Can cranking the engine with no spark flood the engine?

[Winter911]

Originally Posted by HarryD

The resistance between the two studs on your coil (low voltage side) should be around 0.7 Ohms. On the secondary side around 6000 ohms.

Be sure your multimeter is ranged correctly.

Got about 1.2 K ohms, which should be about 1200 ohms checking secondary

[Winter911]

so maybe the coil is bad. 1.2k ohms seems really low if it's supposed to be 6,000 ohms

[HarryD]

OK. Based on the two recent reports.

I checked my known good spare coil. 6 ohms between the two studs and 700 between the center and either stud.

Your numbers are for a 6 pin CDI. This is how a 3 pin one is wired:



With the plug pulled from the CDI box, key on, you will have 12 v at the center (red) terminal.

On one side of the plug is a wire to the primary terminal of the coil.

On the other side of the plug is a wire to the points in the distributor.

Lastly, there is a braided ground.

This is the troubleshooting advice from Permatune for the box itself.

[HarryD]

Also, When you test your coil resistance, disconnect all there connections to test the coil itself.

[Winter911]

Originally Posted by HarryD

Also, When you test your coil resistance, disconnect all there connections to test the coil itself.

Ok here it goes.
With key on (fuel pump running)
From that diagram:

A to B



C(green wire) to ground



D to B



mounting flange to pin D : Zero

[timmy2]

You are supposed to check the terminals on the permatune box, not the harness that connects to it….

[HarryD]

Your readings do not make sense. On the connectors, you are checking for continuity end to end.

Test 1-Measure voltage in center pin. Key on should be 12v
trun key off.
Test 2-Measure resistance from Pin A to ungrounded wire on coil (remove wire from coil). should read about 0 ohms.
Test 3-Measure resistance from Pin C to lead connected to points (remove wire from points connector). Should read about 0 ohms.

These three tests will verify power to the permatune box and continuity to the coil and distributor.

Do the tests listed on the Permatune sheet posted above to check Permatune unit.

[Winter911]

Originally Posted by HarryD

Your readings do not make sense. On the connectors, you are checking for continuity end to end.

Test 1-Measure voltage in center pin. Key on should be 12v
trun key off.
Test 2-Measure resistance from Pin A to ungrounded wire on coil (remove wire from coil). should read about 0 ohms.
Test 3-Measure resistance from Pin C to lead connected to points (remove wire from points connector). Should read about 0 ohms.

These three tests will verify power to the permatune box and continuity to the coil and distributor.

Do the tests listed on the Permatune sheet posted above to check Permatune unit.

Round 2. I really appreciate the patience, but I’m learning a lot.
Test 1:


Test 2:



Test3:




Secondary on Coil with key off shows 1.6 kohms (1600 ohms). Not good

Did I get it right this time?

[HarryD]

Looks good. Did you do the tests on the Permatune box?

[HarryD]

Secondary coil resistance looks high. Did you measure directly on the coil? Or did you use the center lead? What is the resistance of the primary side?

[Winter911]

Originally Posted by HarryD

Secondary coil resistance looks high. Did you measure directly on the coil? Or did you use the center lead? What is the resistance of the primary side?

From permatune tests:

Pin A to D: 3375 ohms
Pin B to C: 99.2 ohms
Pin D to Mounting flange: 0
Pin D to pin B: see pic. Not sure if this is right:



Primary side of coil is 0.5 ohms
Secondary is 0.6 kohms so 600 ohms from inside the coil to ground

[HarryD]

Looks like all appears ok. Making progress.

Next steps are to reattach everything. Go to post 4 and start at step 2. Report findings.

Please post a picture of your distributor internals with the cap and rotor removed.

If you have a helper, with cap and rotor off, have them crank car and see if points are opening and closing.

[Winter911]

Originally Posted by HarryD

Looks like all appears ok. Making progress.

Next steps are to reattach everything. Go to post 4 and start at step 2. Report findings.

Please post a picture of your distributor internals with the cap and rotor removed.

If you have a helper, with cap and rotor off, have them crank car and see if points are opening and closing.

Harry, I couldn’t thank you enough for all the help.
I’ll take the rotor apart tomorrow and will update with the results

[Alex12]

Originally Posted by Winter911

Simple question. I haven’t been able to start my car and I’ve cranked it quite a few times while diagnosing.

I know I’m getting fuel through the fuel lines into the MFI pump.

Is fuel accumulating inside the pump/ engine every time I crank the car?

Sorry for the stupid question but I’m a newbie.

Last thing I would want is blowing something up with a ton of fuel accumulation, and has me slightly concerned once it finally fires up

No, the cylinder will not fill with gasoline. There is less than a 'drop' of vaporized (not liquid) fuel in a cylinder when the engine is being cranked. If this mixture of fuel vapor and air is not ignited, it is expelled by the exhaust stroke of the piston into the exhaust system.

[RDM]

I see progress on your troubleshooting and your confidence already! Keep at it.

You can use a timing light to check for spark in one fell swoop without taking anything apart. If you do find you have spark, no need to fiddle with points and coils and plugs and CDI boxes. If you don't have spark, no need to mess with fuel questions until you do.

Also, I don't think the fuses in the back do anything for engine running. Rear defrost and heater blower for SCs, if I recall correctly.

And, Alex12 answered your original question, no you don't need to worry about your cylinders filling with fuel. I wouldn't take the plugs out.

Maybe I missed it, but what year 911 are we talking about? Put that in your sig and you'll make life just that much easier.

[timmy2]

72 mfi

[Schulisco]

@Winter911

I don't want to be killjoy, but it seems that you're new to car electrics. Please be aware because of the high voltages coming out of the CDI up to 500 volts, these are life dangerous!! Those voltages going into the coil and will be transformed up to 40.000volts! If you do not know what you're doing, please go to a shop!

Nevertheless - one question: Is it possible that one ignition wire dropped of the spark plug while cranking? In that case the spark cannot flow off against ground and instead hits back into the CDI box, already the first spark will destroy the CDI box! So this happened accidentially to mine as well and the box died immediately...

Thomas

[Winter911]

Originally Posted by HarryD

Looks like all appears ok. Making progress.

Next steps are to reattach everything. Go to post 4 and start at step 2. Report findings.

Please post a picture of your distributor internals with the cap and rotor removed.

If you have a helper, with cap and rotor off, have them crank car and see if points are opening and closing.

EDITED:

Okay here are my findings. TLDR, GOT SPARK

Grounded the spark plug threads to a bolt on the chassis and attached other end of spark plug to lead wire off the coil using alligator clips.
I tested the spark plug and it’s working fine.
With key on, I pushed the “arm” with a piece of wood to close the points (is this right?)

Cranked the motor to see if the points were closing and the arm seemed to be moving.
Spark plug also sparked when cranking motor

[HarryD]

Great news. Next is steps 3 and 4. Be sure spark is getting to the plugs.

Also for ga-ha’s check for continuity between the motor ad the car chassis. Just checking that the motor has its ground strap intact.

If 3&4 is successful, As Walt Fricke suggested a shot of starting fluid when you crank Will verify if you got spark.

[Winter911]

Originally Posted by HarryD

Great news. Next is steps 3 and 4. Be sure spark is getting to the plugs.

Also for ga-ha’s check for continuity between the motor ad the car chassis. Just checking that the motor has its ground strap intact.

If 3&4 is successful, As Walt Fricke suggested a shot of starting fluid when you crank Will verify if you got spark.

Got spark at plugs.
I’ll get some starting fluid this afternoon.
I’m starting to think fuel might be a problem.