When the Exhaust coil is turned off, The intake coil is Advanced ?

[rinkadinc]

84 720,2.4Lz eng.  The initial ignition timing is 3 deg btdc plus or minus 2 deg?  Since I have the Carby off my eng, I cant check this.  My FSM talks about the full throttle vacuum switch turning off the exhaust coil and Advancing the intake coil, no number given.  Supposed to decrease the engine noise.   Where is the ignition advanced from, pin D of the EEC control box? or the ignition module?  Probably the control bow.  How many Degrees ?     

 If the vacuum switch turns off the exhaust by grounding the white wire ( from vac switch to ignition module ) which also grounds pin 4 on the EEC control box ?  Could someone verify that, please.

Which then advances the intake coil how many degs, 3, 5, or what ever.

[ggzilla]

I'm guessing it's all done in the distributor. There are several wires inside that connect to the module, one for EX and one for IN

[rinkadinc]

My ignition module has 4 tabs, the white wire, 2 for the coils, and the power wire.  mainly I was asking about the degrees of advance. I forget to clarify things properly. 

[rinkadinc]

The exhaust coil is switched off during Full Throttle or does it happen only in 5th gear full throttle?    

 

I know where the timing marks are, I just have to remove the radiator and possibly the front grill.  Not really, I painted the timing flange with a yellow paint marker, let sit a few sec, and wiped it gently. now all the lines and numbers stand out? I just have to thread past the alternater and power steering belts.

 

I was trying to check the timing and fuel was pouring out from the top of the carb where the fuel goes in. The strainer in the gooseneck was smushed and was spraying.

[datzenmike]

Dual plug timing is 3⁰ because the burn time is so short with two ignition points. When switched to single plug it takes much longer so has to be started sooner (advanced)

 

No advance numbers are forthcoming in the manuals but the previous L series engines, which are single plug, are 12⁰. Some conclusions can be made that it would be 10-12 degrees or 7-9 degrees added. Someone should ground their white wire while the timing light is connected and see what it does.

[ggzilla]

Like some other ignition modules, I would guess the advance difference is built into the Z-series module itself and not calculated/delayed by the ECU

10 hours ago, rinkadinc said:

My ignition module has 4 tabs, the white wire, 2 for the coils, and the power wire.  mainly I was asking about the degrees of advance. I forget to clarify things properly. 

[datzenmike]

The ignition cut to the exhaust plugs and the advance on the intake side was used on trucks without the ECU. It's in the module design and only needs a vacuum switch to detect heavy load and the grounding of the white (fourth) wire.

 

 

 

 

[ggzilla]

Yes, I was thinking about that last night as I was falling asleep. It works on the trucks without ECU such as non-california carbureted Z22 and Z24

[datzenmike]

As to the reason for the ignition cut to 'reduce noise', perhaps the two flame fronts colliding in the combustion chamber sound is loud enough to be annoying?

[ggzilla]

Never understood that statement from Nissan. Has anyone bypassed the switch and noted the sound of the engine? Is it a big noise, or a very slight noise difference?

[datzenmike]

Probably clacked like a diesel idling 

[Sephakrid]

Well now I'm getting curious. Last year I tested the shutoff system and noticed that while the exhust side plugs will stop firing, the timing will not advance. My truck has an ECU, but I'd guess that the ICM controls timing?

[ggzilla]

23 minutes ago, Sephakrid said:

My truck has an ECU

720 carbureted model has no Engine Control Unit. It has a ECC Control Unit for the Electronic Controlled Carburetor

 

it has only a few pins compared to a EFI+spark Nissan ECU

 

 

[rinkadinc]

5+ years ago, when my truck was on the road. I had wired both coils together so they would always work. I didn't notice any great amount of noise. Of course, I have a little hearing loss, espechely with the windows open or the radio up. And even with the carb 2ndarys jetted lean, I was able to keep it at 85 mph, most of the time, until I had substantial head wind. Then it was back to 4th gear.

[datzenmike]

15 hours ago, Sephakrid said:

Well now I'm getting curious. Last year I tested the shutoff system and noticed that while the exhust side plugs will stop firing, the timing will not advance. My truck has an ECU, but I'd guess that the ICM controls timing?

 

Says right in the '84 FSM that the distributor has a switching function that turns off the exhaust side plugs and at the same time advances the intake side. The manual says 'the specified amount' but I can't find this amount listed. If your intake side plugs don't advance then there would be a severe drop in power equivalent to loosing 8-10 degrees of timing. 

 

7 hours ago, rinkadinc said:

5+ years ago, when my truck was on the road. I had wired both coils together so they would always work. I didn't notice any great amount of noise. Of course, I have a little hearing loss, espechely with the windows open or the radio up. And even with the carb 2ndarys jetted lean, I was able to keep it at 85 mph, most of the time, until I had substantial head wind. Then it was back to 4th gear.

 

You had the intake side of the module work both coils? That's doubling the work it has to do. The spark shut off is only under heavy load such as passing or climbing hills mostly at full throttle. It would be easier to unplug the white wire to the distributor so there is no signal to turn of the exhaust side.  

[rinkadinc]

datzenmike, I didn't dig into the wiring or the schematics and find out about the white wire, until January of this year. I just remember reading about a vacuum switch turning off the Ex coil in the Haynes manual.  Or somewhere. I didn't get FSM until last fall.  I disconnected the Ex coil at the 3 way junction for the ignition module and the coils and jumpered both coils together. They were hooked together for approximately 5 years.  I didn't really pay much attention to the vacuum switches or the wiring till this spring when I was trying to hook up the broken wires to that 3rd coolant sensor and trying to get it to pass the tailpipe sniff. That was with the ripped o-ring on the mix solenoid.

The smog Tech said the midrange would be really lean then switch to super rich. It would just osulate back and forth. I think it was getting about 3mhg. for the 30 mi I drove it.

 

[Sephakrid]

I was able to dig into this over the weekend. Swapped my Hitachi ICM for a cheap aftermarket one (HM703). I ran the same test where I disconnect the forward vacuum switch and observe any changes in ignition timing. Both ICMs do the same thing. The exhaust side coil will shut off (verified with timing light) but ignition will not advance at all.

 

Edit: by "disconnect" I mean removing the vacuum line from the switch so it doesn't receive a vacuum signal.

Edited August 11 by Sephakrid
Clarification

[datzenmike]

Well the '84 FSM says the ignition module turns off the exhaust side and at the same time advances the intake side during single plug operation. It's not specified how much but I would assume about 8 degrees +/-

 

The switch detects low vacuum as in under heavy throttle so it has to be connected to work. So how did you manage to get the module to turn the exhaust side plugs off??? The manual says to use a hand operated vacuum pump connected to the vacuum switch. Apply 5.91 inches of mercury (InHg) vacuum to the switch and slowly reduce the vacuum to 3.15 InHg and the exhaust side plugs should shut off. Do the same on the intake side using a timing light and it should advance.