Bad bad s4 part two!

[bluequattro]

First chance I ve had to test car today
Tried plug into mates Eros? And won't connect so I went for a drive on minor roads
Fine for 14 miles, upto temp
Speedo started working
Seems down on power
Reversed n speedo stopped again
Thought all ok
Go to drive home up steepest local road
It cuts out
Drop to 2 nd n started again
When it stalled radio turned itself on!
Maybe a wiring fault affecting ecu then?
Got home and turned engine off
Started up fine so ruling out cam sensor now
Smells of petrol so wondering if dirt in fuel filter
Car had been stood 2 years with small amount if fuel
£60 put in so wondering if pulled up dirt from bottom of tank
Thoughts please
Happy New Year too!

[1781cc]

I think I mentioned the fuel pump in the Bad Bad S4 Part 1 - or maybe a break in the fuel line somewhere that only reveals under increased load pressure

[UrS4boy]

Speedo started working.Reversed n speedo stopped again.When it stalled radio turned itself on! Maybe a wiring fault affecting ecu then?

Sounds a lot like a bad ignition switch. ECU has nothing to do with the radio other than they both get power from the same sources.

http://12v.org/urs/IgnitionSwitchReplacementDIY.pdf

Speedo could be ignition switch related or just a bad 012409191D road speed sensor or connection (or bad instrument cluster printed circuit board traces) (happens).

http://forums.quattroworld.com/s4s6/msgs/168463.phtml

Hmmm....Just had a thought. There is the GALA system that increases the radio volume as the road speed increases. That could be the link between the radio and the speedometer via a bad 012409191D road speed sensor.

[bluequattro]

Aftermarket radio recently fitted so don't think that system will be applicable
I ve a set of s6 clocks to put in to see if speedo works all th time
S4 didn't work until I "tapped" the dash very gently with my fist, so I think that's poor connection behind either joints or wires
I ll get proper vag com plugged in Wednesday when my auto elec expert is back in work
All lights/elecs still work when stalls
I did wonder if the speedo sends a signal to ecu and when stops working it cuts fuel
Will be giving maf a clean and checking fuel pressure too to rule it out

[bluequattro]

Radio was off when it stalled and came on when car restarted
Only iso connected

[prj]

I did wonder if the speedo sends a signal to ecu and when stops working it cuts fuel
Will be giving maf a clean and checking fuel pressure too to rule it out

You jump to conclusions very lightly.

1. The speedo signal does not affect running. Only some tip-in stuff on idle, but lacking that signal you will not notice a thing.
2. The MAF is not going to make your engine stall, if it did, then you'd have fault codes.
3. Intermittent fuel pump is a lot more likely, as ECU can't diagnose that.
4. Dirt in fuel filter would not smell of petrol, it would just have no power. The smell of petrol means you most likely have a fuel leak.

[bluequattro]

Diagnosed as g28 sensor, spare located in my garage I think
Thanks for the advice guys

[merlin's S4]

Diagnosed as g28 sensor, spare located in my garage I think
Thanks for the advice guys

Worth a try but that fault code will always come up when the engine isn't running. I suspect your issue lies elsewhere.

[simon20vq]

After all the posts 'DAVID' had why not check the battery cables. Fuel cheak for a split pipe. Naught S4!!

[prj]

Diagnosed as g28 sensor, spare located in my garage I think
Thanks for the advice guys

Let me guess, engine wasn't running?

[rynaqui]

If engine is off, G28 will always show up, any other codes?

[bluequattro]

This wasn't a good thing anyway
Filth from crank breather
Although I ve read other sites since diagnosis and picked up the engine not running g28 code so now I ve changed g28 I will test again driving and codes with engine running and report back to you all
Fuel lines and battery cables checked out ok

[bluequattro]

G28 and flat battery-but it's had another battery since flat one

[UrS4boy]

G28 and flat battery-but it's had another battery since flat one

If the battery is weak and can't get the engine cranking mechanically at more than 13 RPM, or the G28 is bad and not producing the >13 RPM signal, then the ECU will not fire the J17 fuel pump relay = no start.

J17 info: http://forums.quattroworld.com/s4s6/msgs/22583.phtml

G28 info: http://forums.quattroworld.com/s4s6/msgs/20986.phtml

[bluequattro]

Battery was replaced before these problems started
Battery checked and ok
Car cranks and starts fine
Hot start is fine too
Only intermittent stalling
I have not tested replacement sensor on the road but no starting issues