83 911 SC engine quits when warm

[michealwhelan]

Tirwin,
At long last I received my pressure check gauge. From your write up (nice job, thanks) the WUR Ohms were 30 at 86 degrees. The system pressure was 70 psi at 74 degrees.
The Warm control pressure was 52 psi at 84 degrees (that looked high). The operating pressure was 45 psi at 84 degrees. Only ran it for about 5 minutes as I developed a leak. Waiting for a seal so I can get residual pressures. With the leak it dropped to 20 psi within 30 seconds so no 5, 10, 15 minute check. Cold start was always pretty quick (bump the key) but it did run rough for 20 or 30 seconds and then smoothed out. When I get the leak fixed would it be of benefit to leave the pressure gauge in place and let it idle until it starts it's dance and quits?
Any other thoughts?
Mike

[tirwin]

Micheal,

System pressure should be between 65-75 psi so that looks ok. The warm control pressure should be between 49-55 psi. I didn't see your cold control pressure. It should be around 1 bar or 14.5 psi.

[tirwin]

Micheal,

System pressure should be between 65-75 psi so that looks ok. The warm control pressure should be between 49-55 psi. That looks ok.

I didn't see your cold control pressure. It should be around 1 bar or 14.5 psi. If you are calling the operating pressure the cold control pressure, then you are very high at 45 psi or ~3 bar!

Can you redo the test to verify when you get your seal? When you open the valve after doing the system pressure test, you should see the pressure drop to about 1 bar. Once you plug in the electrical connection to the WUR, you should see the pressure rise slowly to 49-55 psi in 3-5 minutes. Focus on that before worrying too much about the residual pressures.

If your cold control pressure really is that high then we have found a problem. Next will be sorting out why it is so high.

[michealwhelan]

The cold pressure is around 10 psi. Hard to tell as I developed a small leak. The 45 psi was with the engine running but not warmed up as the leak prevented any more. I will re do the test next week end. Parts should be here Friday.
Thanks

[boyt911sc]

Micheal,

Now that you have your fuel pressure gauge kit, do a test when the engine is totally cold. Like after sitting overnight. Check the cold control fuel pressure versus time. For example:
start, 30 sec., 60 sec., 90 sec........etc. until the control pressure stabilize (4 mins. max.). and no need to run the engine. You could do this test by just running the FP. The objective of this test is to see the behavior of the cold control fuel pressure, deflection of the bi-metallic spring, and the over-all characteristic of the WUR. The slope of the chart for this data is not exactly the same as when the engine is running but the correlation is very close.

BTW, what's the number on your WUR? Do you have a USA or RoW car? Keep us posted.

Tony

[michealwhelan]

Reran pressure checks: 75 degrees +-
WRU 30 Ohms
System pressure 68 psi (was 70 at 85 degrees)
Cold control pressure 2.2 bar
Warm Control pressure :
1 min 2.8 bar
2 min 3.0 bar
3 min 3.4 bar
4 min 3.6 bar
5 min 3.6 bar
Residual pressure at 30 minutes 20 psi, 60 minutes 10 psi

I found it interesting on your comment about the CDI. I do remember it got wet a few months back. It took a while to dry things off but they may have not been properly dried. As the engine gets to temperature is when I get the problem. Is there a test for the CDI or do I need to just upgrade. Hate to do it if that is not the problem.
Any other thoughts?
Mike

[tirwin]

Micheal,

I'm traveling and it will be late tonight before I can look up the numbers on the cold control pressure but it looks high at 75 F. That would mean a leaner mixture at startup. I think you're warm control and residual pressures look good.

I'm thinking through what else would be going on after the engine warms up. Let me noodle that a bit.

On the CDI, I seem to remember reading about people having CDI failures after the box warms up. The problem with testing it is you'd have to bench test it under similar circumstances to recreate the problem. Might be easier to see if someone with a known good one would let you borrow it and try it out.

[boyt911sc]

Originally Posted by michealwhelan

Reran pressure checks: 75 degrees +-
WRU 30 Ohms
System pressure 68 psi (was 70 at 85 degrees)
Cold control pressure 2.2 bar
Warm Control pressure :
1 min 2.8 bar
2 min 3.0 bar
3 min 3.4 bar
4 min 3.6 bar
5 min 3.6 bar
Residual pressure at 30 minutes 20 psi, 60 minutes 10 psi

I found it interesting on your comment about the CDI. I do remember it got wet a few months back. It took a while to dry things off but they may have not been properly dried. As the engine gets to temperature is when I get the problem. Is there a test for the CDI or do I need to just upgrade. Hate to do it if that is not the problem.
Any other thoughts?
Mike

Mike,

If you have the technical ability to do the electronic evaluation for CDI or ECU, would be great. There are several members who do this for a living. But for most, we are limited in doing such tests. Due to this limitation, I rely on using known good unit and do the test (switching parts).





Tony

[tirwin]

Micheal,

Check out this thread... It does sound similar to your problem.

What could have caused my 78 SC to stall on the highway?

In particular check out the post by ischmitz.

What type of CDI do you have? The two most likely are Bosch and Permatune.

[michealwhelan]

Checked the article, you are right it does sound similar. Spent some time trying to find one to "borrow" with no luck. During the search my problem modified to starting and running good. Went past the usual 21 minutes. I decided to drive it to work. First few minutes were fine then it lost power, started to backfire and cough then smoothed out. Repeated the process all the way to the local parts store. Out of frustration I picked up a MSD with coil and have it partially installed now. So far the install is easy spending more time cleaning up wire runs and looms than necessary. On a business trip right now so can't finish it until Monday or Tuesday. That is when I find out if I did a stupid thing or the little CDI was flaking out all along. Is there a plug that works best with the MSD, and how do I tell if I have solid core plug wires or not? I will need to get these ordered from Pelican soon so I can drive it before the snow falls.

[SchnellSchweitz]

Typically, the OEM "Beru" wires were sort of gray color with a fabric type jacket. Something like this: http://www.pelicanparts.com/catalog/images/Connect-Images/108533613-M47.jpg

Most of the solid core wires I'm familiar with are covered with a red rubber-like jacket, but I'm sure there are exceptions. Magnecore is the most popularly used.

Pelican Parts - Product Information: PEL-MAGN65-83

Good additional reading: Resistorless rotor

[michealwhelan]

Thanks, mine are dark grey with stainless steel grounded shielding. Would hate to loose the look and they are not that old.

[SchnellSchweitz]

Correction... the "fabric type jacket" I speak of above is actually the grounded stainless steel jacket you speak of.

[michealwhelan]

Ok at long last all parts have arrived. The MSD install went well and was straight forward with the exception of one point I confused myself on. I used the white wire from the MSD and connected it. However I do not think that is correct. Doesn't the 83 3.0 have magnetic pickup? If so, I am not sure where to connect up the magnetic pickup harness from the MSD to. Any help? Thanks.

[SchnellSchweitz]

"the white MSD wire is connected to the main green wire in the connector. This wire should come from the distributor and is connected to the magnetic pickup or points."


Excellent read: Pelican Technical Article: Installing an MSD Ignition Unit - 911 (1965-83) - 930 Turbo (1975-83)

[michealwhelan]

Thanks, I did get it right, just second guessing myself. Been a lot of years since I had time to work on engines. Why I am at it I am replacing the plugs, rotor, cap, (wires look good and they only have a few miles on them). Anyone know if my old Snap On timing light with work with MSD or maybe my Equus 5568?? I never thought about difference is signal when I decided to do this little project.

[SchnellSchweitz]

Your old Snap-On analog light is the ticket. Save the fancy Equus 5568 for your modern cars.

[michealwhelan]

Sorry for the delay, been traveling for 3 weeks. Engine temp was in the normal range. I did some reading on the flaky CDI idea. I am experiencing many of the same issues. So with that under my belt I bit the bullet and started to install a MSI 6 AL. All went well following the combination of instructions from the write up here and the MSD instruction set. One issue I now have is I believe my distributor is magnetic pick up (no points). MSD says to use the purple and green for magnetic and the white for points. The tech write up says to connect the white from the MSD to the green from the harness. I did that but no work. Any idea which is correct? The red led never even flashes. Ground tested and solid, large red to full time power, small red to keyed power, grey to tach all test properly. New plugs set at 1.34, new battery, new cap and rotor. I feel like I have all the parts just the wrong combination in the final wiring.
System test: Key on no LED flash. Turn over ignition, no LED flash no spark, didn't do for long as fuel injection was pressuring the gas to the fuel system. Tested all wires for proper power at proper time. Not sure where to go next.

[SchnellSchweitz]

Try this if the white wire doesn't work:

The dizzy's green wire is actually two wires. Confusing.. yes... I know.

Great read: 930 distributor signal wire

[boyt911sc]

Micheal,

Could you post the identification # of your WUR? What's the value of the heating
resistance (Ohms)? Keep us posted. Thanks.

Tony