oil pressure to resolve once and for all

[ever88]

Hi all

this problem has been talked about but having read through the posts I think the exact ins and outs are not covered enough for me to correct my problem.
And I know for certain oil pressure is fine as fitted gauge directly

The Problem
Oil pressure warning light and Buzzer comes on when engine reved above 2500

there is no oil pressure warning lamp flash even when ignition just turned on and engine still off.

What I've done
1stly I have earthed both oil pressure switches with ignition switched on and still no flash of oil pressure lamp in dash so I suspect lamp is not getting 12 to one side atleast.

with engine revved above 2500rpm and left to idle (buzzer and oil light on)
tried removing both oil pressure switch connections and even earthed them

both of these attempts to resolve have failed.

Thoughts to resolve from other posts

some say circuit board at fault but does not say precisly what to do to disconnect it as I don't mind this option as gauge is fitted.

some say provide another earth to dash clocks but not sure which wire so that I could even connect a simple wire to diagnose this is the fault. others say this wire has to go into the Board somewhere?


So what should I do

your advice is greatly appreciated. I feel I have illiminated the pressure switch senders from the problem as I have removed connections and tried earthing direct. via wire from battery to each wire under bonnet.

sincere thanks to all replies

Paul

[rubjonny]

ok, the pressure sensors work by earthing a 12v feed from the clocks.  The clocks measure the resistance through the sensor, which tells them what the oil pressure is.  The fact that earthing the wire still doesn't give you a red light, suggests to me there is a wiring fault, or the oil pressure PCB behind the clocks is shafted.

Get a multimeter on the oil pressure switch wires, they should have 12v to them with the ignition on.

[ever88]

thanks for help

checked both pressure switch terminals whilst disconnected and there is 0 volts to the oil filter high pressure switch and only 4.9 volts to the low oil pressure switch on the side of the cylinder head.

does this help?

cheers
Paul

[rubjonny]

Hmm, I'll double check on mine what the voltage should be, perhaps its only 5v to the sensors. but 0 volts to the high pressure switch defo isn't right, that would explain why you get the buzzer over 2k as this is when the high pressure sensor is used!  What year is your car?

[ever88]

hi

the car is a mk1 golf with a 16v conversion.

I did the conversion myself and sold it several years ago but have bought it back and trying to put it on the road.  I'm almost there but not rushing it.

as I understand it the cylinder head sensor is earthed when engine is off or oil pressure is low and then when running above the 2000rpm mark if the oil pressure is too high the sensor on filter earths the wire which I believe is connected to the low oil pressure wire somewhere as the haynes manual only shows on pressure switch.

Ideally I just want to do away with this all together as there is a gauge fitted in centre console.  not driving this with light and buzzz doing my head in. Ill go stir crazy.

cheers

[rubjonny]

Ok so I assume it has a pre 90 MK2/late MK1 fusebox?
If so:
http://www.bentleypublishers.com/tech/vw/bentley.vw.fuse.panel.rear.1984-1993.htm
B/15 -> is the high oil pressure switch feed to the clocks
D/21 -> runs to the oil pressure sensor

[ever88]

this may take me a while to find that out.

fuse board and lower dash still in place neat and tidy.

assuming I find everything as you say

B/15 -on back of fuse board is fed to the high oil pressure switch on the clocks

and

D/21  on back of fuse board is fed to the oil pressure sensor

do you have any thoughts or are you suspecting something is not connected.

by the way I do appreciate your help on this.

why VW wanted to set and oil pressure sensing set up like this is beyond me.

[rubjonny]

If you can be bothered you could check those wires for damage, or run a wire direct from the dash clock wire to the sender!  You could start by checking for voltage right at the pin on the clocks for the yellow wire, and see if its still 0 or 5v with the ign on, then you know the break is further into the loom

I have a feeling the problem is inside the clocks though as the pressure light does not illuminate, and I assume it would if the buzzer goes off for any reason...

You can remove the buzzer circuit completely though, you'll find it clipped to the back of your speedo.  Just pull it off

[ever88]

I sussed it John

a bit lucky though.

started engine up and revved it to bring buzzer on as I was struggling to locate where the buzzer was.  as I was gripping the clocks the buzzer went off. so I kept on doing this to locate what location stopped it.  the blue circuit board plastic immediatly above the speedo clock has three prongs onto it and above it agin and toward rev counter clock are some othe solder connections.  these had cracked and come away from the conection.

now I know what to do.  will try to resolder or source new clock

thanks again for all your help.

cheers

Paul

[rubjonny]

Cool, good luck!