Bouncy oil pressure needle - is there actually a solve?

[Tom]

A tip for anyone using the "Carpoke Capacitor" approach. I installed this on my oil pressure gauge to address a bouncy needle, while I had the dash cluster out (for other reasons).

I obtained a suitable capacitor, soldered ring terminal leads, and installed it behind the "football" as suggested. I rigged up some test wires and verified it worked, and I was seeing appropriate needle movement based on different resistors I tested with. All good. When I installed the dash in the car, no needle movement at all. The pressure warning light went out as expected, so I knew I had oil pressure.

I pulled the dash cluster again, and realize the two ring terminals (that lead to C8 and C10), caused the football to lift just enough to lose contact on C5, 12V in. So, no power to the gauge. I put a washer of the same thickness as the ring terminals on the 12V in post (the left pin, facing the back of the cluster), and verified I had good contact. Reinstalled the dash, and all good.

Hope this helps!

Thanks for the tip -- definitely need to be careful. I was in the process of making a circuit board to avoid any/all issue, but got distracted (so what's new). I'll get back to that at some point. What size capacitor did you use? I found the space limited so was using 2 or 3 smaller ones behind the cluster, though currently I just have it under the car at the sender. Probably won't last as long under there, but very convenient to install/change, etc.

[Rveague]

Thanks for the reply.

I used a 1000uF, 25V, 85C capacitor I found at my local electronics shop. I don't know the ESR and can't find a data sheet on it, so it may not be optimal.

I've noticed two side effects: While the needle jitter is gone, my gauge needle shows slightly higher pressure at idle when fully warmed up. It used to bounce around 3 bar, now it reads steady at 3.75 bar under similar conditions. (This is more of a casual observation than a rigorous before and after). When I simulated it on the bench, the needle position was pretty accurate, corresponding to different input resistance.

Second point: When I turn the ignition off, the needle briefly pegs high ("6" in Spinal Tap parlance) before dropping to zero. I'm wondering if the cap discharging would cause this?

Rick

[Tom]

Thanks for the reply.

I used a 1000uF, 25V, 85C capacitor I found at my local electronics shop. I don't know the ESR and can't find a data sheet on it, so it may not be optimal.

I've noticed two side effects: While the needle jitter is gone, my gauge needle shows slightly higher pressure at idle when fully warmed up. It used to bounce around 3 bar, now it reads steady at 3.75 bar under similar conditions. (This is more of a casual observation than a rigorous before and after). When I simulated it on the bench, the needle position was pretty accurate, corresponding to different input resistance.

Second point: When I turn the ignition off, the needle briefly pegs high ("6" in Spinal Tap parlance) before dropping to zero. I'm wondering if the cap discharging would cause this?

Rick

Hmmm... I haven't noticed either of those thins on my car, but will specifically look for them when I get a chance. Both should be easy enough to test...

edit: I assume you used an electrolytic capacitor? Were you careful about polarity? It will stop the jitters in either polarity, but might have odd behavior if backwards.

[Rveague]

I used an aluminum electrolytic capacitor, with the negative lead on the common ground (center tap) and the positive on the signal tap. It looks exactly like the picture you posted earlier in this thread.

I don't have an easy way at present to test the resistance coming off the actual pressure switch on the engine, to compare actual resistance with needle position. Maybe when it warms up here!

Rick

[sefeing]

@Tom FINALLY getting around to this now that the weather's warm. Bought some 1000uf capacitors, but I can't tell which side of the polarity you have going from the sender / ground down at the sender. Do you have the negative side going to the PS pump to ground? New to capacitor theory!

Thank you

[Tom]

@Tom FINALLY getting around to this now that the weather's warm. Bought some 1000uf capacitors, but I can't tell which side of the polarity you have going from the sender / ground down at the sender. Do you have the negative side going to the PS pump to ground? New to capacitor theory!

Thank you

Yes, that sounds right --> negative side to ground; positive on sender's signal. Smooth's it right out.