02 sensor possible contamination

[Walt Fricke]

John
I can't readily think of a common cause for a cold start issue and a rough, feels like running on only four cylinders, issue.

But for sure spraying penetrating oil on the O2 sensor where it screws in isn't part of either issue. The sensor plays no part in starting the car, and it is hard to imagine how its failure (which likely results in a 0 voltage signal no matter what the AFR is) would cause either of your problems. These cars run fine without the sensor - they just don't get the fuel mileage they otherwise would, and may not meet emissions standards. At idle, and at near full throttle, the CIS's frequency valve is controlled by a throttle switch.

A CIS pressure testing tool isn't expensive, or at least doesn't have to be. It consists of a pressure gauge (inexpensive part), some hoses, an open/closed valve, and a bunch of threaded adapters so it can be used on a variety of cars and injection systems. You can spend a lot on one if you want, but the less expensive ones work just as well. Shop around. It is really the basis of troubleshooting cold start issues (at least once you have confirmed that the cold start system is working, which doesn't require a specialized tester). But testing the CIS is how a mechanic starts figuring out cold start issues once the the functioning of the cold start valve system is shown to be fine.

Rough running could have lots of causes. A vacuum hose dislodged from the distributor? If you had spark plug wires off the plugs or off the distributor and plugged two into the wrong places, that would do it, but you'd not likely have fiddled with any of that just driving round. Check the spark timing (calls for a timing light). Did the distributor come loose? Is the distributor cap OK? Is its center electrode OK? Rotor OK Cap on tight? A little bit of apparent wear on this stuff is normal and not a problem, but something broken is.

One approach is to pull and inspect all the plugs - any too rich or too lean? Are all the gaps reasonable?

Another tool a mechanic would use is a leak down tester. That will tell you if you have significant compression leaks around rings or valves. If a valve adjustment has gone way wrong, so a valve doesn't close, this would catch that (typically failure here results in too lose a rocker adjustment, with attendant excessive clicking noise).

Plus, with the valve covers off, you can fairly easily check for broken valve springs. I'd put that well down on the list, as the engine runs well with one of the two springs on any valve broken until you get up to 5 or 6K RPM.

In the old days of carburetors, the mantra for bad running was check the ignition first, then move on to the fuel and other systems.

Having basic things out of whack would certainly not help starting the car, especially when cold, so there could be some connection.

Or is there a shop near by which has experience with air cooled 911s? Differential diagnosis is a great intellectual challenge, but isn't always easy.

[John2244]

Walt,
Thank you for your message. I’ve been looking at CIS testing pressure tools but this issue developed before I made a purchase. As recommended I’m gonna start at the beginning and test pressure. I have a friend coming over in the next couple of days with a set of testing gauges.
Interesting from just a few days ago I could get the car started and apply throttle to get the RPMs up but felt like it was only running on three or four cylinders. Today, wanting to back the car out of the garage onto my scissors lift I had to restart the car 20 times to develop enough pressure beyond a weak idle to move the car. The throttle was not working at all. So it’ll be interesting to determine the final fix and I will certainly share with everyone. I appreciate your participation.

Thanks again Walt I appreciate your comments.
John

[John2244]

A little more history I just thought about. Probably 400 miles back I had to replace my fuel pump. I also replaced my fuel filter as preventive maintenance. I would not think any of these changes has anything to do with my current issues but ………

[John2244]

Want to close out the thread and thank those who offered suggestions and help. I had a friend come over and put a set of pressure gauges on my car. He felt the warm up regulator was defective. I went with his decision and removed the warm-up regulator and sent it out to be rebuilt. The rebuilt unit arrived this afternoon. I installed it on the car and everything is back to normal. The only glitch was I decided to replace the fuel line between the warm-up regulator and the fuel distributor. My replacement line leaked. I had to reinstall the old fuel line. Went for a quick drive around the block and will give it a longer test drive tomorrow. Thanks again for those who offered suggestions.
Regards, John.

[Walt Fricke]

Well, that's all to the good.

You had a cold start issue and a "feels like it is running on only four cylinders problem.

Cold starts problems can be due to the cold start feature of the WUR not working correctly, or the cold start valve not working, or the ECU not getting power. From the resolution here, it looks like it was the WUR.

The WUR is designed to provide a rich fuel mixture when the WUR (and the engine) is cold. As things warm up (the WUR has a heat coil inside - that's what the wires to it are for - and eventually engine heat warms it) the fuel mixture gets leaner. That's why the specs call for a cold control pressure, and a higher warm control pressure. If this system fails, cold starts are a problem, but not warm running.

Another thing which can cause WUR troubles is a clogged filter inside the WUR. This makes both cold and warm pressures leaner, which affects starting, and also running. I'm not sure that it would be so lean that it felt like running on four cylinders, though.

To close the loop for those who have tried to diagnose things remotely, could you be specific as to the results of the tests your friend did? What cold and warm control pressures did he find? What was the system pressure?

[John2244]

Walt,

He only did cold pressure test. What made him believe the WUR was defective was the cold control pressure was over 5 bar. I will have to ask him about the system pressure number.
The company who did the rebuild confirmed the unit was “no good” before the rebuild. Unfortunately they didn’t give any details.

[Walt Fricke]

Thanks.
5 bar is about system pressure, which is what you get with a clogged WUR filter. CPs range from about half a bar to 2.5 bar depending on temperature. No wonder things weren't working right. This filter can be cleaned in at least some cases by taking the WUR apart to flush the filter. I did that on mine. But purchasing a known good replacement is easier for most.

How the filter gets clogged is an interesting question, since there is a pretty efficient external fuel filter in the system. But it happens. I wouldn't expect changing to a new filter would send a flood of crud into the fuel distributor to end up in the WUR. So the how seems an unknown.

[Walt Fricke]

Also, you can see why guys like Tony start out by asking that the person with a problem do the CIS pressure tests. Pointed to the problem right away.

[pmax]

Originally Posted by John2244

Today the car was difficult to start and when started the engine would barely run. I felt like it was running on three or four cylinders. The engine would stall when I quickly reduce throttle.

Interesting the engine still started and ran with the CCP so high due to the clogged WUR.

[John2244]

Pmax,
In the end it would barely start and idle. Had to restart it 20 times or so to move it from one side of the garage to the other. There was no throttle response at all.

[Walt Fricke]

Pmax
I think the CIS is surprisingly fault tolerant, at least when it comes to being able to start (eventually) and run (however well or poorly). When I converted to a Lambda 3.0 I left off the Lambda part. Why would I need that stuff, run that wiring, etc. It was hard to start, at least when cold, but started. Seemed to run OK just driving around. Then I wised up.

With the Lambda the FV runs PWM 50% duty cycle for starting. That 50% affects the FD differential pressure so it is lower, doesn't it? So more fuel flows to the injectors. Without the effect of the FV (I assume it is closed if unpowered, so has no effect of the lower chamber), what is the lower chamber pressure? System?. But isn't the Lambda FD set up to run a lower chamber pressure which is always reduced some by the FV? Or the upper chamber system is set to work a bit differently to compensate for a different base lower pressure? Just curious.

But it ran without noticeable problems (who would notice some HP loss driving around town?).

I don't recall why I ran the pressure tests which caught my clogged WUR filter. I'm sure the car ran. I was mostly fiddling with CPs (I'd made my WUR adjustable for CCP but also WCP as it seemed to have too lean AFRs racing, which I tried to fix - everyone said it was because I had the wrong WUR, but I have the same issue with the "right" one). When I saw system pressure when reading CP I took the WUR apart and fixed that problem.

Sounds like John's blockage was worse than mine somehow.

So yes, it is interesting.

[pmax]

As far as I understand, a closed FV, equivalent to 0% duty cycle, the end result is less fuel to the injector. So if the system is designed to run at 50% nominal duty cycle, I agree that means without the FV working, it will run lean. With the O2 sensor disconnected but lambda CU still driving the FV, the system runs at 50% duty cycle but in your "lambda delete", I assume the FV was always closed so that means the car runs lean unless the WUR has been adjusted. I recall reading that thread of yours where you adjusted the WUR which is what I did to my WUR as well but in my case CCP was low so I had to lean it out.

[pmax]

Originally Posted by John2244

Pmax,
In the end it would barely start and idle. Had to restart it 20 times or so to move it from one side of the garage to the other. There was no throttle response at all.

I'm speculating the CSV was injecting enough fuel each time to eventually "run" the engine, sputtering, even with the CCP that high. The 20 start attempts to get across the garage makes sense to me.