"MM54" (mm54mk2)
03/26/2018 at 20:25 • Filed to: FB RX7
0
11|
"MM54" (mm54mk2)
03/26/2018 at 20:25 • Filed to: FB RX7 | 0
| 11 |
Yesterday while taking the RX7 around the block for the first time of the year, the oil pressure gauge pegged. When I got home I did some basic diagnosis - engine off, key on it pegged. Unplugged sender, still pegged when the key turns on. Problem is not in the sender.
Into the service manual I went for the wiring diagram. There is a capacitor in parallel to the sender - perhaps that went bad. I go to look and...
... the wire broke off the body of the capacitor and was laying on the engine, shorting the 12v sense wire to ground. Tape off the end of the wire, key on, gauge doesn’t peg.
Here’s the problem though - I started the car, very low reading. If you rev it up it would move some, but it sat just off of zero instead of mid-scale where it usually would be at idle. Back to the service manual, 200 ohms should be the first tick mark, 150 ohms around mid-scale.
After checking the wiring for integrity and other such basics, I unplugged the sender and clipped a 150 ohm resistor in its place to ground. Key on, and the gauge sits just above zero. Shit.
So what does this all mean? When that wire decided to pop off the cap and ground itself out, it seems to have burned out the winding of the gauge movement. On the most important gauge in the car.
Anyone have an 84-85 RX7 cluster laying around with a good oil/volt unit?
AestheticsInMotion
> MM54
03/26/2018 at 20:40 |
|
I hear aftermarket oil pressure gauges can be pretty nifty
|
MM54
> AestheticsInMotion
03/26/2018 at 21:00 |
|
No way. I refuse to have a broken gauge on the dash and an aftermarket one to replace it slapped on the side. That’s something I’d do on the crown vic, not this.
Chariotoflove
> MM54
03/26/2018 at 21:02 |
|
Ack. To the dark corners of the internet you go. Good luck.
|
AestheticsInMotion
> MM54
03/26/2018 at 21:25 |
|
Hmm I was thinking more make a custom gauge plate and mix-n-match OEM and aftermarket gauges in a visually appealing way. Putting it all back behind the glass like stock.
Was the rx7 unit fairly decent? I’ve been a bit... Unhappy... With the quality level of the gauges in my Mazda. Bad enough they only supply an on/off oil sender, but after a few tests I realized that the water temp is so far from accurate as to be almost useless
|
MM54
> AestheticsInMotion
03/26/2018 at 21:37 |
|
They are very good, though apparently shorting the signal to ground kills it (as an electrical engineer, I’m surprised that wasn’t considered in the design). I have never seen a partially-aftermarket cluster that didn’t look way out of place, and really, really like the factory cluster so I intend to repair it to-stock. It lasted this long, and would still be ticking if not for a very-crusty wire popping off mid-drive.
DoctorNine
> MM54
03/26/2018 at 22:23 |
|
Try here:
https://www.ebay.com/b/Oil-Pressure-Gauges-for-Mazda-RX-7/33676/bn_1435853
|
MM54
> DoctorNine
03/26/2018 at 22:24 |
|
No. I’m fixing it, not slapping another gauge onto the side of the cluster.
|
DoctorNine
> MM54
03/26/2018 at 22:28 |
|
Try these guys then:
http://dandmrestoration.com/services/clusters/
|
MM54
> DoctorNine
03/26/2018 at 22:36 |
|
There are a couple clusters on ebay; I’ve posted a wanted ad on the forums to see if anyone there has one. If not I’ll go the ebay route in a few days.
wkiernan
> MM54
03/27/2018 at 06:10 |
|
Maybe if you replace the capacitor the gauge would read right? I don’t suppose it was there for no reason.
|
MM54
> wkiernan
03/27/2018 at 12:06 |
|
Smoothing. The gauge is basically a volt meter with a voltage divider between its movement and the resistance of the sending unit.