can we do???
For VW/Audi, measuring value blocks (MVB) 103 and 106 are going to be your best friends. MVB 103 is going to show you your fuel line (low side) fuel pressure. Don't take this number for granted as this is an inferred measurement on later vehicle. MVB 106 will show you the fuel rail (high pressure) pressure and electric fuel pump duty cycle.
General rule of thumb with GDI electric fuel pump is 50% duty cycle at idle. Too much more than that, the pump can't keep up providing fuel to the high pressure side. Looking at the scan capture, you can see the low and high pressure look ok-ish. 50 bar (740 psi) high side, and 4.48 bar (65 psi) low side.
Take a close look at the duty cycle. This pump is screaming at 83% at idle. There is no way that that pump can keep up under load. This in tank pump needs to be looked at closely. Most likely the pump needs replacement, but I will never recommend replacement without some basic checks.
After replacement, this is what MVB 106 should look like.
Thanks for reading
Hey Chris thanks for the awesome write up. I have a question about your choice of scanner. It looks like this is a factory tool. To the best of your knowledge would this fuel pressure information be available in detail on an aftermarket scanner? Not necessarily the generic mode but enhanced mode. Or is it your choice to always pick an OE scanner for this analysis?
This is the Ross-Tech VCDS. While being close, it is by no means a factory scan tool. Measuring value block can be reached with almost any scan tool. You just need to know what they are. You can get this same info with a Lauch, Snapon, Autel, OTC, Gscan etc....
Personally, the way the information is laid out in VCDS is the way I'm used to it. I can find the same info in my Launch and Autel, but it comes in a large list you have to scroll through. The measuring block numbers are the same however. You can also test drive it with the scanner watching the in tank fuel pump duty cycle and watch it peg towards 100% during acceleration, showing it is having
I was gonna ask that same question, so thank you also. We never want to work on German cars here but they get towed-in sometimes anyway, due to our location (at the edge of civilization).
That's my reason for presenting the information this way. I purposely try to not use VW terms for parts and data. Once you get past some of these idiosyncrasies of these vehicles, you come to realize they are just normal cars. 4 strokes, put some gas in it, hook up a battery, and you're good to go. Ok, maybe not that simple. The GDI rules of thumb generally apply to all vehicles, That's why I
I've never even heard of "measuring blocks" until your post. It's a whole different world.
On the Snap-On line it is under expert mode. When you first hook to the vehicle and ID it, it asks if you want vehicle specific or expert mode. The hard part is knowing what blocks to look at, and what the numbers are telling you.
Measuring Value Blocks (Gasoline Engines) • 00 General Engine Data - Summary • 01 Engine Idling Test • 02 Engine Idle - MAF Sensor / Injection Timing • 03 Engine Idle - Timing / Throttle • 04 Engine Idle - Intake / Coolant Temperatures • 05 Engine Functions - Idle Control / Operating Mode • 06 Engine Functions - Fuel Trim • 07 General Engine Data - BDE • 08 General Engine Data • 09 Oil Fill
I notice that the information in 106 is different in the first three screens than the last. Is that beta v release version?