I have a 93 FD and have sporatic problems with my oil pressure gauge. From everything I have read 3rd gens don't have oil pressure problems. Apparently when the sending unit gets a little oil on it, it won't register much at idle and shows low at speed. I can clean it off and its fine for a while, but it comes back a couple weeks later. The car runs strong and there are no problems. Does anyone know of a permanent fix to this aggrevation? Meanwhile, I've adjusted my driving position so I don't have to look at the oil pressure gauge.

 

I don't even think cleaning the contact solves the problem. Maybe rotary engine just doesn't make much oil pressure at idle. I've cleaned the send unit and the pressure is still very low at idle. At speed, the pressure is usually 45-60 ft-lb/in2, which is normal.

I do notice that the pressure is higher when new oil is put into the car.

 

If your car does not make 30 psi of oil pressure at idle, there is something wrong. That is the factory spec. It should also be 60 psi at 3000 rpm, going up to 120 psi at high rpms.

The only permanent fix is to install an aftermarket oil pressure gauge.....

 

The gauge reading erratically seems to be a common problem, and I haven't heard of any FDs with "real" oil pressure problems.

Someone cut open a sender and posted pictures on here recently. It looked like a spring inside the sender or something had stretched out. Certainly the dirty contacts seem to be a problem as well, but it might be deeper than that. I know some folks have been trying to find an alternate sender that works with the stock gauge, but I haven't heard of any success in that area yet.

I plan to replace my stock OP and WT gauges with SPA dual digital gauges and put them in the dash. I have had some SPA temp senders fail, but the pressure sender is still going strong on my fuel system after several years of use. Perhaps a small SS hose could be used to move the oil pressure sender off of the block (with its heat and vibration stresses) and onto the fender. I am considering doing that for my aftermarket sensor, but perhaps it would improve the life of the stock sender, too.

-Max

 

Max,

I will soon be installing Defi's Link series of gauges, including an oil temp gauge. I am using Greddy's oil filter block adapter, as it provides sensor outlets for oil temp and pressure. You can still use the stock filter, but I'm not sure about using a bigger filter (like from the MX-6 for example). You will also have to remove the TPS clip to change your filter (according to "apneablue"). The ease and convenience of not having to locate sender locations is worth it, I think. (Not sure if the senders you have will work with that particular adapter or not.)

 

I have plenty of oil pressure at idle and at speed (30 at idle and 60+ at speed). Its the sending unit thats the problem. I really dont want to change the gauge to one that doesn't match the stock ones. Is there a different sending unit or something that I can do to the stock one that will alieviate the problem?

 

As Max mentioned, I destructively cut open a failed sender and posted my findings as: http://www.rx7club.com/forum/showthr...hreadid=124078

To repeat the short answer, the root of the problem is in the design and/or materials used within the sending unit itself. In practice, this unit cannot reliably handle high oil pressures because one spring inside deforms and eventually comes completely loose. As this failure mode progresses it results in all manner of strange and erroneous readings, as often reported by forum members.

Repair MIGHT be possible but you would need to address: (1) how to locate the appropriate location in which to cut an opening in the sender’s outer 'can' so that repairs could be attempted (I found absolutely no reference or alignment marks of any kind), (2) how to be sure that all foreign matter such as metal shavings were completely removed, and finally (3) how to then insure that such an opening is resealed. I've thought of several different approaches, but nothing that I feel is really very doable by the average DIY’er.

Finding a suitable replacement MIGHT also be possible, but unfortunately I did not measure the electrical properties for what is essentially a wire-wound potentiometer, and my sample is no longer available. I can report that the sender’s internal wiper arm moves along the coils of a formed wire (probably high resistance material) as oil pressure fluctuates, and that increasing oil pressure results in a decreasing resistance to ground. The sensor’s threads appeared to be standard US 1/8” pipe, but they might be British Standard threads, too. Visually, this unit appears to be the same exact sensor assembly used on the Miata 1.8 engine, but I have not verified the part numbers.

Attached is another picture of the inside mechanisim.

 

The common fix seems to be a new sender every 30,000 miles . If you're really good you could in theory adapt an aftermarket sender to the stock guage, which would be pretty sweet, but no one has done it yet.

 

Mazda TSB isn't it, these things are WELL Known for self destructing, I've owned my FD for 7 years and I'm on my 4th sending unit!
Art

 

anyone know where i might find a stock sending unit for a reasonable price on the net?

 

do what i did get the greddy sandwitch that goes inbetween the oil filter and the block it has 3 ports on it for oil pressure, oil temp and maybe an oil feed line. it about 50 bucks then just hook up a gauge to it. i can get any thing you need jsut let me know.