Questions: CIS, cold start, WUR and O2 sensor

[tirwin]

Guys,

Quick questions. Reading some other threads and help me with this to make sure I understand.

83 CIS. Cold start scenario.

1) About how long should it take for the bimetallic strip in the WUR to heat up and close the valve under normal (say 68 F +/- a few degrees) ambient temps? What happens if valve closes too fast or too slow?

2) Is O2 sensor involved during this time? What would you expect if it was bad vs simply disconnected? Does bad O2 relay show different symptoms if bad vs disconnected?

Thanks in advance!

[timmy2]

For the WUR:
It usually takes about 5 minutes for the strip to move to its normal position. Assuming it has a constant voltage applied.
To fast and you run lean, too slow and you run rich.

IDK about the O2 affects during warmup.

[Peter Zimmermann]

If your symptom is poor running cold, is your frequency valve buzzing?

[tirwin]

Timmy2,

Thanks. My WUR seems like it is closing much faster than that. What you said makes sense and I think is consistent with what I see. I think on I'm on to something here.

If someone can answer the O2 sensor question, I think I an close to solving a mystery.

Follow-up question on the WUR... What is the fix for a WUR closing too fast? I assume that voltage applied to the bimetallic strip makes the strip bend at a uniform rate, so is it a matter of adjusting the position inside the WUR?

[tirwin]

If your symptom is poor running cold, is your frequency valve buzzing?

Peter, I believe it is working fine. I am about to double-check it.

I am slowly getting this CIS stuff through my thick head. I have read your explanations and they have helped a lot. My problem is that every time I think I get it I get busy with work and family and then I forget what I thought I knew.

Previous owner(s) left me with a lot of variables in the equation and a shop that I paid to put on a smoke machine to check for vac leaks simply unplugged the pressure plate sensor to "fix" it (and told me they just adjusted the mixture). I've slowly been sorting everything out. Believe I need a new O2 sensor and/or relay. If I plug the pressure plate sensor in, fuel pump doesn't run with key in ON position (like it's supposed to) but I get stumbly cold start and surging idle until the engine warms up.

With the pressure plate sensor unplugged on a cold start, I get a solid start, engine hunts slightly for maybe 45-60s and then I get nice solid idle. Fuel pump runs with key in ON position which is not normal.

Car drives fine otherwise. Good power. I suspect the mixture may be running a little to the rich side because it has that sweet exhaust smell.

One other symptom. If I drive the car for long enough for the engine to get good and warm, park and then start the car again within a short period of time (say less than an hour) it doesn't always crank right up - I either have to keep cranking or sometimes a 2nd crank. If it's longer than say an hour, it will fire right up.

So whaddya think?

[boyt911sc]

Originally Posted by tirwin

Timmy2,

Thanks. My WUR seems like it is closing much faster than that. What you said makes sense and I think is consistent with what I see. I think on I'm on to something here.

If someone can answer the O2 sensor question, I think I an close to solving a mystery.

Follow-up question on the WUR... What is the fix for a WUR closing too fast? I assume that voltage applied to the bimetallic strip makes the strip bend at a uniform rate, so is it a matter of adjusting the position inside the WUR?

tirwin,

I knew you would be back with more questions about your CIS. You have been doing a lot of work to get your car running good but you have too many variables to solve or fix your problem/s. First, the mechanic you paid to do the CIS troubleshooting was not familiar with CIS. He maybe a professional mechanic but not familiar or knowledgeable in CIS. What on earth would someone disable the safety device just to make a CIS engine start in the first place? With the FP running when the ignition switch @ ON position, the engine was easy to start because you have primed the system and increased the residual fuel pressure. This is one reason why the early CIS engines do not experience hot start problem as often as the later SC's with CIS.

Now to answer some of your questions:
a). A good WUR would get to WCP depending on ambient temperature between 3 - 5 mins.
b). The OXS does not come into play until the engine gets to its operating temperature (180°-190°F) or to its specific thermal setting. Not involve during cold start-up.

What made you think that the WUR was closing too early? Have you done a specific test to conclude your observation or you simply thought it was closing prematurely? Actually a good or bad WUR does not close at all but stabilizes at WCP. Keep us posted.

Tony

[Peter Zimmermann]

OK, with the sensor plate safety switch connected, turn on the ignition (as you said, the fuel pump should NOT run). Very briefly push up on the sensor plate arm (with air cleaner removed). Do you hear a pronounced buzzing noise just forward of the throttle body? If yes, the freq valve is OK. If not, you'll have to address the OXS relay under the passenger front seat.

[tirwin]

tirwin,



I knew you would be back with more questions about your CIS. You have been doing a lot of work to get your car running good but you have too many variables to solve or fix your problem/s. First, the mechanic you paid to do the CIS troubleshooting was not familiar with CIS. He maybe a professional mechanic but not familiar or knowledgeable in CIS. What on earth would someone disable the safety device just to make a CIS engine start in the first place? With the FP running when the ignition switch @ ON position, the engine was easy to start because you have primed the system and increased the residual fuel pressure. This is one reason why the early CIS engines do not experience hot start problem as often as the later SC's with CIS.



Now to answer some of your questions:

a). A good WUR would get to WCP depending on ambient temperature between 3 - 5 mins.

b). The OXS does not come into play until the engine gets to its operating temperature (180°-190°F) or to its specific thermal setting. Not involve during cold start-up.



What made you think that the WUR was closing too early? Have you done a specific test to conclude your observation or you simply thought it was closing prematurely? Actually a good or bad WUR does not close at all but stabilizes at WCP. Keep us posted.



Tony

Tony,

Yea, I've been doing a lot. What I can when I can. I keep following all these discussions on CIS.

Actually, the mechanic is a guy known around these parts and does have a history with Porsche. At least so I'm told. But I digress...

I posted a video last year of my fuel pressure tests. Someone suggested then that it was closing too fast. It's around a minute, probably less. You can hear the change in idle at that point.

Thanks for the answer on the O2 sensor. Since it is not involved in cold start, what could cause the hunting idle? I don't think I have false air. The shop says they put it on a smoke machine and saw nothing. The RPMs change when I take off the oil cap.

I need to get the O2 resolved anyway...

[tirwin]

OK, with the sensor plate safety switch connected, turn on the ignition (as you said, the fuel pump should NOT run). Very briefly push up on the sensor plate arm (with air cleaner removed). Do you hear a pronounced buzzing noise just forward of the throttle body? If yes, the freq valve is OK. If not, you'll have to address the OXS relay under the passenger front seat.

Peter, yes, it buzzes.

[tirwin]

One thing I did recently was to "burp it" as Joe Bob says with a can of BG44K. Put it in with a full tank of gas. That tank plus 3/4 of another since then.

Think it could be the fuel filter or accumulator?

[tirwin]

With the pressure plate sensor connected, here is what a typical startup does.

Crank for 2-3 seconds before it starts.

RPMs bounce between 800 and 1200 for about 20s. Then idles surges up to 1400 for maybe another 20-30s. Then idle falls to around 900 and 950.

This might not have been a great test. I moved the car out if the garage this morning before I just hooked up the pressure plate sensor and tried again.

Maybe burping it helped a little. That's the first time I hooked up the pressure plate sensor again after the BG44K.

[boyt911sc]

Originally Posted by tirwin

Tony,

Yea, I've been doing a lot. What I can when I can. I keep following all these discussions on CIS.

Actually, the mechanic is a guy known around these parts and does have a history with Porsche. At least so I'm told. But I digress...

I posted a video last year of my fuel pressure tests. Someone suggested then that it was closing too fast. It's around a minute, probably less. You can hear the change in idle at that point.

Thanks for the answer on the O2 sensor. Since it is not involved in cold start, what could cause the hunting idle? I don't think I have false air. The shop says they put it on a smoke machine and saw nothing. The RPMs change when I take off the oil cap.

I need to get the O2 resolved anyway...

tirwin,

The sudden change in cold idle speed is not controlled by the WUR but rather by the AAR. Are you sure it was WUR? BTW, if the WUR would close or stop allowing the fuel to flow, the engine would stall and stop running. And you could not make it start again!!!!

Hook up a dwell meter and check if the ECU is working and controlling the FV. Refrain from guess-work and do systematic diagnostic tests to determine the culprit/s. Did your mechanic tinker the mixture setting? Keep us posted.

Tony

[tirwin]

Tony,

Trust me. I am trying to refrain from guesswork.

Two questions. First, is the AAV is the round thing on the right side of the engine with a vac line going into it? If so my vac line to the AAV is plugged and disconnected.

I've got a timing light with dwell meter. I'll have to refresh my memory on the procedure. What am I looking for?

Frankly I'm not sure I can trust what the mechanic said he did. I mean, he disconnected the pressure plate sensor and charged me to "fix" the problem so what else can I not trust?

[boyt911sc]

Originally Posted by tirwin

Tony,

Trust me. I am trying to refrain from guesswork.

Two questions. First, is the AAV is the round thing on the right side of the engine with a vac line going into it? If so my vac line to the AAV is plugged and disconnected.

I've got a timing light with dwell meter. I'll have to refresh my memory on the procedure. What am I looking for?

Frankly I'm not sure I can trust what the mechanic said he did. I mean, he disconnected the pressure plate sensor and charged me to "fix" the problem so what else can I not trust?

tirwin,

The AAV you are referring is the deceleration valve for late SC's. The AAV looks exactly a decel valve (for late SC's with lambda) but it does not have the nipple for the vacuum line. The saucer-like device with nipple/tube is the decel valve. It is a common practice by many to detach the vacuum line and plug the connections when they couldn't figure out the problem/s.

One thing I would advise you is to get familiar with the different CIS components and get familiar with their respective function/s with the CIS. How they work and symptoms they exhibit when they fail to work. All these CIS components could be checked and tested on the bench using simple tools. You could easily do it too.

Your mechanic could be a real honest and trustworthy individual. But if he's not familiar or well versed with CIS (Ketronic) which is an antiquated fuel injection system and fast becoming obsolete could be a reason. My approach to CIS troubleshooting is test and confirm.

There is a black test port connection located in the engine bay driverside close to cylinder #3 where you connect the dwell meter. Connect the meter and set it accordingly to get the right reading. Keep us posted.

Tony

[tirwin]

Tony,

I went back and looked. You said AAR and I somehow misread AAV. Sorry. I was tired when I was reading last night.

Just to be clear, the AAR is the thing colored red in this picture, right?

[boyt911sc]

Originally Posted by tirwin

Tony,

I went back and looked. You said AAR and I somehow misread AAV. Sorry. I was tired when I was reading last night.

Just to be clear, the AAR is the thing colored red in this picture, right?

tirwin,

Yes. That's the AAR in RED. BTW, the picture you attached is not for late SC's with lambda. So let's go back to square one. What problem/s the car is having now? Be clear and specific, I might be able to assist you. Just finished working on an '83SC this week and still fresh in my mind the things I did to overcome the CIS problem/s. Thanks.

Tony

[tirwin]

Symptom is surging idle on cold start initially between 800 and 1200 RPMs for 20-30 sec, then it idles high at around 1400 RPM for another 20-30 sec. Then it settles in at a nice idle of 900-950. With the pressure sensor disconnected after warmed up the idle was hunting a little, but that was before I ran the BG44K through it.

Today I can do a good test of a cold start after I reconnected the pressure sensor yesterday. I'll report back on what happens.

I am going to check the duty cycle to the FV as you suggested.

Also going to check the voltage reading at the O2 sensor connection after warmed up.

On the AAR I just used the picture I found from a Pelican search. I will read up on the AAR testing too.

Thanks for all the help. I really appreciate it.

-T

[tirwin]

Tony,

I went back and looked at my notes from May 2011 (has it really been that long? sheesh). At the time when I did the fuel pressure test with a cold engine here is what I observed. Electrical connection to the WUR initially disconnected. Fuel pump jumpered to run with engine off. Valve open between WUR and FD on test gauge. Pressure was 2.4 bar. After electrical connection to the WUR plugged back in, it took ~40 sec for the pressure to rise to 3.6 bar after plugging in the WUR.

This ~40 sec rise in pressure is very time co-incident with the time I see the rough idle go away on a normal cold start. Maybe it is related, maybe it is not. It is at least a data point.

[boyt911sc]

Originally Posted by tirwin

Tony,

I went back and looked at my notes from May 2011 (has it really been that long? sheesh). At the time when I did the fuel pressure test with a cold engine here is what I observed. Electrical connection to the WUR initially disconnected. Fuel pump jumpered to run with engine off. Valve open between WUR and FD on test gauge. Pressure was 2.4 bar. After electrical connection to the WUR plugged back in, it took ~40 sec for the pressure to rise to 3.6 bar after plugging in the WUR.

This ~40 sec rise in pressure is very time co-incident with the time I see the rough idle go away on a normal cold start. Maybe it is related, maybe it is not. It is at least a data point.

Tirwin,

Do you remember the ambient temperature when you did the test in May 2011? Were you able to start the cold engine with this 2.4 bar pressure? This was rather high for cold control fuel pressure in May. These fuel pressures are easy to check and verify.

It is the air/vacuum leak I'm worried. Not being able to locate sources of air leaks does not mean you don't have any. It could be some where undetected or in spots hard to access. This is probably the most critical test for CIS that DIY'ers often ignore.

Let's focus on feedback. Since you are doing the investigation and actual work, all related information and results could help us understand what's going on with your system. Maybe there is something obvious we have over-looked.

Could you check the heating resistance (Ohms) of the WUR? I bet you have a 10 Ohms reading (?). Keep us posted.

Tony

[tirwin]

Tony,

I will check the resistance on the WUR. I checked it way back when and I seem to remember it was fine but I don't remember the specific reading. Easy enough to test again. I will add that to the list and report back.

That May I did the test in the evening after dark. Average temp would've been 68 to low 70's. Note that it was PRIOR to when I took it to the shop for the smoke test.

I think it would be good to re-run all the fuel pressure tests on the car as it is right now. I might have to plan some time when I can sit down and go through it all again methodically.

There was a lot of rumor handed down with the car -- things that were thought to be but simply aren't true. PO believed the O2 sensor was disconnected. It is connected unless there is a break I don't see. It might not be working but that is different. I'm thinking about replacing with a wideband that has narrowband output and mounting an AFR gauge in the engine compartment.

I want to drop the engine and do several things like replacing all the vac lines and also replacing the injector O-rings. I also need to swap the engine pad and replace the engine and tranny mounts so it would be a good time to do all those things that are easier with the engine out.