Nissan 720 Passing Emmisions

[TheProtoSmith]

Hey folks so I just got back from the testing facility and it looks like I failed Emissions.(i tried poking around the threads and couldn’t find anything that directly answered my questions
CO was at 2.5 times the max allowable amount 
NOx was ok. Close to limit but pass

And HC was also High. 6.34/5.00

 

Known factors:

The Good:

120Psi on each cylinder,
newer Cat and Exhaust
functional EGR valve. 
Functional vacuum advance 

great oil pressure

16mpg right now (if you drive like a grandma)

 

 

The Bad:
-There is a Vac leak somewhere, but haven’t bought a tester yet

-one hose I can’t find a home for (i have it inserted into a female socket on the stock carb)

-The stock carb is “new” but still is the weirdest thing I’ve ever worked on. (More famililiar with 2 stroke and old Toyota carbs)

-There is a little positive pressure in valve case (not enough to shoot the cap off when unscrewed but enough where you can feel it when you hold your hand over)
-changed oil twice and its still pretty dark

-I think I’m running rich but I can’t get the engine to stay running if I run it any Leaner. 
-PO said there was something off with the Carb but i wasn’t able to figure it out.
-Had to disconnect clutch idle switch because it would spew black smoke when engaged

-fuel shut off solenoid not working and diesels  on shut off

 

other Things:
I live in Denver.... so thin air

 

 

I’ve read that switching to you have to do a emissions delete, which is not ideal, do i have to go with the stock carb and buy a replacement and keep my fingers crossed.

 

[TheProtoSmith]

Do i need to spend the money on a remanufactured or will the 75$ eBay reproductions work?

https://www.ebay.com/itm/Carburetor-For-Nissan-720-pickup-2-4L-Z24-Bluebird-Caravan-Datsun-Truck-Atras/402292053239?hash=item5daa7994f7%3Ag%3AJJ4AAOSwfHZe4hEO&fits=Year%3A1984|Model%3A720|Submodel%3ADeluxe|Engine+-+Liter_Display%3A2.4L|Make%3ANissan|Trim%3ADeluxe+Extended+Cab+Pickup+2-Door|Engine%3A2.4L+2389CC+l4+GAS+SOHC+Naturally+Aspirated

 

 

[bilzbobaggins]

China stuff is hit and miss.  And shipping is  silly slow right now.  You will also be out that time if its garbage.

[TheProtoSmith]

Thanks for the tip. I’m gonna try pulling the carb, cleaning, and re do vac lines and see if I can do it. Maybe I Plumed it wrong when i did it last time. If that’s a no go ill order, they are just so damn expensive for a remanufacture.

[datzenmike]

CO was at 2.5 times the max allowable amount 
NOx was ok. Close to limit but pass

And HC was also High. 6.34/5.00

 

 

120 compression is not perfect and why you have positive pressure in the crankcase caused by blow by. Nothing much you can do about this.

 

First I would get the idle cut working so you can turn the idle down to set the idle mix..  

 

High CO and HC is from running either rich or poor ignition. 

 

Is the choke fully off when the engine is warmed up??? This would make the oil dark faster.

If this truck was originally from a lower altitude it will naturally run richer as you go up. If you have the carb apart it may have a #107 primary jet. You could go down to a #100. Less air needs less gas. If you have a #170 then the secondary was accidentally swapped with the primary and this is your problem.

 

Make sure your wires cap and rotor are good and you have NGK BPR6ES on the intake side and BPR5ES on the exhaust side. Miss fires = HC ( unburnt hydrocarbons )

 

 

 

[TheProtoSmith]

Thanks Datsun Mike as always you’re a wonderful resource.

 

I got a remanufactured carb to replace the EBay special that was on it (after doing some digging it was definitely not original. Ill start tracing down those problems. 
the car was first registered in Wyoming and this one does have an intact altitude compensation system. However rejecting does sound like a good path. Ill see if i can get any locally other wise jets r us her i come.

 

I haven’t checked choke while running since its just been me working on it but when i do a carb swap I’ll be sure to look. I’m also not gonna be surprised if that was bad. Some questionable electrical work was done adapting from the original harness to the eBay Special carb.

 

I’m also going to check out coils today with a multi meter test
 

RE: blow by yeah that’s what I was thinking, but honestly for an all original engine its not terrible, i was just happy i had a not blown head gasket. This could also be contributing to the carbon in the oil too right? 

 

Rotor seemed fine but I’ll give it another look and maybe a clean and scuff up with some 1000grit. 

Cheers, boys

[datzenmike]

Do not replace a coil until you know it for certain is bad. Most replacements are very poor quality and you may add a problem.

 

Pull an intake wire off it's plug and put an old plug in the end. Lay on a grounded surface and have someone try to start the truck. Look for spark. Now do one of the exhaust side plug wires. Spark on both... coils are good.

 

Get a $4 test lamp and with key on check the lamp lights on the + terminal of both coils.  If the exhaust side coil has no power replace the first fuse (10 amp) on the far left side of the fuse box

 

Check the 2nd fuse (15 amp) in from the far left side. This powers the idle cut and the choke heater. Turn the ignition on off on off (not start) while listening near the carburetor. If there's power to the idle cut solenoid you will hear a soft clicking sound

 

 

If the choke heater and the idle cut are not working the choke won't fully shut off and will run rich. The idle cut shuts fuel off to the idle circuit to prevent 'run on' or dieseling. With both not working it will definitely diesel.

[Charlie69]

As far as testing for vacuum leaks I use what ever is handy carb cleaner, WD40, brake clean, or staring fluid, using the little straw on the nozzle spray with the engine idling around all the vacuum fittings/apparatus and when the engine increases in speed there is a vacuum leak.  Remember if your catch the stream of fluid on fire  just quit spraying and the fire will go out providing you do not have a fuel leak.  Myself I have never caught the stream of fluid on fire and I have bend doing this since the late 60s.

 

DO AT OWN RISK!  NOT RESPONSIBLE FOR ANYTHING!

Edited September 6, 2020 by Charlie69

[TheProtoSmith]

After swapping the carb I did the test again! The emmission were actually functional because the old carb was missing 4 vacuum ports that were all related to emmissions. Went and got tested and still crazy high CO 144.8/55 (but other test were low. HC 4.3/5.5 nox 0.63/5.5 .

Went and tested spark only could get the motor to run off one of the coils. Checked impedance on cables (fine), and found there is no volts at the (-) and (+) terminals on the secondary coil. Stated looking at the wiring diagram and think I need to check the electrical at the bottom of the distributor? But not entirely sure still.any guidance? Thanks so much for your help!!!

[datzenmike]

It's the first fuse on the far left side of the box. Without the exhaust side plugs firing the burn time is much longer.As the timing is set for the shorter burn time with dual plugs the engine will act like the timing is retsrded with a loss of power and mileage.

 

Did you...

 

On 9/5/2020 at 12:20 PM, datzenmike said:

 

 

Check the 2nd fuse (15 amp) in from the far left side. This powers the idle cut and the choke heater. Turn the ignition on off on off (not start) while listening near the carburetor. If there's power to the idle cut solenoid you will hear a soft clicking sound

 

 

If the choke heater and the idle cut are not working the choke won't fully shut off and will run rich. The idle cut shuts fuel off to the idle circuit to prevent 'run on' or dieseling. With both not working it will definitely diesel.

 

This might explain the high CO

[TheProtoSmith]

So I did check the fuse and it was fine. But its the wierdest thing I got the circuit to go live when I get the clutch switch closed, when the clutch it's depressed both coils fire.... 

 

[datzenmike]

That isn't right. I would try  getting rid of that switch so that both coils fire all the time. At least for the emissions testing then trouble shoot it later.

 

There should be two vacuum switches. One to cut the exhaust coils (under heavy throttle) and one to cut fuel to the idle circuit. (when decelerating from high speed) I bet the wires were accidentally switched as the fuel cut is prevented by a clutch and a neutral gear switch.

[TheProtoSmith]

I have one vac switch not hooked up because I couldn't find it in the vaccum diagram! If I switch the hose should that solve it?. If so to which line is that vacuum switch hooked up to?

 

 

[datzenmike]

I only have the '84 FSM so maybe only one switch. It's on the inner passenger side fender. Little round black plastic thing.  Can yopu post a picture of the right inner fender???

[TheProtoSmith]

3 minutes ago, datzenmike said:

I only have the '84 FSM so maybe only one switch. It's on the inner passenger side fender. Little round black plastic thing.  Can yopu post a picture of the right inner fender???

Yes I can as soon as I get out of work. The strange thing is the hood reads federal bit it had the air box of a California

[TheProtoSmith]

Nisaan720 engine woes https://imgur.com/gallery/hPAk266

 

Also was just poking around no vac coming out of boost control unit...

[datzenmike]

 

.There they are. The two black things that look like the tops of two ignition coils. Under all the hoses.

 

I wonder if the electrical plugs could be swapped? The clutch should not turn the coil on and off.

[TheProtoSmith]

Datsun Mike I'm confused I switched the vac tube over to the other switch, same result. I'm thinking that there is something else wrong, and that this is a symptom. The only place I can get vacuum is straight off the intake manifold and off the middle passenger side ports on the carb

 

from what I've read of the electrical diagrams, the secondary ignition coil is available when the car is in gear or the clutch switch is released . Why would they also vacuum control it?   Why would they design the coils to both fire when only in neutral, wouldn't you also want a faster and more complete burn all the time?

 

 

This 720 is making my brain hurt. But again thank you so much for all your wisdom and guidance, you are appreciated

Edited September 10, 2020 by TheProtoSmith
I'm a fool

[datzenmike]

No  no no... try switching the electrical plugs... if they will. The vacuum source is the same so will change nothing.

[TheProtoSmith]

If they are the same switch on different ciruits then moving the vac line should have the same result as switching the electrical connection.. the vac source doesn't change. Unless I'm mistaken those are vac release actuators. 

[datzenmike]

Not sure if one may be on at rest and vacuum turns off and the other may be opposite. I don't know but I don't think the clutch should control the exhaust side plugs being turned off.

[TheProtoSmith]

OK so did a lot of digging and testing, (only sucked up a little bit of gas)

Boste control unit was jammed shut, rebuilt and now the vacuum control appropriately turns on the rest of the vac system and turns on the secondary ignition control. But now the engine has a hard time maintaining steady idle. I think its the TVV (the 3 port temp controlled vac valve) when the car is warm its supposed to send vacuum from the air filter and the Alittude compensation system however there is no vac there. Does this conceptual model line up with surging at Idle. Car is also still running rich. but now there is actually an effect when I do

adjustments. (choke system is working as well as fuel shut off, No dieseling on shut off)

Any thoughts?

 

also Datsun mike. You were right those aren't Vac Release valves they are sensors. Both seem to live in the Normally open state Front one controls fuel (i think) and back one controls secondary coil.

 

Boost control valve was easy to build from inspecting here is what I think its operations are:
When Under normal load -> Convert Vacuum from about 20 mg of merc to about 10 (this can be adjusted by tightening or loosening the back nut with the clip spring) with a variable vac relief valve that pulls from atmosphere

When Under heavy load, Open and disables secondary coil and Gets rid of vacuum advance (I think, haven't been able to observe because i'm only a one man team) to prevent early detonation.
When Under No or negative load, Close and Deprive system from vac, turn on fuel shut off system, create a vacuum advance to burn extra fuel, and turn on secondary coil

for these systems to work clutch and transmission neutral detection must be operation or they will force the open state of system, Ie secondary coil stays on during heavy load  inducing early detonation and excessive heat.

feel free to poke any holes in these theories 

[datzenmike]

The TVV controls 2 things. When the EGR, and separately, when the vacuum advance is on.. 

 

The TVV works this way. When coolant temperature is below a certain limit, the valve is open allowing filtered air in through the top hose, destroying the vacuum signal to the EGR. When the engine warms up, the leak closes and ported vacuum is passed to the EGR. Same with the vacuum advance hose below it.

 

The only connection between the TVV and the High Altitude Compensator is the hose to the air filter.... which is open to the air. The TVV does nothing other than the 2 things mentioned vacuum advance and EGR (although the PURGE signal on the charcoal canister is piggy backed onto the EGR signal)

[TheProtoSmith]

hmmm ok thanks for the info!
any ideas on why i might be surging?
 

[datzenmike]

Vacuum advance is strictly a ported source of vacuum. The port is above the throttle plate so at idle there is no vacuum advance. As the throttle opens to and above the port intake vacuum is applied to the vacuum advance hose. At full throttle the intake vacuum is almost zero so no vacuum advance to the distributor.

 

Surging

Idle too high.

Vacuum leak