I have a 87 N/A and it seems that the trailing coils only fires about 20% of the time. Ive checked the main relay and the coil itself are fine. Ive also noticed that when the tach works the coil fires too. My next step is to check the ECU to see if its sending the input signal to the coil. Any other suggestions?

 

check your plugs.
The Tach will read RPM off the coil by the spark it supplies to the plugs.
If the spark is not there the tach just doesn't read.
If you get spark between the wire and the coil But get no Tach,then your plugs are most likely fouled.

Also it is a good idea to remove the trailing coil and clean up any grounds in that area.Scrape the body and contact points down to metal so it will get a good solid ground contact.

 

ive spark tested the coil and checked the resistance of my plug wires and they are fine. Even if I got new plugs the spark test should have been succesful and it wasnt. It seems that the pulse sent to the coil isnt consistantly being sent but Im no expert here

 

Let me clarify, the spark test was only sucessful 2/6 times. It will always show spark for the first two second of cranking the motor but once the motor is running spark will totally cut out and my tach will stop working. Thats what happens of the test that fail to provide spark

 

What is the voltage output of the B+ wire from the alternator while idling. Too low of a reading and it could cause the trailing coil to stop working properly. Also, did you unbolt and clean the mating surfaces between the coil and fender as this is how the coil/igniter grounds.

 

B+ wire is that black and white one right? If so its reading battery voltage so its good. Ill clean the grounds tomorrow and tell you what happens

 

With the engine in idle mode what is the voltage (and it's the thick cable bolted to the alternator).

 

Oh the output cable!! lol Yea that is putting out numbers within spec. Even voltage drop tested ot and it came out good

 

3 ECU pins associated w/the trailing coil are as follows. 1X (Blue/Yellow) reads 0 volts w/key to on and .8 volts while idling. 1U (Brown/Yellow) reads 4.4 volts w/key to on and 2.2 volts while idling. 1M (Blue/Red) reads below 2 volts w/key to on and while idling (mine reads 1/3 volts at idle).

 

so i should test those wires at the ecu or at the trailing coil?

 

Ecu and the coil plug (connected) if the results test out good at the coil plug.

 

ill check this tomorrow and ill let you know the results

 

Im getting battery voltage at the blue/red with key on and idle

 

Where are you testing the wire from, the ECU or at the coil?

 

I swapped ECUs and the car is running better but still no reliable spark. Me and a few guys think its got something to do with the ignition switch

 

Why? If the lead coil is fine then the ignition switch has nothing to do with it. Did you ever get around to the arduous task of unbolting the trailing coil and cleaning the mating surfaces and bolt threads? The wire you get 12 volts on will occur if the coil/igniter is not grounded properly. If grounding the coil does not fix things then the coil probably needs to be replaced.

 

i sprayed the bottom and contact point with WD-40 and scrubbed them. Whatelse can i do to clean it?

 

Take a piece of sand paper and sand the fender and the back of the coil bracket and clean the threads of the bolts w/a wire brush.

 

did that, it got a little better but still wont fire 100%

 

When you switched the ECU did you test the troubled Blue/Red wire? If it is still the same then the problem is either the coil or the connection to the coil (and or possibly the ECU). Make sure the wire is not pulled back within the plug and thus not mating w/the coil/ECU.