Need help pls. Non running 83 cis 911. Starts very fast then dies.
 

Car will fire up every turn of the key immediately but dies just as fast. Ordered a fuel filter today but doubt that's it. New plugs cap rotor although I know it's fuel related. Any help appreciated. Thx. Mark

disconnect fuel line, put into container (have a friend), hot wire fuel pump (30 to 87a red relay) with ignition on, and measure your flow of fuel. Compare to spec.

Or before you do that, hot wire fuel pump as above, and start it, if it keeps running, then something with the relay wiring.

If not the FP flow, relay wiring, then it sounds like a big vaccum/air leak

p.s next steps would be fuel injection pressures

Might be firing on the cold start pulse, but not getting any or not enough gas from the injectors.

I bet if you disconnect the cold start injector it won't start at all.

It's also helpful when you give some history, since you seem to have a non-running engine as of 4 or 5 weeks ago. All of that is important information that would help us not chase our tails...

Mike. It's same car. I rotated fuses and swapped relay (red) and it fired up but only for that first 1 second. It's def fuel related. I'm going thru a lot of personal stuff with family death, divorcing after 20 yrs, and moving plus building a shop so this car was back burner unfortunately.
I swapped out a fuel pump, added 7 gallons of fresh gas to drained tank, and have 100% battery.

Checking cold start now by unplugging it.

Quick access is to disconnect the thermo time switch, since it's up front. It acts as the ground path for the cold start injector.

Might be a bad connection at the O2 sensor relay under the passenger seat. Had similar symptoms on a friend's SC and this was the culprit.

Mark,

Does the engine immediately die when you release the key from the start position ? The fuel pump runs off one circuit when cranking in the start position, then a different circuit in the ON position, and only when the air flow meter safety switch contacts allow it. A simple test for voltage at the pump can tell you. If it fires, stumbles, tries to run, then dies, that is a common CIS lambda issue with the late 911SC and the solutions are in the archives. Search for CIS lambda.

Paul

Mike, disconnected thermal time switch. No difference.
Should I make a circuit tieing the leads together?

Graham. I reseated the relay a cpl times and checked grounds there.
I'll grab a new relay tomorrow.

Paul. I'm not letting off on the key switch. It's a VERY quick start (firing up) and then cut off.
No indication of any switch issues before now. Drove it to current location.

Mark,

Ok, so you are saying it fires while cranking, then dies while still cranking the starter ? Most people instinctively release the key to ON when it fires to avoid grinding off the ring gear.

Try this test. Remove the air box straps, cover and filter, look into the back and locate the metal elbow that connects the air flow plate to the FD. Turn the key to ON, listen for the fuel pump hum in front, you should only hear the CDI whine in back. Go to the back of the car and lift the air flow plate for 1-2 seconds, you should hear the pump come on and the fuel through the injector rattle pins. Do not do this for more than a few seconds or you will flood the engine or worse. Once you know the FP is running when the key is ON, you have a cold running problem, not a starting problem. Search the archives for CIS lambda. The 02 sensor is irrelevant during a cold start, but the FV must be pulsing for the correct mixture. If the fuel pump is running and the engine has spark, the problem is usually the mixture is too lean and/or the vacuum retard is killing the engine before it can establish a steady cold idle. Disconnecting and plugging the grey vacuum retard line at the back is the distributor will tell you. Avoid pedaling the throttle, this only makes it worse and risks blowing up the airbox. An 83 SC should fire immediately when cranking and settle at a 1200-1500 rpm cold idle, then slowly drop to 950 rpm when hot, without touching the throttle.

Ok. Sorry for delay. Lifting the injector plate I got no pump so I ordered and swapped in fuel pump relay and no change. No pump running.
Then I lightly split the 5 posts on fp relay and got pump noise when injector plate lifted BUT now wouldn't start on first crank like before. It was firing first spin of engine but not getting that now. Bought a fuel filter but I'm guessing that not my problem as I'm smelling fuel around rear of car engine area or exhaust. I bought a cdi from a pelican but it was doa so wondering now if spark is weak and getting flooded when pump is working.
Ideas of what to check next?
Maybe off to harbor freight for fuel pressure guages and swap in another cdi.

Would 02 sensor relay keep it from starting? Can it be jumped out to check it?

Not an expert here. Have an 83sc with same issue. Starts for a second and then dies. Fuel pump check ok by a jumper from fuse box. Did pressure test and found out that the cold control pressure is high. Car starts on cold start valve for a second then stays lean after then dies. Adjusted my WUR cold control pressure and car starts with no issue. Starts up around 1200-1300 rpm then few minutes to 950 rpm. Good luck. Lee

so wondering now if spark is weak and getting flooded when pump is working.
Ideas of what to check next?

Sounds like you have issues with the FP relay socket. Clean all the connection and then verify you have power at the FP when cranking and when you raise the plate with the key ON. Take a look at the spark plugs, you may have flooded the engine and fouled the plugs. Clean and gap the plugs , check the spark and try again. You need to verify that you have reliable power at the FP as step one and you have not gotten there yet.