81 911 SC Electric / Fuel issue?

[srstevenso]

Hi: I've got a bizarre problem with my 81 SC. It will run fine for days and then out of the blue when running will start missing, rough idle that holds at 200 - 400 rpm, even when I step on the gas it just sputters and won't go. Some backfiring when this happens. I'm basically stuck when this happens and once it is turned off for a while it starts and runs fine. (note: if I turn it off when this happens it will start right up but run rough at the 200 rpm level and sputter)

Here's what I've done so far:
1) New Spark Plug Wires
2) New Distributor cap and rotor
3) New Fuel Pump
4) New Fuel pump filter
5) Plugs are less than 1 year old
6) FYI, top end engine rebuild within the last 6000 miles.

Any ideas from anyone out there, I sure could use the help!

Peace,

Scott

[Bob Kontak]

If you have a US car check under the passenger seat and there is a little black relay (one inch square) that is affixed to the Lambda box. That can fail and cause your symptoms. I believe, but not sure, that you can get them at the local parts store if you can't order from Pelican.

[srstevenso]

Thanks Bob, I appreciate your help! I'll give it a shot and hope it works.

Anyone else with recommendations I would be glad to hear them.

[srstevenso]

Bob:

Can you tell me what the Lambda box does, I searched in parts for the relay and lambda box and can't find it.

Thanks.

Scott

[Bob Kontak]

For US models 1980 and later (SCs) the lambda box controls the oxygen sensor system.

911 617 193 00

http://www.pelicanparts.com/cgi-bin/smart/more_info.cgi?pn=911-617-103-X-OEM&catalog_description=OXY.SENSOR%20CONTROL

http://www.pelicanparts.com/cgi-bin/smart/more_info.cgi?pn=821-951-253-M14&catalog_description=Oxygen%20Sensor%20Relay%2C%209 11%20%281980-89%29

[srstevenso]

Thanks again! I hope this resolves the issue. (low cost part too!)

[Bob Kontak]

Here is a trick. When the car starts running like crap, unplug the relay. If it runs the same, you probably have found your problem.

Check all of your fuses as well in the front trunk. The circuit that the front trunk light is on is the same circuit as the O2 system. Probably not as issue as problem is intermittent.

[srstevenso]

Thanks again Bob. I'm hoping with your advice I'll have her back on the road for the upcoming weekend.

Have a good one!

[srstevenso]

Bob:

Just following up to let you know that it looks like the relay solved the problem. Thanks for sharing your expertise!!

Peace,

Scott

[Bob Kontak]

You are welcome. I learned that in this forum from John Walker more than a year ago and have helped three or four people out. Keep tuned in here and you will learn plenty.

All the best!

[Laneco]

Long, long, list of people who John Walker has helped. He's on Santa's "nice" list.

angela

[srstevenso]

Thanks to you and John for sharing expertise! (and saving time and money for me and others)

[Wayne 962]

Glad to hear it worked out and was the relay. If it hadn't been the relay, I would have suggested checking the fuel pressures of the CIS system, as a failing pump can sometimes cause problems like these with the CIS systems (which are very dependent upon fuel pressures). Typically with an ignition failure, the car will either run or not run - not typically a rough condition like this...

-Wayne

[srstevenso]

Thanks Wayne.

[jeffs9146]

I am having the same problem but it is consistant all the time!

If I start the motor it fires up fine and then the idle drops as it should but then it runs rough and if I give it gas it backfires and sputters.

If I push up on the AFR plate it runs great and revs like it should.

I have checked the relay and tried another one. I have swapped out the WUR and it is the same. I have sprayed carb cleaner and cant find any vacume leaks.

Any sugestions would be great