Non running 3.0 SC

[giovannicoccitti]

Hi All have been restoring my 1972 911 which has been extensively modified over the years it is running or not running a 3.0sc engine and I presume engine wiring .It only sparks on first cranking and is popping trying to run , have had cdi tested and was said to be good , supply to cdi is good , have tested dizzy by removing and testing with meter . Have replaced leads, plugs , rota ,cap ,and tested coil with meter. I purchased car as non runner , ignition switch would not return back from position 3 , so I replaced the switch which was a mission in its self . Sorry missed another peace of info it had a parshalley removed imobbliser so have connected wire on solenoid of starter motor and a switch in engine bay . This has helped me to see or not ? what's happening. So open to suggestions , the Northamptonshire area.
hello one again Jon

 

[dij999]

"only sparks on first cranking" does that mean you get no spark at plugs at all after first cranking? Not sure what is described there especially as you seem to have extensively replaced/checked the ignition components, I assume you would have checked spark present in all six cylinders.
If issue not a 'no spark' I guess you would have checked the ignition timing is not way out with a strobe? Plug lead lengths make it reasonably obvious which is the right cylinder each should connect to but worth checking as mis-connection is possible (especially if nonOEM lead replacement with altered lead lengths). Perhaps check firing order corresponds with lead sequence on the distributor cap.

Is the K-Jetronic system delivering fuel? (could take out one or more injectors and check).
I know you sorted the starter side of things but does your immobiliser do something else like interrupt the fuel pump electrical supply?

As it was a non-runner when you got it, I suppose it could have all manner of engine innards issues - is the compression ok on each cylinder?


I had intermittent starting/running issues after an SC engine rebuild some years ago because I forgot to refit the earth braid from transmission to body. Took me a lot of investigating before I realised the obvious, hope yours is a simple (and cheap) one too.

DJ

 

[Old and Slow]

The immobiliser on mine switched off both the starter and the ignition feed, both wires had to be "bridged" to make things work on mine.
"popping but not running" suggests a lack of fuel. If it has been standing for a while there could be water in the tank, or the fuel filter is blocked, or the dash plate in the intake could be stuck: if you remove the air filter lid and the filter you can stick your finger up the air intake and check the plate can move and isn't stuck. It also operates an electrical contact (the Airflow Contact Sensor), which, if I remember correctly is a separate electrical feed to the fuel pump relay, there's one during cranking and then a separate one during running.
IIRC there's also a "Start-up Valve and Thermo Switch" or somesuch, that might be there to enrich the mixture during warm-up, plus other complications.
If it is a fuel pump problem, the SC has an EK P4 pump which is also used on the 924 and 928, but I don't know the availability. There is a filter in the pump (part 928.110.147.05) which could be blocked giving fuel feed problems.
Do you have the "Bentley" manual, or the Haynes Manual? It has the wiring diagram in it, which should help.
Good luck.
Philip

 

[giovannicoccitti]

Hi Thank you all for feedback, fuel starvation should not be problem as I drained all old fuel in tank which looked clean but stale. I replaced fuel filter in tank and in engine bay , can smell fuel coming from tail pipes . Have checked the ignition timing and firing order all seems correct ,it is just lacking a constant spark.Will check all other banks for spark , cdi unit has a 12 volt supply when cranking. Could it be coil ? I have tested with meter is this a problem which any body else had or could it be a rev limiter ? Have not done a compression test yet as have been told rings can stick and will free up once running.

 

[dij999]

Coil does sound like a possibility but you can check it easily with a strobe though doesn't sound like the problem you describe.
I think you replaced your rotor arm but if that's where your rev limiter is (rather than the electrical solid state system which interrupts fuel pump electrical supply) that could also be the problem - it's a simple spring-resisting centrifugal process resulting in short circuit at high revs, which could be the reason for the initial spark which then disappears, should that centrifugal/spring-return system be faulty.

But are you really sure you have good fuel delivery in your injectors - try them all - just pull them out and try each one as someone cranks the engine.
You could try spraying "cold start" into the induction system to see if it will run - if it does you can be sure it's a fuel issue. I think 'Old and Slow's suggestion of lifting the airflow sensor plate is a good one - it should cause fuel delivery which will be obvious - be careful you don't flood it though. If it starts and runs ok with the "cold start" it could be the warm-up regulator or a large air leak on the induction side (the 'rubber' couplings on each of the six induction manifolds are well known to perish and split with time - though unless several are split you would usually only expect rough running). By the way if you do use the 'cold start' be sure to have the air filter cover off (unless you have an after market induction pop off valve fitted) as any backfire can do a lot of damage. Good item to fit anyway if not already done.

 

[giovannicoccitti]

Hi thank you for info , I have replaced rotor arm when cap and leads were done . Sorry did forget to mention I have used easy start when fuel pump was not running and after when I got it runing. Will be picking up new coil tomorrow to see if the original coil is braking down due the high voltage through it.
l did test it as per manual but just in case and what the hell the old girl looks like she has had year of neglect . So how can I bypass rev limiter just in case it is the fault , l have read it just cut fuel pump of but can't see how that would work it must break the circuit somehow?

 

[SilverWT]

So how can I bypass rev limiter just in case it is the fault ,

Only US/Ca cars had an electronic rev limiter, in conjunction with a catalytic converter, as indicated by Dij999 above.

ROW SCs have a rev limiting rotor arm that works by centrifugal force against a spring to cut the spark at a given rpm. You can test for static electrical continuity from the center of rotor arm to the tip. If there is static continuity a faulty rotor arm is unlikely to stop a motor starting, more likely give running problems at higher rpm.

The electronic rev limiter works by cutting power to the fuel pump relay and is triggered by a signal from the Tach.

I know you think it is the spark, but as you have had problems with the ignition switch I would check the fuel pump operation as a simple elimination, just smelling petrol is not definitive.

The fuel pump is power up when either the ignition is in the "start" position, or the air flow sensor plate is moved up off it's rest position when the ignition is "on" (as when the engine is turning over or running).

1. Replace the fuel pump fuse, even if it looks OK.
2. At the fuel pump relay socket you jump connections 87 and 30, then turn the ignition to "on" (not start) and the fuel pump should be heard running.
3. Get an assistant to listen for the fuel pump when you engage start. An ear pressed to the fuel tank should pick up the noise above the engine cranking.
4. Take the air filter out and with the ignition on reach into the air box and momentarily push up on the air sensor plat with the tip of your finger (as Philip indicated above). The starter should be heard running. If you keep the plate up for any length of time you will flood the engine in a big way.

If all tests are OK the pressure/volume of the pump may be a problem, or you are back to hunting down the ignition system.

As an additional comment, you should be able to hear the CDI box working (a loud buzz/whine) in the engine compartment with the ignition "on".

Mark

 

[giovannicoccitti]

Hi Mark fuel pump comes on as soon as position 2 is turned on ignition switch and you can hear fuel passing through filter in engine bay and if you push air sensor it make a noise and fuel pump note changes . I also sprayed easey start when cranking still no go , also fitted new coil today still no difference .I have a switch in engine bay which I use to crank engine over so to see if there is a spark . Also looked at rota arm and it is as you discribed I taped receiver with tape to prevent grounding which made no diffrance . Have never used a sdrobe light before would that help or will that just make sure timing is right only will also check tomorrow if there is a spark on all six . Thanks again for all your help will get her running .
jon

 

[SilverWT]

OK, sounds like you have confirmed an electrical problem!

The thing is, it sounds like who ever did the engine swop has not followed/replicated an SC set up and so you may have some other strange things in your set-up which makes it difficult to diagnose problems.

The fuel pump should not run with only the ignition in "on", while this may not be part of your starting issue it is a safety issue when you do get things running. As it is if you have an accident/incident where the engine stops running the fuel pump will continue to pump fuel, but this is something you can sort out when you have got it running.

You can not check the engine timing with the strobe light if the engine is not running, so little point in going there at this point.

Does the CDI box make the noise I described above? Please remember the CDI box output is dangerously high so make sure you are not touching ignition components when the system is live.

I would pull a convenient ignition lead off a plug and stick an old spark plug in it (easier/quicker than taking a plug out the engine), place it on a good earth on the engine to see if you get a spark as you crank the engine over (making sure you can not get a shock from it). If you do get a spark you could repeat it for all leads, if you do not get a spark you have to start working back through the system. You have new leads etc. and a new coil and so I would work back from the coil. If the wiring between coil and CDI are OK and you have already checked power to the CDI box it only leaves the CDI itself.

If you report back with a spark and still no start I can send you some links to CIS issues diagnosis web pages.

Mark

 

[Old and Slow]

A known potential problem area is running the ignition with the connection from the CDI to the coil disconnected. Without a load on the output capacitor in the CDI the energy can be discharged internally, damaging the CDI. Take extreme care when fiddling with this bit of the circuit as the voltages can be lethal.

 

[giovannicoccitti]

Hi all , have just checked all leads with spark plug and they are all the same , spark only at first cranking. Can anybody tell me what the 3 fuses in engine bay do .The bottom one gets a supply when ignition is in position 2 and fuel pump and cdi get there supply . Have just noticed 4 thick wires from parcel shelf to engine are cut at parcel shelf , 2 brown 1 red with thin white line ,and 1 red with thin black line. Has anyone got any ideas on what these wires feed. Also a pair of red wires near fuel filter and fuel reservoir , and 2 thicker wires brown and gray I think these are engine bay light ? A couple more wire black and red coming from rear light so could be for brake light. I forgot to mention that the bottom fuse is were I get the feed for switch to starter motor.
jon

 

[SilverWT]

Can anybody tell me what the 3 fuses in engine bay do

Fuse 1 = Heater Blower Relay
Fuse 2 = Heater Blower
Fuse 3 = Heater rear window and Rear window wiper.

1 is the bottom fuse, 3 is the top fuse.

The problem is someone has got at your wiring with the engine swap.

The CDI needs power from the ignition switch in the "on" position and you should be able to hear it with the ignition in "on", can you hear it buzzing with the ignition in "on"?

If yes, and then you only get spark on initial cranking something is wrong with the CDI box.

 

[giovannicoccitti]

Thank you for the information, and I total agree that someone with a little knowledge has been at the old girl. Has taken sometime to get light to work as they should, but I digress. Cdi does make the sound it should and have tested supply to it and also took it to an old guy who put it on his test rig as seen on YouTube and all tested good. Have pulled dizzy out and tested with meter when turning it and it makes and brakes on green wire so I must be missing something??

 

[SilverWT]

Is the live feed to the CDI wired to a circuit to which the power is cut during starting? I believe the heated rear window and heater blower feeds are such circuits. You should check that you have 12v at the feed to the CDI during starting as well as just with the ignition "on".

 

[giovannicoccitti]

Power feed to cdi is there when ignition is in position 2 and position 3 is starter motor. I know this as I tested for voltage drop, which I did get before fitting a 110 amp battery.

 

[SilverWT]

Then I would be looking at the CDI unit again, maybe failing under load?

 

[giovannicoccitti]

It dose have a strong spark, it did have an immobiliser half removed when I purchased car I wonder if that is a problem. I remember daughters first car were it would start and cutout with one key and work fine with the otherone. It would be good if some has a spare cdi I can try? To rule cdi out once and for all.

 

[Old and Slow]

Hi Giovanni,
The rear wiper motor has the following wire colours and the loom is on the left hand side just under the parcel shelf:
Brown
Red
Brown+White
Red+Black
If the spark stops when you stop cranking the engine, then try temporarily putting a separate wire from a permanent live to Terminal 15 on the CDI where the Red wire normally goes, and then try turning the starter. You'll need to stop turning the starter very quickly if you find the engine begins to run, and then you can pull this "bridging wire" off to stop the engine.
If you pick up the live directly from the + on the Battery you need to put a 16A fuse in line, just to be on the safe side.
It could be that the wires on the back of the ignition switch are wrong.
Starting the SC is often a 2-stage process - the first time I turn the key it cranks the engine and "primes" the system, and on the second time the engine bursts into life - at least it does on mine.
Good luck,
Philip

 

[giovannicoccitti]

Hi All have had another look at it tonight after all feedback , took plug off cdi and metered supply feed 12.50volts when cranking 10 to 11 volts . Connected it back to cdi and metered 12volt when cranking it drops to 0 . So decided to get supply straight from battery and it did the same 12 volt and when cranking 0 , will take cdi off and take it back to old boy for testing again weekend. Will need to look at a few 911 and see what the wiring should look like . Will be going to NEC next week and hopfully see a few sorted cars to see what the old girl should be like. Are there an member in Kettering area who have cars I could look at as need to still put a lot of items back after repaint . Thanks again for the help guys.

 

[giovannicoccitti]

Hi Guys havant took cdi to be tested again yet as I experienced something weird, I removed fuel relay and turned ignition to position 2. I could hear the cdi straight away, I decided to crank engine over, to see if the fuel pump was the drain to cdi supply, but notice with relay out no spark at all. How could this be so or is it correct?