No spark, coil test?
 

Hi All,

I have an 88 convertible with no spark. I have power and 5V pulse to the coil. Does this automatically mean the coil is bad? Is there a way to ohm out the coil? I popped the cap on the coil and the ohms seemed very low, around .7 or so.

Is there a way to definitely test these things before I spring for a new one?

Thanks!

The FSM specifies the ohm reading but I think it's a rather low number. Have you tried sanding down the mating place where the coil bracket meets the fender as this is how the igniter is grounded. Also, sometimes it's best to test for spark by removing the plug wire from the coil boot and place the wire as close to the boot as possible and turn the key to start and observe for spark.

The famous Satch has replied! I've read your threads before, thanks for the help!!

To answer your question, I did check for spark at the wire, no luck. I did check the ground by reading ohms from the coil body to the engine block and it read very low as it should, I think about .1 ohm. (I did clean up the grounds a couple years ago, and for context I should say that the car was running fine and very suddenly quit, with nothing more than a sputter after that when trying to start it.)

I removed the leading coil and measured under the cap and got about .2 ohms, but later it occurred to me to test the secondary... I went back and measured between the spark plug wire connector and the body and got an open circuit. A-ha...

So questions at this point...
Can I conclude from the open circuit that the leading coil is bad?
Shouldn't it have tried to start with trailing only coils?
Is it possible the trailing coil has been bad for a while, and the leading failed which killed the car?

Thanks in advance!

No tach bounce when cranking, either.

The tach signal comes from the trailing coil.

Yes, the car should start just with a good lead coil.

Make sure the B/Y wire at the lead coil has 12 volts w/key to on if you have not done that already.

Did you test for spark at the lead coil?

I don't think you can conclude the coil is bad from that reading since the voltage is produced in the secondary part of the coil by induction from the current in the primary.

Might not start with only the trailings

Possible, but in most cases when you're diagnosing there is only one problem.

Check for spark from the trailing wires. If Y, then there is a problem in the leading system somewhere and you're on the right track. If N, then then the problem is likely elsewhere like a sensor or something.

It is possible on an S4 like your 1988 to start and run the car on the trailing ignition only by effectively substituting it for the leading: advance the timing via the CAS almost all the way, remove the leading plug wires, disconnect the wiring connector powering the leading coil, put the trailing plug wires on the corresponding leading spark plugs.

Not the only way to test for spark at the trailings but I've done this before and think it's interesting that the car can run just fine off the trailing ignition firing the leading plugs with the timing advanced.

One thing I forgot to add: Coils in FCs just don't go bad very often. It's pretty rare.

I do have 12V and 5V pulse at the Leading coil, but no spark. Could the car start with only a trailing coil? I am thinking that the trailing coil was already bad (no tach bounce) and the leading coil quit which made the car quit.

Interesting. I may try to get a spark front he coil on the bench with a battery... But from everything I've read you should be able to ohm out that secondary coil...

The engine can run on just the trailing coil but it will run quite rough.

So i wonder if they're both shot. I haven't checked the 5V pulse on the trailing, but it does have 12V. No tach bounce on cranking.

So if I have 12V and 5V pulse, and good ground on the coil, but no spark, is the could shot? Or the ignitor? Open circuit on the coil secondary is leaving me with no faith in the coil at this point.

FSM definitely has a test of the resistance of the primary windings by taking a reading at the + and - terminals. There may also be a test between one of those primary terminals and the secondary, in other words, where the plug wire goes into the coil. I'm not sure if with coils if there is always a connection between the primary and secondary within the coil. I would look at the FSM to see if there is that test and the spec for it.

You do not really have the eqiupment to tell what is what. Used replacement coils (including igniter) are easy to find using the parts for sale/WTB section.

OK, going to seek out some parts then.

On testing the secondary, I did find non RX7 sites that say that talk about testing the secondary and the impedance range that it should be... Could one of you guys test the ohms on your leading coil between the spark plug connector and the ground? I'm very curious to see what you get.

I don't have an FC anymore only my FD. The FSM actually doesn't have a spec for it. I looked in the link below page 5.32-33 They only give a resistance reading of the primary.

http://www.rotaryheads.com/PDF/2nd_g...cal_system.pdf

Woo Hoo! I swapped out my leading coil with a replacement and I have spark now, but it still won't start. Checked the fuel pump and things are good there, any ideas? My tach still does not bounce when its cranking, I'm wondering if the trailing coil is bad too, but I may back burner that for the moment...

Trailing coil runs the tach.

There are bullet connectors at each coil (wire which is short length and connects to nothing). Jumper both of these to each other and the tach will work off of the lead coil.

Engine might be flooded.

Engine might have low compression preventing it from starting.

You can spray 1 to 2 seconds of starter fluid into the intake and see if the engine will start up briefly.

I know this was posted a while back but I could not find answers after searching for a while. I'm posting to help others. Here's what I found out that might help:
1. The leading secondary coil does not return to ground. This means that you will read open on the ohm meter if you are probing between GND and one of the high tension outputs. Instead you should Ohm between the two high tension outputs as they are connected to the opposite ends of the secondary coil. I found this out by experimentation but have not been able to confirm. I measured about 14K Ohm.
2. I also had trouble measuring the trailing secondary coil. It was measuring open as well but when I tested it by pulsing the primary with a small cell (used a 1.5V C cell) I got it to spark. I suspect that the secondary is returned to GND but has a DC block of some sort (a smal gap or a capacitor)??? There is a chance that the secondary connection to the high tension output post is broken and the spark is simply jumping across the gap but both of my trailing coils are doing the same thing. I think this is unlikely and the DC blocking is by design to prevent damaging the coil during accidental direct connection to chassis/GND.

It would be good for someone that know this for sure to confirm so people like me are not guessing.