Testing the ignition coil per FSM

[Gary L]

My 76 runs fine one minute and then it suddenly dies. It starts right up again and will run fine for awhile but then will suddenly die. When it does this its like someone pulled a plug, no stumbling, etc. Just dead. The tach will just drop and its dead. I checked the fuel system (eg, pump, regulator, pressure, etc) and everything seems fine. Therefore I'm moving on to the engine electrical systems. I read somewhere that a problem like this when the tach just drops is sometimes related to the ignition control module wich I'm working my way towards examining. 

 

But In the FSM on page EE34, sec 2.2 it gives a procedure for first checking the ignition coil.

 

 

http://www.nicoclub.com/FSM/280z/1976/EE.pdf

 

The ohms across the ballist resistor as shown is supposed to be under 2 (1.6-2). Mine is around 6. A couple of years ago I put an Acel  8140C coil on it which I never measured at the time.

 

My question is, does this mean my ignition coil is no good or wrong or the ballast resistor needs replacing or what. Or is this not really significant ?

 

I really don't no much about this electrical stuff so any input is appreciated.

 

Thanks

Gary

 

edit addendum; After cleaning the ballast resistor contacts really good, the measured ohms is down to 3. The ohms across the ignition coil itself is 1.9.

Edited September 5, 2015 by Gary L

[Zed Head]

What kind of meter are you using?  All of your numbers seem high.  Spec. on the coil is 1.4 ohms.  If you don't have an adjustment on the meter, touch the leads together and record that number.  Then subtract it from whatever reading you get on the parts.

 

More details on what happened before the engine starts dying might offer a clue.  Is the engine still cold or is it hot (ignition module's fail from heat), has it been idling for a while or have you been driving it, is the idle speed low (AFM contact switch), once it starts happening is it repeatable or does it go back to just fine for hours or weeks?  Stuff like that.  Context.

[Gary L]

Admittedly the meter I'm using is an inexpensive cheapo from Walmart. When I touch the leads together they do go to 0.

 

I always warm my car up for 5 or so minutes before taking off so this is happening when the car is warm. It seems to start OK and revs OK and when I take off it seems fine, but then randomly and unexpectedly it'll just die as noted above, with no forewarning.  The tach will just instantly drop as it stalls, but then may jump alive again, and so on. If  it completely stalls, it'll start right up. It doesn't seem to happen when just idling, which I've got set about 900 rpms. Part of the problem is I can't get it to do it when I want, but then unexpectantly it'll happen. As I mentioned, I recently put on a new fuel pump, FPR, and checked the fuel pressure which is 28psi at idle and steady. That's why I'm now looking at the engine electronics. Also, I should mention I went thru the 35 pin connector testing on the ecu per the efi bible and everything seems within specs. I'm hoping its not the ignition control module because I see they are expensive. And it looks like I'd need an oscilloscope to test it, which is beyond my knowledge and know how.

 

Gary

 

PS I hope everyone has a great Labor Day weekend and gets to enjoy some great outdoor weather and activities, preferably in a Z!

Edited September 5, 2015 by Gary L

[Zed Head]

then randomly and unexpectedly it'll just die as noted above, with no forewarning.  The tach will just instantly drop as it stalls, but then may jump alive again, and so on. If  it completely stalls, it'll start right up. It doesn't seem to happen when just idling, 

Sounds more like a bad electrical connection, or a bad module.  The "jumping alive" again part is odd, but does remind me of a problem I've seen described with the wires to the pickup coil in the distributor.  The breaker plate moves with intake vacuum and the wires to the pickup coil flex back and forth each time.  They can wear through the insulation and short.  You might check those carefully.  When the engine dies the breaker plate would go back to its starting point and all would be good.

 

You can measure resistance at the terminal block while you twist the breaker plate, or just take the distributor rotor off and look closely.  If the distributor is old be careful because the breaker plate bearings get rusty and break their plastic cage.  You don't want to do that.

 

If you have a Federal 76, you'll have two pickup coils, one for cold engine and one for warm engine.  If you find a bad wire, you can rig things up to use the other.

 

And a cheap but effective ignition module swap is the GM HEI module.  Many of us use it.  ~$25 and some time.

[Zed Head]

Here's a picture of the pickup coils.  The wires are typically red and green.

[Gary L]

I thought I'd take a look for some loose wires before I take off to the cottage for the weekend, not in the Z of course.

 

I pulled the distributor cap and rotor as suggested but couldn't find any worn/shorted wires. This is a California model so there is just one pickup coil in the distributor.

 

However, I did notice two things with the ignition coil that may or may not be significant. First, the ballast resistor has two wires to a center post and one of them was very loose and flopping around. I'm not sure the role these two center wires play in the ignition system.

 

Then I see the high tension wire that comes out of the ignition coil and runs to the center post on the distributor was kind of looped around by the wiring harness (eg, ran over the area around by the throttle switch, cold start valve, AAR, etc). According to the FSM this wire should be keep away from the engine harness. When I put things back together I'll be sure to route it differently.

 

But otherwise, yes, it dies and then jump back alive just like there is a short or loose wire so I'll keep looking.

 

Thanks

Gary

[rcb280z]

Gary, if the loose wire on the ballast resistor doesn't fix your problem I would check your fusible links under the white cover on the passenger fender. Does it happen when you hit bumps while driving it? I recently had a similar problem though my Z but it didn't shut down completely. It would act as if it going to though. Like a hiccup so to speak. It would really act up when I hit those round lane dividers on the freeway while changing lanes. I traced it to a fusible link.  So what I'm trying to say is it seems as if you have a loose wire for sure and you may have already found it but if not.....

[Gary L]

Hi Robert, what you describe is pretty much what I've got going on. I'll be sure to check those fusible links again. When I looked at them not too long ago they looked OK, but I'll check them for continuity. I hate fusible links and don't know why they just don't use regular fuses. I blew a bunch once on my Bronco II and what a pain it was tracking them down and replacing them. Gary

[rcb280z]

They are a life saver actually on our systems. All I had to do was tap on the fusible link holders and I could get her to "hiccup" so to speak (due to loose link). Its worth a shot for sure. Would be nice if it turned out to be that easy huh? If there is ANY corrosion and I do mean ANY you will have problems eventually. I clean all my electrical connections once a year and when I had this problem a month ago it was during the time I should have done my annual cleaning. Thats what I get for putting it off. I live next to the beach in Southern California and have problems with sea salt and marine layers. So.... 

Edited September 5, 2015 by rcb280z