Leading spark gone after engine warm

[rexall]

I am perplexed about my 1984 with the 12A.One fine day the rpms didnt drop but the engine didn't sound right.I just couldn't find anything wrong with the fuel delivery.And the spark was good or so i thought.My coils are good, my ignitors are good but if i do a cold start with choke on it runs strong.The choke eventually goes off and it idles real nice then after 6 or 7 minutes it almost dies then eventually dies after 5 seconds.So i discover that the leading spark is gone. Now after it cools down i check the t1 an L1 plugs well grounded to to the strut towers i get spark top and bottom. Has anyone ever had this happen to their Rex? Its had a small oil leak from the oil cooler heat exchanger and the oil is dripping onto the coolant sensorAnd sometimes the engine fan won't engage for fast draw cooling.An rx7 expert said that's not causing my problem but refused to offer any help unless i let him check it out and pay him a lions share. The car has 82,000 originals and has been carefully driven and maintained. Bone stock except racing beat muffler and new cat. Thanks to anyone who can offer a viable suggestion. Chris, P.S. i switched coil wires at distributor and the spark moves naturally to the top and not bottom.Not sure if this is good idea but had to know.

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[Rogue_Wulff]

You could be looking at either a bad coil or ignitor. They can test good when cold, but fail when warm.
Also, when the leading quits firing, have you checked for power to the coil?

[Rx-7Doctor]

Originally Posted by rexall

I am perplexed about my 1984 with the 12A.One fine day the rpms didnt drop but the engine didn't sound right.I just couldn't
find anything wrong with the fuel delivery.And the spark was good or so i thought.My coils are good, my ignitors are good but if i do a cold start with choke on it runs strong.The choke eventually goes off and it idles real nice then after 6 or 7 minutes it almost dies then eventually dies after 5 seconds.So i discover that the leading spark is gone. Now after it cools down i check the t1 an L1 plugs well grounded to to the strut towers i get spark top and bottom.

Has anyone ever had this happen to their Rex?
Its had a small oil leak from the oil cooler heat exchanger and the oil is dripping onto the coolant sensorAnd sometimes the engine fan won't engage for fast draw cooling.An rx7 expert said that's not causing my problem but refused to offer any help unless i let him check it out and pay him a lions share.
The car has 82,000 originals and has been carefully driven and maintained.
Bone stock except racing beat muffler and new cat.
Thanks to anyone who can offer a viable suggestion.
Chris,
P.S. i switched coil wires at distributor and the spark moves naturally to the top and not bottom.Not sure if this is good idea but had to know.

If the engine has good compression and the ignition components are in good working order, the engine should not die when you lose leading ignition. It will have a loss of power but will run just the same.

As Rogue has pointed out, the coil or ignitor if bad can show the symptoms when they get hot. Usually it is the coil but I have seen both. Check the connections at the coil and the ignitors. Also recommend that you check the coil leads for corrosion and if you have a ohm meter to test them. I have seen where the ignition rotor was bad and would cease to function after warming up. It is very rare but do not rule it out.

As far as your cooling issue. The coolant temp switch has no bearing on the operation of the fan clutch. Electric fans have a coolant fan sensor that controls the operation of the fan. Ours have a thermostatic fan clutch that engages by reading temp at a bi-metal strip. When the engine is at operating temp, shut if off. Then spin the fan by hand, there should be some resistance, meaning generally the fan should not spin more than one revolution. If there is no resistance then the clutch is bad.

[rexall]

Thanks for the info.The engine dies but i can restart and drive the car but it wont idle for more than 2 seconds.it fires right up again.I bought a new coil and a good igniter and have been switching coils and igniters trying to find a combination that eliminates the bad component.No luck yet.There is a small amount of play in the distributer shaft but with 82,000 miles i would think that is not the real problem unless they are an inherently short lived ignition component.I dont have correct idle set or mixture set perfect now as i was trying to get a combination to work before i discovered the "no spark"problem.My idle is 1100 rpm after choke off but im not turning it down until i get spark.This car has the capacitor that is mounted to the side of the distributor.I have heard this is for radio hum suppression and heard it controls ignitor spikes.The Haynes manual doesn't supply enough info on the capacitor that i can find.
One post says the ignitors work or they dont work.No matter what i've done to this point it is the leading spark that cuts out using the coils and ignitors that work on the trailing spark.
I guess it all comes down to the ohm meter.I will get one today.
Thank you all for your generous contributions.its much appreciated.
Chris,the old guy with the Dover colored REX

[rexall]

Side note:I changed the spark plugs 2800 miles ago.when i pulled them after the problem arose.T1 and L2 were perfect beige color and L1 and T2 were a little more bronze in color.I thought this to be strange.I suppose the new spark plug wires have quality issues.
I put a timing light on it to check the wires and was unable to get anything from the T1 T2 coil wire.After spending many hours playing with combinations occasionally i would get a few flashes from the timing light so I surmise that here is a very limited amout of juice coming thru.

[rexall]

The lead pickup for some unknown reason did not respond to the ohm meter check.Bought a used distributor.Runs great again.

[RXnos1200]

^^^^^^^^ good to hear.

[Jeff20B]

I had a bad leading pickup wire once. Glad you found your problem.

[Kentetsu]

Thanks for the info on that. I would not have thought of the pickup going bad, you don't usually here that one. Glad you got her running good again...

[Rogue_Wulff]

Thanks for updating us with the info.
The pickup coils can go bad, but it's a rare thing. If you have a dizzy that keeps knocking out ignitors, the pickup coil(s) should be checked. Most people just assume the ignitors keep going out due to age, but repeated failures can often be traced back to a faulty pickup coil.
This same advice applies to any electronic ignition system. The GM ignitor that is now so cheap, wasn't always as affordable, and had frequent failures, usually from a faulty pickup coil.
Electronics have a specified range of voltage/amperage/resistance in which they can operate. Outside of that range, bad things happen.

[Jeff20B]

The pickup wire that was bad in mine was in a spare dizzy I aquired, porobably from a core engine or something,. It looked like the PO didn't pay attention to the wires when he installed the aluminum cover. It pinched one of the wires which led to its eventual failure. So pay attention!

[rexall]

Thanks for all your help guys.It really is essential to have a voltmeter and ohm meter.Its near impossible to figure out whats wrong when your dealing with an electrical problem without meters to check continuity and such..I got a combo for $13.95 at a local auto parts store.I realized what a GREAT TOOL it is to have around.

[Jeff20B]

Yep. That's how I found out the wire was bad.

[HadaGSL-SE]

This sounds similar to a problem that I am having. Where is the pickup coil located on the distributor?

I cannot get leading spark. I have switched around coils, ignitors and can get visible spark to the leading coil but not to the spark plugs. The plug wire are less than 6 month old.

Thanks,

Greg