Occasional CIS problem
 

Car is an 81 911SC, Stock motor except for SSI's and MSD ignition.

I drove it to work this morning, about 25 minutes. After work, about 20 minutes into the drive it started running poorly. I have an AEM air/fuel gauge, as I passed 2000 RPMs the gauge would go to 16 and onto the peg. Upshift and it was better. Idle and low RPM's it actually ran pretty well and the mixture was around 14.7.

I reached my destination after 5 minutes or so of this and parked for at least a half hour.
When I restarted it immediately had the same problem, for about 5 minutes. At some point the problem went away (I was nursing the car on back roads so it was subtle).
Once I realized it was running properly again I tried to make it misbehave - large throttle openings at low RPM, running up the revs - it was mostly perfect "seat of the pants". Occasionally the AFG needle was bouncing around.

This car did this at least twice last fall. I unplugged the O2 sensor and it didn;t do it again until today.

Any ideas? I can't imagine what part of CIS could fail lean, then come back.

So you have SSIs and the CIS O2 sensor? Where is the O2 sensor bung located?

Obviously you’re way lean if your AFR is 16. The car is trying to tell you something. It is leaning out. It probably got to the point where the O2 can’t correct it. You disconnected the O2 so it went to fixed 50% duty cycle. Bandaid. It will get worse and next you’ll have a lean backfire.

First thought is you have unmetered air getting in somewhere. If you let the car warm up and idle in the driveway, take the oil filler cap off. If the rpms don’t change you have a significant vac leak. You’ll need to track it down. Smoke test or carb cleaner/unlit propane around the usual suspects method.

O2 bung is just after the collector on the left manifold. There is a significant RPM drop when the oil cap is removed.

I have done a ton of searching for unmetered air - Propane test and smoke test. I found and fixed some fairly minor leaks last year, replaced the warm up regulator with a rebuild one by Tony and replaced the injectors. All pressures are in spec.

No question - it's trying to tell me something. I thought the O2 controller under the seat was bad.

If it happened while I had the car home I think I could find it. by the time I got home last night it was running sweet.

What could allow unmetered air that gets bad, then gets better? And if it's unmetered air, why is it worse at higher RPM's and load?

I'm leaning toward fuel delivery but I can't imagine what would come and go

Thanks

I'm not an expert on CIS, but I believe at higher RPMs your vacuum is greater, so if there is a small leak, you'll get more leakage and things will get worse.
Also, there are a bunch of components that change size/behavior at different temperatures. So those could explain why the system changes behavior over time.

My experience with vacuum leaks tends to be that they are the most obvious at idle (when vacuum is high and air flow is low) and smooth out at higher RPMs.

Tirwin's comment has me wondering if it could be the frequency valve itself. I'm not coming up with anything else electrical that could affect mixture at higher RPMs.

I had something similar (ish) with my 80 SC five years ago now.

Popped and sputtered at around 3k, then went away after a few seconds. Got to work and left it, came back after work and thing would barely start. Turned out to be a bad lambda ECU - one of the solder joints was completely burnt.

Did you check whether you get a buzz/vibration from your frequency valve with the car off, key in the on position, and the plug at the AFM unplugged?

Could be O2 relay as well...

Lots of diagnosis threads for all of the components above in the Pelican archives.

It's been a while since I fooled with troubleshooting the Lamba system - I will get after that this weekend.

It just seems really weird that the problem comes and goes.

How old is the O2 sensor? Is it possibly time for a new one?

Just to make sure I understand correctly... do you have the stock narrowband AND a wideband O2 for the AFR gauge? Or do you have a wideband with a narrowband output to the CIS Lambda unit? My experience is that the K-Jet box doesn't respond well to a non-stock narrowband output. But disconnecting would eliminate that as a potential problem.

You can check the duty cycle of the FV with an oscilloscope or some meters. With the meter approach, you have to test how the meter to see how it represents the duty cycle. 40% ON and 60% OFF are the same thing -- you need to know which is which though.

If you have poor/weak spark, you would have unburned fuel in the exhaust which would read rich.

Lean condition would suggest poor fuel delivery.

Had another thought.

A quick check would be to test the O2 sensor relay under the passenger seat. Not a bad idea to have a spare in the glove box anyway. You can test the relay to see if it trips. That is what controls the FV duty cycle. Maybe the old relay is failing intermittently.

^ Good call. Get the low hanging fruit first. Interior lights turn on?

The O2 sensor was brand new when I installed the AEM - so a couple thousand miles. AEM has an output to emulate the old single wire O2 sensor. It wouldn't be much trouble to swap back to the original sensor, but then I wouldn't see the mixture on the AEM.

I always used a dwell meter to read duty cycle.

When it's misbehaving it always goes lean. I'm pretty confident that everything on the ignition side is solid.

I had forgotten the o2 sensor relay - I do have a spare in the glove box.

I finally got around to looking at this (busy weekend).
Dead silent when I turn the key on without starting.

I hooked the o2 sensor back up and took it for a 1/2 hour drive - it ran beautifully. Steady state mixtures around 14.3-14.8. excursions during accelration/ decel.

After I got it home I checked frequency. About 43% at idle, 50% with the o2 disconnected.

Well I'm back - but with the opposite problem.

Now the car tends to go full rich - like 10.0 - as rich as the AEM will indicate. When it first happened it came and went. I finally had it happen close to home and started troubleshooting. All indications are that the frequency valve is operating properly (I don't have an oscilloscope). I cleaned the throttle and distributor plates and thought it was fixed - but it came back after a couple days. Now it's not so rich (Like 11.1 -11.5 at idle) but very sluggish and backfiring. once it gets over about 2200 RPMs it comes on like gangbusters and the AFR comes up.

I checked ignition timing and it's dead on, smooth advance, no sign of spark misfire on any cylinders.

Could I be having trouble with the fuel distributor? Possibly try injector cleaner? I don't have a good source of ethanol free gas, but it almost always gets Shell premium.

Thanks guys

cis problem
 

I had a similar problem with my 1982 SC a few months back where it would intermittently go full rich to around 10.0 AFR. After doing some testing it turned out to be a problem with the WUR allowing the warm control pressure to drop drastically resulting in such a rich mixture that the O2 sensor system could not compensate.
I had the WUR rebuilt and the problem was solved.
I will also mention that at one point I had a problem where I was not seeing any enrichment on my AEM air fuel ratio gauge when the throttle went past the 1/3 enrichment switch which directs the system to go to "open loop", I have the mixture set so it achieves 12.7 -13.1 at full throttle depending upon ambient air temperature. It was somewhat difficult to determine the cause due to the fact that the 1/3 switch checked out OK etc. It turned out that the WUR "push valve" return line in the fuel distributor was clogged causing the control pressure to be so high that the system was unable to achieve the mixture enrichment as it should when in "open loop" past 1/3 throttle. I forced some air through the WUR return line to the Fuel distributor which cleared the blockage.
Just as info, I have an addition bung installed in my cat bypass for the for the AEM wide band O2 sensor. I have found that being able to monitor the air fuel ratio has been invaluable in seeing and solving any cis issues.

Dave

I will check the WUR tonight. It was rebuilt by Tony about 2 years ago so I have been assuming it's good.

Thanks!

Drop the WUR to me........
 

Michael,

I will be home the next three (3) weeks finishing my WUR commitments before leaving for Europe late July to early August. The earlier I get your WUR the better and you could have it back after 24 hours. Or wait after my return. Thanks.

Tony

HI Tony,

Thanks for that. I will check it out tonight and if it has any issues I will get it down to you.

Mike

It will be WURth it!

About time to correct this terminology.........
 

Tim,

Why do people still call this relay as OXS relay? This relay controls the operation of the FV (frequency valve) and should be referred as FV relay. This is like calling the FP relay as Control fuel pressure relay or the like. Just my two-cents.

Tony

I finally got around to the pressure test.

System and control pressures are both 4.6 Bar - No change with time.

They go to 2.0 Bar with pump off and very slow fall-off - like 1.6 Bar after 1/2 hour.

The WUR resistance measured 40 Ohm before starting (88°F ambient).

So - Fuel pressure regulator?

Thanks!

Sound like maybe someone messed with the WUR and opened it up. And when closing the WUR back up didn’t get the pin that controls pressure properly seated in the diaphragm.

Bill

Read dhanl82's post, check the return.

If the return's OK and the problem turns out to be the WUR, please report back the findings for future reference. Too many of these CIS threads end up with no resolution or if there was a resolution, it is hidden in private exchanges never to see light of day.

Thanks

9


Mike,

For control pressure to equalize the system pressure you have a flow restriction at or after the WUR. Closing the valve for the CIS pressure gauge kit mimics a clogged WUR or the return line immediately after the WUR. If the flow restriction occurs before the gas tank, the pressure reading would be greater than the system pressure.

A good way to test this problem is opening or breaking the fitting of the return line under pressure. But I am afraid you don’t have the correct set up to do this test in situ. Drop the WUR and I will do the test while you wait.

BTW, I will be leaving on July 24 for London & Paris with the whole family including my grandchildren for 3 weeks. Give me a call. PM sent.

Tony

So - no flow through the return line from the WUR - either compressed air or vacuum.

I will try the return line from the fuel distributor to the tank.

I could be considered family, kind of, in a Porsche way. I can babysit.

Just saying.....

My passport is current. :D

I don't eat much.

FWIW, I have just one factoid to pass on. A dude here in Atlanta many years ago on hot days would develop horrid running of his Lambda SC for short passages.

Turned out it was the rear wall 12 pin connector that was a little skunky as to connection to the frequency valve. The symptoms were the same as a dead O2 relay or pulling the Oxy fuse. Only in killer ambient heat did it surface when the connection was lost.

Here is a vid I made of pulling the O2 relay which would replicate the symptoms.

<iframe width="560" height="315" src="https://www.youtube.com/embed/5tdpCYyvqSc" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

Dear Bob,

But you take lot of seat space. That means we have to rent another mini-van. And I could not sleep in a bedroom with somebody snoring. Getting another room for you is not an option. I noticed lately that you have been in good behavior. Take care.

Tony

Well if Bob’s out of the running ... I’ll assume I’ve no shot. Tony, fabulous you can go to London and Paris and take the grandkids too. Have the best of trips.

The restriction is somewhere in the distributor - the return line line from the firewall to the tank is open.

cis problem
 

As I mentioned earlier, I had the same problem. I will list the steps that I took to isolate and solve it.

1. I disconnected wur return line and connected another line from the wur return port to a container for the fuel - ran fuel pump and had correct control pressure, this ruled out a bad wur.

2. I then disconnected the wur return line at the fuel dist. attached a rubber hose at the wur end and blew through the hose - this determined that there was no blockage between wur and fuel dist.

3. Keeping in mind that I would not be able to blow through the wur return line and through the fuel dist. to the tank due to the "push valve" being closed as it is designed to be when fuel pump is off, I removed the pressure valve from the distributor. I then attempted to blow air through the return line and fuel dist. by placing my finger over the fuel dist. open pressure regulator orifice where I had removed the pressure regulator assembly from. At first I was unable to blow through it but suddenly something broke loose and the air went through the wur return line through the fuel dist. and I could heat it bubbling in the fuel tank.

4. I put the fuel pressure regulator assembly back into the fuel dist. reconnected all line, ran the fuel pump and saw that system and control pressure correct - problem solved.

5. It appears that the return blockage was either at the orifice leading into the fuel dist. or the one exiting into the wur return line after the "push valve'

I hope this may be of some help. Please contact me if you have questions, as I may not have done a good job of describing my approach to problem.

Dave

Hi guys,

Tony is testing my WUR today.

After sleeping on it I understand Dave's approach. Assuming that we rule out the WUR, I will pull the pressure regulator and try to clear the lines.

Thanks Guys!

Mike

Fuel flow test.......
 

Mike,

Since you have already removed the WUR from the car, inspecting the FD is a prudent course of action. I sent you a message last night about the PPV (primary pressure valve) inside the FD.

I will lend you some fittings and fuel lines to test fuel flow in situ. Like I mentioned earlier, the restriction based from your information is likely at or after the WUR. By the time you read this post, you would probably out of the house on your way to work.

Let me test the WUR first and I doubt it is the culprit. But we have to test and confirm before we could eliminate it as a culprit. Then locate and identify the location of the restriction point somewhere in your system. Point of interest is the cavity where the PPV is located. See you later today.

Tony

cis issues
 

Mike,
I failed to mention something.
If you determine that all lines and orifices in and out of the fuel dist. are clear then it may be in the PPR assembly itself. There are, in the wide neck part, of the PPR assembly, 2 very tiny entry and exit orifices where the return fuel from the wur enters into the Push valve" chamber through one, goes past the push valve tiny green "O" and then exits into the PPR chamber and then out through the fuel dist. return line to tank when the fuel pump is running and the push valve is open.
If either of the orifices is clogged or if the interior push valve chamber is obstructed, there will be no return of fuel from wur allowed and thus the very high control pressure.

I disassembled my old PPR to see how the push valved worked - very interesting! There is a tiny "C" clip holding the assembly together, once removed, the shaft pulls out to reveal the push valve "O" ring etc.

I would be remiss if I did not mention that my back and forth communications with Tony were invaluable while I was attempting to solve this problem - he taught me a ton about the cis system during this process - thanks again Tony!

Dave

Dave,

I know Tony pretty well - he has been helping me for years and he is nearby.

Thanks for the clarification on the PPR.

I haven't been giving this the attention I should - My son's 944 is torn apart to get a clutch and torque tube, My daily driver dumped it's coolant on Tuesday, The other kids are home for the holiday, the house water heater died yesterday - I have just been crazy busy.

The car was running sweet after the WUR from Tony and a careful tune using the AFR Meter. The transient way this problem came on has been frustrating, I'm thinking I have a chance to get back to running happily again.

Thanks Guys!

I got to watch Tony do the magic today and the WUR is condemned.

I will report back after it is replaced.

Mike

The car is back together and running sweet.

Tony found that the WUR was plugged up. I left it with him. I think it took him a bit longer than usual to calibrate and there was a snafu with USPS, but I got it back today.

While the WUR was gone I changed the fuel filter and pulled and cleaned the pressure regulator. The filter had a bunch of fine, translucent particles in it - not plugged up, but floating in the fuel I recovered. The filter paper itself was clean and had no visible tears. It was a Mahle filter, less than a year and 1000 miles old.

Before I put the WUR back in I flushed the fuel. It came out very red at first - maybe from having the line open for a week? No particles though. Put everything back together, pressures looked good, No start.

I pulled the injectors and checked flow. Everything looked good - fuel was even a better color.


http://forums.pelicanparts.com/uploa...1563586058.jpg

I started checking wiring - apparently I had pulled the power lead off my MSD unit while I did the filter. Plugged that back in.

Started it up and it ran rough, as you would expect badly flooded. It did smooth out. I let it sit an hour then started it and took it for a drive.

It's running very well. AFR looks good on my AEM gauge. Idle is a bit high fully warmed up - I will adjust tuning the next chance I get.

Thanks Tony!

WUR-090 heater resistance value........
 

Mike,

Could I ask you a favor? Please post the heater resistance values (Ohms) that you obtained from your recent test. Thanks.

Tony

84° 25.8 Ohm

88° 25.7 Ohm

92° 25.4 Ohm

My problem is back.

I attempted to take the car to work this morning. Started right up but went crazy rich.

I thought it might clear up as it warmed up. It got worse.

I just got home and hooked up the pressure gauge.

4-1/2 Bar closed.
1/2 Bar open.
1-1/2 bar residual pressure.

Is it possible that the WUR failed in a couple days?

1/2 bar open?

Not sure what you mean. 1/2 bar is after the car has been driven? Is that engine running? Can you explain how you tested?