Mis-Fire on CA smog test

[seazap]

I live in California and have a 1986 Pulsar NX with an automatic transmission and 80,000 miles. The car runs and drives great, except when its hooked to a smog test machine. Once hooked to the smog machine the cars runs fine for the initial part of the test, but once the technician puts the car under load the engine sputters and eventually shuts off. The car only does this when testing and not when driving. I have taken to 3 mechanics who cant diagnose problem.  I even took to a smog repair station, even they couldn't figure out the issue. Replaced fuel pump as a guess and that didnt fix it. All vacuum lines have been checked, all are good, no cracks or loose connectors. Any advice of what to check for or what could cause this issue would be a great help. 

[datzenmike]

Fuel or spark.

 

Fuel

Take it to the longest steepest hill you can find and floor it going up. If it quits or stumbles on you but returns to normal when you stop, the fuel filter is probably part plugged. Increased load will require more fuel. If the fuel filter is part plugged it will be fine driving around normally can't keep up when needed.

 

Spark

Check the coil for cracks or carbon tracking. Carbon tracking is where the spark has jumped to the negative terminal and burned a path. Once tracked it's easier for it to arc the next time. When an engine is under load it's harder for the spark to jump the plug gap and it will look for an easier path to ground. Now check the inside and outside of the distributor cap and then the rotor. Check the plugs are clean on the outside, or if old replace them.  Replace the wires if old, definitely replace the rotor and distributor cap if not sure.

[Stoffregen Motorsports]

1986 is carbureted, right? I'm betting it's not so simple. There are a dozen antiquated VSV's and solenoids and such, not to mention the mile of vacuum hoses, which can make this era of car a nightmare to diagnose. It's probably EGR related.

 

There is a shop in Auburn that specializes in 80's and 90's Japanese cars and trucks. It's called "Strictly Toy-ondas" - https://www.strictlytoyondas.com/about-us.html

 

They helped me get am FJ60 to pass a few months ago.

[datzenmike]

It may be carburetor but if it is, probably a feedback system (like the late 720) with solenoid primary jet and an O₂ sensor. California? definitely EFI by 'mid '80s.

[seazap]

It is carbureted, 1986 was the last year for that. Thanks for all the suggestions. I am going to try the test Datzenmike suggested this weekend and if that doesnt help me Ill try the shop in Auburn.  

[datzenmike]

Almost for sure a feedback carburetor. Look on the exhaust manifold for an O₂ sensor.

[Cheetahking]

I would find out what they are hooking up to your car when doing the test.  If the problem is only repeatable when testing - I would be looking for something the test would be changing (spark plug lead or???).   

[Ooph!]

What Cheetahking said . I have a 99 pickup with a Diesel, when hooked up to an older machine it would shut off and not run until unhooked.

The Tech stated it was the software on the machine, it hasn't done it at the shop I go to now.

[nl320what]

If you ever do complain about a shop or that they failed you wrongfully and called the BAR, they will say to try another shop, no help at all.