4-7 firing issue; posting for a member

[LGAFF]

As stated in my first post, I would start with Dark Blue wire off the bottom of the DIS Circuit 932.....its the one wire that is isolated to 4-7 in the factory manual.

[scottfab]

Originally Posted by LGAFF

As stated in my first post, I would start with Dark Blue wire off the bottom of the DIS Circuit 932.....its the one wire that is isolated to 4-7 in the factory manual.

As stated on my first post:
"Fortunately you can do end to end wire tests on
the harness that runs to the coil from the DIS."

But since there's no points or score keeper, eh... doesn't matter.

[Paul Workman]

Having a 90, and not wanting to muddy the water with a possible irrelevancy, I've kept to just lurking up to now. But, now I have an observation and a question:

Out of curiosity, I took direct measurements of the primary and secondary windings of a set of AC/Delco ignition coils and was surprised to see two of them read open on the secondary (spark) side. However, the other two read 5.682kΩ and 5.590kΩ. However, the primary resistance was .4xΩ for all 4 of them.

The thing is, I changed the coils as a matter of routine at about 35800 miles as part of a starter and ignition R&R project. Up to then the coils seemed to be working OK.

I recon I'd not put the "open" coils back in service, but curious what others may have experienced when measuring resistance across the secondary (SPARK) terminals?

Another thing...

At the risk of that irrelevancy I mentioned, my ('90 FSM) shows an individual driver circuit for each coil, mounted to the coil module. Is that also the case with 91+ coil modules? If so, then the driver for that coil needs to be considered (in turn) and we can get to that. But, first is there a dedicated driver (ganged or descrete) mounted on the coil mod?

BTW, pulling the plenum is a right of passage for a ZR-1 owner. Might as well get that one out of the way!

P.

[scottfab]

Paul, I believe the "solid state driver" shown (4 of them) in the FSM to
be an error. The only drivers I know of are in the DIS.

As for the "open" measurement on the coils that work try using a 10k ohm resistor in series. I suspect you DVM is not handling the inductive kick from the coil very well. Or set up 100k rheostat in series with the meter and the coil then turn the 100k down to 0k. The reading then will be the coil resistance.

[Paul Workman]

Originally Posted by scottfab

Paul, I believe the "solid state driver" shown (4 of them) in the FSM to
be an error. The only drivers I know of are in the DIS.

If that is the case (and you may well be correct) then since the DIS was swapped and there was still no spark from the 4/7 coil, I have to think wiring or a bad coil. Course we're assuming (and THAT'S never good) the replacement DIS and the coil were not faulty. But, as Dom points out, the chances of that happening...on the same 4/7 coil are maybe 'bout the same as winning the lottery!

Originally Posted by scottfab

*snip* As for the "open" measurement on the coils that work try using a 10k ohm resistor in series. I suspect you DVM is not handling the inductive kick from the coil very well. Or set up 100k rheostat in series with the meter and the coil then turn the 100k down to 0k. The reading then will be the coil resistance.

Well...not wanting to vere into an esoteric discussion, I think you were referring to current lag due to inductive reactance. However, since the core has to become saturated (or tries to) in a few mS (at 7000 rpm), certainly the inductive reactance value would have gone to practically zero in the several seconds of applying a DC voltage (from my Fluke DMM), leaving only the wire resistance (ohms) of the windings. As for inductive "KICK", it occurs when current is cut off and the magnetic field collapses (actually). (Besides, two coils read open, but the other two read OK. Reactance/kick or what ever would be the same for all 4, I would think.)

But, the coils with an "open" reading were working at the time they were removed. However, being the "open" appeared on the secondary (read: high voltage) side, it isn't too hard to imagine if there was a tiny break in the internal connection or solder joint between the winding and the spark wire post, it is conceivable the voltage would be high enough to jump the breach anyway. (The coil is firing two plugs at the same time, so what's one more gap - more or less? High voltage introduces a whole nother aspect to troubleshooting. Saw a poor Navy Firecontrol striker dude lean past an open high voltage slip ring pin fitting (that had who knows what open loop voltage was on it!) and drew an arc about 8 inches long to the side of his neck.)

Anywayz...I agree with you re the wiring/connectors. The fact that the problem didn't really crop up until the injectors were replaced...by some mechanic...makes me wanna say HMMMmmmmm....

P.

[scottfab]

Originally Posted by Paul Workman

If that is the case (and you may well be correct) then since the DIS was swapped and there was still no spark from the 4/7 coil, I have to think wiring or a bad coil. Course we're assuming (and THAT'S never good) the replacement DIS and the coil were not faulty. But, as Dom points out, the chances of that happening...on the same 4/7 coil are maybe 'bout the same as winning the lottery!

Agreed, very unlikely another bad DIS but to be kept in the back of our collective minds. And as for the missing "solid state drivers" shown on the FSM we'll have to wait for someone to find them

Originally Posted by Paul Workman

Well...not wanting to vere into an esoteric discussion, I think you were referring to current lag due to inductive reactance. However, since the core has to become saturated (or tries to) in a few mS (at 7000 rpm), certainly the inductive reactance value would have gone to practically zero in the several seconds of applying a DC voltage (from my Fluke DMM), leaving only the wire resistance (ohms) of the windings. As for inductive "KICK", it occurs when current is cut off and the magnetic field collapses (actually). (Besides, two coils read open, but the other two read OK. Reactance/kick or what ever would be the same for all 4, I would think.)

I'm thinking the other way. The instantaneous current required by the DVM's constant current source (ohms range) can get confused. (lockup) I've seen it happen having evaluated competitors DVMs to Tektronix DVMs.
The range locks up and gives unexpected results. However, if you measured consistent "open" on a coil then ???? could be you theory bellow. In any case using a reasonable resistive value in series eliminates this.
The early HPs were bad for this. Long story of how I know this.

Originally Posted by Paul Workman

But, the coils with an "open" reading were working at the time they were removed. However, being the "open" appeared on the secondary (read: high voltage) side, it isn't too hard to imagine if there was a tiny break in the internal connection or solder joint between the winding and the spark wire post, it is conceivable the voltage would be high enough to jump the breach anyway. (The coil is firing two plugs at the same time, so what's one more gap - more or less?

I've never seen this but, very plausible.

Originally Posted by Paul Workman

High voltage introduces a whole nother aspect to troubleshooting. Saw a poor Navy Firecontrol striker dude lean past an open high voltage slip ring pin fitting (that had who knows what open loop voltage was on it!) and drew an arc about 8 inches long to the side of his neck.)

Ouch. not good.
I've been zapped hard a few times in my career, once by the HV section of a large screen CRT that just happened to be voltage regulated. It felt ME as a load and simply provide the necessary current to maintain it's V. I think I flew in the air a waz. Maybe 5ft.

Originally Posted by Paul Workman

Anywayz...I agree with you re the wiring/connectors. The fact that the problem didn't really crop up until the injectors were replaced...by some mechanic...makes me wanna say HMMMmmmmm....

P.

My best guess at this point is the connector at the input of the coil. Bent of broken pin.

Someone needs to go over and help get an answer. The suspense is sure there.