fuel pressure with VCDS

B6/7 S4/RS4
#1

I am wondering if fuel pressure can be measured through vcds without the car running? I just bought my Ross Tech cable so im really new with its options, i read in another thread that groups 103, 106, 140 have this information but then read its only for FSI engines?

I am going to check out an 2004 S4 that the guy says has a bad fuel pump, instead of spending an hour fumbling around with vcds when i get there it would be nice to have an idea which blocks to check to see if it is in fact a bad pump. The car will not run, I am going to give it a full scan to see if anything else comes up that would stop it from starting.

I would try it on my car but it’s still apart in the garage.

I hope this hasn’t been covered a ton of times before and my search abilities are that bad.

#2

on the B6 S4 there really isnt a fuel pressure block to log. I guess you can log the in tank pump voltage but I dont know if that would tell you much.

You can try to use the out put test on vag com to see what comes up when you test the pump.

What you can check is block 034 see if there is any data there somethimes there is data available before you start the car. Remember if you clear codes you clear all the data in the fuel trim banks.

If you start the car you can log block 001 but the car will need to be at running tempiture and the 02s will have to be warmed up and working.

#3

Sounds good! Thank you for the info

#4

With the B6/7 S4s it is easy to manually check that the fuel pump is sending fuel to the rail. Disconnect the fuel line (it is a 17 mm nut on thd end of the line and the fuel rail hold is a 14 mm) at the rail, put the end of the line into a big empty bottle like a gallon coolant jug or washer solvent jug, and try cranking the engine for like 5 rotations. If there is a lot of fuel in the bottle then you are getting fuel and the fuel pump is working.

Do you know if the engine cranks or not? Depending on if the engine cranks then that is a big step for diagnosis because it could be a few different things either way.

#5

I haven’t asked too many questions through email, the owners ad a few weeks ago said the car ran fine and had a CEL but he didn’t know why. I noticed the ad again today saying its not running and it needs a fuel pump, I’m assuming he’s guessing its a fuel pump. I’m unsure whether it will crank or not, if it doesn’t even crank I’m going to assume the issue is more than just a fuel pump and hopefully codes will lead me to a cause or a ball park.

I’m unsure if he’ll let me pull lines off it but if he will I will definitely see how much fuel comes out. Doing a search it seems like it could be a relay rather than the pump itself.

Thank you for the advice!

Andrew

#6

It was pretty rare for the fuel pump relay to fail. More often the fuel filter would clog up and kill the fuel pump over time.

If the engine doesn’t crank then it is usually easier to fix unless the starter died.

#7

Andrew

If you get a chance make sure he hasnt cleared the codes. That will tell you way more of what is going on. If there is a pump issue he will probably have codes for it and if not the fuel trim codes should show something.

sounds like the owner isnt sure of what is going on and he is trying to sell the car. You just dont want a car that he is selling because he cant fix or find what is wrong

#8

For most people I strongly agree with the bolded part of what you said. Some of us are better setup to deal with problem/project cars/trucks though so we can get away with buying a fixer upper. I know that all my vehicles are fixer uppers other than my one year old trailer. Speaking of which I need to finally get around to posting an update to my Jimmy’s Garage thread about how I had to fix my A6 recently.

#9

I’ll check the codes for sure to see whats going on, I suspect the car needs a lot of work so it may just end up as a parts car depending how cheap it is. If it is worth repairing(depending on issue) then I may just hang onto it to fix down the road once mines sorted.

Thanks guys, I’ll report back anyways once I go look at it even if I’m not getting it lol

Andrew

#10

If you get the codes feel free to post them here. We can give you some idea on what else might be going on. You can always copy codes from vag com to a word program on any laptop

#11

Didnt go look at the car, owner was away and it was -30 all day so i wasn’t gonna hang out in that lol.

#12

Thats smart you really want to look over the car top and bottom. With it that cold its possible you would want to get though the outside look over quicker then you would like