82 911SC Running Issues

[mike621]

Thanks to everyone on this forum and the CIS Dummies thread for the helpful information to help troublshoot my new-to-me SC. I'm posting a thread relating to my own vehicle hoping to get some perspective from experienced owners, as this is my first Porsche. I am pretty confident at DIY, have a decent set of tools, and a Bentley Manual.

The main symptoms I am attempting to solve for: 1) poor idle when cold, including intake backfire when I attempt throttle. Levels out eventually, but my other symptom presents itself once warmed up and driving. 2) Randomly loses power completely, and if I attempt to add throttle in response, will backfire out the exhaust and stall. Will start right back up and keep driving.

Here's my current data based on the CIS Dummies thread format, checked with CIS gauges:

1. Year of engine: 1982
2. US or RoW (Rest of World): US
3. WUR model number: 0438140
4. Ambient temperature at time of test (in degrees C): 19*
5. WUR Resistance (in Ohms): 9.5
6. System Pressure (in bars): 4.9
7. Cold Control Pressure (in bars): 2.1
8. Warm Control Pressure (in bars): 3.5
9. Time delta for Cold -> Warm Control Pressure (in minutes & seconds): 2 min
10. Residual Pressure @ 5 min (in bars): 1.4
11. Residual Pressure @ 15 min (in bars):1
12. Residual Pressure @ 30 min (in bars):0
13. Residual Pressure @ 60 min (in bars):0

My main concern among this data is the loss in residual pressure, though I am not sure my main conditions I am experiencing relate to this. Entirely possible I have multiple problems. I bought the car AS IS with issues.

There is a receipt from several years back stating the car was sitting and had the fuel filter done, mixture adjusted and pop-off valve added.

I've had the car two months and have done some work so that it will pass smog and complete the ownership transfer to me:

-Oil Service (Cooling Lines, Hoses, Feed Lines over cams)
-Valve Adjustment
-Ignition Service: Plugs, Wires, Cap, Rotor
-Vacuum lines Replaced off the throttle body, distributor
-Smoke Test (Airbox OK)
-New Catalytic Converter
-New Oxygen Sensor
-New Oxygen Sensor Relay
-New Ignition Switch
-Cleaned and replaced most fuses in the front fusebox
-R&I'd fan and replaced alternator ground
-Replaced Battery Terminals
-Set timing 5*, Z1, vac lines on (now seeing conflicting info to disconnect one or both vac lines, so some clarity here would be great!)

I am considering the following as next steps:
-Compression Check
-Fuel Injector check (will order new o rings and anything else necessary to reinstall)
-Swapping Fuel Filter (Last done in 2017)


I'd appreciate any advice or thoughts on where to turn my attention to next. I don't want to throw any unnecessary parts at it in lieu of solid troubleshooting.

[GothingNC]

Try replacing the Oxygen sensor relay under the passenger side seat and check for vacuum leaks.

[Dave Kost]

Just a quick check to confirm Frequency valve is working. Also, its easy to purchase the wrong relay if you bought it at a local parts store.

Pull the relay under the passenger seat while the car is idling. If there is no change in the idle, the problem is the relay, relay wiring or frequency valve- in that order. Rarely its the Frequency valve. Or of course the wrong relay.

[kenzinger]

I'm having similar problems to #2 - haven't been able to troubleshoot on my own yet but a lot of the research I've seen points to CDI or ignition coil. Didn't see that you had looked at those. CDI is expensive so most recommend finding a friend with a good matching CDI and swapping to see if there is any improvement.

[mike621]

Originally Posted by Dave Kost

Just a quick check to confirm Frequency valve is working. Also, its easy to purchase the wrong relay if you bought it at a local parts store.

Pull the relay under the passenger seat while the car is idling. If there is no change in the idle, the problem is the relay, relay wiring or frequency valve- in that order. Rarely its the Frequency valve. Or of course the wrong relay.

I bought the relay online - I suppose I can swap it again. When I bought the car, there was a relay with a BMW logo in its place. Will look to troubleshoot this in my next session.

Found a mystery plug resting on the fan shroud near the airbox. Could anyone identify?

[997at]

I have an 82sc and had every variety of running issue when I first got it. It took a very methodical approach to fix every issue. My limited experience would tell me that rarely is there only one CIS issue at hand.
My advice before anything else is to check for vacuum leaks. You need to do a proper smoke test to really verify. Only after you have zero leaks would I even consider next steps. A leak can be band aided by tweaking somewhere else in the system but that is not what you want.
There are nuances to consider before doing random tests. For example, if your mixture is far enough out of adjustment then the frequency valve won’t be able to compensate and pulling the relay won’t change the idle even if the relay is working.
Feel free to PM me for help if you want.

[mike621]

Originally Posted by 997at

I have an 82sc and had every variety of running issue when I first got it. It took a very methodical approach to fix every issue. My limited experience would tell me that rarely is there only one CIS issue at hand.
My advice before anything else is to check for vacuum leaks. You need to do a proper smoke test to really verify. Only after you have zero leaks would I even consider next steps. A leak can be band aided by tweaking somewhere else in the system but that is not what you want.
There are nuances to consider before doing random tests. For example, if your mixture is far enough out of adjustment then the frequency valve won’t be able to compensate and pulling the relay won’t change the idle even if the relay is working.
Feel free to PM me for help if you want.

Thanks for the advice. I used a smoke machine and tested from the airbox. No deficiencies found after i replaced the vacuum lines I mentioned above. Will dig into things more tomorrow.

[Dave Kost]

After you confirm the frequency valve is working you need to set the idle mixture. The real way to set the mixture is by CO %. There should be a CO % decal on the engine lid underside.

Let us know.

[mike621]

Thanks Dave. When I plug in the relay, I get a solid "CLICK", but no change in running condition whether the relay is connected/disconnected. Would that point to the frequency valve not firing at all?

Also for reference, this is a new Bosch Relay, Part #0332 019 150

Note to Self:911SC Frequency Valve problem

[mike621]

I am curious about the "harness quick disconnect" mentioned in another thread regarding the FV circuit. May poke at that as its mentioned being near the left rear shock tower.

I know that my oxygen sensor connector is broken but appears to be connected.

[Dave Kost]

Mike,

Carefully, reach behind the engine near the firewall to locate the FV. Engine off.

OK. Start the car.

Reach behind and the FV should be vibrating. If not the trouble shooting begins. If it is vibrating the next step is to set the CO% properly.

You can mask a non running FV with the AF adjusting screw .

I check the part number of the relay.

Dave

[timmy2]

Originally Posted by mike621

Found a mystery plug resting on the fan shroud near the airbox. Could anyone identify?

Plug for ROW vacuum time delay pod. Not used on US Lambda cars

[997at]

If you are certain that you have no vacuum leaks, then I agree that next step is to verify frequency valve is working and your O2 sensor is connected and also working. Let us know if you need help checking these two items.

[997at]

One more thought. Did your smoke test check the entire system including fuel injectors, intake runners etc?

[mike621]

Originally Posted by Dave Kost

Mike,

Carefully, reach behind the engine near the firewall to locate the FV. Engine off.

OK. Start the car.

Reach behind and the FV should be vibrating. If not the trouble shooting begins. If it is vibrating the next step is to set the CO% properly.

You can mask a non running FV with the AF adjusting screw .

I check the part number of the relay.

Dave

Dave,

I felt no vibration with my fingers on the banjo of the FV. Maybe I'm having trouble distinguishing between it and the engine. Pulled the black connector next to the shock tower and found some corrosion on the two pins closest to me cleaned it up a bit and plugged that back in. Car seems to run a little smoother, though no vibration felt on the FV, still. Block is now warm at 195*F so I will let it cool down and then test again. Based on the block temp, maybe the FV was already out of its operating timeframe, so I'd like to try with a fully cooled engine.

I'm wondering if the PO's mechanic fussed with the mixture to compensate for a fault in the FV or its circuit.

[mike621]

Originally Posted by 997at

One more thought. Did your smoke test check the entire system including fuel injectors, intake runners etc?

Thanks, 997. Based on your suggestion, I am now casting a little doubt on the effectiveness of my smoke test. Where do you generally port in? I used an old air filter , bagged, with a port in it. I could only find smoke squeaking around the filter seal, but once i clamped it in tighter, no smoke on rest of system. Runner boots were replaced a few years ago by the PO.

[Dave Kost]

Originally Posted by mike621

Dave,

I felt no vibration with my fingers on the banjo of the FV. Maybe I'm having trouble distinguishing between it and the engine. Pulled the black connector next to the shock tower and found some corrosion on the two pins closest to me cleaned it up a bit and plugged that back in. Car seems to run a little smoother, though no vibration felt on the FV, still. Block is now warm at 195*F so I will let it cool down and then test again. Based on the block temp, maybe the FV was already out of its operating timeframe, so I'd like to try with a fully cooled engine.

I'm wondering if the PO's mechanic fussed with the mixture to compensate for a fault in the FV or its circuit.

FV is always in play.

When you start the car have someone hold onto he relay under the passenger seat. it should click. Please confirm.

It the relay clicks and the FV isn't vibrating, you will need to trace out the wires to the FV.

Are you sure you located the FV?

Check the connectors on the ECU under the seat too.

[mike621]

Originally Posted by Dave Kost

FV is always in play.

When you start the car have someone hold onto he relay under the passenger seat. it should click. Please confirm.

It the relay clicks and the FV isn't vibrating, you will need to trace out the wires to the FV.

Are you sure you located the FV?

Check the connectors on the ECU under the seat too.

Thanks Dave!


Update:
ECU connections good
Relay clicking

FV vibrating "sometimes".

Found what appears to be the root cause of the issue. Unplugged the black connector on the left shock tower and found corrosion on the pins. Sanded male ends of pins a bit but finding difficulty getting an abrasive into the female ends of the plug. Now, when I jostle the connector while running, will run well intermittently, and FV will run (audible buzzing). Connection is unreliable and when FV stops or connector moves, then everything runs poorly. Any advice on something tiny i can get in there to clean up the pins? Would like to try this before disassembling the connector.

[Bill Douglas]

Mike, research a product called Stabilant 22

[mike621]

Originally Posted by Dave Kost

FV is always in play.

When you start the car have someone hold onto he relay under the passenger seat. it should click. Please confirm.

It the relay clicks and the FV isn't vibrating, you will need to trace out the wires to the FV.

Are you sure you located the FV?

Check the connectors on the ECU under the seat too.

Thanks again Dave. Cleaned up the black connector pins male and female with a small dremel abrasive bit twisting in my fingers, a pick, 220grit paper and a brass brush. Expanded male pins slightly with a pick so the connection is a bit tighter. Finished off with a swab of dielectric grease. Condition appears to be resolved. Will report results after a fully cold start and a test drive.

Originally Posted by Bill Douglas

Mike, research a product called Stabilant 22

Thanks Bill. Will look into this to supplement my dielectric grease applications.