Relay under passenger seat '83SC

[WB3]

Does anyone know what the small relay next to the brain box does? I have read if you disconnect it the engine will run poorly. If you disconnect it and nothing happens...then the relay is bad. I don't know the name of the part and have looked for it but can't find it (like at Pelican parts). Just thinking this could be the cause of cold start problems, lean mixture, and rough running all around?

Thanks!

Bill

[Doug Zielke]

Bill,
That relay works in conjuction with the CIS Frequency Valve.
Your car will run poorly if this relay is NG.
With the car running, pull the relay and note any operational changes.

[john walker's workshop]

it's a generic relay, but it's called an oxygen sensor relay. the relay also needs to have power to function, so check that before just replacing it. power comes from the dome light fuse on the front fuseboard. do the dome lights work?

[WB3]

Hi! Now we're getting somewhere! NO, the domelight and the glove box light are out. The fuse BLEW and I didn't have a 5 amp fuse to replace it. I just thought I would be without a dome lite for awhile. Man! I hope this is the problem. I just took the Jetronic box and relay out. There's another box that looks like a pack of cigarettes almost directly next to the jetronic box (actually attached to the box by a small 8mm bolt/screw). It has an 8-pin round type connector and is part# 911 617 131 01. But I don't think this is the one? Now the relay that I THINK we're talking about is like a small cube and has 5 electric posts. It attaches to a shelf on the floor with a spring clip. It has a VW and what looks like an Audi emblem embossed in it. The part# 82195123....it also has SR 9833 on it. And it says 12V Max 2x10A. As long as I had the Jetronic box out I pulled the cover off and the circuit board looks ok...no corrosion or anything. Matter of fact, it looks almost brand new. Thanks sooo much!

[Mookster]

I have had the 02 snesor relay fail on me twice. The part number is 821 951 253 with a cost around $34.

When it goes your car will buck like a 15 year learning to drive a 5 speed tranny. Both of the times mine faileded you could hear the relay clicking like mad. When it failed intermittently, the car would act like it was starving for fuel (buck)and would suddenly clear up in a few seconds (no clicking sounds).

If you have the CIS system and remove the O2 relay, your car will run like #@!* or stall.

Check the fuel pump relay and connections if you hare having intermittent fuel issues. I really dont think, based on my experience, the O2 relay would allow your car to run rough all the time.

[WB3]

Exactly Mookster! It's bucking like a wild bronco sometimes. See the post from JW? I mean Zap! And thanks so much for your input. I really appreciate it alot! Now I'm gonna put the brain back in and look for a 5 amp fuse.

you guys are super! Thanks!

[john walker's workshop]

it's the little square jobby. they cost less than $10 except at the dealer.

[radcon]

Where are some other places where you can buy the relay other than at the dealership?

[WB3]

Thank you Superman for your reply and advice. John, you nailed it. Mookster, you were right on as well. Eureka!!! Problem solved!!! I would never have guessed that such a vital circuit would be wired into the interior lights...glovebox, dome, hoodlight, etc. Man, I am so happy now I can't tell you!!! All this over a 5 amp fuse. I started to think back...when the rectifier on the alternator went south that's when I was opening the hood alot and the interior fuse blew. Turns out, the switch that turns the hood light on and off was shorting out and blowing the fuse. The 02 relay wasn't bad it just wasn't getting any power. Man!!!!

Anyway, I robbed the 5 amp license plate light fuse and plugged her in. In ONE crank the engine fired and the difference was noticeable right away. No more backfiring through the pop valve and it sounded right on! Idle is rock steady @ 1000 rpm. Throttle response is smooth and beautiful once again. I am overjoyed!

I would like to THANK each and everyone of you that responded to my thread...all three of them. Even if your advice did not help me solve this problem, I still thank you very much for your time, effort, and advice. This is a really, really, great forum to have! If I could take you all out to dinner I would! Thank you again everyone, and special thanks to John Walker, Mookster, Konish, Doug Zielke, Gram Archer, and Sammyg2. You guys are great!

HORRAAAYY!!! THREAD(S) ARE CLOSED AND HOPEFULLY THE HISTORY CAN HELP SOMEONE ELSE!

Thanks again!
Bill

[ruf-porsche]

Originally posted by radcon
Where are some other places where you can buy the relay other than at the dealership?

Try Rat Shack automotive relay, less than 10 bucks.

[mikemdd]

Just curious. What is the difference between pulling the plug on the O2 sensor relay and disconnecting the O2 sensor? I think the answer is that the relay controls the frequency valve (ie makes it inoperable) and the O2 sensor disconnect simply makes the frequency valve go into an open loop mode, but it still works. Therefore, the pulled relay makes it run like crap and the disconnected O2 sensor simply makes it run rich. Is this right?

[radcon]

I replaced me relay, but the frequency valve still doesn't buzz, at least not that I can tell. Any hints on where to look next. I agree with the bucking and stumbling comment. My car runs like crap at anything less than completely warmed up.

[911Ken]

I'm having the same problem. Engine runs rough at start-up - back fires, bucks, etc. and not the power that you'd expect especially after putting a Fabspeed cat-by-pass and a B&B tri-flow muffler in. Here are some pictures of the Lambda brain. Can someone confirm which is the relay?

I know that I have intermitant power to the interior light on the Targa bar (1981 911SC 3.0) but no light in the glove box or front hood! Didn't really bother me....

Extremely frustrating!

Thanks,
Ken

[WB3]

Ken,

The 02 relay is the small one which clips to a small bracket on the floor. It may or may not have Audi/VW stamped on it. It's the smallest one in your photo and not mounted to the Lambda brain box itself. Part # 821 951 253. You say in your post that you only have intermitant power to your interior lights? The 02 relay is wired into that circuit. If the lights aren't working or the fuse is blown, your 02 relay isn't going to get power. Go to the fuse box and check out what's the condition of the fuse. An intermitant interior light (Targa) could just be caused by a bad door switch. But check that 5A fuse. If that looks ok and your interior lights are working it might be the relay itself. Good Luck.

[911Ken]

Bill,

Thanks for the info. That's what I plan on doing when I get home tonight. The targa bar light works when you move it around but doesn't stay on. Also, the glovebox and front hood lights don't work, or at least I haven't fooled with them. I did check the fuse box before and it looked like they were all ok. I'll do a closer inspection though.

Just for kicks I just ordered that relay from Pelican as they had it in stock (supposed to be special order). Also order a new targa interior lamp unit...but I'll check the door and hood connections/ground first.

I really hope this is the problem as others have found out. I haven't had decent power for quite some time.

Ken

[Mookster]

911ken,

Based on my issues with the O2 sensor relay/CIS electronics (the car bucked intermitenly, and I could hear the O2 sensor clicking when this happened) may I suggest a few items in your trouble shooting:

1. Be sure you are getting power at the O2 sensor relay, pin 30. The relay, as mentioned, is powed by the dome light fuse. I believe the power reading on my cheap VOM was 12-14volts.
2. Replace the dome light fuse.
3. Be sure your fuel pump relay is working. Personally, replace it if you do not know when it was last replaced. Save the old one as a spare.
4. Jiggle the fuel pump relay while it is in its socket. I found I was able to duplicate the bucking problem when I did this.
5. My final diagnosis was a combo of things. The fuel pump relay socket was worn and had to be replaced, I replaced the fuel pump relay (cheap insurance to divert future problems) the O2 relay sensor failed due to all the on/off bucking, and my CIS computer crapped on me. (I did replace the CIS computer and acceleration enrichment relay with a used unit).
6. Once you have the problem resolved, change the plugs and have your vehicle fuel mixture checked and adjusted properly. Once all these parts were replaced on my car, you wouldn't belive how far off the fuel mixture was!

Keep asking questions and report you findings. This forum is a wealth of help.

[radcon]

I checked the voltage at post 30 on the relay connection as some had suggested and it was approx. 12 volts. The relay I got from Advance Auto is plastic, so I popped the cover off to make sure the relay was closing when the power was on. The relay closes when you turn on the key, but now my question is - Is the relay just suppose to close and stay close when you have the key on, or is the relay supposed to cycle? If the relay is just supposed to stay closed, then what makes the frequency valve cycle? Two final questions to bug everyone - is there a place that can test the Lambda computer and where does the Lamba computer get it's power from?

I would be able to look up most of this, but my Bentley manual is with all my other property and won't be delivered till next weekend. My 911 will finally have a home again after sitting out in the elements for 6 months!!!!

[radcon]

bump

[radcon]

bump

[911Ken]

Excuse my ignorance - but what does "bump" mean?