82 SC rough running

[jasonlee]

Hey all,
been a while since I asked the brain trust for help. That said, up until yesterday 82 SC running like a top. starts up no problem, but runs super rough, plugs and wires all fine, new, new Distro cap, no vacuum leaks. Was not a intermittent problem, just happened yesterday. car moves under power but feels supper sluggish. It is the original Bosch CDI, but wondering if I should be looking elsewhere. Any insight provided would be greatly appreciated. Car is currently in San Juan Capistrano CA warm and dry

thanks,
Jason

[RDM]

These sound like the classic oxygen sensor relay failure symptoms. It's under the passenger seat next to the big silver Jetronic box. If you have a spare relay, trade it out and see how things run.

[jasonlee]

thank you I will give that a shot. Just bought a replacement from our host as I do not have a spare.

[405]

Are your dome lights, clock, and frunk compartment light working? from what I understand they are all on the same circuit with the o2 sensor relay. If the relay is out none of them will work.
Also may seem fairly obvious but did you check fuse 18?

[boyt911sc]

Originally Posted by RDM

These sound like the classic oxygen sensor relay failure symptoms. It's under the passenger seat next to the big silver Jetronic box. If you have a spare relay, trade it out and see how things run.

Dru,

Do you realize that there is no such thing as oxygen sensor relay? Yet all these years people keep referring to the frequency valve relay as oxygen sensor relay. The oxygen sensor in your CIS does need or use a relay. Look at the wiring diagram where the frequency valve is located and you will find the “oxygen sensor relay” you are referring. This relay controls the frequency valve and the oxygen sensor is not even located in this circuit.

Removing this said relay has no effect to the operation of the oxygen sensor. What is affected is the frequency valve. But why do people still refer it as oxygen sensor? Just my two-cents.

Tony

[jasonlee]

Tony, thank you for the clarification. I did order the relay and will see what happens.

To 405's point I will have too check those as well as the fuse 18

thank you all for the help in diagnosing.

[boyt911sc]

Originally Posted by jasonlee

Tony, thank you for the clarification. I did order the relay and will see what happens.

To 405's point I will have too check those as well as the fuse 18

thank you all for the help in diagnosing.

Jasonlee,

Fuse #18 provides power to the frequency valve, glove box light, clock, etc. A blown fuse #18 would disable all these accessories. So the first step is to check fuse #18.

Tony

[boyt911sc]

Originally Posted by 405

Are your dome lights, clock, and frunk compartment light working? from what I understand they are all on the same circuit with the o2 sensor relay.If the relay is out none of them will work.
Also may seem fairly obvious but did you check fuse 18?

405,

Read the wiring diagram(section V). The dome lights, glove box, clock, trunk lights, frequency valve, etc. are all getting power from fuse #18. They are in parallel connections and do not depend from the other loads. The FV relay which people commonly refer as OXS relay does not control the other loads like clock, glove lights, dome lights, etc. However, fuse #18 controls all these loads.

Tony

[jasonlee]

So if they all work what does that mean. Both my clock and dome lights are still working

[boyt911sc]

Originally Posted by jasonlee

So if they all work what does that mean. Both my clock and dome lights are still working

Jason,

That means there is power supply to the circuit. What you need to do is test and confirm that the FV is vibrating when the FP is running. Test run the FP without running the motor. If you could feel the vibration of the FV, both FV and relay are good.

Tony

[pmax]

OXS relay is apt because it's connected to more than just the FV ...

Carry on.

[jasonlee]

thank you. Will test the FV with the FP running

[AndrewCologne]

Tony is right in his senseful definition.
OX-Relay is just the common name of the unit where everybody knows whats meant.

With engine cranking, means while strarting und running this relay closes and passes through current from terminal 30 (hot at all times) to the ECU, the Acc.Unit(81-83) beside the ECU and last but not least the frequency valve.
If ECU or the FV itself gets no current, the FV gets closed and the pressure of the lower chambers within the fuel distributor rises that much so the metal diaphragm gets pushed in such a hard way so in the upper chambers the openings of the thin fuel lines get almost closed which prevents the fuel being forwarded to the injenctors. And thats what causes the rough running.

[jasonlee]

Update. Received the new FV relay, replaced. No change to the rough running. The o2 sensor is not currently connected, but truth be told its never been an issue. What else should I look for, for a possible cause

Thanks,
Jason

[Dave Kost]

Originally Posted by AndrewCologne

Tony is right in his senseful definition.
OX-Relay is just the common name of the unit where everybody knows whats meant.

With engine cranking, means while strarting und running this relay closes and passes through current from terminal 30 (hot at all times) to the ECU, the Acc.Unit(81-83) beside the ECU and last but not least the frequency valve.
If ECU or the FV itself gets no current, the FV gets closed and the pressure of the lower chambers within the fuel distributor rises that much so the metal diaphragm gets pushed in such a hard way so in the upper chambers the openings of the thin fuel lines get almost closed which prevents the fuel being forwarded to the injenctors. And thats what causes the rough running.

Thank you Andrew.

First, Did you check that the FV is vibrating? It must be in order for the CIS system to work as designed.
If not vibrating ....
1.) Are you sure you have the right relay? Not a cross referenced one from a local parts store. This is a common mistake.
2.) The wiring could be bad.
3.) Check the plug on the firewall inside the engine compartment on the driverside. This is where the wire from the ECU gets thru the firewall to the FV.
4.) The ECU under the passengers seat could be bad also. Typically water damage.

Keep us posted.

[AndrewCologne]

plus ...

if FV is vibrating ....

- check the CO setting with sensor disconnected
- afterwrads check the CO setting with sensor connected
- Check the system and control fuel pressures

Originally Posted by jasonlee

Update. Received the new FV relay, replaced.

Is it the correct relay? As it comes with two 87 and 87a terminals where both will be connected to terminal 30, means always current/hot.



Correct relays come with the BOSCH N° 821951253 or 0332019109

See here the whole 930.16 engine Workshop:
https://nineelevenheaven-wordpress-com.translate.goog/der-911-us-sc-3-0-motor-mit-g-kat/?_x_tr_sl=de&_x_tr_tl=en&_x_tr_hl=de

Site is still in german only but with your friend the Google translator you'll understand whats all about.

[jasonlee]

Perhaps I should have asked the question first, is where is the frequency valve located? And if that is indeed the issue how easy is it to replace

thanks

[boyt911sc]

Originally Posted by jasonlee

Perhaps I should have asked the question first, is where is the frequency valve located? And if that is indeed the issue how easy is it to replace

thanks

Jason,

The frequency valve in your motor is located behind and below the throttle body. The picture below shows the FV (white plug) right in the center of the photo. You could remove the frequency with an engine partial drop.



There are three (3) critical power sources you need to verify present during the test at the relay:

• #86 (from FP).
• #30 (from fuse#18).
• #87a/87 (FV relay output to FV).

You also need a good working ECU. Test and verify you have a good ECU. Otherwise, you will be wasting your time and effort trying to solve this problem. Or have someone knowledgeable perform the investigation. Keep us posted.

Tony

[AndrewCologne]

Originally Posted by jasonlee

Perhaps I should have asked the question first, is where is the frequency valve located? And if that is indeed the issue how easy is it to replace

thanks

Check the link I posted above, there everything is included what you need for your type of engine.

Also the location of the FV:



Removing the FV is quite difficult, but honestly a flawed FV is very, very uncommon.

[jasonlee]

thank you all. Hope its electrical checked the plug on the firewall all good, and the ECU under the seat was working fine, and it has never been submerged or wet, so I am hoping that is not the issue so will put a new relay in and check all the fuses and fingers crossed. if new relay doesn't fix how likely is it its the ECU? I cannot image that will be a cheap replacement of fix if needed, or even where to go to repair such a thing