Electrical issues with the oil light, help please.

[r2oo]

Hi all.

Went for a nice drive on Saturday & after about 10/15 minutes I parked up & something strange happened (see attached Youtube Video). Oil light started flickering intermittently when stopped on tickover, blipped the accelerator & it stops.

http://www.youtube.com/watch?v=bjOphTWpEX4

There was also a weird clicking coming from the Electric fuel pump relay presumably because it is connected to the oil pressure light as a cut off.
I opened the engine lid & held the dipstick & it was only luke warm.

Drove the bug back home & every time I stopped it did the same thing, once in the garage whilst trying to work out what the hell was going on I think we may have narrowed it down to a bad earth in the Oil light tunnel. Eventuallty the light wouldn't even come on with the key turned to ignition on before turn over! As you can see from the pic below with the bulb holder removed there seems to be a metal tab on the right hand inside that touches the body of the bulb holder. This then seems to be connected to the blue spade at the bottom of the pic, is this the earth:

http://s1067.photobucket.com/user/r2ooo ... 5.jpg.html

If so that spade is connected the other end to the fuse box (top right hand spur) Is this correct, see pic, I am touching the connection with the screwdriver to identify it:

http://s1067.photobucket.com/user/r2ooo ... c.jpg.html

Now after fettling about with it all, the light doesn't even come on when in the hole in the speedo. However as we suspected a bad earth I connected up a crocodile clip to the body of the bulb holder and the other end to an earth (you can see both ends in the clip) and hey presto the light works.

http://s1067.photobucket.com/user/r2ooo ... e.jpg.html

How do I fix this??, any help appreciated.

[SCOTTRODS]

Clean all the mounting and grounding points on the speedo housing.... Re-assemble. That means ALL the contacts that are on everything on the speedo housing and it's associated components. a little scotchbrite goes a long way. Be careful with any compressed air if you use it, making sure not to blow int the hols real hard... that screws things up... moves lenses and stuff. NO scotchbrite, Fine Sand paper or even something as simple as a pencil eraser helps in some cases.

[r2oo]

Just did a check on the power to the base of the speedo & the lead has power when the ignition is on.

[Buggin_74]

As you can see from the pic below with the bulb holder removed there seems to be a metal tab on the right hand inside that touches the body of the bulb holder. This then seems to be connected to the blue spade at the bottom of the pic, is this the earth:

http://s1067.photobucket.com/user/r2ooo ... 5.jpg.html

No it's not the earth, that is the positive power to the bulb.

the charge, turn signal and oil lights in the speedo all work by the fusebox supplying ignition power to the outside of the bulb holder and the middle terminal is the ground, in this case supplied by the sender in the engine block.

It just sounds like you have a lazy sender, just try replacing it, its probably getting old and being dual purposed to control your fuel pump relay coil has tipped it over the edge.
I actually used the charge light for my fuel pump trigger rather than the oil light as it has a tendency flicker at idle on a tired engine thats hot.

Just make sure you get the correct M10 thread for VWs, most senders are 1/8th inch tapered and many people have cracked VW cases fitting them.

[Marc]

The "shell" of the bulbholder receives power from the ignition switch (via the black wire you indicated from the fusebox - BTW, that comes from the "hot" side of the fuse so there is no fuse protection - it would be better if the wire were smaller so that in the event of a short it would sacrifice itself before taking out the ignition switch or the wire from it to the fusebox...this is why the factory used a .5mm² wire there, equivalent to AWG20).
When the oil pressure is insufficient to hold the contacts open in the sender, a ground path exists through them from the engine case to the terminal on the end of the warning lamp bulbholder - if there's power to the shell, the lamp should light.

It is typical for the oil pressure light to flicker at a low idle speed after a long highway run, especially on a veteran engine that's developed some extra clearance at the bearings or if the oil pump has excessive clearances - hot oil is thinner and the pump has a harder time keeping up with what's lost at the bearings. Another potential cause of thin oil is a leaking fuel pump diaphragm allowing gas into the crankcase, but you have an electric pump so that's not a suspect here.
If oil viscosity is not the problem, there's one more possible reason for a flickering light. The diaphragm in the sender may be leaking and allowing pressure to partially equalize across it, effectively lowering the setpoint of the switch (the "lazy" sender syndrome that Buggin_74 mentioned). This is usually accompanied by external leakage of oil from the end of the sender, typically where the electrical connection penetrates the case. If you suspect the sender, buy the correct one by the part number, 021 919 081B ...which is a tapered thread, BTW - it's just not a 1/8-NPT thread. There exist "straight" threads with the same pitch, as found on water-pumper VWs, and they will not only fail to seal in an ACVW case, they will go too deeply into the passage and occlude it (and typically have a higher setpoint as well).

You say that you're using the oil pressure signal to control the fuel pump, so there must be some sort of relay involved. You should be aware that if it takes a completed circuit through the oil pressure sender to shut the pump off, you do not have a "fail-safe" system - any failure of the sender, the relay, or the wiring between them will render the safety circuit inoperable so that the pump will NOT shut off upon loss of oil pressure. This is why it's preferable to use the charging system warning light signal instead - a fuel pump control circuit based upon it is fail-safe, in that any failure of the control circuit results in the pump stopping.

[r2oo]

Thanks Guys, all good info...

Findings so far:

Power is going to the backs of all the bulb holders with the ignition on but no lights come on for the oil or charge (red or green) however the indicator light does work. tried switching the bulbs & holders but the same thing happens. The only thing i haven't got is a bulb in each holder, only two but they both work in the indicator flasher but not the oil or charge light holders.

I have switched the relay safety piggyback from the oil sender light to the charge light & this seems to have stopped it firing up with just the ignition on. The bypass button still works.

???

[Marc]

...I have switched the relay safety piggyback from the oil sender light to the charge light & this seems to have stopped it firing up with just the ignition on. The bypass button still works. ???

My bad, I assumed you'd understand that you would have to change the safety circuit so that the relay is energized to keep the pump running rather than energized to stop it - just moving one wire doesn't accomplish that...put it back for now, we can deal with that another time.

Disconnect the wires from both the generator and oil pressure warning lamps. Turn on the key; use a jumper wire to supply ground to each lamp in turn - they should be coming on when you ground the terminal...if not, more work is needed at the bulb cluster.

If both lamps are confirmed to work that way, they should also come on when you touch the wire from the oil pressure sender to them (engine off, key on)...if not, the sender's not furnishing a ground. Touch the sender wire directly to the engine case...if the lamps still don't light, there's a break in the wire or bad connection to a terminal at one end or the other.

Again, pull the fuel pump relay wire off of the generator warning lamp circuit for now - it could be introducing issues that you don't need confusing you right now.

[r2oo]

Good news...I think!

Done that, this morning & by touching the oil sender wire on the engine block & the light DOES come on..when connected to the sender it doesn't.

So does that mean I have a dodgy oil sender? Its only about 6 months old as I replaced it when I rebuilt the engine. I purchased this one from Machine7 : http://www.machine7.com/product.php?xProd=3029

Although when it came it didn't look like that, here's a photo of it in the block:

http://i1067.photobucket.com/albums/u43 ... whge3a.jpg

[Ol'fogasaurus]

Periodically there seems to be a spate of "dodgy" oil, brake light and other similar sender problems: such as leaking or not working correctly. In the past it usually is a result of businesses/suppliers pulling the contracts from one country, when the labor prices rise too high to make big profits, and moving the contracts to another country with lower labor costs. It usually lasts until the new owner of the contract gets it figured out but by that time it is time to move the contract again .

This little irritation has been a bane to mankind for quite a while not and it is not always an irritation especially when it results in a "wasted" engine because of no warning or you getting rear ended because your brake lights don't come on.

Lee

[Marc]

The picture at the web page isn't representative of what a stock sender normally looks like - but the one in the block appears to be correct. One thing I notice is that it's screwed in pretty deeply...might even be bottomed out...which says that the threads in your case are pretty worn. Have you used any sealant on them which might be acting as an insulator and interrupting the electrical path between the case and sender?

[r2oo]

Hi Marc, can you explain what you mean by 'bottomed out' please.

Yes it was screwed in a fair way, it loosened and came out ok though, the thread in the hole looks ok, there were a couple of tiny metal shavings not it's certainly not stripped by any means.

When I fit the new one should it be only hand tight?

[Marc]

"Hand-tight" isn't a very precise term, but I'd say it should be a little tighter than one can turn it with no tools. It's a tapered thread in soft alloy and should draw up snug several threads before the body of the sender hits the engine case. Since the senders are steel they experience very little thread wear, I wouldn't expect a new one to fit much tighter. There are fixes one can make if necessary but let's not cross that bridge unless we come to it.

[r2oo]

Thanks Marc I shall report back when I've fitted the new one.
Thanks
Adam

[r2oo]

Received the new Oil pressure switch today & check this out. The one on the right is the old one from Machine 7 and the left is the new one from Coolair, totally different size nut & thread!

The new one also seems much better quality.

[Marc]

Any part number or pressure setting stamped into that switch? It almost looks like the 056/068 straight-thread Rabbit switch I warned against. These have longer threads which are not tapered, since they are intended to go all the way into the head on a Rabbit engine and rely upon a copper washer for a seal. When you put them into an ACVW case they go in too far and actually restrict flow through the passage to the cooler.

Typical straight-thread waterpumper switch:


Correct 021 919 081B switch for the ACVW:



The ACVW switch setpoint is .15-.45 Bar (2.2 to 6.6psi) while the waterpumper switches come in several versions, some of which are too high for the ACVW so they will give false alarms.

The thickness of the "nut" is not a reliable indicator, it may vary from one manufacturer to the next.