83 911 SC engine quits when warm

[timmy2]

I just wrote up the instructions for installing an MSD street fire CDI and it is identical to the 6al system.
Here:
MSD street fire in 78sc

[michealwhelan]

30 Ohms, I will have to get the WUR number later this morning. MSD thinks this may be a bad unit. The red LED never lights under any test condition. I will be exchanging it in the morning. Thanks.

[boyt911sc]

Originally Posted by michealwhelan

30 Ohms, I will have to get the WUR number later this morning. MSD thinks this may be a bad unit. The red LED never lights under any test condition. I will be exchanging it in the morning. Thanks.

Micheal,

I know you got 30 Ohms in your earlier test and that's the reason I wanted to know the numbers on the WUR. It should not read that high if you have the right WUR!!!!! unless you have RoW engine. Do you have 0-438-140-090 or -089? Keep us posted.

Tony

[michealwhelan]

Tony,
Took some time to get the WRU out so I could see the number. Mine is 089 or better stated 0 438 140 089. The Ohm is 30.04
New MSD box did the trick as far as producing spark. Have not been able to get engine to fire. I know the coil MSD Blaster 2 is kicking out juice (be careful what you touch when doing the white wire test) but did not go any further as the fuel was flowing to the engine and did not want to pump it full. Let me know about the WRU. Not sure if I can tear it down and clean or if there is a rebuild kit. Maybe It just needs replacement??
Mike

[Jim Williams]

Originally Posted by michealwhelan

Tony,
Took some time to get the WRU out so I could see the number. Mine is 089 or better stated 0 438 140 089. The Ohm is 30.04
New MSD box did the trick as far as producing spark. Have not been able to get engine to fire. I know the coil MSD Blaster 2 is kicking out juice (be careful what you touch when doing the white wire test) but did not go any further as the fuel was flowing to the engine and did not want to pump it full. Let me know about the WRU. Not sure if I can tear it down and clean or if there is a rebuild kit. Maybe It just needs replacement??
Mike

Mike,

Sorry if I missed it, but is your '83 a US or a ROW model? The CIS on these cars is quite different. US models with Lambda use a 090 WUR, the Row non-Lambda models use a 089 WUR. You can't mix and match.

Check here:
http://www.jimsbasementworkshop.com/CIS/pages/test_pressures.html#wurspecs

[boyt911sc]

Originally Posted by michealwhelan

Tony,
Took some time to get the WRU out so I could see the number. Mine is 089 or better stated 0 438 140 089. The Ohm is 30.04
New MSD box did the trick as far as producing spark. Have not been able to get engine to fire. I know the coil MSD Blaster 2 is kicking out juice (be careful what you touch when doing the white wire test) but did not go any further as the fuel was flowing to the engine and did not want to pump it full. Let me know about the WRU. Not sure if I can tear it down and clean or if there is a rebuild kit. Maybe It just needs replacement??
Mike

Mike,

So you have an '83 SC RoW engine/car with no lambda system? If you do, you have the correct WUR installed. Thanks.

Tony

[timmy2]

Mike, the engine will never fire if you are using the white wire for points on your magnetic trigger distributor...
Please read the wiring instructions I posted in the link in my earlier post....

[michealwhelan]

Originally Posted by timmy2

Mike, the engine will never fire if you are using the white wire for points on your magnetic trigger distributor...
Please read the wiring instructions I posted in the link in my earlier post....

I must have missed that post. Is that your on the 78 SC? I will put it to use. Thanks

[michealwhelan]

Originally Posted by boyt911sc

Mike,

So you have an '83 SC RoW engine/car with no lambda system? If you do, you have the correct WUR installed. Thanks.

Tony

Correct no lambda. I didn't know I had the RoW for sure. Are my Ohms to high on this WUR, if so what are the options? Thanks

[timmy2]

Use these instructions... they are the same as I posted earlier in the same thread with the pickup wires oriented correctly.

MSD street fire in 78sc

[boyt911sc]

Originally Posted by michealwhelan

Correct no lambda. I didn't know I had the RoW for sure. Are my Ohms to high on this WUR, if so what are the options? Thanks

Mike,

The heating resistance for WUR-089 is about 30-31 Ohms. Check your fuel pressures too.

Tony

[michealwhelan]

Originally Posted by boyt911sc

Mike,

The heating resistance for WUR-089 is about 30-31 Ohms. Check your fuel pressures too.

Tony

Thanks, fuel pressures are all in spec. Ran those two weeks ago. I will reinstall the WUR and follow the wiring setup you posted. Let you know where I end up. Thanks,
Mike

[michealwhelan]

All,
Thanks for all the help on diagnostics. I reworked the wiring last night. Hit the starter and it fired right up. Ran rough for a bit with a lot of smoke from the fuel from previous attempts. It then cleared and began to smooth out. After warm up I had some hesitation on blipping the throttle. I guess resetting the timing is next. Any thoughts on what new settings should be? New plugs gapped at .054 as this was a recommended starting point. Not sure what the advance should be or if there should be one. Again thanks for the help it is good to have her running.

[boyt911sc]

Originally Posted by michealwhelan

Thanks, fuel pressures are all in spec. Ran those two weeks ago. I will reinstall the WUR and follow the wiring setup you posted. Let you know where I end up. Thanks,
Mike

Mike,

Good job!!!!! Next time you were asked for technical information like fuel pressures, it would be more informative if you post us numbers instead of an adjective. They maybe all within spec but numbers are more specific. Check the WUR's heating characteristics by recording the cold control pressure versus time until it stabilizes to WCP. This would be your baseline data and save this data. Set your ignition timing using an inductive timing light and how sure are you that you don't have unmetered air going into the system? Keep us posted.

Tony

[timmy2]

Good to know you got it running. Any changes to the wiring instructions I directed you to?

[michealwhelan]

Your instructions were right on. The only change was to the coil. The old wires were pretty scruffy so I used the MSD supplied and ran them direct. When winter comes I will look into pulling the harness apart and putting new coil wires from the connector to the coil. I spent today working on timing and buttoning up the project. I was at the factory spec (5 deg) and had no real idea as how far to advance it. I used the old tried and sometimes true method of ear timing, drive it, and do it again. After the 4th run I think I am pretty close so let it cool over night. Hot start is great, warm start is great but will have to let it cool over night for cold start. Should be a good test as it is supposed to be in the 40's tonight. Thanks for the help. I will get the combination of items written up and posted for and 83 just in case someone else has the same issues in the future. Now to learn more than I knew about timing and how far I can advance it to get maximum performance.
Mike

[timmy2]

Mike,
I know someone that can remove all scruffiness from your harness!

Don't advance it too much, by the time you hear it pinging, it's too late!

[SchnellSchweitz]

For future reference:

I wish I would have found this for you earlier...

1980 Porsche 911SC distributor connection - MSD Tech Support Forums

The Green wire...

[michealwhelan]

Originally Posted by boyt911sc

Mike,

Good job!!!!! Next time you were asked for technical information like fuel pressures, it would be more informative if you post us numbers instead of an adjective. They maybe all within spec but numbers are more specific. Check the WUR's heating characteristics by recording the cold control pressure versus time until it stabilizes to WCP. This would be your baseline data and save this data. Set your ignition timing using an inductive timing light and how sure are you that you don't have unmetered air going into the system? Keep us posted.

Tony

Tony,
The numbers are posted earlier in the thread. They were in a series of posts between trwin and I. My project is now collecting all the information and consolidating it into a single post for all to consume. Hope to get time to do that this week.
Mike

[michealwhelan]

After many weeks of assistance and advice I would like to thank all that pitched in. The following are a combination of what was done and the results from the tests, checks, and even a few moments of cussing due to my lack of understanding all that I should. Again thanks to all. It now runs like a 911 was intended.
OPENING Statement
I have a 3.0 with 155,000. Good shape but has started a bad habit. Cold it starts quick but sputters until warm. When warm it idles with occasional misfire. After 30 minutes of driving or idling it begins to sputter, backfire and quits. Starts up with little issue and then runs rough for a few minutes. Then runs fine until the next bout with sputter, loose power, backfire, and quits. Fuel full, oil and temp in normal ranges, checked as many vacuum lines (as I can find). Any ideas as where to start my search?

ADVICE 1: Check for vacuum leaks. Results found no leaks even replaced a few lines that were beginning to show signs of aging. Pop off valve was cleaned and lubed and sealed well. Pulled oil filler cap received dramatic change in engine running. Put it back on and returned to normal. Used carb cleaner to spray around lines and connections with no change to engine idle. I might add it did require the repainting of a few engine parts. So be careful with that stuff around painted surfaces.
ADVICE 2: Check fuel filter, O2 sensor, WUR bimetallic reading (83 RoW uses Type 89 spec at 30-32 Ohms not Type 90 as U.S. cars) and O2 relay. Result replaced filter and O2 relay. WUR test at 30.04 Ohms (in spec). The O2 sensor disconnect had no affect but is still suspect and will be replaced when my wrench is found.
ADVICE 3: Check fuel pressures. Results:

WUR Ohms were 30 at 86 degrees.
System pressure was 70 psi at 74 degrees.
Warm control pressure was 52 psi at 84 degrees.
Operating pressure was 45 psi at 84 degrees.

Reran pressure checks: 75 degrees +-
WRU 30 Ohms
System pressure 68 psi (was 70 at 85 degrees)
Cold control pressure 2.2 bar (High should be at 1)
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

ADVICE 4: New direction. "If you have the technical ability to do the electronic evaluation for CDI or ECU, would be great." I did not and could not locate another CDI to test with. Ended up biting the bullet on the MSD 6AL based on the reading in the following:
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.
That one and a couple of threads convinced me a replacement may be what I need.
Results: Purchased MSD 6AL, MSD Blaster 2 coil, new plugs, cap and rotor.
Removed old CDI #good for a future rebuild# pulled and analyzed plugs #all normal# gaped new plugs at .054 per MSD and thread recommendation. Next step was to clean up the old mount, move a relay #rear window defogger# and bolt up the new box.

Next came the wiring. Started with " Excellent read: Pelican Technical Article: Installing an MSD Ignition Unit - 911 #1965-83# - 930 Turbo #1975-83#" and finished with "MSD street fire in 78sc" thread. The combination of the two articles provided what I needed to cross the chasm and bring her to life.
To quote:
You will need 6- .250 male stake on quick connectors for the cdi connector.

1. Heavy red for constant power goes to one of the top 2 fuses on the rear 3 fuse panel that has an open terminal #top one#, fuse appropriately #I used a 25A??#
2. Heavy black ground it to a screw holding the fuse panel in place or other suitable good ground
3. Red connects to red wire in 6 pin connector #Center bottom#
4. Orange connects to white wire in 6 pin connector #Right bottom#
5. Black connects to the 2 brown wires in 6 pin connector #Right top#
6. Grey connects to purple/black wire in 6 pin connector #Center top#
7. GREEN Connects to the green wire in 6 pin connector #Left bottom#
8. VIOLET connects to the shield wire that may have black heat shrink in 6 pin connector #Left top#
Here is where I diverted as my power and ground to my coil were looking a bit brittle. I used the supplied MSD wires direct to the coil.

No Tach adapter required.

I mounted the unit sideways #wiring and rev limiter pointing up for easy access# in pretty much the exact spot the original CDI was. Drilled new holes through the mounting tin.

I also replaced the coil with an MSD at the same time, as well as the plug wires #I recently replaced the rotor and cap and spark plugs, and had my distributor rebuilt last year - so that's my ignition system renewed.

Results: My 911 SC fired right up. I adjusted the timing by ear as the 5 BDC spec was not the answer. When I get time I will get my light on and post the actual timing figure. The only thing left is working on the first 60 seconds after a cold (40 degrees# start. It runs rough until the temps come up and the smooth's out as God had intended.

At long last I had a half of day to do some tuning. The MSD required 12 BDC to run properly. Starts quick and smooths out after about 30 seconds. No more backfire or stumbling as it comes up to operating temperature. Warm start is a bump of the key. High RPM 5000 to 6200 simply hums. Not sure if these settings help anyone but they made mine run like a Porsche. Now to get time for some tuning.

For the person that know what they are doing this is an easy project. For me, well it really was easy with all of your support. Thanks, Mike