Exhaust coil

[DwayneOxford]

What's easiest way to make it fire all time? Would like to jumper a connector.

[datzenmike]

1/ Single plug operation only happens (or should only happen) under heavy load full throttle conditions. There is a vacuum switch which reads low intake vacuum and this shuts off the exhaust side coil at the distributor.

 

 Dwayne, your distributor should have 4 wires going to it. Three wires wrapped together and a forth white or maybe gray wire with it's own plastic plug. Disconnecting this plug should defeat the single plug operation and make both fire at all times..

 

2/ If you only have the intake side firing then the first fuse on the left side is blown. Replace it and this powers the exhaust side coil. If still only one side check that there is 12v on the positive sides of both coils. If there is then perhaps the distributor module is bad. 

 

 

[DwayneOxford]

Thanx Mike, mine's got all 4 wrapped, plugs into big connector with room for 2 more wires then the spade connecter at vacuum advance.

Where's the vacuum switch? Is coil control its only job?

[datzenmike]

The switch is activated by very low intake vacuum indicative of full throttle/heavy load. The switch tells the ignition module in the distributor to turn the exhaust side coil off. It also advances the ignition timing from 3 to 10? degrees as a single plug cylinder will take longer to burn.

 

 

Find that gray or dirty white wire wire on the harness to the distributor and unplug it. This will defeat the single plug operation and all plugs will fire all the time.

 

Nissan's reason for single plug running? It says to reduce engine noise under heavy load.

[DwayneOxford]

Where's that switch? Not seeing anything with wires about intake except for carb heater.

[datzenmike]

Over on the passenger side inner fender. There are two, don't know which is which, the other shuts off fuel on hard deceleration using the idle cut solenoid. There are round, have wires and share a vacuum hose to both.

[DwayneOxford]

Thanx agin!

[DwayneOxford]

My '85 seems to only have one. It's AT. 

Got another oddity. Clipped timing light on #1 intake, nothing. Tried exhaust, OK. Tried coil wires, exhaust working, intake not. Reversed them on dist., one plugged into int. not working, exhaust OK. Whichever coil wire is plugged into int. on dist. cap quits working.

Thoughts?

[datzenmike]

 

From your text, it would seem to me that there are two problems

 

1/ It's very easy for someone to have reversed the coil wires to the cap so don't worry about them. The intake is wired directly to the fusible link but the exhaust is run from the fuse box. If the fuse is blown, no exhaust coil.  First, try replacing the first fuse on the left side of the fuse box. This should get the dead coil working. Let me know.

 

 

2/ If the intake side remains dead even with a good coil firing then the cap or the rotor is bad.

 

 

If one coil not working and the intake side is dead on the distributor I assume if the dead coil is on the exhaust and the good coil is on the intake the truck won't start?

 

 

[DwayneOxford]

Thanx Mike,

Either/both work plugged into the exhaust position, neither work plugged into intake. Hate throwing parts at stuff but sometimes...

Will let you know what it is when I do.

[datzenmike]

Sounds like both coils working so has to be the cap or rotor damaged.

[DwayneOxford]

On 11/19/2023 at 8:30 PM, datzenmike said:

Sounds like both coils working so has to be the cap or rotor damaged.

Was rotor.

Had rotors leak coil fire thru to dist. shaft in past on single coil, but wasn't needing to time, never tried timing light to see if it'd do same as this did. I shoulda tried to see if that was case here but didn't. Odd to me that it totally stopped coil from firing.

[datzenmike]

Two coils firing has shorter burn time so less timing is needed, like around 3⁰

 

If one is not firing then the timing needs to be advanced like 10-12⁰ The engine will run poorly and get bad gas mileage if at 3⁰ on single plug. You should notice better performance, mileage and idle speed higher.

[DwayneOxford]

The dist. and rotor are off a lower mileage donor truck I never ran. Pretty sure other rotor was OK in dist. I swapped out, may check it sometime.