cafebullet

I have an '87 GXL NA, ignition completely stock (as far as I know), but while checking timing for the first time since I bought it 6 months ago, I noticed I have no spark from my leading plugs. I've tried searching for 2nd gen igniter issues, but here has been my troubleshooting:

• I've let the car warm up, turned off, then pulled the trailing leads and tried to restart without luck.
• Trailing coils trigger my timing light, leading do not.
• I tested my leading coil resistance, it starts at 0 ohms, climbs to ~0.1/0.2 ohms, then fluctuates back to 0 on my original coil. Thinking it was a bad coil, I bought a new replacement that behaves exactly the same with my multimeter.
• New coil doesn't produce spark either
• CAS shows ~180 ohms across both sets of terminals according to Haynes manual test.
• CAS appears to be fully advanced, car seemingly runs and starts alright on trailing coils but is lacking power?
• Coil power connector black/yellow wire shows 12v, the signal wire shows 5v/0v when turning the alternator
• Leading ignitor/coil assembly shows a good ground to the frame through it's mounting bolts

Everything seems to point to a bad igniter, if I'm getting signal and power at it's plug, good CAS, replaced coil behaving same as original, but no spark. Does this check out?

cafebullet

An update, for anyone who sees this.

• I replaced the leading igniter and coil, still no change.
• I ohm'd out the new coil and my meter shows it having the same behavior as the other two, so I think I can rule out the coil and igniter.
• I reset the timing at the CAS, then tried a different set of plug wires to no effect.
• I bought an inline spark detector, trailing plugs show a bright light in the bulb, but leading shows the dimmest red in the element. Is this weak spark or some kind of unrelated feedback?
• I checked the 2 prong connector to the igniter, it is fully seated and there is no problem with the blades inside.
• I disconnected the ECU and checked the two CAS pins in the same way I checked above, both show the same ohm reading as above.
• I checked pin 1V's resistance with the leading coil unplugged, it read open as per this post:
  Quote:

  Originally Posted by HAILERS

  First skip the bs about looking for 5v coming and going. Pure clap trap. Go to your ECU and pull the large plug on the right off. Ohm out pins N to P and then pins T and Q. On my car I get 170 ohms on each. That is ohming out the cas when you do that. If that does check close, then I give up. I'd patch in a known good ECU and have a go. I'm attaching two jpg's of the ignition so you can ohm out the above plugs and it wouldn't hurt to ohm out the pin V with it disconnected from the coil assy to make sure its not being or touching a ground. Should read wide open if not connected to the coil assy.
  from https://www.rx7club.com/new-member-r...-coil-1038157/
• I then plugged in the leading coil, checked the ohms on 1V and it read open still, I then made a jumper wire for the G/Y wire (the trigger wire?) to GND and pin 1V showed 0 ohms.

I think I can assume the harness from the ECU through 1V to the coil G/Y wire is solid, but I'm not sure if my open reading with the leading coil plugged in on 1V is right as HAILERS seems to allude that you would only see an open circuit with the coil unplugged? The only other thing I can think is that my leading plugs are fouled and giving a weak spark, does the attached pic look fouled enough to do that (Left plug leading, right trailing)? I feel like I'm at the end of my rope.

diabolical1

iTrader: (3)

welcome to the board.

sounds weird ...

i suppose you could try putting your trailing plugs in the leading position and see if you get a different result. that should give you some insight.

Akagis_white_comet

iTrader: (4)

Ouch, both Leading and Trailing looks like they've been drowning in fuel for FAR too long. Since you've gone through the proper diagnosis procedure and ruled out a failing coil/igniter (they rarely fail in a stock car, these are built like tanks), there is one other factor that could be creating the no-spark condition you're seeing. Your coils are not grounded, so they cannot fire. Try removing the Leading coil, flip it over and take a look at the mounting area around the bolt holes. Is it Shiny Bare Metal? If not, that is why they are not firing. The coils are grounded through the metal case of the Igniter, then goes through the Ground cable back to Battery Negative. Ignition coils are quite electrically "thirsty", so any ground weakness will show up here first with misfire/no-fire.

Here's some more info on how to address ground issues correctly, easily and reliably:
https://www.aaroncake.net/RX-7/grounding.htm

cafebullet

Thanks for the replies and Merry Christmas! I figured the plugs looked pretty crusty, but I flew out for the holidays before I could swap them or get a new set in to test. I'll replace them and will probably reduce my premix ratio somewhat in an effort to not foul another set so soon.
When I looked at the three mounting posts, it looked like only the bolt had been masked for paint, the area of the fender at their base isn't bare metal. I tried cleaning them up with a stainless brush as one of my troubleshooting steps, but I will now try and strip some paint for a better ground. Now I'll have a to-do list when I get back, can't wait to get this thing running right.

Akagis_white_comet

iTrader: (4)

It's been a minute since I saw one, but the inner fender shouldn't need paint removed to accomplish this. Cleaning up the surface on the Igniter and mounting studs should do the trick. Realistically, the Main Ground Cable is a more likely culprit because of the Middle Body Terminal being open to corrosion. Simple solution is to toss the old cable in the trash and replace with two 24" long 4AWG cables (Battery to Body, Body to Starter Mounting Bolt). Prep and Rehab the area per Aaron Cake's article and you should be good to go. It does help to thread the new M6 bolt in from the wheel side though, making it a stud to hook the cables onto during reassembly. Space can be cramped there, so it helps to work smarter, not harder, whenever possible. For this reason, I'd suggest a Dremel to tackle the prep work. I generally use a higher-grit sanding drum to get through the paint on each Ground Point,

Last, there are quite a few bolt holes on the strut tower. They're capped off with fir tree style trim clips. If it suits your purpose/preference, you could move the Main Ground Cable up to a more accessible one if desired. Cable lengths may need to be adjusted a bit for this though. As long as there's a good, solid connection to the body, the car doesn't care if it's in the stock location or 4" above it.

cafebullet

I'm back in the garage and have gotten no further.

• I pulled the CAS and then a trailing and leading plug wire to check for spark using the new plugs out of the engine. With the key ON and spinning the CAS gear by hand, the trailing gives a healthy spark and I can hear the coil clicking, the same test with both leading plugs shows no spark.
• I removed the Main Battery Ground bolt, cleaned it, the fender hole, and the grounding tab up with a wire brush and reinstalled. It already looked really good (this was a desert car), and a continuity test from Neg. battery connector to the tab, then to a random frame bolt had no resistance.
• I pulled the coil and igniter again and cleaned all metal-to-metal contacts to ensure it was well-grounded.
• The G/Y trigger wire for the coil shows 5V, 2x with a single revolution of the CAS, the B/W wire is constant 12V, and the tach bullet connector shows 1.4V per CAS revolution.

I couldn't get to the ECU ground, but I feel like with the coil having a good frame ground through its posts, 12V power, and the 5V signal pulse, an ignition coil should fire a spark plug unless it's internally grounding? I hate to throw money at problems, but I ordered another igniter/coil combo in the hopes that I somehow have gotten two bad igniters in a row.

cafebullet

I fixed it! While back-pinning the leading coil connector, and referencing photos of coils pulled out of junk cars with the wires snipped (thank you scrappers) I realized that someone in the past repinned the harness-side connector wires reversed . Fixed that, retimed, and the thing rips. In hindsight, I should've checked that in the beginning, but at least I now have a thorough understanding of the S4 ignition system and about 3 extra leading coils. Thank you Akagi's white comet, diabolical, HALERS, and these forums for having troubleshooting posts from two decades ago!