Odd CIS no-start problem
 

My 82 SC with mostly stock CIS has been running fine for years as my daily driver, but I've had an odd intermittent issue lately.

This morning leaving for work, I didn't hold the key in the start position quite long enough to start the engine, and it happened for the third time. How it starts is always the same. After the aborted start attempt, the car would not start...it cranks strong but never gives the slightest pop or any sign of turning over.

The last time the exact same pattern happened, I tried everything I could before finally getting a tow home. Fuel level is fine. I can get the fuel pump to run by jumpering it, the frequency valve runs, the fuel relay is functional (I can hear it click when it's inserted). I even cracked the fuel line at the CPR to bleed any air from the system. I don't think its ignition related After I finally gave up last time and had it towed 2 miles home, I tried it one more time in the driveway and the car started, but ran very rough...I immediately drove it to a gas station, and it ran rough the whole way, to top it off with fresh gas and made it back home. The next day, it was fine and drove without issues for another few weeks. I assumed it was either the elapsed time or jostling on the tow truck that got it to start.

The second time was also leaving for work when I didn't quite get it started, but I drove another car to work and it started fine when I got home later, which made me think it was some odd transient "vapor lock" type of issue. It happened again today, but would not start when I got back home. I tried all the troubleshooting again, but never heard another pop from the motor. When I cracked the fuel line at the CPR this time, there was no fuel present other than a few drops. Even when cranking and when running the fuel pump, no fuel at all.

Has anyone seen anything like this before? Could it be a foreign object somewhere occasionally blocking fuel flow? The most confusing part for me is how it always happens right after a failed start attempt.

Thanks in advance,

Olivier

It obviously sounds like a fuel issue, I would check your pump fuses and if the 82 has it the Lambda system stuff (I have a 78 which does not have the Lambda system so aside from its existence I dont know much about it). If they have never been replaced this would a good time to change out the fuel lines it is a job many do on these cars often. If im not mistaken there is also a mesh grill in the fuel tank in front of the output hole to keep large objects out of the lines. That may have become clogged and require attention. You say this is your DD, do you have another car to rely on for the time being or do you need this on the road ASAP?

Regards
Dave

Oliver,

The next time this happens, turn the key to ON, get out of the car, remove the air filter and push up the air low sensor for 2-3 seconds. You should here the fuel pump run and the injectors chatter. Then start the car. You may have a stuck plunger or a bad microswitch.

Fixed it...(sort of)
 

Sleeping on it (and this advice) helped...I realized I was hearing the frequency valve and not the fuel pump...there was definitely no fuel pressure in the system as the air plate had no resistance when I moved it.

Hitting the pump with a hammer got it all running again. I either have a loose wire (unlikely), or the possible 30-year old fuel pump is finally becoming unreliable. The only other odd thing is that, even after I got the pump running again, it would cough and sputter and backfire, but not start...hooking up another car battery with jumper cables made it start like a champ on the first revolution. It's still weird how it always seems to happen consistently when I have a "failed" start attempt...

Thanks again...I now have a hammer in the car until I can replace the pump (and install Tony's EFI kit that's waiting in the garage)

Olivier

Load test the battery and check the amp draw of the fuel pump. Bad battery, voltage drop on cranking, high fuel pump draw, low or no fuel pressure.

I just went through this:
http://forums.pelicanparts.com/porsche-911-technical-forum/666821-911-sc-just-died.html

Given the intermittentcy of your issue, it may be worth looking into.

FWIW, I just went through the first five pages, looking for my thread. There seems to be one or two SC FI issues per page. As they say in the show I work on: "It is time." :D

good advice from paul.

if you bang on the FP and it runs, its the pump.

the bad running could be due to bad fuel pressure, both system and control. you could also be fouling the plugs due to their age/condition and mixture problems when starting, and after it is started, again, pressures and air leaks.

do a search for my starter rebuild thread. at the very least, pull the starter apart and clean the brushes and the part the brushes ride on. use fine sand paper.
clean ALL grounds and main power connections.

O,

Have you replaced your fuel pump relay? I don't believe you mentioned that. It could be as simple as that. I had the similar issues but found it to be the result of vacuum leaks all over. Have your airbox checked for leaks. Also, your injector seals may be worn. you'd be surprised of the leaks they develop.

Chek your ignition wires. Replace them if they're the original. 30 years is about due time to change the factory wires.

Thanks everyone...these are all good ideas I had not thought of. I've been spending so much time driving the car daily that it's been a while that I've done anything other than routine maintenance. I should be installing the tbitz kit in the next couple of weeks, and I will check and replace all the old components that aren't replaced as part of that effort. I do need to check the current draws and grounds...it's been a while on those.