82 911SC Running Issues
 

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.

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

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'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.

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?http://forums.pelicanparts.com/uploa...1604164237.jpg

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.

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.

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:http://forums.pelicanparts.com/porsche-911-technical-forum/741033-911sc-frequency-valve-problem.html

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.

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

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

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.

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

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.

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.

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.

Mike, research a product called Stabilant 22

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.

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

Good news.

I use a product called DEoxit D100L 100% on all connections. I good preventive maintenance practice to clean all connectors and grounds.

Now go get the CO set and you'll be set.
Also, your residual pressure seemed low and dropped quicker that spec. You may have a little difficulty on warm starts.

Keep us posted.

Hi Dave,

Took it for a test drive to Oakland and back to SF. Cold start appears improved and FV appears to be buzzing. However, backfire on highway presents itself upon coasting once in awhile (3x during the drive). After a stop in Oakland, the warm start issue presented itself.

My impression is that mixture may be rich, and I may have a residual pressure issue at the regulator on the fuel distributor. Open to suggestions, and appreciate the help.

Considering either finding a shop with the proper equipment to set mixture, or buying a CO meter to do so.

Don't do anything more until you set the CO. You should be able to find a local shop to set the CO or a local Pelican to help. This could cleanup the popping.

If it were me a would pull off the entire CIS system and replace all the gaskets and rubber parts. But thats me. The only true way to ensure no unmetered air. You can take the injectors to a diesel shop for testing too.

You've done all the right things to this point.

Enjoy.

Just another thought- you may have some leaking injectors too. Don't forget to check the cold start valve.

Thanks again for all your insight in this thread. After cleaning up the connector and test driving the car, the cold idle issue appears resolved. The backfire while driving around town was continuing, so I adjusted the mixture screw lean until the idle became irregular, and then went just slightly rich.

Took the car for a drive to a Porsche shop that was recommended, Pacific Motors here in SF. Had a 930 in the doorway and a bunch of long hood cars inside. The owner didn't seem super interested in talking to me about making an appointment and told me they are busy for the next two months and to check back another time. Popular guy, it seems! Drove over to The Smog Shop where I had my smog done & they had a Pagoda mercedes getting work done last time, so figured they'd be willing to do work on an older vehicle. Referred me to Metric Motors around the corner. Metric wrote the name of some "oldschool" guru and a number on a piece of paper and told me to call them. I was hoping to get a shop to set the mixture with a meter, but coming up empty so far. Willing to accept a recommendation if anyone knows a shop in/ around SF to dial in the mixture

The car continues to run a bit hot around town according to the gauge, but no stall for the first time ever! :D I checked all the oil pipes with a temp gun and the t-stats appear open. 140-190* for all pipes, including t stat and trombone. 180*F at the intake runner, Sump plate/case tested at 300* F. I think I may have some remaining obstruction at the (leaking) engine oil cooler where I had vacuumed out a mouse nest.

I'm sensing my next project will involve a drop or partial drop in my garage to do the cooler cleanup & seals and TOD. I'm a little worried about scope creep as I DIY, but I'm going to grab the 101 Projects book and make a plan to approach that session.

Thanks again.

What plugs are you running?

Also, think about getting the O2 sensor connected and doing a more comprehensive smoke test. You still could have unmetered air causing lean running and high temps. Like i said you won't know until the mixture is set properly.

Maybe a local Pelican can help with the mixture setting.

Thanks Dave. o2 sensor is connected though the connector plastic looks brittle and cracked. I purchased NGK Iridium plugs from our host. I'll ask around about shops in SF.

If you’re interested I can set your mixture for you through the test connection for the frequency valve. As long as your ECU, O2 sensor and FV Are working this is a very accurate method.

Wow, that'd be great! Yeah, these components are all either working or new. Are you based locally?

@Mike
Do you have a DMM which supports the reading of Duty Cycle? If not you should get one as its an essential tool for proper lambda based 911 engine maintenance.
On the left side of the engine compartment theres a plug called test port. There you can connect your DMM to.

But lets see first if 997at can assist you here on your site before going into a deep tutorial here.

Hi Mike. I'm in the East Bay (Orinda). Just PM me and we can figure out a time that works for you to come over.

Watching from the sideline...........
 

Mike,

I’ve been watching this thread since the beginning. You mentioned that you did a smoke test. How did you do it? If you did not isolate the system properly from atmosphere, your smoke test won’t locate or find the hard to find air leak source/s. This is a very important and critical test.

Not until you confirmed the absence of unmetered air going into the system, your CIS motor will not run well. You could tinker the fuel fixture setting to compensate for the unmetered air but this will not solve the problem. How many times have you adjusted the fuel mixture setting since you bought the car?

Maybe you don’t have any air leak sources or unmetered air? But you don’t know that as a fact. And you are hoping there is none. You can not depend on luck all the time. Test and confirm. Stop guessing. You either have unmetered or don’t have any. Pick your choice.

The other problem is your residual pressure loss. You could easily locate or identify the culprit/s by doing a fuel pressure test. This is widely discussed in the forum. Keep us posted.

Tony

997at- When you meet up with Mike, show him how to test the Throttle switch.

http://forums.pelicanparts.com/porsche-911-technical-forum/1068880-cis-afr-idle-vs-wot.html

Thanks Andrew. Have read up on the tutorials on this site and I have a basic understanding of how this is accomplished.

Will do. Appreciate the offer.

Thanks Tony! I agree with you, and have read many of your posts. The mixture setting cannot be the primary cause for the intermittent backfire on the highway. I felt like the PO messed with the mixture (like many on here) in the effort to mask a running issue and vac leaks, which I have addressed with new hoses, etc.

As the cold start issue turned out to be electrical, my thoughts turned to this. I took the car out last night to have two tires mounted and have the alignment checked and spent a bit of time on the highway. Things I noticed about this "backfire":

-The car will lose response and quit running as if randomly
-After a second or three of trying to get the car restarted while coasting, will start with a backfire out the exhaust,

Epiphany?: I realized that the quicker I performed the key off and on restart (within a couple seconds), the smaller the backfire. By this, I realized that I am likely dropping spark while the car is hot. Key back on restarts the ignition and BOOM ignites the extra gas in the cylinder. I will look to test the coil and cdi box for proper resistance values, before any adjustment is made to the mixture. I presume these values may be in the Bentley manual, but I will also continue reading and searching the forum.

997at, I will take you up on your offer, once I can confidently get on the highway again!

Mike, it is very likely that there are a few issues impacting your CIS. What I ended up doing in my case was dropping the engine and systematically tested, replaced, and refreshed every single one of my CIS/injection related items. It was a great learning journey for me because now I know how they all function, what part they play, and how to test them. As you know, air, fuel, and spark is what is what is needed but CIS adds a few things extra to look at.
I'd be happy to also take a look at your entire system and can help you troubleshoot and test. I have a smoke machine to repeat and confirm no leaks as well...it is critical that this test looks at the entire system and not just the air box.
I also learned that spark is not always what it appears to be. After my complete CIS rebuild I could not get the car to fire. I visually checked for spark and it was there but perhaps not super strong. So I replaced the coil and it fired up before even the first full engine rotation. You really have to test each and every component to have another 20-30 years of trouble free running. As another aside, I replaced my blown air box and did not install a pop off valve in my new one...it is just one other item that can lead to air leaks down the road. If your CIS is tuned properly and you have a spider inlet (new) air box it is not necessary.
Your CDI could also lead to some of the the issues you are having...mine started to crap out when I first got my car. I replaced it with an MSD ignition and coil...trouble free ever since.
The journey can be frustrating...I can't tell you how many times I almost threw in the towel and considered getting rid of the car. Stick with it and once solved, these babies run beautifully and you won't have to worry for decades to come. Let me know how I can help.

I foresee a full or partial engine drop coming sometime in 2021(probably). Oil cooler and TOD or RMS leaks.

Tested the coil this morning and resistance values are out of spec between the small posts (.9). Appears original so I am going to swap in a MSD 8222 (avoiding all the Brazil coils out there after reading all the reviews) from our host and try a couple test runs on the highway before I attempt to make it to Orinda in the coming weeks :cool:

Would welcome any retesting and thoughts from your experiences!

Update here. Installed the MSD HV 8222. Awaiting a non-rainy day to do some road testing to see if the warm stall has been mitigated.

Sunny day in SF today. Took the car out around town to run an errand. Super pleasant the first 20 mins. After the store, car was having hot start issue (I have low residual pressure at the CIS) Thinking a check valve for that is in my future. Wonder if I should do that on or off the car...

Though it's running a tiny bit cooler around town, still had the stall issue once, so my guess at the coil proved to be wrong. I'm still convinced the "stall" is spark related, as I cycled the key back to the run position and the car continued on after a backfire. Maybe its time to turn my attention to CDI box.

After 20 mins or so of city driving, this thing is running at the upper white mark on my temp gauge, and still smoking a lot from oil leaks. I'm also feeling that it may be time before too long, for a partial or full drop to really dig into the demons.

I read through this thread http://forums.pelicanparts.com/porsche-911-technical-forum/1033026-81-sc-dying-speed-3.html for some inspiration. Going to take a look at the connection at the CDI & distributor. May dig further into the CDI depending on my appetite.

Did you ever set the CO to spec?

Did you test the throttle switch?

Sorry I'm too lazy to re read the entire post.