I’ve got the GRT EIS Model 4000 engine monitor on my C-90 powered 750. The past 12 to 18 months I’ve been getting eratic readings on OP showing anywhere from perfectly normal to spikes upwards of 99 psi. I bought a new VDO sending unit,and am experiencing similar, but not equal issues. I’ve never had a dedicated ground wire for it, so I experimented with grounding it out directly by attaching a ground wire from the hose connection at the sending unit to a good ground on the firewall. I am still getting erratic readings, sometimes perfectly fine, to sometimes off-the-charts wrong. I find it hard to understand that if the VDO Oil Pressure sending unit requires a ground, then why isn’t there a ground terminal built in to the unit? 
Has anyone else experienced similar issues and let me know how you dealt with it? 

Thanks - Jimmy Y

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Not sure, Jimmy, but I think most VDO senders are screwed directly into the block so they are grounded and don't need a terminal - looks like yours is remote mounted, so it definitely needs a ground.

Erratic spikes and high spikes are signs the sender is wearing out.  I'll bet replacing it fixes your problem.  I highly recommend a solid-state sender such as the "Swift" sender that Spruce sells - it can't wear out!  However, it will require a power lead and an EFIS or gauge that you can calibrate.



I solved my problem with a direct grounding wire as shown. Used a hose clamp over the sending unit itself to secure the ground wire, then safety wired everything so it stays put. My oil pressure #’s are back to normal, here is a pic of what I did. 
I plan to make the Open Hangar event again this year, hope to see you there. 

I plan to make the Open Hangar event again this year, hope to see you there.

Yes, I'm planning on flying-in and will see you there!

Glad the ground fixed your problem.


I also have the same exact problem and didn't have the issue until 100+hrs, also I have GRT EIS.
I was going to ground with wire to side of sensor, but maybe a waste of time.


That is exactly what I ended up doing, and it worked. I installed a hose clamp to the sending unit to secure the ground wire & ran that to a screw on my engine baffle. Oddly enough, mine worked for years without a dedicated ground wire, then began to get erratic readings off and on. Somehow for years it was grounding through the hose I am using.

By the way, I really like the looks of your 750 and followed your engine install and work done at FlyCorvair. I went to a couple of Corvair Colleges and learned a lot about them, but ended up with a Continental. Nice job!


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