help,mk3 vr6 keeps popping fuel pump fuses!!!

[rubjonny]

Our Polo ran fine without, are you sure?
I would have thought it would switch to 'limp' mode.  I'm sure VW would have designed the ECU not to kill the cat if the lambda is disconnected...

[AudiA8Quattro]

Check this
http://www.gti-vr6.net/library/engine/vr6_technical_manual.html

Its a pretty accurate guide. I would say the cat would probably be ok as the other sensors should supply the ECU with enough information. However the oxygen sensor is a safeguard, so i would leave it unplugged for to long...

[rubjonny]

I found this in that guide:

There is no substitute function for oxygen sensor (G39).  If signal fails, no oxygen sensor regulation takes place.

I take that to mean the ECU uses a fallback map

[AudiA8Quattro]

I found this in that guide:

There is no substitute function for oxygen sensor (G39).  If signal fails, no oxygen sensor regulation takes place.

I take that to mean the ECU uses a fallback map

I took that as meaning what it says, no regulation takes place, in other words the ecu uses other sensors for fuel injection calculation.

[rubjonny]

well yes obviously, but its still going to need a default value for the lambda output, you can't complete a complex mathematical equation with a completly missing value

[AudiA8Quattro]

well yes obviously, but its still going to need a default value for the lambda output, you can't complete a complex mathematical equation with a completly missing value

Thats what the guide is saying if you read the whole lot.
The lambda does not have a default value, unlike some of the other sensors.
When some sensors are faulty, a different sensor reading is used instead, some sensors just have a default value when faulty, and some like the lambda is bypassed when there is no reading.

Like i said, unplug it, but don't leave it unplugged for too long.

[rubjonny]

Exactly, it doesn't say anything about substitute senor feeds being used if the lambda isn't working, so it must use a default fuel map!

If you have a complex fuel equasion to calculate how much fuel you should use for any given ammount of air, you cant just remove the value recieved from the lambda and expect it to work, you need to use a default fuel map value of some kind instead.

The lambda output is used to tune the map to exactly the correct air/fuel ratio at any given time, without it, a default fuel map is used, as per any ECU driven injection system which has no lambda.

[AudiA8Quattro]

If you say so.
I took it to mean the opposite, no regulation means the sensor is ignored.
If there is an air flow meter, inlet air temp sensor,throttle potentiometer, engine speed sensor, cam position sensor etc etc.. of course the ECU will be able to calculate fuel injection and timing.
Up to you at the end of the day, i wouldn't unplug it for long.
Whether you are right or i am is regardless, you can't have a 'safe' value for an oxygen sensor.
What i'm saying is i wouldn't want to guarantee that the cat won't get damaged.

[rubjonny]

well how does the 9a 2.0 16v manage without a lambda then

[HARDCOR3]

big dub's on his Hols, but we've replaced the lambada sensor, the cat, the fuel pump relays, pretty much everything barr the fuel pump, my next suggestion is for him to change the fuel filter, as these allways get well clogged, maybbe it's this restricting fuel flow, resulting in the fuel pump struggling, then popping the fuse???