84 720 Failed California Smog :-(

[northoak]

Looks like my truck just failed smog for the first time!  Passed it about two years ago.  The fella at the shop said its running rich and here is the actual printout.  Any suggestions are very much appreciated!

[Toxicrain]

probably your air/fuel screw loosened overtime and its running a little rich. just tighten it quarter turn in until it stalls out then back it out until smooth idle. 

 

Edit: this may not be hitachi carb but should be close to what it looks like. air/fuel screw is down by base of carb somewhere. I have a weber its located on the back right corner.. Cant remember where on Hitachi. Im sure someone else will pitch in some input to get past the torture of california smog.

Edited August 14, 2018 by Toxicrain

[datzenmike]

The '84 idle mix adjustment is set at the factory and plugged so the owner cannot mess with it. If you are caught with the plug removed I'm sure they will fail you anyway. Besides this measurements are not at idle, but low speed. You have the electronic feedback carb (ECC) which has a solenoid primary jet which opens and closes rapidly many times a second by the ECU with feedback from water and air temp, throttle position, RPM, and an O2 sensor to keep the mixture near stoichiometric. If there is a failure in the system, it reverts to a 'Limp Home' mode which is an over rich setting to prevent any chance of a lean condition which could harm the engine.

 

Before messing with that I would make sure the plugs are clean, wires in good shape, cap and rotor checked or replaced. Are both the intake and exhaust side plugs firing???? If the ignition system is not up to par it won't burn all the gas and the HC content will rise.

 

Might not hurt to drive some miles and burn up that 2 year old gas and replace with fresh. If an oil change is near, definitely change it and the filter. Does it burn much oil??? Try a thicker 15w40 oil.

 

Set/check the valve lash and the ignition timing.

 

Is the fuel level in the carburetor at the dot on the glass in the front of the carb??

 

Is the choke fully OFF or OPEN with flap vertical when warmed up?

 

 

[northoak]

Truck has been a daily driver for about two years so the gas is fresh.  Plugs, Wires, coils, cap and rotor were all replaced a couple months ago.

 

I also unplugged the o2 sensor and ran the truck and the idle jumped super high.  I plug it back in and gave the pedal a push and it settled back down to about 850 or 900 rpms.  Would that be an indication that my o2 sensor is good?  I'm considering just throwing a new one at it since they are cheap.

 

Fuel level looks a lil above the dot on the carb window but I am looking from above so i believe thats all good. ?

 

I pulled one of each plugs after driving, the intake one looks pretty light, the exhaust one a lil dark maybe?  Not sure what that could mean?  I assume they are both firing since neither are completely fouled.

 

intake:

exhaust:

 

I'm going to take a peek at the choke plate next time I ride it.

 

Timing and valve lash are those two things I still haven't checked out and fear because I've never done them on this truck.  maybe its time to learn.  Thanks for the input!

 

[datzenmike]

 

13 hours ago, datzenmike said:

 Are both the intake and exhaust side plugs firing???? If the ignition system is not up to par it won't burn all the gas and the HC content will rise.

 

 

 

Never assume. Pull any wire off an exhaust and intake side and put an old plug in it. Lay it on a grounded surface and use the starter to turn the engine over. Got spark? It's very important that both sides fire.

[northoak]

went ahead and checked a plug from both sides and spark is there.  Also wen't ahead and replaced the o2 sensor since it was cheap and easy to get to.  Haven't really noticed a difference so I guess its on to timing and valve clearance.

[datzenmike]

There are still many other things to check. Does the engine warm up in about 10 min. Does the temp gauge read about half way into the normal or run range. If thermostat is stuck open the engine never warms up and this can fool the ECU into thinking it is constantly warming up and never goes into closed loop operation with the O2 sensor.

[northoak]

I’d say it fully warms up in about ten min.  The temp gauge always rides right in the middle once it’s warmed.  Also confirmed that the choke plate is fully vertical when warmed up. 

[northoak]

Oooops, I broke this vaccum switch putting the lines back on after I adjusted my valves ?  All the ones i'm seeing online have two fittings but mine has 3.  Anyone know a source or part number for this? thanks

 

[northoak]

damn this thing is stuck on, any advice for removing the old ported vacuum switch its also much appreciated

[northoak]

update: got the damn thing off with a 7/8 box wrench, still trying to find a replacement

[Rays74]

The NOX being near upper level could indicate it's running lean, possible vacuum leak somewheres would also trip the HC levels to be high as it isn't burning the fuel it's given.

I live in So Cal, smog laws can be a b*tch

[datzenmike]

5 hours ago, northoak said:

damn this thing is stuck on, any advice for removing the old ported vacuum switch its also much appreciated

 

It's broken anyway, break the others off and use a deep socket and breaker bar. This goes into the water jacket so drain a gallon out of the rad first. No... first get a new one.

[northoak]

Well.... I changed my O2 Sensor and adjusted my valves, and put a new ported vacuum switch on but I failed smog again!

 

Since failing I put a new thermostat in, any other ideas?  The state will pay up to $500 in smog repairs to a shop since I'm low income but it looks like half that is going toward diagnosis.

[northoak]

Also the smog shop said the timing looks good