Coil firing with ignition in "on" position. Need help.

[NC280z]

Good evening everyone,

 

So I've been fighting a bundle of electrical issues in my '75 280z. The current issue I have is that the coil is firing every few seconds when the key is in the "on" position. I found the issue by checking the fuel injection manuals "Ignition coil trigger input" test, looking for battery voltage on the ECU's pin #1. What I have instead is an unreadable, constantly changing voltage, coupled with the coil firing every couple of seconds. Anybody have any clue what the issue might be? I've started checking the wiring, and found that the white/black wire that goes to the coil +pos  side goes to ground, is this correct for this wire?

[ggzilla]

Not correct.

 

* with IGN on, engine OFF it should have 12+ volts

 

* with IGN off, it may indicate ground

 

Check the dual ballast resistor. Remove the middle wire and verify the wire has 12v with IGN on.

[datzenmike]

Does engine run?

 

Coil positive should have battery power from the ignition in the on position... and during start. The coil negative side should go off and on to ground to fire the coil when starting and running.

[NC280z]

It runs, but poorly. The car is running very rich (I've got a wideband A/F) and it's because of the current coil problem I've got. The coil should have power in the "on" position, but it shouldn't fire when the engine isn't running, which it is currently doing.

[datzenmike]

It fires the coil when the ignition is off ???????

[NC280z]

No, it fires every few seconds when the key is in the "on" position (making a loud click sound), and the engine can start but runs rich. With the key in the "accy" position the coil does not fire.

[ggzilla]

The engine cannot run if the coil only sparks every few seconds. So is the engine running?

 

How are you testing to see if the coil is "firing"?

 

The click you hear every few seconds - what makes you think it is related to the coil?

[datzenmike]

Pull the coil wire off and hold near ground, engine off, key on .... see if it sparks.

[NC280z]

I've already done that and it does spark. I know its the coil because with the coil removed the clicking stops. I'm not saying the coil isn't funtioning correctly, but the coil shouldn't fire with the engine off. And the engine does run, but its a hard start and it runs rich, as previously stated. Could it be the transistor ign unit?

[datzenmike]

I suppose so. Where is the box located? Make sure it is properly grounded and any connections electrically 'tight'.

[banzai510(hainz)]

Im not a Z expert but 1975 is this still a point ignition?

If external volt reg also I heard of run on with key OFF and it was the external Volt reg But Im only giuessing

To me a coil fireinf means there is 12volt to charge coil and a signal ground that opens to fire it off.

[datzenmike]

My info shows a remote igniter style used '75 and up. Probably not the high output EI we are used to. Just breakerless.

[ggzilla]

It used a low energy EI with a dual-ballast resistor.

 

Problem is we don't know what the symptoms are. What he says is not stated in normal terms. By 'coil firing' I wonder if means 'engine tries to catch'. Or does he actually mean 'coil sparking'?

 

Also I've never heard, nor heard of, a coil making noise when it 'fires'. The engine makes a noise when cranking yes, but not the coil. Maybe its the choke relay that is making the click. Or the starting injector timer.

[datzenmike]

Pull the coil wire off and hold near ground, engine off, key on .... see if it sparks.

 

 

I've already done that and it does spark. I know its the coil because with the coil removed the clicking stops. I'm not saying the coil isn't funtioning correctly, but the coil shouldn't fire with the engine off. And the engine does run, but its a hard start and it runs rich, as previously stated. Could it be the transistor ign unit?

[ggzilla]

Coils don't click.

 

"with the coil removed the clicking stops" sounds like a wiring issue. What is powered by the coil wiring? On some 30 year old cars, previous owners have connected various devices to the coil, eg. electric choke.

 

"the coil shouldn't fire" - does he mean "the coil shouldn't click" or "the coil shouldn't spark"?

 

"Could it be the transistor ign unit?" -- Not unless you hear the click coming from under the dash where the TIU is located.

[NC280z]

By "click" I mean the sound a high-tension cable or any high-voltage source makes when it discharges. What I mean by firing is that the coil is discharging every few seconds with the key in the on position, and since the engine isn't running the coil is audible. If you've ever heard a spark plug or electric grill igniter discharge, that is the sound a coil makes when discharging. The FSM states that the TIU controls the coil, which is why I was curious if anyone else has had similar issues with the TIU as the cause.

 

*EDIT* I should clarify that I'm not trying to be a smartass. I just want to clear up any misunderstanding in my description of the current issue. I've read in the FSM that the TIU controls when the coil is grounded (among other things), which then causes the coil to discharge. The coil should not discharge unless the engine is running, but mine is discharging at a steady, constant rate every few seconds with the key in the "on" position and, of course, the engine not running. I should have battery voltage at the ECU #1 pin, which connects to the coil negative, the TIU, and the tachometer. I don't have battery voltage, but instead have a wildly varying voltage because the coil is in a charge/discharge state. This is causing ignition issues, and causing the engine to run rich because most of the mix is passing into the exhaust unburned. The FSM simply states to trace the wiring, with very little (by that I mean no) information on what cables should have voltage or grounds, and under what conditions. Only which cables connect to what, and under what switch conditions/key positions. I believe my issue is in the coil negative side, since whether or not the coil is grounded decides if it fires or not.

[datzenmike]

Grounding the negative side of the coil doesn't fire it. It's the removal of the ground and the stopping of current flow that causes the magnetic field to collapse across the secondary coil and induce a high voltage spark.

[NC280z]

So then not having a ground present in the "on" position would cause it to fire? This makes sense, and thanks for clearing that up. I'll check to make sure that the ground for the TIU is in good order, as well as the rest of the blue cable on the coil negative side that leads to the ignition switch and ECU. Does anyone have the wiring diagram for the '75 280z? I've got one for the '76 and older, but the '75s don't have the ignition relay, which is in the diagram I have and on '76 and later S30's.

[datzenmike]

Generally there is ignition power to the coil + side. In operation the negative side is grounded by points or some other electronic method. At some time the points or the electronic circuit opens and there is a spark. 

 

As your engine is not turning I can only assume that something is triggering the electronics to close and then open the circuit every few seconds.

[banzai510(hainz)]

12volts one side of coil(key ON)

when a ground is present the coil charges. ground is Lost the coil that is charged up will collaspe the magnetic field thru the 2nd winding thus producing a spark(if a coil wire is near grouind, like the center wire from distributor).

 

something is telling it to fire off. Since you dont have points it has to be electric module or your ignition switch is intermittant. Meaning the coil is grounded but the power going to it is ON off intermittant. But I guess you would see this in the instrumentation lighting in ignition or soemthing.

 

 

I would clean ignition connection first the look at the distributor or ignition module if you have one in this.

Im not a Z expert

[NC280z]

So just a quick update on my situation, I'm still having the same issue with my Z's electrical system. I can get the car to start, but it runs very rich, even after warming up. My wideband shows it at around 11~12 AFR at idle. I've read the comments and suggestions here, and I believe I may have some dirty connections at the ballast resistor or perhaps the coil that is causing it to behave this way.

 

On a side note, whenever I turn the key from "accessory" to "on" the tachometer's needle flicks up for a split second. It does it every time I turn from "accessory" to "on". Could it be the ignition relay or ignition switch causing both this tach issue and my issue discussed previously?

[datsunaholic]

I think the tach jumping is normal, mine did that.  If it jumped every few seconds (like when you say the coil is firing) then I'd say not normal.

 

If you've made sure all your wires are good, connected tight, and not broken/shorted/etc, and it's STILL firing the coil for no apparent reason, really the only 3 culprits are:

 

1) the distributor (which has the ignition pickups that feed the

2) Transistor ignition unit

and all of that is powered by

3) the ignition relay.

 

So I'd disconnect the distributor to see if the problem goes away.  If it doesn't, at least you've eliminated that one. 

 

As for the TEI,  replacing the TEI is kinda the only way short of running bench tests to see if it's the problem.

 

As for the rich issue, mine had a faulty temperature sensor that made the ECU think the engine was always cold.  I think I ended up connecting the sensor wires together to make it think it was hot (made it hard to warm up, though) but it quit flooding.  My Z had 3 separate water temperature sensors- the temp sensor (for AF mix), the thermotime switch (for the cold start valve), and the wholly different, 1-wire temp sender (for the dash gauge).

[NC280z]

*UPDATE*

 

I did some testing on the car today, and found that disconnecting components connected to the Transistor Ignition Unit (the coil, water temp relay, ballast resistor etc), turning the key to "on" and then reconnecting the component will stop the coil from firing while the key is in the "on" position. Cycling the key from off to on after disconnecting/reconnecting components causes the issue to come back, though. I've also found that removing the ignition relay does not stop the issue, basically the coil will still fire every few seconds even with the ignition relay removed. I've used a continuity tester to check the ignition switch, and there aren't any shorts. I'm going to purchase a 7-wire TIU off of ebay, and see if replacing it helps any. Otherwise I'll have to chalk it up to wiring, and start the painful hunt for any shorts the harness may have.

 

Also, the ballast resistor gets quite hot while the coil is firing. Seeing as how it's a large ceramic resistor, I'm certain it's made to withstand heat but should it get too hot to handle during normal operation?

[banzai510(hainz)]

 hot while the coil is firing 

 

that's a clue.  coil should be hot also.

 

Is this a stock coil. a aftermarket one might not be matched for your system buy only a coil for that type of car. Ohm resisitance wise.

 

Might be something else but Im not a Z expert.

[NC280z]

So I've replaced the old TIU with an E12-13 module from a '76 280z. The coil no longer fires in the "on" position. The car does still run rich, however. I may start looking into the fuel system for causes, since everything ignition-wise is new and has been tested. The fuel pump/regulator are new as well, but there may be something going on with the wiring for them.