mryuri

Hi all, got a 72 240Z, would be grateful for any tip relating to my issue. When I crank the car, it fires, but as soon as I let go of the key, it dies. So I could keep it running if I kept the started motor going. The car will not even run for more than half a second after I let go of the ignition key.

It may be relevant I was having some juddering issues while driving and needed to add revs and a bit of choke to keep it from juddering. When I gave it gas, it sort of bogged down and wanted to die momentarily, unless I used some choke. The SUs were tuned really well by someone that knew what they were doing (Classic and Race, Sussex) and it ran as sweet as a nut for about 6 months until the juddering started. Went to the car the other day to look at coil connections, saw a small disconnected lead, for a thin wire, looked like it slid off a coil connection. So put it back on. Thought I may have cured my juddering issue, but got a new, non-starting issue! I removed the wire again, still not starting. Now, I am not sure if it was a coincidence about the lose wire. As the car sits a lot. and I am thinking maybe the coil is now dead? And the wire was intentionally pulled off by someone that knew what they were doing?

What is the symptom of a totally dead coil? (don't have an Ohm meter, was going to get one, just ordered a new coil instead) Fires up, but won't run when I let go of the ignition key? New coil was installed about 5 years ago. Ordered a new any way. Along with rotor, and leads. (it's converted to electronic ignition)

Fuel filter pretty new. (6 months) But I have run the gas tank nearly dry a couple of times. It is a clear filter. Looks a bit grubby, but I don't know what is ok or not.

Any tips on the initial juddering and now non-starting issue?

Cheers

I am the only 240Z running around London UK. Silver with spoked wire wheels, wave if you see me. Everyone else does! Get more photos taken of me driving the car then the local Veyrons, Ferraris and Lambos

beg3yrs

Not sure if this is true for the 240Z but in my 260Z the coil has a resistor in series with the +12v when the ignition switch is in the run position. In the start position the resistor is bypassed to give more "oomph" for starting. The wire you fiddled with may be the resistor and it could have been replaced incorrectly or, you may just have a bad resistor.

If your car starts, your coil is at least working with full current running through it.

You can easily check these things with a multimeter. You can get a good-enough one at Harbor Freight for well under $10 and sometimes free with any other purchase if you have a coupon. I have a couple (always free) and they're definitely "good enough". Oops - just realized you're in the UK so Harbor Freight isn't an option for you. Return the coil and use the money for a multimeter.

BTW, I used to go to London quite a bit before retirement. Great city and yes, a Z car would really stand out against all the other high-end cars. Right hand drive I suppose too.

mryuri

beg, Thank you for the reply. Kind of you.
The car does not start. It fires when the ignition is turned, but dies instantly when I let go of the key. Won't run even for a microsecond when I release the ignition key. It sounds like it starts fine, until I let go of key and am not turning it to start position. I will check the resistor connections again.

Thank you again.

beg3yrs

I understand. I should have said "fires" instead of start. If it is firing when the ignition switch is in the start position, you've got spark and that means your coil is working, at least with the inline resistor bypassed (which it is in the start position).

When you release the key and let the switch move back to the run position, the coil resistor is placed back in the circuit. That's when your engine dies. This plus your comment about some dodgy wiring around the coil/resistor is a huge clue regarding the source of your problem.

During normal engine operation, the resistor is in the circuit to limit the current through the coil, lengthening its life. Your resistor may be "open", i.e. disconnected or just broken. I wish you had a multimeter. You could measure voltage at the coil with the key in the start position. If you don't have any, you've got a wiring/resistor problem. If you do have voltage, THEN I'd suspect the coil has deteriorated with time and doesn't have enough capability to spark the plugs with the resistor back in its circuit.

mryuri

Thanks. That makes sense. So my resistor could be kaput. But my Coil can't be totally kaput as the engine fires (?) I have a small multi meter somewhere, just not sure where How would I check voltage at the coil when key in start position? I guess I would need a second pair of eyes? Plus there were quite a few connections as I remember.

beg3yrs

Yep, said something wrong again. You check the voltage at the coil with the key in the run position. You won't need a helper for that!

Only two connections on the coil. Set your meter to read volts, choose a scale that maxes out over 12V (my meter has a 20V scale) and use your probes to measure voltage between the + connection and ground. Your reading should be around 12V. If you have nothing, your resistor or its wiring is bad.

I suggest you study up on basic electricity. It really isn't too hard and it will help you a lot with issues like these. Maybe you can find an online beginner's course.

In the meantime, I'll look for a course on proofreading posts before I submit them!

mryuri

Ordered a multi meter. Thanks.

theramz

If you don't have voltage with the key on it could be the switch itself. You can test by removing the + wire from the coil and with the key on strike it quickly to ground. No spark probably means the ignition switch is bad.

beg3yrs

Doh! I should've thought of something simple like that. Who needs a multi-meter when a spark will do? A test lamp would have worked too. Oh well, mryuri needs a multi-meter anyway...

theramz

A multimeter is a little much for an inexperienced person. A 12 volt test probe is satisfactory for many things. My favorite tester is getting the girl friend to hold the dumb end of the coil wire. Very effective but you might get turned down that night.

beg3yrs

I see. That's why you have so many "helpers" instead of girl friends ...

theramz

yeah, they don't fit under the car to good. I keep burning up girl friends too but it's good for $hit$ and giggles. Never a shortage of women.

mryuri

just posted an update. Not sure why it didn't display? Anyhow: Got the multi meter. Resister seems good. But no voltage at coil when key in run position (but not running). So was advised contacts in key barrel. Took it out. Checked it with Ohm meter, seems to work good. Of course, I could be wrong, but one set of connections (central pins) are open when in run position and other (top pair of pins) only opens when in start position, so I'm assuming it works...
Any thoughts appreciated...
To me it seems somewhere between key barrel and coil, there is a bad connection...

Steve260Z74

Do your turn signals work when the key is in the ON position? If they do, you have 12 VDC on the circuit that should go to the ballast resistor. If your turn signals work, but you don't have 12 VDC going to the black/white wire at the ballast resistor, start looking at the dash harness. One place to investigate are the connectors between the dash and engine harness.

There are two connectors with black/white wires in the dash harness going to the engine harness. One goes out to the ballast resistor from the ignition key, and the other goes out to the coil from the tachometer. The connection from the coil to the tachometer is good. Otherwise your car wouldn't start. I'm not sure if the 4-wire connector or the 6-wire connector should be your focus. Unfortunately I don't have a 72 at my disposal to help you narrow your focus.

By the way, did you buy this car not running? If it was running when you bought it, what did you do to it before it stopped running?

mryuri

Thanks for that useful info. Much appreciated. You seem to really know a lot about this stuff. The turn signals work, but no voltage at the ballast. So does this mean it can NOT be the key connections? You suggest checking the dash to engine harness. Do you know where the dash harness meet the engine harness? I was thinking to try hot wire the car, i.e. not using the key's ignition connections. But I'm pretty scared I will fry something. I have ordered a new key ignition. But from what you say, it seems it can't be that?

The key connection has a five pin plug. I'm pretty sure the middle two pins are the 'on/off' connections and the end pair are for the starter. But not 100%. I was going to stuff a paper clip across from one pin socket to other and see if by passing the key ignition, it would run, thus telling me if the key ignition was faulty. Although the ohm meter tell me key ignition contacts work, they may not carry enough voltage. Parts guy says these things do tend to burn out.

The car was used regularly. But I left it sitting for a few weeks. It hates that. It was running rough just before that, for a few weeks. Juddered and wanted to die. I would have to increase idle revs and use some choke to keep it running. Thought the coil might be dying? Then got so fed up of it not running right, I parked it up for a few weeks. Had the car since new. My father bought it in '72.

Steve260Z74

Yes, I have studied the wiring diagrams of many of the years.

Now you have me wondering. Have you set the gap and dwell on the points lately? Improperly set points could give you fits, and under the right circumstances, it might appear to be a bad coil due to the weak spark.

Please do not take offense, but I have learned to doubt meter readings provided by novice users. Heck, I tend to doubt the results given to me by some of the engineers I work with due to my knowledge of their diagnostic skills.

Eventually, I hope to make some instructional videos on doing some of these diagnostics, focusing on where to place the leads from the meter and how to interpret readings.

It would be a good idea to download a copy of the factory service manual. There is a link in my signature to a website where you can download it.

Also, where do you live? Is there a Z club nearby? Around where I live, we are always helping each other with our Z cars. That is one of the benefits of joining the local club.

mryuri

The meter readings I am sure of are the voltage ones at the coil (zero in run position) and the resister (also zero in run position) But I am not 100% sure on the key connections. Really, I needed some small crocodile clips to make sure contact was continuous when I turned to start position.

No Z clubs about. Not many running Z's in this country... I have seen only two others in London in the last ten years.

We will see what happens when the new key connection peice is replaced.

I have not touched the breaker points. I have the factory manual downloaded. Cheers

Steve260Z74

When you measured voltage at the coil, did you measure from the coil positive to chassis? For the resistor, did you measure from one pole to chassis? If so, what color was the wire? Also were the points open or closed? Those are factors that affect your measurements.

Also, there are several Brits over at ClassicZCars.com. At least a couple are in the London area.

mryuri

Finally took out the resistor. It was kaput. burnt through. Replaced it, fired up fine :-)

Thanks for all the help on here. It is very much appreciated. If you are ever in London, and see a silver 240Z with wire spoke wheels, wave me down.

mryuri

Car still does a bit of a hesitancy thing when you pull away. Have to give it more revs than normal so it won't die. If I give it revs too quick, it bogs down and feels like it wants to die. Fuel filter relatively new. Could it be rich/lean fuel issue?

When cruising about 30 but in second gear (yes, revs will be a bit high) the engine doesn't run smooth. Sort of judders, again, like a fuel filter issue. Could a dying coil do something like this?

Steve260Z74

Make sure it is set to the factory specifications: spark plug gap, points gap/dwell, ignition timing, valve adjustment, etc.
Make sure you have a good distributor cap, rotor and points.
Tune the carburetors.