CA Smog

[720Ryder]

Hey everybody,

 

New to working on my own cars and I recently purchased an '84 720 from a buddy & have had some issues getting it to pass smog. I've put in a rebuilt Hitachi carb, o2 sensor and coolant temp sensor. Still running rich. Carb shop I contacted suggested that I replace the smog pump, double check the cat & the 'EGR system'. Can't seem to find a smog pump anywhere, nothing really comes up when I search online.. any help or suggestions appreciated!

[datzenmike]

The Z series engines do not use a smog pump. You'll find one or two pipes running from the exhaust manifold to the air cleaner. This system uses exhaust negative pulses to suck air past a one way valve down into the exhaust pipe. This oxygen rich air works with the catalytic converter to burn off emissions.

 

 Do you know what failed you?  CO?               

[720Ryder]

Ok, good to know. Yeah, it measured high on CO.. here's a link to that section of my report.

 

https://m.imgur.com/r8agOpr

[datzenmike]

Has a round 6 wire electrical connector on the carburetor?  That's an ECC or feedback carb. Has a solenoid that adjusts the primary jet mixture as you drive. If there is a system failure it has a default or 'limp home' mode that forces a rich mixture rather than an accidental lean one that might harm the engine. If you replaced the carburetor then the problem is in that plug (known to have broken wires inside the insulation) or one or more sensors.... or even the ECU. (the little box under the driver's seat. )

[720Ryder]

Ok, so then I probably need to replace that electrical connector? What's the name of that piece?

[datzenmike]

I'm only saying the wires are rather short and get bent a lot removing the air filter. 720 owners have complained that the wires flex and can break inside their insulation.

 

 

 

The factory service manual (not Chilton's or Haynes) the Nissan one gives test voltages to check to trouble shoot this and the ECU.

 

 

Check the fuel level in the round sight glass on the front of the carb. Is it at the dot on the glass? Is it maybe over full?

 

Is the choke fully open (off) when warmed up???

[720Ryder]

Oh, ok. So, going back to what you said regarding the sensors.. You're saying it could possibly be the MAP sensor &/or the TPS sensor? I've been reading around and seeing that the fuel mix will commonly run rich if either of these is out as well as the EGR valve and the EGR modulator valve. I have no idea of any of these parts have been replaced in recent years so I'm thinking these are most likely the culprits.

 

Per your last reply, I will check on the fuel level in the carb and the choke and get back to you.

 

 

[datzenmike]

This is a very rudimentary system that bridges between a carburetor and a fuel injection system using just rpm, throttle position, engine temp to calculate a mixture by the primary jet solenoid with feedback from the O₂ sensor to keep it close to stoichiometric. There was no MAP sensor and the throttle position just indicated idle or full throttle.

 

EGR is almost totally used to reduce NO in the exhaust and has no affect on the carburetor.

 

16 hours ago, datzenmike said:

 Check the fuel level in the round sight glass on the front of the carb. Is it at the dot on the glass? Is it maybe over full? Flooding?

 

Is the choke fully open (off) when warmed up???

 

Some obvious causes of being over rich need to be eliminated first including a bad misfiring ignition.

Bad distributor wires, cap or rotor.

Plugs BPR6ES for intake and BPR5ES for exhaust. Use only NGK plugs.

Are both the intake and the exhaust side plugs firing? Check for spark on both sides.

Is the AIS (air injection system) working so that the catalytic converter can burn the excess fuel away?

Is the Catalytic converter any good? Does it need replacing?

[720Ryder]

Oh, wow! Well, that helps a lot. I'll get a pic for you when I can but one thing that comes to mind is that, and I think this is the right part, the hot air duct does not have an actual fitted hose running from the air filter. What's on there looks more like somebody took a piece off of a clothes dryer and made it work. Sits loosely on both ends with no clamps either. Could that be a major reason for running the way it is?

[datzenmike]

The drier hose is probably for the ATC. (Automatic Temperature Control) It allows the carb to draw warmed air from around the exhaust manifold up into the snorkel on the air filter. Here its mixed with cold air from in front of the rad and regulated at about 100F during warm up and specially in cold weather. The engine then runs better thinking is summer rather that winter outside. Failure of this system would not impact the carburetor richness.

 

The AIS or Air Injection System uses negative exhaust pulses to draw air into the exhaust through one way reed valves on the side of the air filter. No pump is needed and the oxygen in the exhaust is easier for the catalytic converter to burn off any excess un-burnt fuel. Failure of this system would mean no burning off of any un-burnt fuel by the catalytic converter..

 

[720Ryder]

Alright, I'll leave that hose alone then. So, then I should take a look in the Air Injection valve case? I've got several places to look over and evaluate so I'm trying to make a list lol

[Tinman]

Oh boy!!!  Another CA smog horror story!!!

 

Check everything as mentioned, but be prepared to swap carburetors until you get one that actually works.

I bought a (several)  fully re manufactured carb from a "reputable" carb shop only to have it run way too rich.  After fighting with this for some time, 

I just rebuilt my old one again and all was good.   I own a smog analyzer, btw, so I do know what's what with these trucks.

 

A lot of these rebuilds have jets in them for other states and while running well, they will NEVER pass CALI Smog.

I hope that's not your problem, but something to think about once you eliminated everything else.

 

One thing you CAN try is to actually RICHEN the mixture to test if your CAT is actually lighting up.  Some carbs have been so starved by the smog gestapo that 

they ran too lean to light the CAT.   So it also won't pass.  I DID have this happen to me.   Was "close" but too close on the edge of failing.  I riched the mixture and suddenly the needles

on my old snap-on gas analyzer went up, then back down.  Almost to ZERO.   HUH....   Passed with loads of room to spare.

 

And don't forget.... Cali wants all old vehicles GONE, so they are lowering the bar until old cars simply will not pass any more.

 

I'm thinking of doing an electric conversion in the future just to give them the middle finger.  I love my little 720.  Had him since 91.

[datzenmike]

The catalytic converter needs oxygen to burn off any unburned hydrocarbons. This is what the AIS (air injection system) does. The exhaust has almost zero oxygen in it and why it's used for EGR. Older engines had air pumps to force oxygen rich air into the manifold to aid in burning it off. The 720 uses a catalytic converter and a passive air injection system. If the AIS is not working the cat cannot either.

[DIY 1985]

Not every 720 came with a AIS.  My federal spec. late '84 build had a non-reed-valve air cleaner and a cat.

[datzenmike]

Didn't know this. A little research shows the Z20 and the Z24 after '84 didn't have it.