1988 S10 4.3L Smog Test Results and some questions

Is it at TDC with the bypass wire connected or disconnected? You need the wire disconnected to set the base timing to TDC. If it is TDC with the wire connected you will have problems.

When you say the reading was low, or close to the limit, which gas are you talking about?? Co, Hc, or NOx????

If it smells "gassy" it is likely high on Hc. - which could be due to a misfire, too rich, or too lean (causing a missfire). Kinda hard to diagnose with such a poor description of the test results.

snipped-for-privacy@snyder.on.ca was thinking very hard :

The California Smog Test Mechanic (this was a Star station qualified to repair smog problems on the spot) said the timing was right on so I assume, since I did not poke my nose in, that it was done to the required CA specs.

So how can a 1988 Chevy S10 4.3L V6 with throttle body injection run to rich at idle? What would cause this? Does it have choke that might be sticking slightly? The truck was hot since I drove it for a while before going in for the test and the test mechanic said the engine was hot due to the fan clutch not fully engaging so I would think that the choke would not be activated at temperature.

If a misfire then maybe plugs, wires and rotor cap is in order? All very doable by myself.

Co, Hc where close to the limit at 15mph and low at 25mph. NOx was low at all speeds.

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No choke, but being TBI I'd bet more than a coffee it is a bad injector or a bad regulator.

If the Nox was low, it wasn't too hot. Make sure plugs, wires, and cap are OK and DEFINITELY check the injectors for leakage and spray package. Check the fuel pressure as well.

Bad TPI pressure regulator is the probable cause. Next would be a failing injector. Both are rather common on that vintage. Especially with todays "gas"

So, I can change out the ignition stuff: plugs, wires, dist cap and rotor.

How difficult is it to change the regulator Where is it? How difficult to change the injectors (there are two)?

not sure it is fuel system since only a two years ago I had a problem that turned out to be the fuel pump (in the gas tank) the Chevy dealer did the work and I would think that they would have checked the fuel systems. They also changed the filter. They checked the fuel pressure and that was what led them to changing the fuel pump (a Chevy new fuel pump). So as I ould expect they would try to make more money and let me know that the regulator and injectors were in need of replacement.

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The injectors and the regulator are part of what looks like a carburetor, top center. Replacement kits are available and within the capabilities of a reasonably skilled handiman.

Both items are on top of the engine mounted in the throttle body unit. Not hard to change.

This is what the regulator repair kit looks like.

They are in this.

Both items are immediate failure items. They don't show trouble until they fail. Injectors are nothing more than a solenoid valve, they wear but the common problem is dirt, it only takes a small amount to hold the injector open enough to cause problems.

The regulator is a rubber sheet and they just fail.

I had the same issue on a 92 Gm safari. It got to the point, where raw gas was running out he exhaust pipe. one mechanic walked away from the issue. A family friend, solved it right away. Replaced the spider plenum, and a line it was connected to. it was cracked. and fuel was escaping.

Except this vehicle doesn't have a "spider" - it is a TBI unit.

This may help.