83 SC no start

[delaneyd]

Hey looking for help in diagnosing a sudden 'no start' condition on my 83 911 SC.

Was letting car warm up in carport before taking out for a weekend drive. Car started like always which has for 17 years been almost 'instantly'. Can ran for about 2 min then alternator seemed to load up (my term for belt squealed for a few seconds---not totally unusual for a cold day)....then just shut off. Sounded just like I had turned it off with the key. No misfire, no sputter, no nothing unusual...except I was 10 ft from the car.

Engine turns over fine...but won't start.
More info: typically when I turn key to 'on' the fuel pump runs for 2-3 seconds. Always has. Now...fuel pump won't do that by turning key to 'on'.

So I bought 2 new red fuel pump relays from host. No change.
Read posts here and tried jumping terminal 30 to 87a. Fuel pump runs normally and sounds normal.
Won't start with jumper in place.
Tested relay port. All 5 terminals check good per info here on this forum.
If key is 'on' and you plug relay in...both original and replacements 'click' and seem normal.
Lifting the disk in the airbox does turn fuel pump on with original & replacement relays.

Next: tested ignition coil per info here on the silver Bosch coil. Totally middle of road in both the primary and secondary resistance readings.
***Can coil test good with ohm meter and actually be bad/non-functional in actual conditions?

Pulled plugs...and it's firing when turning over.
Pulled distributor cap and inspected it and the rotor. All look good.

CDI is original and makes the same high pitched whine as always.

I'm lost now. What should I check next?

Thank you in advance !

[AlKidd]

Any fuel on the plugs when you pulled them?

[RobFrost]

Earth straps to both engine and battery. Battery connections tight, main positive connection to alternator. Check all fuses. Check 12v at all the fuses.

Then check you have sparks. Pull a plug and ground it to the engine while cranking.

Maybe alternator has shorted. Does it run with wires off the alternator, i.e. off battery power alone?

Loosen fan belt and check alternator turns freely.

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[RobFrost]

Check the seating of the relays in their sockets. See if you can power the relay in situ to make the fuel pump turn on the car.

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[boyt911sc]

Originally Posted by delaneyd

Hey looking for help in diagnosing a sudden 'no start' condition on my 83 911 SC.

(Edit).....

Don,

Hook up an inductive timing light and check for ignition signal. Take a closer look at your ignition coil. If this silver ignition coil was made in Brazil, this could be the culprit.

Tony

[walt]

Yeah, never heard anything good about silver ignition coils. Even if that proves not to be the problem, just change it.

[Walt Fricke]

One test to separate fuel from spark issues is to spray some starter fluid into the air filter while someone cranks the ignition. If it starts, but quickly stops, you have spark, and it is likely adequate. So you can get to testing the CIS fuel pressure values.

[Schulisco]

Originally Posted by walt

Yeah, never heard anything good about silver ignition coils. Even if that proves not to be the problem, just change it.

This is no more applicable in all cases, in the meantime Bosch made a new version of the silver coils, more details: https://www.911-hkz.de/Zuendspulen.htm

I wouldn't furthermore replace all suspicious components without determination if they're bad indeed. As already mentioned - check the spark before replacing anything.

What was made lastly at the car? This is mostly a good starting point for the troubleshoot.

Let's recapitulate: The car was idling and suddenly the engine stopped as you described, like the engine was shut down by igntion key normally, right? So most/all of the mechanic CIS components have been working normally until the sudden stop.

A sudden stop like this might be an electrical problem. The mixture should also be ok, concluding that as well the cold start as the idle were good. So only the electrical components are suspicious for me.

You wrote that the fuel pump started to run for 2-3 secs while turning on the ignition wihout cranking, right? My '81 SC does not run the fuel pump unless I crank the engine! And this is the standard behaviour of the engine as designed by Porsche. So probably somebody (you?) changed here something in the past. The fuel pump is operated by a switch in the sensor plate housing - when it's slightly lifted while cranking then the fuel pump relay get's power to power on the fuel pump. This is security circuit preventing pumping fuel when the engine has stalled in case of an accident.
Check if there is a unused plug at the sensor plate housing at the front side of the engine (between the firewall and the engine). When it's unplugged, then the fuel pump runs directly and continuous on ignition (and not only 2-3secs).




You also should - as already mentioned - check the fuel pressure. Probably the fuel pump is old, so it might runs while cold, and the after some minutes the pump warmed up and fails probably. This happens suddleny as well so that it seems that sb. turned of the ignition.

Also a broken cable (the screened green one to synchronize the ignition) may be hardened and broken, also they could last until they're warmed up by the engine and then loosing contact.

HTH.

Thomas

[T77911S]

check fuse 18
spin it.

[targa80]

First thing, it is all about spark and fuel, take the advise from boyt911sc and Walter Fricke. You can do the shotgun approach and look at fuses, grounds, or replace relays and you might get lucky. My philosophy is if it the issue isn’t obvious (hits you in the face) then start with the basics and work your way back.

Electrical: do you have spark?
Use an induction timing light and a multimeter to fault isolate from the spark plugs back through the ignition circuit using the schematics for your model year if you have no spark.
If the timing light shows a bright flashing light then you have spark move on to fuel.

Fuel: do you have fuel pressure?
Pull a fuel injector and place in clear bottle, crank engine, look for fuel in bottle or Jumper fuel pump relay turn on ignition lift air plate do you have fuel coming from injector? Still no fuel? Possible bad fuel pump or bad fuel pump circuit. Check fuel pump circuit using multimeter and schematic for model year. Fuel pump working? Then I would then break out the CIS gauges and test system fuel pressures. Do a search for the thread on CIS for Dummies.

Good luck and let us know what you find to fix your issue

[Schulisco]

One more thing: Don't forget the oxygen sensor. How old is it?
This fits also to the behaviour because it needs time to warm up. Test: Disconnect the oxygen sensor so that the ECU (under the passenger seat) will switch to "limb home mode" with a fixed duty cycle of 50% for the frequency valve. Maybe this signal is missing or worse enough that the ECU doesn't recognize it as worn, don't know how the ECU handles exactly a dying oxygen sensor, those are generating a more and more lower signal amplitude when getting older. New between 0V and almost 1V, worn sensors even less.

[delaneyd]

Thank you everyone for the help so far. Will follow suggestions and report back. Thomas sir, no oxygen sensor on mine. (been removed by PO prior to my purchase 18 years ago). Apparently this was a popular mod at the time....but don't know and can't confirm since it's always been without an O2 sensor since I've owned it. But it does make 204 rwhp on dyno, so not sure if just the K&N air filter and my custom exhaust (no cat, Dynomax 2.5" muffler ) helped that much or not.

[jjeffries]

Question for the gurus: could a worn ignition switch cause these symptoms?

John

[Walt Fricke]

204 RWHP is pretty amazing for a US SC of this vintage. With a better exhaust and muffler a Euro (big port head, runners, Euro fuel distributor) I can see this value. But Euros didn't have oxygen sensors or the mini-brain under the passenger seat.

The ignition switch wear I have had has mainly been a failure of the spring loading to move the key back from the start position when it starts, or a mechanical failure preventing consistent ability to turn to the start position. But these things do wear. Easy to check with an volt meter, as this kind of thing, like failure of a CD box or fuel pump, can go from apparently working fine to not working with no advance warning. Happened in about 1985 with my headlight switch - internal contact failed.

[targa80]

Originally Posted by jjeffries

Question for the gurus: could a worn ignition switch cause these symptoms?

John

Pin 15 on ignition switch supplies 12 volts through fuse 16 (25A) to pin 87a and pin 86 on fuel pump relay.
Pin 87a NC contact supplies 12 volts to fuel pump via pin 30.
Pin 86 on fuel pump relay energies the fuel pump relay coil.

Pin 50 on the ignition switch supplies 12 volts to the NO contact pin 87 to pin 30 of the fuel pump relay when fuel pump relay is energized.
Pin 50 also, supplies 12 volts to pin 50 of the starter solenoid.

With fuel pump relay energized 12 volts supplied at pin 87 connects to pin 30 of the relay. Pin 30 of fuel pump relay supplies 12 volts to pin TD on electronic ignition unit.

So a faulty ignition switch at pin 15 could prevent fuel pump from energizing and a faulty ignition switch at pin 50 could prevent the car from running or even starting.

There are many scenarios that can cause a no start and using a logical approach to troubleshooting the fault symptoms could result in a bad ignition switch or it could be some other component or fuse or wire fault.

[delaneyd]

More great info here...thank you all ! Will get back to checking this evening. One note if it matters....when trying to start the engine the tach now is bouncing around near 3000 rpm while in 'start' position (not 'on' position). Not sure it that's relevant...but passing that info along.

[T77911S]

jumper the FP so it runs all the time or remove the connector on the back of the AFM to run the pump. a good test anyway.

make sure the frequency valve vibrates with key on.

if no start you could push up the sensor plate to put a little fuel in the cylinders. injectors should squeal.

you can use a timing light on #1 and check timing while cranking, also checks for spark.

[targa80]

Originally Posted by delaneyd

More great info here...thank you all ! Will get back to checking this evening. One note if it matters....when trying to start the engine the tach now is bouncing around near 3000 rpm while in 'start' position (not 'on' position). Not sure it that's relevant...but passing that info along.

I believe a bouncing tach can be related to low battery voltage or issue with charging system. Also the TD terminal previously mentioned in my prior post is a signal going to the tachometer from the electronic ignition module.

I just noticed an error in my prior post: With fuel pump relay energized 12 volts supplied at pin 87 connects to pin 30 of the relay. Pin 30 of fuel pump relay supplies 12 volts to pin TD on electronic ignition unit.

Pin 30 actually connects to pin 3 of rpm limiter switch. Sorry for the error.

I believe the TD signal from the electronic ignition unit provided the pulsing signal to move the tach needle.

[Schulisco]

Originally Posted by delaneyd

More great info here...thank you all ! Will get back to checking this evening. One note if it matters....when trying to start the engine the tach now is bouncing around near 3000 rpm while in 'start' position (not 'on' position). Not sure it that's relevant...but passing that info along.

Bouncing needle - yes, but not at 3000....should be with the real rpms, while cranking this is far less than 500rpms, guessing about 200rpms.... This might be a hint to the fault:

Is it possible that one of the igntion cables were loose / fell off and disconnected on a spark plug? If this happens - even for a very short moment - it causes a "back flap" into the CDI box itself and destroying it, because the spark (up to 40kv) cannot go anywhere else in those cases. See the superb page about ignition coils of Ing. Gerberding for more details.

Also a faulty ground connection could cause this.

Thomas

[AlKidd]

Stated the car is turning over and spark at the plugs when pulled. Wouldnt that indicate that the ign switch / CDI isnt an issue?