1988 3.2 ignition coil resistance measures when wrong

[gdp_samson]

Hi,

my brother's P is not starting anymore after 1y of standing still. There is fuel in fuel filter, engine turns over, ...

but no spark. Cables seem intact, distributor cap super clean.

When measuring the ignition coil resistance, I measured 1.2 Ohm primary on terminals 1 and 15 (where Bentley says 0.4 to 0.7)

and 2.8 kOhm secondary, where Bentley says 5 to 8

Is this still OK ? or does this indeed mean that as Bentley values are not met, the coil is bad ?

[mysocal911]

Originally Posted by gdp_samson

Hi,

my brother's P is not starting anymore after 1y of standing still. There is fuel in fuel filter, engine turns over, ...

but no spark. Cables seem intact, distributor cap super clean.

When measuring the ignition coil resistance, I measured 1.2 Ohm primary on terminals 1 and 15 (where Bentley says 0.4 to 0.7)

and 2.8 kOhm secondary, where Bentley says 5 to 8

Is this still OK ? or does this indeed mean that as Bentley values are not met, the coil is bad ?

Found this, read here under Typical Ignition Coil Values;
https://www.systemsc.com/diagnostic.htm

And yes, the coil at 1.2 ohms will provide an adequate spark to start the engine.

[GH85Carrera]

If he has a silver Bosch coil on the car, it is very possible it is DOA right from the box, or in short order after installation. They are all junk. If you have the original 37 year old coil, it likely is fine unless it is oozing tar.

I have yet to find a good replacement coil with all the correct voltages, that really works. It is sad Porsche dealers will sell you a new coil made in Brazil that is just junk.

[mysocal911]

Originally Posted by GH85Carrera

If he has a silver Bosch coil on the car, it is very possible it is DOA right from the box, or in short order after installation. They are all junk. If you have the original 37 year old coil, it likely is fine unless it is oozing tar.

I have yet to find a good replacement coil with all the correct voltages, that really works. It is sad Porsche dealers will sell you a new coil made in Brazil that is just junk.

The MSD 8222 is a good choice.

[76FJ55]

The first place for a no spark I would check on a 3.2 is the speed and reference sensors. they are identical sensors so you should be able to compare resistance values between the two.

[gdp_samson]

Hi,

we have measured the resistance on both sensors, and they seem to be OK.
Between 1-2 pin, 936 ad 946 ohms, and between 1-3 and 2-3 the digital multimeter was not able to measure the resistance, so I'm assuming that is 'more than 100,000 ohms' as Bentley's saying ?

so: 12.5 volts at ignition wire at the coil (ordered new coil jic but coil measured correctly, I think)
sensors giving correct resistance,
distributor cap and rotor super clean, spark plug cables clean (no breakage or bad rubber or...)

spark plugs are light brown and were replaced last year
but no spark plug...

will await the new coil (ordered the MSD 8222) and then check further.

Do I need to look at ECM (relay ?)

[mysocal911]

Originally Posted by gdp_samson

Hi,

we have measured the resistance on both sensors, and they seem to be OK.
Between 1-2 pin, 936 ad 946 ohms, and between 1-3 and 2-3 the digital multimeter was not able to measure the resistance, so I'm assuming that is 'more than 100,000 ohms' as Bentley's saying ?

so: 12.5 volts at ignition wire at the coil (ordered new coil jic but coil measured correctly, I think)
sensors giving correct resistance,
distributor cap and rotor super clean, spark plug cables clean (no breakage or bad rubber or...)

spark plugs are light brown and were replaced last year
but no spark plug...

will await the new coil (ordered the MSD 8222) and then check further.

Do I need to look at ECM (relay ?)

Yes, this provides key 12V power to the ECM. Also, the ECM connector (35 pins - female connector) needs to have 12V on the three corner pins (1, 18, 35) with key-on.

[PopsRacer]

The coil (really a transformer) is hard to test out of the car due to the voltages involved. I have a HiPot tester here and it only goes to 1200V. The coil is probably banging out 30X that. If the insulation isn’t happy you may just wind up subbing another coil to see.
The DCR readings (just checked on an OEM coil on an 88) are:
1 - 4: 5.89k. (this is the secondary)
1 - 15: .6 ohm (this is the primary)

reading 4 - 15 should look the same but is really 5.89k + .6 ohm. The ‘ground’ side of both coils runs to pin 1.

the coil should get +12V on terminal #15 when the ignition is on.

[gdp_samson]

Originally Posted by 76FJ55

The first place for a no spark I would check on a 3.2 is the speed and reference sensors. they are identical sensors so you should be able to compare resistance values between the two.

can I assume this is OK ?
between 1-3 and 2-3 the digital multimeter was not able to measure the resistance, so I'm assuming that is 'more than 100,000 ohms' as Bentley's saying ?

[gdp_samson]

Originally Posted by PopsRacer

The coil (really a transformer) is hard to test out of the car due to the voltages involved. I have a HiPot tester here and it only goes to 1200V. The coil is probably banging out 30X that. If the insulation isn’t happy you may just wind up subbing another coil to see.
The DCR readings (just checked on an OEM coil on an 88) are:
1 - 4: 5.89k. (this is the secondary)
1 - 15: .6 ohm (this is the primary)

reading 4 - 15 should look the same but is really 5.89k + .6 ohm. The ‘ground’ side of both coils runs to pin 1.

the coil should get +12V on terminal #15 when the ignition is on.

have ordered the MSD8222 but I do have the correct voltages...
will provide feedback when arrived and installed

[gdp_samson]

Originally Posted by mysocal911

Yes, this provides key 12V power to the ECM. Also, the ECM connector (35 pins - female connector) needs to have 12V on the three corner pins (1, 18, 35) with key-on.

I did not understand this...

what is 'this' in 'this provides key 12V power to the ECM'...

must be my English (not native)

[mysocal911]

Originally Posted by gdp_samson

I did not understand this...

what is 'this' in 'this provides key 12V power to the ECM'...

must be my English (not native)

It's the DME relay, which provides 12V to the ECM, & fails often. Did you check the three ECM pins for 12V?
Buying another coil at this time without further diagnostics is a waste of money. If the coil is black & the original one, it rarely fails.

[gdp_samson]

Originally Posted by mysocal911

It's the DME relay, which provides 12V to the ECM, & fails often. Did you check the three ECM pins for 12V?
Buying another coil at this time without further diagnostics is a waste of money. If the coil is black & the original one, it rarely fails.

auch...no, I did not check that...the coil indeed seems original...

will try to learn from the Bentley manual on how to check these first...hmmm...

[PopsRacer]

If the coil is getting 12V on terminal 15, the missing piece is probably getting the trigger from the DME unit. That could be wiring, dirty plug contacts, a DME fault..

The crank sensors are hall effect units, like a guitar pickup only the magnet isn’t in the coil, it on the flywheel. Not much to go bad but the wiring insulation flakes off over time. If the position sensor (bottom one in the bracket) is not sending a signal the DME usually won’t send a spark or fuel (since it does not know where the crank is!) this is a failsafe (generally, I don't know the specifics of this Bosch unit)

The manual states 960 ohms, +/- 96 ohms (10%) for those sensors. That is between pins 1 & 2 (counting from the bottom of the connector) 1-3 and 2-3 should be very high - they're just looking for bad insulation. My reference sensor value measured 1,055 ohms on my Fluke DMM, which is the top end of the acceptable range. The insulation tests were both off the scale which is great. (way into the MegOhm range) hope that helps a little

[mysocal911]

Originally Posted by PopsRacer

If the coil is getting 12V on terminal 15, the missing piece is probably getting the trigger from the DME unit. That could be wiring, dirty plug contacts, a DME fault..

The crank sensors are hall effect units, like a guitar pickup only the magnet isn’t in the coil, it on the flywheel.

Actually, they are variable reluctance sensors.

Originally Posted by PopsRacer

Not much to go bad but the wiring insulation flakes off over time. If the position sensor (bottom one in the bracket) is not sending a signal the DME usually won’t send a spark or fuel (since it does not know where the crank is!) this is a failsafe (generally, I don't know the specifics of this Bosch unit)

TDC for two cylinders. After starting, it's no longer needed.

Originally Posted by PopsRacer

The manual states 960 ohms, +/- 96 ohms (10%) for those sensors. That is between pins 1 & 2 (counting from the bottom of the connector) 1-3 and 2-3 should be very high - they're just looking for bad insulation. My reference sensor value measured 1,055 ohms on my Fluke DMM, which is the top end of the acceptable range. The insulation tests were both off the scale which is great. (way into the MegOhm range) hope that helps a little

[gdp_samson]

All posts helped tremendously...

it was a faulty DME relay
swapped one and car started immediately...

then suffered a lot with reinstall of the front seat that I did not bother to see what part of the old relay was (not) working

really happy with all the forum help I got, learned a lot

--> we did suffer with another issue (you wouldn't believe the story) but as it is another subject, I will start another post (after first going through the Search Forum option, of course)

thanks to all !

[gdp_samson]

Oh, forgot to mention, as I made my brother buy a new ignition coil first, I did install that new one.

MSD 8222 as was suggested, is a direct swap, in the existing bracket. Install was a breeze and the car runs great (which might still be the case with the old ignition coil, I know...he will keep it as a reserve)

[wazzz]

Yes, he should keep his black original coil as a spare, even if I find the secondary ohm test (2.8K) on the low side. When I checked mine it was 5.7k at the secondary. And 0.4 at primary.

[mysocal911]

Originally Posted by wazzz

Yes, he should keep his black original coil as a spare, even if I find the secondary ohm test (2.8K) on the low side. When I checked mine it was 5.7k at the secondary. And 0.4 at primary.

Yes, that's basically the value shown here (1st coil values - 911) under Typical Ignition Coil Values; https://www.systemsc.com/diagnostic.htm

[gdp_samson]

Originally Posted by wazzz

Yes, he should keep his black original coil as a spare, even if I find the secondary ohm test (2.8K) on the low side. When I checked mine it was 5.7k at the secondary. And 0.4 at primary.

will do !!