1984 Nissan 720 Project "Stan"

[sTanTruck]

I am in the process of fixing up this truck which I will document and ask questions using this thread.

List of fixes so far:

- Replaced air, fuel, and oil filters

- Changed fluids: transmission, t-case, engine oil, coolant  

- Replaced valve cover gasket

- NGK spark plugs

- Replaced upper and lower ball joints, and various other suspension bushings 

- A/T tires 

- Changed CV's 

- Oil pressure gauge, voltmeter

- Resealed rear window

- New belts 

- 180 Degree Failsafe Thermostat

- 3D printed OEM style gauge cluster (I may make a few and see if anyone is interested in one, post later with more info)

 

Next Steps

- Front brake lines

- Reseal windshield

- Radiator hoses 

- Transmission mount

- Accelerator cable 

- Retorque head bolts and adjust valves

- Weber 32/36 and remove vacuum lines

- Fix interior rust, paint, soundproof, vinyl floor mat

 

 

[sTanTruck]

Does anyone know if you can use the factory wiring harness for the Tachometer to run an aftermarket gauge? My truck did not come with a tach originally and I would like to wire one in without paying for one of the expensive gauge clusters with original tach. 

[datzenmike]

You can pull a factory tach from a gauge cluster in a wrecking yard and put right into your cluster. It's already wired for it.

[Seven Two Oh No]

I put an aftermarket tach into the cluster of my '85. Been meaning to do a write-up so I'll post one soon

UPDATE: created a how to here  -

Edited May 6 by Seven Two Oh No
Update

[sTanTruck]

On 5/5/2024 at 2:21 PM, datzenmike said:

You can pull a factory tach from a gauge cluster in a wrecking yard and put right into your cluster. It's already wired for it.

The issue is there are no 720's at the local yards and online prices for an OEM tach are outrageous. 

[sTanTruck]

21 hours ago, Seven Two Oh No said:

I put an aftermarket tach into the cluster of my '85. Been meaning to do a write-up so I'll post one soon

UPDATE: created a how to here  -

WOW! This is exactly what I am looking to do! Please let me know when you decide to post the tutorial. Were you able to use the wiring already there or did you have to install your own sensor? 

[Seven Two Oh No]

Check the link to the how-to, just posted it last night. You don't need a sensor, the tach uses the signal from the coils to operate. At minimum you'll need to run three wires - one from a coil, one keyed 12v power source, and ground. If you want to control the dial brightness, you'll need a second power source and ground.

[sTanTruck]

I believe I have a slight misfire at idle. I keep failing emissions for high HC levels at idle but I am passing with flying colors at 2000 rpm test for everything (I have to pass by 5/19 or I can't drive the truck until I figure this out). I noticed a little stumbling at idle but assumed this was an "old truck thing" so I never worried about it. What can I look for as a culprit for this? I have looked at the distributor cap and cleaned it out some but its not great (some of the contacts were pretty corroded. (already changed the air filter, and spark plugs but not the wires because they looked fine)

Would a good test be to test I have spark on every plug? 

 

 

Also, I retorqued the head bolts and examined the timing belt. I took a short video posted here: 

Link to Video

https://youtube.com/shorts/1Z3XBeidOM0?si=Ig3DWN_TeR2iTzq1

 

I had a really tough time seeing what the condition of the guides/tensioners was but I would assume I would see that in the oil right? 

 

Thank you,

Dylan 

[Crashtd420]

9 hours ago, sTanTruck said:

I believe I have a slight misfire at idle. I keep failing emissions for high HC levels at idle but I am passing with flying colors at 2000 rpm test for everything (I have to pass by 5/19 or I can't drive the truck until I figure this out). I noticed a little stumbling at idle but assumed this was an "old truck thing" so I never worried about it. What can I look for as a culprit for this? I have looked at the distributor cap and cleaned it out some but its not great (some of the contacts were pretty corroded. (already changed the air filter, and spark plugs but not the wires because they looked fine)

Would a good test be to test I have spark on every plug? 

 

 

Also, I retorqued the head bolts and examined the timing belt. I took a short video posted here: 

Link to Video

https://youtube.com/shorts/1Z3XBeidOM0?si=Ig3DWN_TeR2iTzq1

 

I had a really tough time seeing what the condition of the guides/tensioners was but I would assume I would see that in the oil right? 

 

Thank you,

Dylan 

Out of curiosity I was wondering what causes high HC.... 

Misfire is a possibility and it mention timing and being too rich.....

 

Have you ever messed with the air/fuel screw on the carburetor?

That effects idle the most, you should be able to lean it out a little...

 

Will they let you adjust anything during the test?

 

Other wise an air/fuel gauge comes in handy for this situation....

[datzenmike]

HC is just unburned gas.

 

A miss will dump the unburnt contents on one cylinder into the exhaust.

 

Poorly adjusted idle mixture, too rich. Of course too lean might be the cause of the miss.

 

The AIS air injection system isn't operating. This is a pair of pipes from the exhaust manifold to a one way reed valve mounted on the outside of the 720 air filter. Each exhaust pulse is followed by a vacuum pulse. The one way valve only allows vacuum  pulses to open it and gulp some filtered air into the pipe. This adds oxygen rich air into the exhaust so the cat can burn the HC.

 

Worn out catalytic converter.

            

[sTanTruck]

On 5/10/2024 at 1:39 PM, datzenmike said:

HC is just unburned gas.

 

A miss will dump the unburnt contents on one cylinder into the exhaust.

 

Poorly adjusted idle mixture, too rich. Of course too lean might be the cause of the miss.

 

The AIS air injection system isn't operating. This is a pair of pipes from the exhaust manifold to a one way reed valve mounted on the outside of the 720 air filter. Each exhaust pulse is followed by a vacuum pulse. The one way valve only allows vacuum  pulses to open it and gulp some filtered air into the pipe. This adds oxygen rich air into the exhaust so the cat can burn the HC.

 

Worn out catalytic converter.

            

I'm confused about the AIS. Could mine have been deleted when the previous owner did EGR delete?

I believe I have a miss at idle. Here is a video of it idling, you can see it shakes a little: https://youtu.be/rsg9w4YbcBY?si=6ZXyCh_eU0_GRyCQ

 

I noticed a few things after driving it around a bunch the last two days. One, the engine will run with the idle fuel mix screw fully seated. I was trying to find where it was too lean to run by going a half turn on the mix screw-in until it was fully seated and still running. Does that mean it is running off of the transfer slot? Two, while trying to figure out which spark plug was not firing I pulled each plug, one at a time, and listened for the idle to decrease. I wasn't able to notice anything significant with any of the exhaust side of the spark plugs but very noticeable on the intake side. I then unplugged one of the coil packs and tried to start the engine. It barely started and immediately died with one of the coil packs unplugged. I then switched to the other coil pack, unplugged it, and started the engine. It ran almost how it normally is but slightly lower rpm and a little more stumbly. This makes me think that I could have a bad coil pack or distributor cap. 

 

What are your thoughts on this? 

 

Thank you

[sTanTruck]

Also, what is the best way to post pictures on this forum? 

[sTanTruck]

Test Picture Post 

[datzenmike]

I see an O₂ sensor so feedback carburetor and California emission compliant. If that's the case it may not have AIS because there are virtually no left over HC to burn.

 

What's your idle speed?

 

Pull the lead off one of the coils, stick an old plug in the end and hold against the head or something grounded. Have someone turn the engine with the starter, got spark? now do the other coil. Got spark? If yes to both, the coils are firing.

 

Pull one spark plug lead from the intake side and put an old plug in the end, hold against the head and have someone turn the engine with the starter, do you see spark? Now do one from the exhaust side, got spark? Does one side look better than the other?  

[sTanTruck]

My idle speed is probably around 1100. I know that's high but the engine seems to run fun with it like that. Still no Tach in the truck so this is a guess. 

 

I will try that with the coils when I have someone who can help me, which may not be till Thursday. a new distributor cap couldn't hurt, right? the current one looks a little crusty and probably isn't helping. The spark plugs are new, wires seem all alright but haven't been changed.

[sTanTruck]

Does anyone know of a way to test that an O2 sensor is functioning? 

 

Also, I am going to switch the coils tonight and see if that changes anything. I am still waiting on a distributor cap and rotor to arrive. 

[datzenmike]

1,100 idle speed is above where the mixture adjustment does anything. it's running on the primary barrel. Turn down the idle speed slowly till it falters. Then turn the mixture out till it stabilizes. Lower the idle speed and again increase the idle mixture. keep going till 700-800 and running on the idle mix. Now go through the procedure to set the mix and the idle speed.

 

0²  sensor circuit can be checked that it is secure but I don't think there is a test for the sensor itself.

[sTanTruck]

Ok I will try that. Is there a tried and true method for setting the idle and mix screw? I have watched a few youtube vids but everyones method is a little different. Any good write ups you recommend I follow? 

 

Can you explain the purpose of the two spark plugs per cylinder? is one side doing the majority of the ignition? I find it odd the engine would run with one coil plugged in and not on the other coil. 

 

Also, I believe the O2 sensor uses the ground wire from the exhaust manifold to the firewall to complete the circuit. My ground wire was toast so I just put a piece of wire there which almost instantly melted so I probably need to figure that one out. 

 

[ElliotV]

46 minutes ago, datzenmike said:

1,100 idle speed is above where the mixture adjustment does anything. it's running on the primary barrel. Turn down the idle speed slowly till it falters. Then turn the mixture out till it stabilizes. Lower the idle speed and again increase the idle mixture. keep going till 700-800 and running on the idle mix. Now go through the procedure to set the mix and the idle speed.

 

0²  sensor circuit can be checked that it is secure but I don't think there is a test for the sensor itself.

Do you have a picture or reference where the idle mixture is on these carbs I can't figure the stock one out.

[sTanTruck]

3 minutes ago, ElliotV said:

Do you have a picture or reference where the idle mixture is on these carbs I can't figure the stock one out.

Yes its the little brass colored screw below the vacuum lines. Right under air cleaner on Pass. side 

[datzenmike]

4 hours ago, sTanTruck said:

...

 

Can you explain the purpose of the two spark plugs per cylinder? is one side doing the majority of the ignition? I find it odd the engine would run with one coil plugged in and not on the other coil. 

 

Also, I believe the O2 sensor uses the ground wire from the exhaust manifold to the firewall to complete the circuit. My ground wire was toast so I just put a piece of wire there which almost instantly melted so I probably need to figure that one out. 

 

 

1/  Both plugs fire at the same time equally. Two points of ignition shortens the burn time so the timing can be reduced to 3 degrees BTDC. If there were only one plug the timing would be more like 10-12 degrees. Because it takes longer to burn, you have to start the burn sooner. 

 

The reason for the less timing advance is the peak combustion temperatures exist for a shorter time also and peak temperatures are when the nitrogen in the air combines with oxygen producing NO, a pollutant. Dual spark plugs are part of the NAPS Nissan anti pollution system. NAPS is also used on the CA series engines in the 3rd gen. S12 200sx.

 

2/  The wire to the firewall is a just a ground insurance for the 0² electronics. The negative battery cable should have a bolt through it grounding it to the body sheet metal as well as the intake. Over the years the cable was likely replaced and this was left off. That's why it melted. Make a jumper wire of 10 or 12 gauge wire and ground from the block to the sheet metal. Anywhere. 

[sTanTruck]

@datzenmike You are the man! I used what you told me to lower the idle and adjust the mix screw. Its crazy how much more responsive this engine is when the carb is happy. I unplugged one spark plug on the intake side and plugged a spare plug into it with the engine running, then repeated this on the exhaust side. Both sparks looked similar and the videos to that test are here:

Exhaust test: 

https://youtube.com/shorts/pLAelxSI1A4?si=Bw-OMXWhb5Cs_sIK

 

Intake test: 

https://youtube.com/shorts/WR-AUZ5QCzo?si=EYMoOjOkusNaJW4l

 

 

I tried switching coils and the engine ran the exact same. I then tested both coils with a multimeter measuring the resistance between the positive and negative terminals and the positive and output terminal and they appear to be within spec. I did notice that the negative terminal on each has a lot of resistance to the ground. But both of them were this way so I figure it cant be the issue. I then tested to see if my exhaust manifold was grounded and it was not (very high resistance in the M ohms). This makes me believe that the O2 sensor is not grounded so I doubt its functioning properly. I will add a new ground wire to fix this. 

 

I also noticed that the output shaft seal on my transfer case decided to start puking fluid 😞. Does anyone know a good way to change this? I would assume you disconnect the rear driveshaft and have to pull the yolk off. Is it pressed on? What tools will I need to do this? 

 

Thank you to everyone who is taking the time to follow along and offer advice. It is greatly appreciated.  

[datzenmike]

The negative sides of the coils better have a high resistance to ground. It's the distributor that switches them on and off to ground to generate a spark.

 

Remove the large nut in the center. Try in first and low range to get maximum resistance. I got mine off by tapping the flange on the back side with a large socket. Might take 50 taps but the flange does slide off the splines. The seal can be pried out with a large screwdriver. The new one tapped into place. Get it started, then cover with a block of wood to protect it and hammer it home. Grease the flange where the seal rids on it so it doesn't start moving dry. Flange nut tightening is 87-100 ft. lbs.

[sTanTruck]

Does this look like the right seal? I found it on rockauto 

[datzenmike]

Pretty sure that the same seal was used on all flanges. The flange changed for larger driveshafts around '83 but not the seals.

 

 

Nissan part # 33114-C6900