1985.5 944 No spark after coil..

[Ontarioporsche]

Wondering if anyone could help me out with a no spark issue or have ran into the same issue, first 944 and don’t know much about them!

I picked up this 1985.5 944 couple days ago and the guy I bought it from said it ran 9+ years ago, I drained the fuel tank, changed fuel filter and rear fuel line rubber section, changed oil/filter and the car cranks over not a problem, rpm bounces on the cluster like Iv read it should but I get zero spark, I have 12v power at the coil power wire/ground but can’t get my test light to function when I plug it between the coil wire and distributor, so I loose power either at the coil or coil wire, But after doing a test I found on Clark’s garage, both negative and positive ohm at 0.5, which is between 0.4-0.6 it says! And when I go from negative coil contact to output contact I get 5600ohm which is between the 5000-7200ohm clarks says… so I would think the coil is good, Will be testing with a good coil in the next couple days but,

Only thing I’m stumped on is the car has a Alpine security system, would that possible cause a no spark situation, Iv read the factory security system cuts power to the starter not anything to do with spark, but would a aftermarket system hookup different!? Appreciate any input!

[wwdwgs]

This is your 944 bible: Clarks Garage https://www.clarks-garage.com/shop-manual/repair-procedure-index4.htm

[Ontarioporsche]

Originally Posted by wwdwgs

This is your 944 bible: Clarks Garage https://www.clarks-garage.com/shop-manual/repair-procedure-index4.htm

Iv already done the security bypass but didn’t really change anything, engine still cranks but I get zero spark from my coil, but everything ohms out, will try a new coil and hopfully that works but I’m stumped!

[walfreyydo]

Troubleshooting a no spark condition
https://www.clarks-garage.com/shop-manual/ign-04.htm

Based on your description, sounds like you either have a bad coil or bad wire running to the distributor.

Aftermarket alarm - just remove it. Locate the brain box, follow the wires back and disconnect them.

[Ontarioporsche]

So after inspecting the ohms of the speed and reference sensors somthing wasn’t right, would this speed sensor cause a no start in this condition!? Looks like it has kissed the flywheel!

[Monkey Wrench]

if the sensor is damaged it can cuase an issue.
yu migth measure the distance down that the sensor physically reaches and the distance down to
the pin or flyweek cogs then subtract to get the air gap.

if you remove the starter, any bits of gunk in there? maybe rubber from a rubber centered clutch/

I had it happen in a volvo where someone started, did not let up off the key, gave throttle,
it blew up the starter gear and bits carried around the flywheel area, that damaged the crank sensor and in that case the " volvo flex plate" has holes in it that it reads and that was also mangled.

In the porsche I believe it reads a pin and the ring gear teeth.

the sensors will have a resistance, im not sure maybe 2000 ohms? I think they are the same.

If you wag a screwdriver in front of them and have it connected to a volt meter you should see a volt or so generated momentarily.

if you connected the sensor to a scope and cranked it that would make a trace on the screen, from that you can measure the amplitude ( voltage) of the pulse and it's duration

if you connected it to a radio input (like a microphone plug) imput youd hear a sound from it.

its a coil of wire, when it passes metal it generates a pulse , the metal affects the coil of wire and generates an electriucal pulse.

If it has no continuity it may mean the coil of wire has a break in its winding. I'd check one with a meter and then the other, if one is open and not connected through one lead to the other, its bad.
if they are the same part number, it stands to reason , they should have close to the same resistance or very close.

of course any wiring shakes, gets oil soaked and sees heat cycles all 3 may cause issues with the wires or connectors.

I believe one is a TDC sensor , so that the ECU ( MCE) knows where the engine is at all times, physically, the other is a speed sensor. I think the pin is the TDC sensor. it knows the engine RPMs

the ECU needs that info for the engine to run. if either sesnor fails , motor dies.

If you check with a small bulb across the coil , when cranking the bulb should rapidly flash, that would prove them to be working, as i tproves the MCE is able to generate a pulse on the primary coil..

if you have a pulse at the primary coil I;d check with a timing light from the coil wire to ground, if you have a prinmary pulse and no output on pluug leads then it could be a bad coil or maybe rusty connection posts on the coil.

from the coil lead, the high voltage pulse goes through the distributor cap and to the appropriate wire. it would not get there if , for example, you forgot to install the rotor ! perhaps if plug wires were not seated right.

when key is on, coil is hot, when crnakng the MCE provides a pulse on the NEGATIVE side.

there is a little amplifier involved , it will be between the coil and the MCE electrically and physically somewhere around the DS fender area, you can check it's connector to make sure wires there are clean.

setting that airgap propely, maybe Clarks garage describes how, in a volvo I thik it is a 2 mm gap, it will be something close to that.. best to get that actually correct. if it got whacked it must nbe too close, or perhaps something got in between.

if the MCE has problems understanding these pulses the engine will die. If you had the clearance wrong it may affect the pulse and cause difficulty for the MCE to interpret. perhaps cause stalling.

if the MCE is able to create a pulse at the coil's primary coil then it is getting and understanding the pulses.

the MCE is also interpreting speed and other info and making adjustments to the fuel injectors. I think it fires two injectors and then the other two.

the ECU may be getting input form other engine sensors and that may affect the timing or duration of fuel injetors and such,, As tech advanced, year by year, manufacturers introduced more levels of complexity.