Ignition Coil, No-Start Questions
 

The proper specs for coil resistance for my 87NA are 0.4 to 0.6 (ohms) for the primary (measured between the positive and negative coil contacts), and 5.0 to 7.2 (Kohms) for the secondary (measured between the negative coil contact and the central coil to distributor contact.

My existing coil measures 0.3 ohms (slightly below spec) for the primary, and 5.74 Kohms (within spec) for the secondary.

So…taking to heart the advice that any amount of deviation from spec. warrants a replacement - I went ahead and got a new coil. With this new coil - the primary reads 0.3 ohms, just as with the original coil, and is thus out of spec. Secondary reads 6.02…which is just a bit higher than that from the original coil, but is still within spec.

When I ran the above tests with another, brand new multimeter at the local O’Reilly’s, the results were the same.

I’ll be getting yet another new coil tomorrow, but regardless of how it specs out I have a question: could the above mentioned deviation of primary resistance have caused my car to stall way back when…and could it also be the culprit in my current no-start situation? (could not get a spark from the coil to distributor lead contact at the coil)

My gut says that while the primary resistance of my original coil is slightly out of spec, this would not have led to the current no-spark situation, and that I should dig a bit deeper.

Next question: If I’m not getting a spark at the coil but the coil itself is “fine,” and keeping in mind that I’ve replaced the battery, the DME relay, both reference sensors (and have tach bounce), alternator tested great, I have good oil pressure, the PO replaced distributor/rotor/all spark plug wires, I can smell gas on the spark plugs (new Bosch fuel pump and rebuilt the injectors), and I cleaned all grounds…where should I look next?

One more thing - I mashed the cruise control stalk during a recovered seat install…so that the stalk now feels very sloppy and the area of the (steering column) housing just below this stalk is cracked. So, I’ve disconnected the cruise control cable in the engine bay. Could this have in some way caused the ignition to cut out? Is my understanding that this should make no difference, ignition-wise…correct?

Finally…a note about my stall back in Oct. of 2019 (have not started the car since then). About two months prior to this, the car cut out for about two seconds at highway speed. Then the engine re-caught, and I put about a thousand trouble-free miles on the car until it finally stalled again in October, after having driven it about ten miles that day (after a rainy night).

Again…with all of the above - where to next? I’d specifically like to know if there is anything else I might test before I go ahead and open up the Motronic to check (and possibly re-flow) any visibly cracked solder joints. Thanks!

1) The cruise control has absolutely nothing to do with spark.

2) If you are getting a tach bounce, the ECU is giving a signal to the coil. Check for a spark at the end of the main ignition wire (between the coil and the distributor cap). If no spark there, use an insulated screwdriver to check between the coil and a ground.

If no spark, check for continuity between the green coil wire and the ECU pin #1

Thanks George! No spark from the main ignition wire...so tomorrow I'll do coil to ground - then ecu pin #1 to coil green wire as you've suggested. Gotta nail this!

Two new coils spec'd out like my original...so I returned them. Super-cleaned all contacts, re-installed the distributor cap, and then noticed something interesting - that the coil to distributor wire slipped into the coil contact a bit too easily, and upon inspecting further, saw that the two blade contacts inside the coil side contact boot had been fully compressed inwards...which would likely compromise the flow of electricity.

So I re-bent the blades outwards and put everything back together. Have not tried starting the car yet. Will try this soon. To be honest...I feel a bit like that Frank (or Hank?) Nolan character (played by Tom Hanks) on the movie Castaway - about to get off of that island...

Oh...and a hint about getting the protective cover off of the coil. If it does not slide off without a struggle, then do yourself a favor (in addition to the more obvious moving aside of the PS reservoir) and loosen the two 10mm bolts which position the headlight motor assembly and, after scribing in some witness marks for later repositioning - slide the whole thing forward to allow the coil cover a bit of clearance. In fact this will allow the entire coil/cover assembly to slide out - making removal of the cover that much easier. Will save time, busted knuckles, and just a bit of (appropriately) colorful language!