02 sensor possible contamination

[John2244]

Yesterday in anticipation of replacing my O2 sensor in the next couple of weeks I sprayed a liberal amount of liquid wrench at the base of the O2 sensor were it is screwed into the catalytic converter. I did this a couple of times thinking it would help the removal process. 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. Is it possible the liquid wrench product contaminated the O2 sensor creating this problem??

Also, assuming this is a contamination issue what is the proper way to clean the sensor??

Thank you for your help, John

[dannobee]

Look elsewhere. O2 sensor has no effect on initial cold startup.

[PeteKz]

Ditto what he said. When the engine is cold, it runs off an open loop map, so the sensor has nothing to do with it. Likewise at full throttle it is running open loop.

I think it's more likely that you knocked something else loose while you were working on the engine.

[76FJ55]

I agree with the above that the O2 should not cause the current starting/running issues, but if you are inclined to you could always unplug it an force the system into open loop.

If you were in the engine bay working on the O2 connector and not just under the car trying to loosen the O2 sensor itself, the first place I would look would be at the connector for the CHT sensor on the bracket on the left intake plenum. those connectors get super brittle with age and messing around in that area can easily know that connector loose if the plastic has started to fail. try reseating the CHT sensor connector and see if that effects the starting/running. if so replace the connector/sensor as necessary.

[John2244]

Thank you for the replies and recommendations. I will start looking for other possibilities for my problem.
Other recommendations are welcomed.

Regards, John

[John2244]

I did a check of my engine compartment and didn’t find any loose or disconnected vacuum lines. I did find a couple of loose wires connected to a loom that goes to the back of the engine compartment. Looks like these loose wire have been disconnected for years. You’ll also see my broken oxygen sensor connector. I have this part on order from Kroon.
Also, not sure this car has a CHT sensor. I can find this part on pelican for an 84 but not an 83 engine. If I’m wrong about this or you see it in the picture please let me know..
Thanks, John

[John2244]

[PeteKz]

SCs do not have CHT Sensors. They still use the thermo-time switch for cold starts. It’s on the chain cover just to the left of the dizzy.

[pmax]

Originally Posted by John2244

I did find a couple of loose wires connected to a loom that goes to the back of the engine compartment. Looks like these loose wire have been disconnected for years.

Assuming this is a lambda CIS transplant, the "loom" should eventually lead to a control unit under the passenger seat.

How long has the car been running with the 3.0 ?

[John2244]

Hello pmax,

No information as to how long ago the engine was replaced. What was told me the original engine was replaced at about 40,000 miles with a 1983 3.0 L engine with similar miles. The car just turned 80,000 miles.

[pmax]

Do me a favor. Look under your passenger seat and post a pic.

What is this part circled in red ?


That infamous O2 connector is also in the "wrong" place but understandably so, still very intriguing how this was done.

[John2244]

I have no idea about the item circled in red.
I’ll post some pictures I have on file as to what’s under the passenger front seat.

[pmax]

Alright, it does have the right CIS lamba electronics. That thick black wiring goes to the engine loom.

The silver box is the frequency valve/O2 relay, it's a known failure point. Carrying a spare relay is a good idea. A quick test is removing the relay and checking if the poor running symptoms remain the same.

[John2244]

PMax, thank you.
I’ll remove the relay tomorrow and check the running condition.
The engine will still start and run with the relay removed??
I’ll also place an order for a spare.

[pmax]

Start the engine first then unplug the relay for a short while.

Here's a helpful video one of PP's long time denizen made
https://forums.pelicanparts.com/porsche-911-technical-forum/996286-cant-measure-due-cycle-dwell-help.html#post10034405

Alternatively, and arguably a better option given it can't possibly make the engine run worse, replace the relay with the new one first and see if it makes a difference. If not, you still end up with a good relay as a spare.

Hope this helps.

[John2244]

Couple years ago I received a box of various bulbs, switches, and relays. As luck would have it the relay Pmax recommended I change was in that group. Unfortunately no change in the running conditions. I hope to have a friend coming over in a few days with some gauges to test the pressure in the system. I’ll keep everyone posted as to the outcome.

[Walt Fricke]

I added a 3.0 lambda engine to my 2.7. The 2.7 has no provision for the O2 connector, so you have to fabricate something or otherwise hold the plugs so they don't flop around.

The red circled black thing is a 12 pin connector (similar to the big 14 pin one at the left rear) for various CIS wires. The black cylindrical thing with a cap is the test port for checking the pulse width modulation sent to the frequency valve. It isn't connected, but with a wiring diagram you should be able to connect it - in stock configuration it has a red wire connected to one of the fuses on the rear panel, a brown wire to ground, and the 3d wire (normally green) to one of the FV control wires. It doesn't affect the operation of the CIS.

The silver cube relay is just a power relay - when on it provides 12V to various CIS Lambda components. The frequency valve is actually controlled by the main "computer" big box, which grounds the frequency valve circuit to create the pulse width modulation. So the relay points close when you start the car, and opens when you shut the engine off. Easy to test the relay - put your fingers on it and start the engine. You should feel it click.

[John2244]

Walt,

I want to thank you very much for the Detailed information. It is very helpful. I did check the relays with a 9 V battery and a multimeter and they both tested OK. Next time I’ll just put my hand on the relay and feel for the click.

I want to restate my problem. This car feels like it’s running on four cylinders. I thought possibly by spraying some liquid wrench on the base of the oxygen sensor I Might’ve created a problem.

Some recent history.
Two weeks ago the car started to develop a cold start issue. Instead of starting instantly it would take two tries before the engine would start without applying gas.
Last week I went on 140 mile drive on some of the back roads in Southern California. There were about 6 to 7 areas where water was crossing over the road due to the recent rains. Water depth ranged from 1 inch to 6 inches. Proceeded through these areas with no apparent problem. On the way home there was a road closure and there was a 30 minute detour of stop and go traffic around the closure causing my old temperatures to elevate up to about 250°. Once through this closure, I pulled over and let the car cool down to about 210 and proceeded to drive 20 miles home. No apparent issues.
A couple days later I was about to go on a drive when I notice my current problem. The cold start issue was not new and was planning to deal with that after a trip I had planned for this weekend.
The fact that the car now only seems to run on four cylinders is my biggest concern. The only changes made to the car between running great and its current condition was the preparation for my 400 mile trip this coming weekend. Checking air in tires and spare, re-torquing in the wheels, just normal things.
The other change as stated above was to apply liquid wrench to the base of my oxygen sensor thinking that would help the removal process when the replacement part was received.

[PeteKz]

So it sounds like a cold-start issue now. When you havr a cold start problem, you want to check the cold start valve operation. Check that the thermo time switch receives voltage from the CSV, and then shuts off after a few seconds. Test at the connector to the CSV. It's hard to get to because it's in the "triangle of death." Check that the ground to the CSV connector has continuity. If you can pull out the CSV and test it with fuel pump running to see if it squirts, so much the better. Then check the WUR per instructions Tony (boyt911sc) has posted on other threads, or use the Bosch Fuel Injection book. Do you have a CIS pressure gauge setup? You should check the cold and warm control pressures too.

[John2244]

PeteKz,
Thank you for your reply and the areas of possible problems.
I felt the developing cold start issues was probably a different issue versus the car running extremely rough but maybe not.
I hope to be checking CIS pressures in the next few days.
John