Oil pressure sender

[vjay48]

I know this is a bit of a frequent topic, but I am sure you guys can help,last journey in car showed the oil pressure gauge starting to flicker. Put car away for winter, tvr spec sender out of stock so bought sender from USA to match stewart warner spec. Got car out for spring fitted new sender,reading lower than before,but no longer flicking gauge. Is the resistance of sender wrong,causing readings to be low? Is the genuine TVR part the answer?

[v8s4me]

Is the gauge earthed? If it is it might be worth checking it's good.

[vjay48]

Yes, might clean terminals just to check all ok.

[phillpot]

Can't see that the gauge needs an earth, other than to make the illumination circuit?

The earth is through the sender unit

[vjay48]

Sender on car had 2 terminals,yes I know that was not the original,worked well for 4 years,,one terminal to gauge, the redundant terminal to ground,terminal G to gauge,terminal WK to ground. My hope was not advice on wiring,but on resistance spec. of sender.

[Blue 30]

From memory alone...
Vdo auxiliary gauges such as oil/water/fuel are 3-wire working.
Whereas Smiths gauges are 2-wire working.
So the Vdo gauges will require a good earth.
Think of it like a volume control.
TerryB.

[lewdon]

Mine has a 7 bar (100psi) 2 wire sender fitted.
One wire is from the oil pressure gauge. The other one is from a warning light if fitted (mine hasn't got one). Both connections earth through the sliding resistance to the sender body and thence to the crankcase.

edited to correct resistance; I have just seen a note i made in the margin of my "bible" in 2012 =. "resistance measured as 250 ohm at 0 pressure. So, allowing for the inaccuracy of my analogue meter, i believe correct range should actually be 33 - 240 ohm.

Edited by lewdon on Monday 6th May 09:36

Edited by lewdon on Monday 6th May 12:42

[vjay48]

Thanks, I think its a earth problem,will get the multi meter out,bet the battery has gone flat!

[vjay48]

Not getting very far with this,bought the TVR parts sender to try and get the problem put to bed. Fitted,one wire, connected that,since this sender earths to engine? Nothing,not a signof gauge moving! Surely the big lump of cast iron under the bonnet will be a earth?

[GreenV8S]

How many terminals on the sender? Warning lamps will typically switch to ground, but a pressure sender is more likely to use two terminals.

If on doubt, just use an ohm meter to see what the electrical characteristics are.

[vjay48]

One terminal,tvr parts list this for Stewart Warner gauges,car does not have a warning light,old sender had 2 terminals,was a Chinese special.

[phillpot]

If you put the wire to earth (yes, the engine block should be well earthed thats how the starter gets its return path) does the gauge go to max?

[vjay48]

My multimeter has died,i assume the yellow/black wire is the power feed,is this sender the right one? I will rig up a earth,trying to find my power probe.

[phillpot]

Yellow/black?

whatever colour the wire to the sender is (should be brown/green or blue/green on earlier cars) hold it to earth, i.e. the block, and get someone to tell you what the gauge does.


a quick look at the wiring diagram would suggest (on a 2.8 s1) that black/yellow is feed to by-pass the ballast resistor, from the starter motor?

[vjay48]

The car has been "re-wired", I am getting to the point its ebay time,my son races minis and my efforts should go in that direction. I really hate bodgers.

[GreenV8S]

vjay48 said:

One terminal

old sender had 2 terminals

So it's not electrically compatible, then.

[vjay48]

Sorted,idiot who owned car was diy wiring "expert", used a old piece of wire off a loom for a earth,wrapped wires in black so you couldn't see the colour. Tvr sender works oil pressure good. Thanks guys