80 SC - Super Rich on Cold Start

[LWJ]

All,
I have an 80 SC. It has been a champ for many years and until last Winter I effective daily drove it. I put it up in December for some maintenance issues that stretched into early Summer. Fired it up, and drove one and 1/2 gas tanks through it.

Here is the issue. On a hot day, the car started surging on the freeway. Bad. I kept on driving and am pretty certain it was fuel related. The surges calmed down and I assumed my car had consumed some chunks of old gas varnish or similar through the fuel system. Drove home uneventfully.

I went to start it the next day I can barely start it and if I hold my hand over the intake retricting about 2/3 airflow get it to warm up to where it runs good enough to drive. When warm, it does not drive perfect.

I checked for vacuum leaks with propane, carb cleaner, and the shop vac trick. Nothing found. There is a BIG differential on my cold A/F mix. I replaced the fuel filter, checked the thermo-time switch and it is fine.

Here is my question. Before I go nuclear on my CIS and check pressures, test everything, etc(it is October, and I want to drive my damn car in 2014!) does anyone have a quick idea about what caused my cold start to be so very very rich?

I expect I will do a full diagnostic this Winter but I would really like to drive the car in the next 5 weeks before it gets nasty. As you can see, I am a slow mechanic.

Thank you all in advance!
Larry

[Paulporsche]

You may have to check those pressures sooner than you would like! If it turns out that you have no air leaks and you are indeed running rich, your WUR may be out of spec. This seems to happen gradually until suddenly things don't seem right. Also, sometimes the bimetal strip within fails and the control pressure doesn't vary with time and heat.

Check your dome light. Is it working? The O2 sensor is on the same circuit and it could have failed.

As a rule of thumb you should always make sure your ignition system is operating correctly before looking into the fuel system.

[LWJ]

Paul,
Agreed as to the timing. Dome light is fine. This is clearly a fuel issue. Interesting about the WUR failure. Didn't think of that.

Thanks,
Larry

[boyt911sc]

Larry,

Do you have WUR-072 on your engine? Is your car an '80 SC USA model? Check and measure the resistance (Ohms) of the WUR with the engine cold. Knowing the control fuel pressure profile would be good for troubleshooting. Keep us posted.

Tony

[john walker's workshop]

do the interior lights still work? pull the domelight fuse when it's running and see if the idle drops off and runs rough.

[LWJ]

Thanks. Will do. Interior lights do work. I will check pressure and ohms.

Thanks all!

Larry

[LWJ]

Update:

1) I am occasionally a moron. The car is running LEAN.
2) WUR reads 13 - 15 on the x200 Ohm scale - I assume this is approximately 2800 Ohms. The ohms moved from 15 to 13 per my notes. It was a while ago. I do recall that the resistance changed over time as I measured it.
3) I typically run with the decel valve disconnected. I tried with it connected and without. Not a significant change.
4) Fuel flow is 1 liter in 15 seconds. (measured pre-replacement on the Old Fuel Pump)
5) Cold control pressue is 54 (low - I know) WUR 072 (measured prior to new fuel pump #9) So this measurement is not currently valid.
6) Drained and inspected fuel. It seems ok. May have had some water separation in it. Blew out the line with gentle pressue. Left the line open for a long while to dry everything out.
7) New fuel filter installed earlier.
8) Checked screen on gas tank - SQUEAKY clean! (this had been on my to-do list for about 5 years. Funny.)
9) Fuel pump runs at 7.9 amps. This signals end of life. Replaced with a new Bosch + check valve
10) Car is better with New Fuel Pump. I think the fuel pump was certainly contributing to the issue. But not the central issue. It has always started with a lusty note but then peters out and dies. With the new fuel pump, it ran after several start / die sequences. However, if I gave it any gas, it would pop the popoff valve in a lean backfire.

What I didn't check - return line for a clog. I don't think that would give me a lean situation however.

Reading my Bentley manual, I believe the WUR or the Fuel Distributor are the only culprits left. I didn't get the system pressure at rest as my fittings were a touch leaky. Another thought could be if I did have water separation, could a nasty rusty injector or two cause this? I don't think it would start so even and smooth if it were a bad injector.

Questions: 1) Opinions? 2) Where to obtain CIS fittings for a Snap On Fuel Pressure test kit?

Thank you,
Larry

PS - thank you for the responses so far. Boyt911SC and John Walker are some big guns in the 911 world. I appreciate it!

[timmy2]

I have a CIS fuel pressure tester and a Gunson CO meter I'm not using if you want to borrow them.
I'm just down the road in Salem.
Send me a PM if interested.

[LWJ]

Timmy2
Thank you! Very generous. I may take you up on this.
Larry

[LWJ]

Timmy2
Thank you! Very generous. I may take you up on this.
Larry

[wolds]

So you are reading between 13 and 15 ohms not 2800 ohms as stated. What is spec for your WUR?

Originally Posted by LWJ

Update:

1) I am occasionally a moron. The car is running LEAN.
2) WUR reads 13 - 15 on the x200 Ohm scale - I assume this is approximately 2800 Ohms. The ohms moved from 15 to 13 per my notes. It was a while ago. I do recall that the resistance changed over time as I measured it.
3) I typically run with the decel valve disconnected. I tried with it connected and without. Not a significant change.
4) Fuel flow is 1 liter in 15 seconds. (measured pre-replacement on the Old Fuel Pump)
5) Cold control pressue is 54 (low - I know) WUR 072 (measured prior to new fuel pump #9) So this measurement is not currently valid.
6) Drained and inspected fuel. It seems ok. May have had some water separation in it. Blew out the line with gentle pressue. Left the line open for a long while to dry everything out.
7) New fuel filter installed earlier.
8) Checked screen on gas tank - SQUEAKY clean! (this had been on my to-do list for about 5 years. Funny.)
9) Fuel pump runs at 7.9 amps. This signals end of life. Replaced with a new Bosch + check valve
10) Car is better with New Fuel Pump. I think the fuel pump was certainly contributing to the issue. But not the central issue. It has always started with a lusty note but then peters out and dies. With the new fuel pump, it ran after several start / die sequences. However, if I gave it any gas, it would pop the popoff valve in a lean backfire.

What I didn't check - return line for a clog. I don't think that would give me a lean situation however.

Reading my Bentley manual, I believe the WUR or the Fuel Distributor are the only culprits left. I didn't get the system pressure at rest as my fittings were a touch leaky. Another thought could be if I did have water separation, could a nasty rusty injector or two cause this? I don't think it would start so even and smooth if it were a bad injector.

Questions: 1) Opinions? 2) Where to obtain CIS fittings for a Snap On Fuel Pressure test kit?

Thank you,
Larry

PS - thank you for the responses so far. Boyt911SC and John Walker are some big guns in the 911 world. I appreciate it!

[kodioneill]

54 psi ccp is high not low. This will cause a lean condition. What's the system pressure? If you still have 54psi ccp after the fuel pump replacement you may have a clogged screen in the wur. I think the system pressure is 54-60 psi . cold pressure very s depending on the temperature say 40 deg f should be around 1.5-2.0 bar.
Do a search for your specs I'm sure you'll find them.

[boyt911sc]

Larry,

My offer to you for a free WUR & FD tests is still available. I have 6 weeks left before I take off for a two-month travel abroad. So decide now before it is too late to do the tests. I won't be entertaining any testing by mid-January due to the coming trip. PM for details.

Tony

[timmy2]

Originally Posted by LWJ

Timmy2
Thank you! Very generous. I may take you up on this.
Larry

I am off work for a couple of weeks over the holidays. I could probably find a day after Christmas to get together and do some proper testing on your car.
My garage or yours, if it is a nice rain free day I will run up to Lake O with my P-car and the test equipment.
I also have a set or two of good injectors if that turns out to be a cause.

[LWJ]

Thanks gents! WUR sent to Tony for test / repair. I appreciate the offers greatly.

Larry

[zl0ca]

I'm sure you already considered the basic but my car had a bad O2 sensor and would run very rich at cold. A trip to the local auto store($17) and 20 minutes of labor and she was humming and no smoke.

[boyt911sc]

Larry,

I picked up the WUR-072 from the Post Office this morning and went back home to test it.

At 60°F/16°C the control fuel pressures should be between 1.8 - 2.3 bar ( 26 - 33 psi.). See control fuel pressure chart for -072. Measured control pressure @ 60°F = 20 psi. This is low at 60°F and after heating for 4 mins., there was no change in the pressure reading. The bi-metallic spring in your WUR is not deflecting sufficiently to increase the control fuel pressure. Your engine would have a very erratic running condition.

One thing I noticed with this WUR-072 is that it has no vent tube/post on top of the regulator. The ones I have with 'Germany 086' on the body have all vent tube on them. Yours has 'France 916' and no vent on it.

Tony

[Paulporsche]

Tony has confirmed what I suspected earlier--that your bimetal strip has failed.
This happened to my engine several years ago. It meant that I was able to set the engine up to run well but start poorly, or vice versa. I had the bimetal strip replaced with a good one and reset the control pressures to get things back in shape.

BTW Tony was an immense help to me then in getting my problem solved!