bobboinski

Did you check for vacuum leaks? This will cause high HC (in my experience).

PZB993

I started checking vacuum leaks today. I found that the blower motor vacuum actuator wasn't pulling in at all while operating the HVAC controller. I can suck air right through it, so I think there's a rip in the diaphragm. I'll plug the vacuum line feeding it and try smog again.

samurai_k

I think there may be confusion between a vacuum leak with the actual vacuum system vs. a leak in the intake (also referred to as a vacuum leak).

When your intake has a leak after the mass air flow sensor you will have a rough idling engine. Does yours idle smoothly despite the high hydrocarbon reading?


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PZB993

I think the car runs smooth at idle. It doesn't stumble or surges when idling.

I thought I read a thread about insidious power robbing vacuum leaks that had to do with vacuum actuators for the fresh air flap behind the CCU and at the blower motor.

bobboinski

I think normal idle vacuum for these cars is 15-16 inhg from previous threads. After you fix your leak hook up a vacuum gauge and see if you are close. I think the leak you have could be contributing to your problem. I've definitely had cars with a vacuum leak that idled smoothly but failed HC at idle. Either way the leak needed to be fixed.

Pharcydeabc

+1

pp000830

I feel for you and your frustrations on what appears to be a squirrelly problem.

I had the same issue with that bad boy on my engine, No OBDC code. The question is, is it actuated during normal engine operation or is its vacuum supply line cut off by the vacuum solenoid valve upstream of the actuator. If cut off it doesn't influence the vacuum in the system.

Keep in mind the emissions changes we are discussing are very small so the root cause may be something small and subtle.
Andy

pp000830

HC - Hydrocarbons are basically unspent fuel. If the engine is OK it seems the only other place things can go wrong is with the effectiveness of the catalytic converter. There are cleaners for this although the results are mixed as to if they work. I suspect analyzing the signal from the oxygen sensor can tell you if the gasses from the exhaust are in-specification. If they are then the catalytic converter should be evaluated. Most better OBDC readers will let you see running data with Durametric on my OBDCII 96' 993 I can graph oxygen sensor and rpm data concurrently on the same graph to do this, You may be able to do the same on your OBDCI car.
Andy

PZB993

Just a data point:
I cut my faulty vacuum actuator open to see first hand where the leak was coming from. Thought it might be cool to share.

pp000830

Quote:

Originally Posted by PZB993

Just a data point:
I cut my faulty vacuum actuator open to see first hand where the leak was coming from. Thought it might be cool to share.

Yes, and the replacement will have a translucent/uncolored diaphragm that looks like it is made of silicone rubber, much more durable.

PZB993

I made a smoke machine and smoked the vacuum system. The only place I could see smoke come out was at the shaft of the resonance flap at the lower center of the manifold. Is there a seal in there that needs replacing.

PZB993

Another disappointing day at the smog check. I replaced the air temp sensor and some rubber vacuum fittings before I took it in this time. I had high hopes this would do the trick.
The car still holds good HC numbers for 20 seconds then shoots up to 140s within the last 10 seconds. The tech told me he let the test run longer and it keeps climbing to the 250 range. Any other ideas.
Thanks and happy holidays

Spyerx

I suspect you need a cat. They work better when hot... i suspect this is why it passed under load.

What did your plugs look like when you swapped them? Any indication of burning oil? Do you burn oil or measured it?

But, high HC at idle is an indication of running lean (high CO at idle is rich). You could try the spray carb cleaner around the intake base gaskets and that valve actuator shaft. see if idle changes.

Smog is SO frustrating on these older cars.

PZB993

I tried the carb cleaner around the engine, no change in idle.
I removed the cat to take a look inside. I know you can't see much and the other half my be damaged but it doesn't look broken or melted. I blew air through it with my compressor and some dust blew out.
Here are the plugs that came out. 2 of the cylinders look more oily then the others.

Spyerx

Plugs don’t show indication of burning oil

is that the input or exit on the cat? For a visual you need to see the input.

id be tempted to borrow cats from someone and give it a go....