tachometer woes.

[Jason Wright]

Wasup fellow 720 owners. Still working on the ride, and have another issue. The factory tachometer has stopped working. Tried all the basics with no results. So I wired up a sunpro super tach II. But it lags terrible. Am I missing something here? Are the coils weak. Not sending out a strong enough signal?

[smoke]

This may seem like a stupid question, but are you sure you have the new tach on the correct setting?

[Jason Wright]

Yep. Have it on 4 cyl. Hook the signal wire to the negative side of one coil, the needle would go up slowly then start falling the higher the rpm rose. So I went to the other coil but now it's just lagging until about 2500 rm then it picks up speed.

[datzenmike]

Wasup fellow 720 owners. Still working on the ride, and have another issue. The factory tachometer has stopped working. Tried all the basics with no results. So I wired up a sunpro super tach II. But it lags terrible. Am I missing something here? Are the coils weak. Not sending out a strong enough signal?

.

Are the fuel and temp gauges working? If not the 4th fuse over from the left side (15 amp ) needs changing. This will get the factory one working.

 

Next is the tack resister usually tapped up on the harness behind the drover's side headlights and near the coils. It is 2.5K ohms and if open or broken connection the tach won't work.

 

 

Last is the connection from the resistor to the intake coil negative side. (doesn't really matter which coil, either will work but intake is best) There should be a Brown wire firmly attached to that negative terminal.

[ZackeryNM]

Just want to chime in as I'm having a little tach issue of my own. I put a sunpro tach in the stock slot am hooked it up using the correct wires. It doesn't read so well anymore. It jumps all over the place but somewhat tracks here and there. Any thoughts?

[ggzilla]

Slightly corroded or loose connections will cause that. Clean all the tach connections to bare shiny metal and it may start reading steady.

[Robert]

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Are the fuel and temp gauges working? If not the 4th fuse over from the left side (15 amp ) needs changing. This will get the factory one working.

 

Next is the tack resister usually tapped up on the harness behind the drover's side headlights and near the coils. It is 2.5K ohms and if open or broken connection the tach won't work.

 

 

Last is the connection from the resistor to the intake coil negative side. (doesn't really matter which coil, either will work but intake is best) There should be a Brown wire firmly attached to that negative terminal.

 

 

One shuts off when manifold pressure drops. year dependent?

[ggzilla]

Which one shuts off when manifold pressure drops?

[smoke]

I have never heard that, but it kinda makes sense. Drop the exhaust under heavy engine load to help prevent pre-ign maybe.

[Robert]

 

I have never heard that, but it kinda makes sense. Drop the exhaust under heavy engine load to help prevent pre-ign maybe.

 

 

Yes. I stated "year dependent" because I only tested this on two. 1984Carb. and 1987 TBI.

 

One I could here knocking under load (1984) and was caused by wrong vacuum line arrangement. It was converted to a weber before I got it and the lines were not properl y placed. There is a vacuum switch that cuts off the exhuast coil when vacuum drop below X kpa. It was wrong and the exhaust coil was failing to disable under heavy loads. That and the timing was also set at 13 deg without vacuum line connected which meant it was set 10 deg to advanced.

 

The 1987 would cut out when i gave it more than half throttle. When I check spark, only the exhaust coil was firing. The intake coil had a spark path burnt to the ground wire. When the switch went active, the exhaust coil would shut off, and the engine would shut down until you let off the throttle again. Switched the exhaust coil to the intake and it worked fine until I replaced the bad one.

 

I am speculating but i would say all models are this way.

[Robert]

 

Just want to chime in as I'm having a little tach issue of my own. I put a sunpro tach in the stock slot am hooked it up using the correct wires. It doesn't read so well anymore. It jumps all over the place but somewhat tracks here and there. Any thoughts?

 

 

Some after market Tachs WILL NOT WORK using older coil systems. They are looking for a square signal coming from the ECU and not the coil discharge frequency of older systems. After about 1986 all vehicles went to ECUs and the ECU drove the tach. if its a new Tachometer it will trigger poorly if at all. You will need to make a trigger curcuit to fire it.

 

I have an AEM standalone ECU on my truck and it will not drive the stock tach. I had to simulate a coil discharge by running the ECUstach wirng the wire on a relay coil I cutt out of a relay and then through a 10k ohm resistor and then to ground. The coil in the relay disharged just like the ignition coil and gave the correct signal to run the stock tach.

 

Your problem is the oposite....you need to convert the coil discharge signal to a square one. To do this you need to take a zener diode inline with a 1k-10k ohm resistor (start with 1k). Conected the NON-banded side of the diode to the positive side of your coil, then to the resistor, then to the tach. If you get a random signal try changing the resistor until you get it right. This uses the coils square input from the points and sends it to the Tach without drawing all the power from the coil. Somtimes you can connect the resitor to ground and the tach wiring inbetween the diode and resistor.....try the first method first.

[Robert]

 

Wasup fellow 720 owners. Still working on the ride, and have another issue. The factory tachometer has stopped working. Tried all the basics with no results. So I wired up a sunpro super tach II. But it lags terrible. Am I missing something here? Are the coils weak. Not sending out a strong enough signal?

 

 

See my above post.

[datzenmike]

Which one shuts off when manifold pressure drops?

 

 

I have never heard that, but it kinda makes sense. Drop the exhaust under heavy engine load to help prevent pre-ign maybe.

 

I think it was the later Z24 dizzys that had this feature.

 

Usually there are 3 wires to the dizzy module under the rotor.... +12 and one wire to each coil negative terminal. Z24s had an extra 4th White wire that went to a vacuum switch that would sense low manifold vacuum (heavy load) and would ground that wire. On the module, the now grounded white wire would cause two things to happen. One... the exhaust side plugs would turn off. Two... the intake side plugs would automatically advance their timing (8-10 degrees) because of the increased burn time, in order to keep performance the same as dual plug operation. The reason for this Nissan says is "To reduce engine noise under heavy load".... whatever that means.

 

The factory tach is always on the intake side plugs which are always firing.

 

The intake side plugs are powered from a fusible link connected to the battery so there is no 'fuse' to blow on them.

 

The exhaust side plugs gets it's 12 volts from a fuse in the fuse box, so yes it can blow or have loose or poor contact. If this fuse blows the motor will run poorly as the timing is set at about 3 degrees for the very short burn time of dual plug operation.

 

 

Three wire module

 

Added 4th white wire with it's own plug

[ggzilla]

Ah he was talking about a coil dropping out. Yep, some year/some regions did that. The tach signal uses the primary coil.

[Robert]

Here is the diagram for it.

 

http://nissannut.com/projects/z24i_fuel_injection/720_z24_ecu_wiring.jpg

 

 

 

Just checked. ALL dual plug Zs had the same feature. My 84 has the same distributor and it was carb'd.

 

ALLDATA showns the same thing.

 

Makes sense though, under a load, you certainly dont want two flame fronts converging, that would be the same at detonation.

[Robert]

 

The reason for this Nissan says is "To reduce engine noise under heavy load".... whatever that means.

 

 

Sounds like they padded that one. Reduce engine noise?

 

 

Probably didnt want to scare people by saying..."to stop detonation".

 

But when my 84 did it, it was pretty severe. I would say almost on the level of a diesel knock. Sounded like my valves all began tapping at once. Actually took me sometime to figure out what was going on. I thought it was horrible carbon build up so I flushed the cylinders, changed plugs, used high octane, checked timing chain, and changed ingine temp sensor....I finally figured it out by cheking the timing of both coils and noticed coil 2 didnt shut off when I rev'd the motor.

[datzenmike]

Not all Z engines have this. Later Z24s did. I believe there is a term for the two flame fronts colliding but it isn't detonation. It does however make a distinctive noise that may sound like pinging. Nissan says single plug operation is "to reduce engine noise under load". If it was detonation or pinging I think  they would say so as that carries more weight than 'noise'.

[smoke]

It's more of a flame 'overlap' than a collision in this case anyway. I was thinking about this earlier and I don't think it's detonation (like Mike said). Because as far back as the late teens and early 20s, engines manufactures of aircraft engines where going to a dual plug system to actually stop detonation, and it did. So yeah, I'm thinking it might just be an oddball noise that a person does not want to hear, so they fixed it.

[Robert]

 

Not all Z engines have this. Later Z24s did. I believe there is a term for the two flame fronts colliding but it isn't detonation. It does however make a distinctive noise that may sound like pinging. Nissan says single plug operation is "to reduce engine noise under load". If it was detonation or pinging I think  they would say so as that carries more weight than 'noise'.

 

 

No its not detonation....I am saying that because thats what detonation is, two flame fronts colliding.

 

 

I just found some more info, not sure how reliable it is, it says that only manual transmissions had this feature....BUT I know this to be false since my 87 was automiatic. I also found it says that later models had this and only NON cali....BUT, my 84 has it. Driving me nuts now. I was happy with the thought that all Z's use this feature.

 

I am not 100% sure all have it, I know you must be seeing the same information I am about not all models BUT, I am beginning to believe that ALL dual plug models have this feature.

 

My reasons are, two plug operation no matter the model will create a detonation condition, the fact that they all used the same distributor, they all had the same vacuum has diagram, and when they say only manuals came with it yet my automatic has it, and my 84 has it also.

 

Have you seen a model without it? I will check my software and see it there is any diagrams without the vacuum switch.

 

Up until recently I thought they all had it..then I seen some info saying only certain models have it, then again I cant find any models without it....I feel like a ping-pong ball.

 

If anyone can give me a year and model that doesnt have it, I will pull up the vacuum and wiring diagram for it and double check. Not that my life will be empty without knowing, its driving me mad now.

 

lol

[Robert]

Let me throw this one in there.....

 

 

 

Anyone see a knock sensor on their blocks?

[datzenmike]

The '80 Z20S and Z20E non California A10 and S110 did not have dual plug distributor (all '80-'81 Canadian 200sx didn't either) But all Z20/Z22/24 series were dual plug from '81 on.

 

I have a Z22 720 engine dizzy and it does not have the single plug shut off feature. I'll check when I get home but pretty sure only some Z24s have it. The Z24 came out in Oct '82 ish

[Sealik]

All my 8 plug Z22 engines utilize the 3 wire dizzy. 81-82 4x4....Canadian

Z24s................................................4 wire dizzys

I am running a Z24 dizzy on my LZ23 (white wire unhooked) with a aftermarket tach

For some reason I could not get the stock 720 tack to work with the 2.2 ohm resistor in the 510

[Robert]

The '80 Z20S and Z20E non California A10 and S110 did not have dual plug distributor (all '80-'81 Canadian 200sx didn't either) But all Z20/Z22/24 series were dual plug from '81 on.

 

I have a Z22 720 engine dizzy and it does not have the single plug shut off feature. I'll check when I get home but pretty sure only some Z24s have it. The Z24 came out in Oct '82 ish

 

 

The shut-off feature is not only in the distributor. FI engines used the distributor, carb engines used a vacuum switch.

 

my 1984 uses a vacuum selenoid to disable the power to the secondary coil. The coil positive goes through the switch...when vacuum drops it opens the circuit. My 1987 used the distributor controlled from the ECU.  Thats why I believe the author of the book noted only some vehicles had the coil drop feature not being aware that some used a vacuum switch and not the distributor. Yet in the same vacuum diagram shows the vacuum actuated coil switch.

 

If anyone has a dual plug engine that they feel doesnt drop a coil when under load, please check for me. Disconnect your primary coil and see if the engine dies under load.

 

I just checked 4 other dual plug trucks and all drop the secondary coil.

[Robert]

The '80 Z20S and Z20E non California A10 and S110 did not have dual plug distributor (all '80-'81 Canadian 200sx didn't either) But all Z20/Z22/24 series were dual plug from '81 on.

 

I have a Z22 720 engine dizzy and it does not have the single plug shut off feature. I'll check when I get home but pretty sure only some Z24s have it. The Z24 came out in Oct '82 ish

 

I wasnt saying all Zs are dual plug (if thats what you were referencing). I meant that I thinnk all the dual plug Zs had the feature. I want to verify that statement though. Book says "some", yet I havent found one yet....so its atleasat "most".

 

What year is your truck? cali or fed? TBI or carb?

 

Im trying to narrow down which ones have it and which do not. If all your wiring and vacuum lines are srock, just unplug the primary coil and drive it...if it shuts off under load it has it. The vacuum switch for it is on the passenger fender wall or near it. Mine was missing and I had to replace it since someone swapped the carb out.

 

Its not important, but I am a bit like you, I love frinding out new things. I really want to find one that uses both coils under load.

[Robert]

Cam across this research paper.

 

http://www.ijsr.net/archive/v2i8/MDIwMTMyNDM=.pdf

 

 

Good read.

 

 

So, is this one...

 

http://www.ijars.in/iJARS%20549.pdf

 

 

 

I heard alot about dual plugs reducing detonation....I read these to figue out how and why that works. BUT dual plugs preventing det must coincide with a well designed combustion chamber or it will promote detonation. Now this is something I am familiar with since I have turbo charged dozens of different makes of engines and some need serious reshaping to prevent knock even on low boost.

 

Anyway, I learned dual flames dont knock (well atleast in most engine designs). Thnx for posting the aircraft using dual plugs to prevent this or I wouldnt have found it.