No Spark

[VA944]

Hey everyone. My 1987 944S 16 valve is not getting any spark whatsoever. Not at the coil and not at the spark plugs. I have tested numerous times with different spark plugs and different coils that I know are working. I also have a new speed/reference sensor. On the S there is only one. I properly spaced the new sensor and have gotten the car to run with it installed. Even though the sensor is new I checked the resistance at the sensor and at the dme harness and both times it came out well within specifications. I also checked for ac voltage at the dme harness and that also passed the test. I am getting 12 volts to both sides of the coil when the ignition is in the on position. I have gotten the car to start off and on and sometimes it will run for a couple days then I come out one morning and it will not start at all. I have tried different dme relays, dme computers, ignition relay, ignition control module and still nothing. I am maybe thinking it has something to do with the ignition switch because I'm not sure what else it could be. Any thoughts? Thanks to everyone who responds its much appreciated.

[djnolan]

Correct, there is only one reference sensor at the bell housing but I think there is another sensor behind the distributor housing. I have seen this connector crack due to heat. How many different ignition modules have you tried? Also here is an ignition switch test procedure: Ignition Switch and Wiring Test

[VA944]

There is a camshaft position sensor on the back of the cam cover that I also replaced because it cracked due to the heat as you said. I have only tried one other ignition module. I might just have to bite the bullet and remove all the stuff in the way of the ignition switch so I can test it. On the earlier cars its a bit easier to get to than on the later ones.

[djnolan]

For the 87 S the Vol4-electrical has the schematics: 944 Workshop Manuals

i might be inclined to check for proper voltages at the DME relay pins before doing that.

[walfreyydo]

If you connect a spark plug to the coil as outlined on Clarks, are you getting spark? (guessing no)
Ignition System Troubleshooting

-Have you done the resistance tests on the coil?
-I was going to mention the ignition control module (down near drivers side headlight) as well, but you say you have already replaced?
-Did you check the cap and rotor?
-Correct speed sensor part number?
-The sensor at the distributor is the cam position sensor - did you test that?
-Do you have a factory alarm? Disabled?

I would think if the ignition switch was the issue, you would not be getting 12V on both sides of the coil.

Ignition switch test
http://www.clarks-garage.com/pdf-manual/elect-17.pdf

[VA944]

I am getting spark from the coil when doing the test on Clark's. I have tried a good coil off a running car and still nothing. I also have four spare coils that I tested and still nothing. I do have an extra ignition control module that I put in the car and it didn't change anything. I have cleaned the cap and rotor but I don't think either one of those are the issue because I'm not getting spark from the ignition coil and thats before the cap an rotor. I have also tried a different coil plug wire. Im pretty positive the speed sensor is the correct part number but Ill double check. I also replaced the cam position sensor on the back of the cam cover. If that was broken I believe the car would still start the timing would just be retarded. I do not have a factory alarm.

[Monkey Wrench]

the primary of the coil should see a pulse. I think of you just put low watt test lamp across the two primary connectors on the coil and crank it you should see your lamp flickering. in that state it will be in parallel with the primary of the coil..

it might be possible to use an oscilloscope to probe the sensor wires for the two sensors and disconnect them to check their resistance. after the DME the pulse should be amplified through a transistor and on to the coil. I bet you could check the input and output of the transistor for presence of that pulse.
in some cars it's called a module, I'm not sure what Porsche calls it. basically the pulse from the DME isn't strong enough to fire the primary of the coil so it's amplified somewhere between the DME and the coil.

someone with better familiarity could likely verify this and maybe help with the pinouts to check.

If you dont have as scope you can check into the downloadable oscilloscopes, you might find one that is Just a free download and uses an input like the sound card. I tried one using an older desktop computer and found it worked fine, that one used the sound card but I don't doubt you can just use a cell phone app these days.

if you want to fool around with those you can just try one there are a bunch if you search for Oscilloscope app. you dont really need to study the wave form, probably just seeing the wave form appear is enough to prove if it is present or not.

I bet if either of those sensors fails to show a pulse to the DME it probably won't start at all or run. If someone has a working car they may be able to verify. I suspect that if the DME sees no pulse you'll have no spark at all , no firing. no start.

from whet I've seen with my Volvo, it may be similar, the TDC sensor is a coil of wire with metal pin through the core. if I hook one to a volt meter without it being connected to anything else, and wag a screwdriver past it, I can see a voltage pulse even with a DMM meter. then you can just take the two probes and compare that to a known good one and see if the resistance is about the same number of ohms.

I'd expect you'd see something like maybe 3000 ohms ,(guessing) .. if the coil is broken somewhere,it could be zero resistance. (open)
if the coil was shorted part way through the bundle it could be less ohms. . Likely the cables are near oil and hard with age, They may get oily and cracked from heating cooling. engine vibration may contribute to the insulation decay there.

if you replaced a sensor you might check the old one like that. Just put a meter across it, see how many ohms between the pins then you can check yours in the car at the connector , same way. If you used an anloge meter (an old style meter with a needle display) youd be seeing the needle wag as the sensor saw its pulses.
Some DMM meters have a little bar representation, you could probably hook that to the sensor with all else unplugged, crank the motor and note some sort of a pulse. the sensor likely has a connector near the sensor and runs to the plug for the DME, if you can sense a pulse at the sensor itseelf, next you can verify that at the correct pins you see the pulse, that would verify that the wire between the sensor's plug and the DME is ok.

after the DME does it's thing it is going to produce a waveforem to be amplified and sent to the coil so you can next verify if that pulse exists.

I think there is a high likelyood the cause of the trouble is a wire got tugged, bad connector, bad ground, not necessarily a failed component. maybe the DME relay is not providing power to the DME.

[VA944]

I have an oscilloscope on order should be here tomorrow funny enough. It's really the only way to check and see if the sensor is sending the pulse to the dme. I think the transistor is inside the Dme on these cars but I could be wrong. I was thinking of also using the oscilloscope to check the pulse directly at the coil at the negative terminal, but I could also try the light.

[walfreyydo]

Originally Posted by VA944

I am getting spark from the coil when doing the test on Clark's. I have tried a good coil off a running car and still nothing. I also have four spare coils that I tested and still nothing. I do have an extra ignition control module that I put in the car and it didn't change anything. I have cleaned the cap and rotor but I don't think either one of those are the issue because I'm not getting spark from the ignition coil and thats before the cap an rotor. I have also tried a different coil plug wire. Im pretty positive the speed sensor is the correct part number but Ill double check. I also replaced the cam position sensor on the back of the cam cover. If that was broken I believe the car would still start the timing would just be retarded. I do not have a factory alarm.

Did you do the coil resistance checks as outlined on Clarks? Yes you did voltage, but also test resistance.

[VA944]

I did also the resistance check sorry I forgot the mention that. I also put a coil from a running car in and it did not spark.

[walfreyydo]

I didnt think I had a factory alarm either until I saw the OEM alarm module next to the DME in the passenger footwell. I did not have an additional keyhole in my door or any other "indicators" of a factory alarm. Are you absolutely sure?

I am getting spark from the coil when doing the test on Clark's. I have tried a good coil off a running car and still nothing

Sorry not understanding. First sentence you have spark but the second sentence you say you have nothing. Typo?

Try to run your resistance checks for speed sensor (confirm part number is correct) from the DME pins to eliminate any issues with the harness or plug. The speed sensor plug (up near the O2 sensor plug near the firewall) is prone to heat and can become brittle and crumble (mine literally turned to dust), so verify the readings at the DME, not at the sensor.

[VA944]

I have the passenger floorboard apart right now and I only see the dme. I’ll check the option codes because I think it will say it on there. I have spark when I do the test on clark’s where you attach the spark plug to the coil and ground the negative side of the ignition coil. Sorry for the confusion. I replaced the speed sensor because it looked pretty ugly a while back. I also did the tests for the sensor from the dme like you said and I got good results.

[walfreyydo]

Wow so the coil produces spark when testing, but nothing when cranking? How can that be? Are you sure you dont have spark when cranking? Spark tester?

[VA944]

I’m guessing whatever sends the ground the negative side of the coil is not doing it’s job. I am 100% positive I don’t have spark. I have a running 944 and I did the exact same tests for spark that I’ve been doing on the nonrunning car and the running car is sparking and the nonrunning car is not. I’ve been cranking the engine with a spark plug in the plug for the ignition coil that attaches to the distributor and I have been grounding the spark plug by attacking a ground wire to the threads.

[djnolan]

if you can check for a pulse on the ignition controller, then there should be a pulse on pin 5 the input from the DME and a pules on pin 1, the output to the coil. the schematic for the 88 s is in Vol5-elect.

[walfreyydo]

Heres a pinout diagram I found for a 944 S. I think the pinouts that djnolan referenced are correct for a N/A but different for a 944S. I think pin 1 and pin 2 are the equivalent to pin 1 and 5 on an NA (could also be pin 8?). That said, the advice remains the same. Check for signal coming from pin 2 and from pin 1. I assume if a signal comes in through 2, it should go out through 1. Im not sure if you need an oscilliscope or if a simple test light would work. I think the best way would be to back probe the pins

[VA944]

Im going to try this test and a couple of other things in the next day or two and I will post the results here. Thanks for the help so far everyone.

[Monkey Wrench]

in the abscence of a scope, You could likely just feed the signal into the input of a radio, like for example if you have a cheap portable radio that you dont care too much about with a microphone input or "line in" a phono imput will do. those are usually pretty sensitive inputs.

you can protect that input with a 1 meg resistor, it will allow the signal through , just not lots of amperage. instead of the pulse being represented as a wave form trace on a scope, you'd hear a buzz or a whine being amplified through the radio. if frequency changes you can hear the tone change. - this is basically a "poor man's oscilloscope".

you probably just need the one wire. I'm sure most here have tried connecting things to an amp and noted that even just touching those inputs with your hand will produce noises, because they are very sensitive.

if you want to couple things like that without an electrical connection placing a few loops of input near a few separate loops leading to the amp will provide coupling, its called a loose coupler or loose coupling.. lets say 10 turns around a toilet paper tube and another ten near to them, like that..

Then there is no actual electrical connection other than what is being passed though the air by way of induction. all you are creating is basically a transformer that has no electrical connection between its input and output and that can be used to protect your circuits from each other. the potential across such a transformer is limited, you can't create a hot or ground path between the two. its just a way to protect both circuits from each other by keeping them physically insulated from one another.

[djnolan]

The pins i referenced are the ignition module unique to the S models.

[VA944]

After what you guys have said and after looking at the wiring diagram. I think I am first going to make sure that I am getting the pulse from the speed sensor to the dme. If its getting the pulse then Im going to move to testing terminal five on the ignition control module plug. If the control module is getting the pulse from the dme then I'm going to check the condition of the green wire that runs from the ignition control module to the coil. If the green wire turns out okay then it seems like the igniton control module is the issue.