oil light blinks after driving 2 minutes and makes buz nois

[matt1234]

1985 golf 1.6 non turbo. replaced alternator and now after driving exactly 2 minutes every time that annoying buzzer behind dash goes off and the oil can light blinks. Theres no problem because nothing happens to the car. im assuming its the sender. i pull fuse 21 and it stops blinking and buzzing. Is the sender the thing with the one wire going to it on the top of the oil filter housing?? thanks guys.

[Vincent Waldon]

Is your new alternator diesel-specific with the W-wire that drives the oil pressure warning system?

[matt1234]

yeah it is bosch original 65 amp alternator, not rebulit. it has that one green wire which i think if i remember correctly had the "w" stamped on the alternator. The spade connector broke but i stripped the wire and wrapped it arond the terminal, didnt help??

[82vdub]

The spade connector broke but i stripped the wire and wrapped it arond the terminal, didnt help??

Recommend getting a little electrical kit and properly terminating the wire for starters then see what happens. Have you checked your oil pressure with a manual gauge to verify what it is?

[Vincent Waldon]

It's suspicious that this started as a result of you changing out your alternator... although of course sometimes stuff just happens.

It could be that your new alternator has a defective/disconnected W terminal... if you have a multimeter with an AC range you can check.... you should see about 8VAC at the W terminal with the engine running.

[matt1234]

thanks guys ill try that

[tollertdi]

Vince, do you know the minimum voltage required at the W terminal to keep it from buzzing. I know at 0 volts it buzzes.

I'm beginning to think this is the root cause of most of these problems. High impedance from corrosion anywhere along the W terminal circuit...

[Vincent Waldon]

It's actually not a voltage thing but a frequency thing... rather than watching the frequency of the points on an gasser's ignition system on a diesel the oil pressure warning system watches the frequency of the W terminal.

Using a AC voltmeter as a test it's kinda all or nothing... if you're getting a proper W signal it will measure around 8VAC... otherwise it will read 0V.

So, no minimum minimum voltage, since the system is really measuring the frequency of the W signal. On an oscilloscope the signal looks like this:



Does my explanation make any sense?

[tollertdi]

Vince -

Yes. I already realize that in actuality it is a pulse. But doesn't the control system (high pressure relay) work off of the average voltage? Also, let's assume that we put an impedance into the system between the W terminal and the relay. That would in effect bring down the pulse amplitude and thus you would end up with a lower average voltage?

At some lower average voltage, I believe, you'll proably trigger the relay.

Thanks for your expertise.

[Vincent Waldon]

Thanks for your expertise.

Nah, dunno about that... just posting what I've learned while experimenting with my two Jettas (one gasser and one diesel) and my antique B&K oscilloscope. Perhaps I need to get a life.

But doesn't the control system (high pressure relay) work off of the average voltage?

Not as I understand the system... either there's a clean signal that it can measure the frequency off of or not... voltage doesn't play into the actual reading as far as I know.

One additional reason why I think this is the case is that the gasser voltages and waveforms are very different, yet the warning systems and tachs of both gassers and diesels can be made to adapt to each other by changing the calibration range only, not their voltage sensitivity.

Here's the corresponding gasser signal at the ignition coil... completely different waveform with a completely different average voltage... but completely readable by either system, once the calibration range is adjusted:



Having said all of the above... I'd completely agree that additional resistance in the circuit (bad connection, contact corrosion etc) certainly can degrade the signal... and if the signal is degraded enough false triggers will very likely result.

[joat]

tachs have a capacitor in series with the line coming in ... passes AC pulses, not the voltages.

[CoolAirVw]

There is some background info in the "oil pressure" link in my signiture.

EDIT: seems my signiture doesn't show up like it used to... forum change or something...
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