Lambda CIS suddenly running rich

[troth]

Recently took my ‘81 SC on a 2000 mile trip from south Texas to Connecticut. Despite the extreme heat (105 plus degrees in Texas), oil consumption was near zero and only failure was a fan belt.

Now that I’m driving around CT I noticed some poor running once warm. Put the dwell meter on the frequency valve after a spirited drive to heat the car up and it was pegged at 80-90% indicating that it’s very rich. I leaned it out accordingly. I hate compensating with the mixture screw for something that is clearly wrong. Cold running obviously is very poor now. Some mild lean popping in the exhaust on deceleration before it fully warms up.

My top suspect is obviously the WUR. But my pressure gauges are in Jacksonville, FL. I warm the car up, and drive another 1000 miles down to Florida. Car runs fine except for one instance of a heat sunk solenoid at the new Buc-ees in South Carolina. Push starts warm no problem.

Pressure gauge on the next day… and the WUR is fine. Darn. Maybe leaking CSV… nope holds fuel pressure to spec. Thermo time switch failed causing the CSV to fire constantly? Pulled the connector on the CSV and there’s no change in running. Obviously the lambda system is entering closed loop mode so the 15 degree switch is working. I suspect the 35 degree temp switch is also working because unplugging the idle micro switch does not make a difference in dwell. Difficult to test the warm up cycle because ambient temp is just about 95 F, 35 C here in Jax.

Seeking any other ideas that might suddenly cause the lambda to indicate very rich running.

[Marc Bixen]

Check your interior lights. Are they working? The same power circuit powers the Lambda control under the passenger seat. If the fuse blows, fuel pressure goes up, etc. Also theres a Lambda control relay under the pass. seat.

[troth]

Originally Posted by Marc Bixen

Check your interior lights. Are they working? The same power circuit powers the Lambda control under the passenger seat. If the fuse blows, fuel pressure goes up, etc. Also theres a Lambda control relay under the pass. seat.

Yup, some research before opening this thread led me to test that fuse. Interior lights work, and when I pull the small relay under the pass seat the car runs poorly.

[Marc Bixen]

Sounds like Lambda is ok!

[timmy2]

O2 sensor working correctly?

[troth]

Originally Posted by timmy2

O2 sensor working correctly?

This is my next suspicion. Despite reading 50% dwell on the freq valve, I can get a significant rise in rpm by manually manipulating the air flow sensor plate. The O2 sensor is not OEM so it is obviously not 40 years old, but I do not know the last time the PO replaced it.

[ahh911]

wur heating element checked at the time of pressure tests?

[troth]

Ugh after some fiddling, I'm still struggling with this. I disconnected the O2 sensor and set the mixture the old fashioned way by manipulating the airflow sensor and listening for a rise in rpm. Runs good when warm, but still seems to be way too lean when cold. No missing or backfire but I really need to keep my foot on the gas to keep it running.

I did discover an incorrect AAR was installed. The part number corresponded to a 78-79 car. Luckily I had the correct AAR here. It tested good, so I swapped it in, but still not seeing any improvement.

Originally Posted by ahh911

wur heating element checked at the time of pressure tests?

I just rechecked this. With an ambient temp of 82 Fahrenheit I'm getting 2.7 bar with the WUR unplugged. After plugging it in pressure rises very quickly (approximately 60 seconds) to 3.6 bar. This seems to be in spec, but it rises so fast I'm not so sure.

[AndrewCologne]

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&_x_tr_pto=wapp

Here's all you need to know for a proper setup of a lambda based K-Jet engine.
I did let google do the translation, so be prepared for some odd terms, but it will help and let you understand.

[boyt911sc]

Originally Posted by troth

Ugh after some fiddling, I'm still struggling with this. I disconnected the O2 sensor and set the mixture the old fashioned way by manipulating the airflow sensor and listening for a rise in rpm. Runs good when warm, but still seems to be way too lean when cold. No missing or backfire but I really need to keep my foot on the gas to keep it running.

I did discover an incorrect AAR was installed. The part number corresponded to a 78-79 car. Luckily I had the correct AAR here. It tested good, so I swapped it in, but still not seeing any improvement.

I just rechecked this. With an ambient temp of 82 Fahrenheit I'm getting 2.7 bar with the WUR unplugged. After plugging it in pressure rises very quickly (approximately 60 seconds) to 3.6 bar. This seems to be in spec, but it rises so fast I'm not so sure.

Troth,

When you get a chance, check the heater resistance (Ohms) of the WUR when the engine is cold preferably in the morning. Pull the electrical plug to the WUR and measure the resistance across the terminals. Post the value of the resistance (Ohms) and the ambient temp. Thanks.

Tony

[troth]

Originally Posted by boyt911sc

Troth,

When you get a chance, check the heater resistance (Ohms) of the WUR when the engine is cold preferably in the morning. Pull the electrical plug to the WUR and measure the resistance across the terminals. Post the value of the resistance (Ohms) and the ambient temp. Thanks.

Tony

Tony, I was hoping you’d chime in. It’s funny that you think the engine will be “cold” in the morning. Try 80 degrees ambient. I’m showing 8 ohms. Maybe a little low allowing it to draw more current and lean out faster? An internal short? I should add that I don’t entirely trust my ohmmeter. Bezos is sending me a Fluke that should be here early next week to confirm. I remember coming across a post from you of all the different WUR resistances, but I’m having trouble finding it now.

[ahh911]

81 sc should have wur with markings 090.

26 Ohms up to some temperature, then 10 Ohms above a set temperature. Not sure what that temperature is nor how critical it is. I've bypassed the second heater winding completely, i.e. just left it at 26 Ohms over all temperature for several weeks just to see what will happen and I swear there was no noticable difference to drivability, I have it set to switch in for 10 Ohms around 75F which is really just a best guess based on what I've read, it probably should be higher. Anyhow, at around 80F, Tony might let you know if it should be 10 or 26 Ohms.

Phil

[boyt911sc]

Originally Posted by troth

Tony, I was hoping you’d chime in. It’s funny that you think the engine will be “cold” in the morning. Try 80 degrees ambient. I’m showing 8 ohms. Maybe a little low allowing it to draw more current and lean out faster? An internal short? I should add that I don’t entirely trust my ohmmeter. Bezos is sending me a Fluke that should be here early next week to confirm. I remember coming across a post from you of all the different WUR resistances, but I’m having trouble finding it now.

Troth,

I am traveling in Spain right now with my family and will be back home by August 1. I will lend you a WUR-090 (rebuilt, calibrated and tested) that you could install in your motor. You are not obligated to buy it but simply have an experience how a properly calibrated WUR-090 works. Send it back to me after the test. Your CIS will always have a cold idle problem unless you correct your WUR.

PM me if you are interested. Thanks.

Tony

[troth]

The adventure continues. Tony and Phil, thank you for the input. I will probably have to take you up on your offer to send me one if I can't get it worked out before your return. In the meantime, I have my WUR apart on the bench. I did find a small piece of insulation presumably from the main heating element broken up in the bottom, but it doesn't look like it should effect anything.

I'd like to try adjusting the 9 ohm to kick in at a much higher temperature (if that's even possible?) or at least bypass the 9 ohm resistor so it's always at 26 ohms like Phil mentioned while I have it apart. I don't really understand how the switching action occurs just by looking at it. Any input here? I'll post up some pics soon.

[troth]

After some fiddling I think I've answered my own question. I backed the little set screw out 1.5 turns and am now showing 26 ohms at room temperature (75 degrees).



Picture sourced from pelican user "Won" here.

Wife just got home from work, so will have to wait until later to get it all back together and test it.

[Schulisco]

Concerning the fact that the car suddenly ran too lean (and the lambda control increases the duty cycle up to 80% and more) after a 2000mile trip I wouldn't expect a wrong WUR or another wrong part on the engine. Of coourse the WUR could go worse over time.

But first and foremost it must hang together with the sudden leaning out the mixture. So either a component went bad from one moment to another and this leads the lambda control to enrichen the mixture as much as possible.
So I would first search for a vacuum leak or, if nothing like that can be found, I would check the fuel pressures (system and control pressure) and the fuel delivery rate of the fuel pump itself. Porsche specified for the SC 's a fuel delivery rate of 1000cc in 30secs and a system pressure of 4,5 - 5,2bars (65 - 75psi). If these values can be measured, then check the fuel accumulator if it spills in trhe overflow connector (bottom output).
You can safely find a vacuum leak only with a smoke generator. Brake cleaner and cigarette smoke aren't a good choice because they indentify the huge leaks only. The smaller the leaks are, the harder they are to find and therefore you need a more dense and slightly pressurized smoke from a smoke generator.

Thomas

[Walt Fricke]

Thomas - I have been concerned about fuel delivery on my '82 US 3.0 track only car. Looking at my AF gauge accelerating down a straight (where I can glance at it), it seems an AFR of 12 or so goes up to 15. And I can't quite pull cars I should be able to pull even if my qualifying type lap times are better. Someone suggested measuring the fuel delivery. Unhooking a fuel line in the engine compartment showed 2 liters in 30 seconds. Glad I had a big container, but fuel delivery to the fuel distributor probably not a problem. And system pressure is within spec.

But if the standard is to measure fuel delivery after the system pressure regulator, how would one do that?

[Schulisco]

Originally Posted by Walt Fricke

Thomas - I have been concerned about fuel delivery on my '82 US 3.0 track only car. Looking at my AF gauge accelerating down a straight (where I can glance at it), it seems an AFR of 12 or so goes up to 15. And I can't quite pull cars I should be able to pull even if my qualifying type lap times are better. Someone suggested measuring the fuel delivery. Unhooking a fuel line in the engine compartment showed 2 liters in 30 seconds. Glad I had a big container, but fuel delivery to the fuel distributor probably not a problem. And system pressure is within spec.

But if the standard is to measure fuel delivery after the system pressure regulator, how would one do that?

Walt, I don't get the question...why should you measure the delivery behind the pressure regulator? If the fuel is not burned and not drained out of the engine, it will return to the fuel tank...The whole line behind the regulator is not pressurized any more, it returns the surplus fuel back to the fuel tank.

If your engine runs lean as indicated on the AF gauge then it must be another reason...don't know the setup of your track car...I would try to add additional fuel when the AF gauge show too l ean mixture....e.g. with an additional fuel injector like the CIS cold start valve.

In the beginning of the troubleshoot on my CIS car I added a button in the cockpit giving +12V on the CSV manually to identify whether my car runs too lean or too rich (hadn't had a AF gauge by that time). So I could enrichen the mixture by pressing the button on purpose to see if it starts better or brings extra power or not...I would do the same on your track car...

I found out that the amount of additional fuel by the CSV is enough for my car to make a huge difference between running to lean (and poor performance on high rpms) and rich enough on high rpms...

Thomas

[troth]

Adjusting the WUR did not have any effect. It still takes less than a minute to reach warm control pressure. Cold running still crappy. Still runs fine hot.

Originally Posted by Schulisco

Concerning the fact that the car suddenly ran too lean (and the lambda control increases the duty cycle up to 80% and more) after a 2000mile trip I wouldn't expect a wrong WUR or another wrong part on the engine. Of coourse the WUR could go worse over time.

But first and foremost it must hang together with the sudden leaning out the mixture. So either a component went bad from one moment to another and this leads the lambda control to enrichen the mixture as much as possible.
So I would first search for a vacuum leak or, if nothing like that can be found, I would check the fuel pressures (system and control pressure) and the fuel delivery rate of the fuel pump itself. Porsche specified for the SC 's a fuel delivery rate of 1000cc in 30secs and a system pressure of 4,5 - 5,2bars (65 - 75psi). If these values can be measured, then check the fuel accumulator if it spills in trhe overflow connector (bottom output).
You can safely find a vacuum leak only with a smoke generator. Brake cleaner and cigarette smoke aren't a good choice because they indentify the huge leaks only. The smaller the leaks are, the harder they are to find and therefore you need a more dense and slightly pressurized smoke from a smoke generator.

Thomas

I was about to correct you that I suddenly started running rich not lean, but I just went and reread the original post and how dwell was showing very high on the freq valve. Not sure how I got it in my head that it was rich.

I don’t suspect a major vacuum leak. The airbox is practically brand new as well as the intake runner boots and gaskets. Rpm’s drop significantly when I take the oil cap off. System pressure is 4.8 bars, so fuel supply is not an issue.

Out of desperation I refreshed the ignition system. New cap, rotor, plugs. They were about due anyways. A clue presented itself: plugs for cylinders 1 and 2 looked lean while all others are slightly rich. Hmmmm. Tried spraying some starter fluid on the injector ports and didn’t notice any change. I’ll try to seek out a proper smoke machine for a definitive test. The o-rings are fairly fresh, but who knows. I suppose the injectors or lines could also have somehow clogged. My head studs are no more than 15k miles old… I REALLY hope that’s not it. A compression test would help me sleep better tonight.

[troth]

Almost a year later I’m still fighting cold running issues. Starts on first crank, idles about 900 rpm then dies when the AAR closes after about 60 seconds. Second start is much more difficult requiring a lot of cranking. Once it’s hot it runs great.

A big clue is that on warm starts after sitting about 5 minutes after a hot shutdown it idles very high (almost 2000 rpm) before settling down to a normal 950 rpm after about 60 seconds.

After much fiddling today I found that the green wire the o2 sensor plugs into has about 8V with or without the o2 sensor plugged in. The o2 sensor it self is “normal” for a rich condition (0.6-0.8V). Is this normal to have 8V at the connector? I’m getting some wonky readings from my dwell meter. I don’t know if it’s the meter itself or the ecu telling the freq valve to do weird things.

To reiterate, all the basics are good. Valves, timing, WUR, vacuum, etc.