Why does oil pressure sender fail?
10-15-02, 11:47 PM
#1
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Why does oil pressure sender fail?
It’s a well-known failure that seems to re-occur, but why? After owning two brand new 3rd gens (first was 93 base, current 95 pep) and replacing 3 senders, I wanted to know why. So I cut one apart to find out.
The picture shows that inside there is a spring whose end loop(s) gets stretched out of shape. Not only does this cause the oil pressure to read slightly high (say 1-5 psi), the spring will eventually come off completely.
At that point the readings become very erratic, often varying as much as +/-10 psi, and seemingly stuck at times even while the engine RPM changes. I've even experienced a case where the spring, now loose inside the metal housing, shorted out and caused the indicated pressure to drop to zero. Think that won't get your attention while doing 75 mph down the highway!
It seems that anything that raises your oil pressure above what Mazdha expected will simply hasten this failure. Another good reason NOT to rev your motor until it’s fully warmed up.
The picture shows that inside there is a spring whose end loop(s) gets stretched out of shape. Not only does this cause the oil pressure to read slightly high (say 1-5 psi), the spring will eventually come off completely.
At that point the readings become very erratic, often varying as much as +/-10 psi, and seemingly stuck at times even while the engine RPM changes. I've even experienced a case where the spring, now loose inside the metal housing, shorted out and caused the indicated pressure to drop to zero. Think that won't get your attention while doing 75 mph down the highway!
It seems that anything that raises your oil pressure above what Mazdha expected will simply hasten this failure. Another good reason NOT to rev your motor until it’s fully warmed up.
10-15-02, 11:59 PM
#3
The Cursed FD
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Very nice write up man. Do you by chance know the price on a new sending unit? I'm glad someone took the time to diagnose this problem that a lot of use have.
What's up with the AWS revving to 3k if it's bad on the sending unit to rev high when cold? I know it's to help speed up the engine warm up period, but it seems to contradict itself? Help me out here.
What's up with the AWS revving to 3k if it's bad on the sending unit to rev high when cold? I know it's to help speed up the engine warm up period, but it seems to contradict itself? Help me out here.
10-16-02, 12:11 AM
#4
Rotary Freak
The mazda people had to make the car pass cold emissions ,that is what the pre cat and the,(junk get rid of quick ) AWS is for. in Nashville we do not have cold start testing.
10-16-02, 12:28 AM
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Last one I bought was just over $100.
Yes it does make you wonder about a 3K warm-up. I guess Mazdha expected it to last until after the warranty ran out…
Buy the way, I found that by adjusting the cold idle settings you could lower that 3K warm-up rpm. In my case I found that the wax rod was never fully extending enough, even when hot. So I adjusted screw ‘A’ and got a lower cold idle, but then found that the hot idle had dropped down to 300-400 rpm. So I adjusted the air bleed screw in the throttle body (sorry I can’t find a picture right now, but if you take off the elbow and get down real low and look at the throttle body below the primary butterfly and back toward the firewall you can just barely see the brass screw with a single straight slot). Now I have a more reasonable ~2K cold idle and a nice 750 when hot. More tweaking could probably lower the cold idle speed even more.
Yes it does make you wonder about a 3K warm-up. I guess Mazdha expected it to last until after the warranty ran out…
Buy the way, I found that by adjusting the cold idle settings you could lower that 3K warm-up rpm. In my case I found that the wax rod was never fully extending enough, even when hot. So I adjusted screw ‘A’ and got a lower cold idle, but then found that the hot idle had dropped down to 300-400 rpm. So I adjusted the air bleed screw in the throttle body (sorry I can’t find a picture right now, but if you take off the elbow and get down real low and look at the throttle body below the primary butterfly and back toward the firewall you can just barely see the brass screw with a single straight slot). Now I have a more reasonable ~2K cold idle and a nice 750 when hot. More tweaking could probably lower the cold idle speed even more.
