twin plug z24 head. simultaneous plug firing? any info

[rod JL]

hows it goin :)

 

just wondering there was any way i could get both my plugs on my z24 twin plug head firing at the same time? dizzy mods perhaps?

let us know

[datzenmike]

They fire together at the same time from the factory. Who told you different?

 

Later Z24s had a cut out to switch to single plug when accelerating under heavy load. Your dizzy would have a 3 wire harness and a single extra 4th WHITE wire with it's own plug. If you unplug this WHITE wire it stays on dual plug operation all the time.

 

 

Notice the extra WHITE wire with it's own plug?

[Farmer Joe]

already through about it. 

 

wont work.. 

 

youll technically need 2 distibutors to make both plugs fire at the same time with the same voltage. 

 

the factory system is almost this, but the second batch of plugs fires like 5 deg after the first set. 

 

it just a waste of time, unless you have some coil packs, and a mega squirt system laying around.. 

[datzenmike]

already through about it.

 

wont work..

 

youll technically need 2 distibutors to make both plugs fire at the same time with the same voltage.

 

the factory system is almost this, but the second batch of plugs fires like 5 deg after the first set.

 

it just a waste of time, unless you have some coil packs, and a mega squirt system laying around..

 

 

 

Joe you are baked.

 

The Z series with the NAPS dual plugs fire together, at the same time, as one, simultaniously. There is no 5 degree difference between the intake and exhaust side plugs. Sorry but this is an urban myth.

[ronnny]

I have not paid attention to this on my trucks much but with 2 coils and 1 distributer you can make 2 plugs both fire at the same time.  That is why there is two coils.  If you just had 1 coil you could not make both fire at the same time even if you had two distributers or the power would still go to the one of least resistence causing 1 to be weaker than the other and less effective. 

[datsunaholic]

As Mike said, they already fire simultaneously.  The misconception, or why folks think they are 5º out is because when one side goes out, it effectively retards the timing by about that much.  An L20B static idle timing is 10-12º, whereas a Z22 is 1-5º.  More notably is the Z20 engines- in 1980 they had one plug per cyl and 12 degrees of advance, but in 81 they went to 2 plugs and 4 degrees of advance.  The engines were otherwise identical.  The reason for that is flame front speed.  With 2 plugs on opposite sides, there are 2 flame fronts that meet in the middle.  With one plug, there's only one flame front so it takes approximately twice as long.  That's why larger engines with side-fire spark plugs have more static advance (the Allison V1710s I work on, which have 5 1/2" bores, fire the plugs at 28/34 degrees BTDC).  Center fire spark plugs reduce the advance, but that was extremely rare on OHC/OHV engines prior to the mid 80s (really old flatheads used center fire, though!).  Plus higher octane fuels have slower flame fronts so they need more advance (that's why cars designed for high octane ping with low octane.  Modern cars use a knock sensor and automatically retard the timing for that very reason)

 

/lesson

[datzenmike]

That right. The later Z24s did have a vacuum operated switch that sensed full throttle low vacuum and grounds an extra added on wire to a special later dizzy. When grounded, the dizzy will not only cut the exhaust plug coil but will also advance the distributor timing to (about) 12 degrees so that performance is not affected buy single plug operation. Nifty.

 

The reason stated by Nissan is to reduce engine noise under heavy load conditions. This was likely the two flame fronts colliding. Probably sounds like a Babbitt Diesel motor.

 

Regular twin coil Z series dizzy module. One power and one wire each for each coil. Terminal E B C

 

 

Later Z24 dizzy with four wire. Power, two coils and one for the shut off. Terminals E B C I 

[hurts donut]

 hey there  while pulling apart my 720 for a timing chain replacement, the plastic tip where the dizzy connects inside chipped . the metal flat screw looking head is still in tact and should still be ok right?  i thought we had a z22 in it ..turns out after a non fitting timing chain arrived that it is in fact a 1986 z24 somone swapped years back. 

is there a difference in the "dizzys"..do z22s have the 8 plug thing goin on to? 

(trying to figure out how to post pictures btw.)

[datzenmike]

They all had 8 plug. A Z22 dizzy will work on a Z24 or the other way round. If you have an '82 it wouldn't be wired for the 4 wire dizzy anyway, but it will work.

[Mr.Dean_Yates]

They fire together at the same time from the factory. Who told you different?

 

Later Z24s had a cut out to switch to single plug when accelerating under heavy load. Your dizzy would have a 3 wire harness and a single extra 4th WHITE wire with it's own plug. If you unplug this WHITE wire it stays on dual plug operation all the time.

 

 

Notice the extra WHITE wire with it's own plug?

[img=http://i138.photobucket.com/albums/q251/datzenmike/Nissan%20Electrical/Z244wiredistributorcalisingleordualplugfiring.jpg]

 

Mike, can you post a few more pictures of this "mod"?

 

It sounds interesting...and if I'm gonna go through with the z24t project...this could be very useful.

 

Thanks

[datzenmike]

If you happen to have the 4 wire distributor... which is simply an earlier 3 wire with an extra white wire added. Just leave the white wire unplugged and the distributor remains in dual plug operation. Not really a mod.

[Mr.Dean_Yates]

Alright I'll have a look this weekend. Thanks

[poopypants720]

Mike... I was just thinking about this myself, wanting to fire both plugs at all times cause I like to run supreme... I have the z22 in my '81 n was still under the impression that one of the coils cuts out under certain circumstances, 4th wire or not...

 

I was going over the wiring diagram and the brown wire that is the power lead for the exhaust coil has many different break points starting with the vacuum switch then the (M)anual neutral switch(automatic inhibitor switch), n also the clutch switch...

 

if any of these are triggered it breaks continuity n kills the exhaust coil, does it not? if not, what DO these switches do?

 

 

Now, to overcome this, I was thinking of using the power lead from the intake coil n bridging it to the exhaust coil(disconnecting the brown lead of course) n then be able to fire both coils simultaneously all the time...but I wanted to brainstorm n see if this was feasible, now your making me second guess my assessment of the diagram and what I'm looking at in my own engine bay...

 

also the 3 wire distributor is EBI, not EBC....

[poopypants720]

this was driving me nuts... I swore we discussed the difference of an early model set of switches compared to the newer model 4th wire both cutting off the exhaust plugs....

 

it was over on 720 world(http://720world.com/forum/topics/engine-misfire?id=2016119%3ATopic%3A19463&page=1#comments) and was brought up by tiger, cause initially I was under the same impression that you are expecting here...

 

we had talked about getting together some pictures of the wiring diagram n my new phone has an awesome camera, so hopefully you can see that it maps out on the exhaust power line(speaking of the switches along the way)...

 

 

tiger suggested that just unplugging the vacuum switch would alleviate the problem of shutting down the E Plugs... but I'm still wondering if those neutral and clutch switches would also have an effect on their own?

[poopypants720]

 

 

[poopypants720]

Gotta figure removing the switches from the equation can't hurt anything, it's just one brown power wire providing 12v for the coil and a couple other unnecessary(or in my case non existent for many)things, but mostly it's the blue and white wire that then kills it keeping it from getting to the source...

 

so considering my truck starts in any gear, clutch out or not, I don't have an automatic transmission and I have an aftermarket Weber carb I just went ahead and disconnected the 3 switches and its got nothing to possibly impede it...

[datzenmike]

If you look you'll see that this switch does not disconnect any power from the coil. It does direct some power to the Blue White wire to the auto choke heater and the clutch switch

[poopypants720]

so your saying the entire reason for series of the switches is to actuate the auto choke heater? cause it's not one switch to power another switch..

 

 

a well written explanation of what is actually going on here and for what reason would be awesome to find in a manual... cause given these schematics it seems that is either a grounding loop or one elaborate set of failsafes to actuate a simple choke heater...

 

n why would a neutral position or clutch pedal have any bearing on whether or not the choke heater is needed? or even vacuum?

 

all of those things would make perfect sense if they were being taken into consideration for the number of spark plug banks firing, especially considering they are factors in later 4 wire dizzy models...

[datzenmike]

Shit sorry.... The vacuum switch (plus other things turns the idle cut solenoid off under certain conditions of high speed and engine vacuum. On sudden deceleration when the carb is closed fuel normally supplied to the idle circuit is being sucked into the motor and wasted out the tail pipe. If the clutch is not in, if the trans is not out of gear, throttle closed and there is high vacuum the idle cut will close to save gas..... oh and also reduce hydrocarbon emissions.

[halfdome]

Hi folks -

So --- is there any harm done to the engine if you discover that the exhaust coil has not been working for a LONG time.....like 100,000 miles? 

From what I have read here, the vacuum advance will still work fine under full throttle (it simply cuts the already not working exhaust coil). 

 

Only downside would be from an emissions standpoint?

[ggzilla]

It don't damage the engine. It increases emissions and you lose a bit of power.

[datzenmike]

It takes a small but finite time to burn the fuel and air. The ignition point is set so that the expanding hot gasses reach their peak at about 15 degrees after TDC. This is the most advantageous point to transfer energy to the down moving piston. On a single plug engine it may be around 10 degrees BTDC. Two plugs mean two points of ignition so the fuel and air will burn completely in a shorter time, so you would time it to light later to hit the 15 degree sweet spot. A dual plug Z24 timing is about 3 degrees. If the timing is set at 3 and one of the plugs isn't firing then you are actually set (7 degrees) too retarded.

 

Most Z24s have an exhaust side plug shut off. When activated the distributor has a built in advance for the single plug operation so that power is not lost.

 

Running single plug won't hurt anything, as evidenced by having driven 100K, but it is very inefficient and would lack power and good mileage. There's no way to know that the exhaust plugs were not firing for the whole 100K. Usually the first fuse on the far left of the fuse box blows and this is what shuts off the exhaust plugs. 

[Ash_johno86]

Hi Mike, would you have a wiring diagram for the distributor and twin coils, something's not right with the set up I have, the bloke before me has hacked at it all!

[wayno]

Hi Mike, would you have a wiring diagram for the distributor and twin coils, something's not right with the set up I have, the bloke before me has hacked at it all!

 

What year is your truck?

[datzenmike]

 

 

Set to TDC compression stroke on number one cylinder. The rotors should be (intake 1I) At 9 o'clock, and (exhaust 1E) at 4 o'clock. Nissan caps have the wires marked. There are 4 slightly outer intake plugs and 4 slightly inner exhaust plugs.

 

If not, it's likely the distributor drive spindle has been out and put back in a different configuration. Take the two distributor mount bolts from the base pedestal and look down in. The drive spindle should be oriented like this...

 

 

Note that there is a small and large half moon that only allows the distributor to be inserted in one position only. Let me say here that if you can set your ignition timing properly, then the distributor position doesn't matter much, but if you are at the extreme range, re-positioning the drive spindle will put this right. It's even possible that someone else has moved all the plug wires around on the cap to 'make it work'.

 

To re-position the spindle, the oil pump must be removed. Expect dripping. The spindle will likely drop out with it. Engage the spindle into the oil pump and turn to align the punch mark and  two oil hole as in this picture...

 

 

 

When the oil pump is installed, the correct 11:25 distributor alignment should occur as in the 3rd picture.