Ox sensor relay keeps dying - 1981 911sc
 

Hi,
I'm pretty new to posting on this forum... I've been pretty good at searching for all the incredible answers I found... Made me wonder why Porsche mechanics don't search on the forum instead of searching on my car for hours charging me for it.
The problem I have, amongst others, is a constantly unreliable Ox sensor relay (under passenger seat).
It was horrible for a while (car would die or not start) and I have replaced the relay with the oem one from Pelican, it got a bit better, but quickly got bad again. I then installed one from Napa, it seemed better than the oem one from our host but it is still not working properly (I have to bang it every time I start the car and sometimes as I'm driving when I feel the power go down).
I have looked at the connections on the sensor control box and they all seem good, I looked at the wires and connections around the relay, all ok. I don't know where else to look for bad connections or else...
Has anyone had this problem?
Thanks for your help
David

Maybe the frequency valve itself is failing?

Might also try unplugging o2 sensor just to rule it out as a possible culprit.

check the plug real good. green corrosion, loose contact on any one of the terminals in the plug.

Could be a poisoned cat...ever put leaded gas in the tank?

Thanks for the info guys, I already run with the O2 sensor unplugged because if I plug it in after adjusting the CO (0.3-0.8V on sensor), it ends up going way rich and hunts so I run it a bit rich and unplugged. I should check the frequency valve... I think I have to shake it and see if it moves in there or something like that right? It never had leaded gas in there.

Is the FV buzzing? Should be audible.

Once I knock the relay around a bit, it does buzz...
It seems like an unreliable relay but it is the 3rd one that goes in there...

Sounds like the FV is ok then. Gotta be a bad connection somewhere. Doubt that 3 relays would be bad. Sure you got the right one?

I got the one from Pelican and another one from Napa, both were listed as the right one. The diagrams were identical to the one that was there before so it must be a connection. The thing is I am not sure where else to look for a bad connection and I was wondering if somebody else had experienced the same problem.

The relay is bad, I have had probs with the new oem relays. Dont waste your time with the Napa ones, you must use the correct Bosche metal cased relay, as they run pretty warm and the plastic ones distort. I think these "new" oem relays are really old stock, I put one on a guys car a few months ago, it went bad the next day, replaced it with another new on, been fine ever since. Mine has failed a few times over the years, and most cars that come to the shop are inop, and bubba has turned and twisted every screw trying to "fix" it. I would hook your 02 sensor back up to, sure makes for good fuel milage and driveability.

post#4. what's the verdict?

yea, and alway do what JW says. there is another connector in the rear you might as well clean, the main 02 gang connector behind your blower motor next to the left shock.

Thanks a lot guys,
I cleaned every connector inside the car close to the unit. I cleaned up the ground as well. I will go to take a look at the connector behind the blower motor next to the left shock as soon as my wife comes back (otherwise my 2 y.o. is a bit dangerous inside the car... he loves the Porsche a bit too much). I will let you know what happens. I have to place an order from our host and I will order a couple new relays. The last one I got from Pelican was a plastic cover one although the picture on the website is a metal cased one. Same part number as the metal cased one though.

I just found out from another pelican that PP is now selling the plastic relay. If i were you, I would take the part # to the local vw dealer or other euro dealer and see if you can get the metal one. Its a vw relay. The plastic one will not last long ( in my experiance anyway) they get almost hot sometimes.

I replaced the original metal relay with the exact same relay but in plastic. No issues here for 8 months now. And I drive mine very often. My spare works fine too.

Not doubting Don. Just saying that I've not experienced bad relays out of the box. Agree about sticking with Bosch though.

OXS relay and terminals test.........
 

David,

Did you check the relay? How were you able to tell it was bad unless you have tested the relay. The test is very simple. Terminals #85 & #86 are the coil terminals. When energized (#85-#86), the normally open #30-87/87b will close. Terminal #30 is the power supply from fuse #18 that controls the interior, glove compartment, clock, etc.

When the coil is energized, the NO (normally open) terminals will close, thus supplying power to the FV. Most likely culprit/s is poor connection or a bad OXS relay. You could check the relay and the terminals. They are either good or bad. So you don't have to guess whether these are the culprits. If they passed the test, these are not the problem/s.

Tony

the fact that you could wack it and it would work for a while smacks of either a bad relay or a bad connection there.

I agree with Don

Why replace a good component??????
 

Buying or replacing the OXS relay could solve the problem if the relay is really defective!!!! What if the problem is the connection or electrical contact/s? But if you really want to know what's the real problem, perform some analytical test and identify the problem/s.

Replacing one suspected component with a new one is a way of troubleshooting that rely on luck!!!! Well sometime it is better to be lucky than good. But you cannot depend reliably on LUCK. Just my two-cents.

Tony