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Failing smog & leaking oil – ’79 Ford 460 Robin Dunbar 2-22-05  
Our ’79 is 5 months past registration and I’m looking for advice. It is failing smog with high hydrocarbons. Until this past weekend, it was running great (sounded great at least). We added a fuel additive and took it out for a drive. On the interstate, my husband revved it up to change lanes and the throttle stuck open. He was able to get it closed by shifting into neutral. After that, it sounded like there was a vacuum leak, a faint hissing that grows louder as the engine is revved. Back on our own street, he got the throttle to stick again by revving up the engine a lot. There was oil all over the top of the engine, pooling, but could not tell from exactly where. He decided to replace the oil pressure sender, thinking it leaked from there. After replacing that and some vacuum hoses, it ran better and he was not able to get the throttle to stick again. Yesterday, he ran it again and there is oil leaking again.
This is on top of failing smog and not being able to find the source of the high HCs. He is good with cars and engines (has a ’57 Chevy and built an off-road car) and he’s very wary of taking it to a mechanic (doesn’t trust them). We wants to fix it himself, but is frustrated with where to begin. He’s been told to have the carb rebuilt, but is not sure that is it.
Other options include replacing the engine or the motor home itself (although we completely remodeled the inside, so we’d like to get it fixed if possible).
I want to help him, but not sure where to start. So, I’m here :)

Any help/advice/suggestions/recommendations of San Diego RV mechanics would be much appreciated!

Re: Failing smog & leaking oil – ’79 Ford 460 Wayne Brumett 2-27-05  
It would help if you could give me ALL the gas readings of the failed smog inspection. A high reading (say 3-10%) on the CO gas reading on the smog test indicates a rich (overfueling) air/fuel mixture. A low CO reading (less than 0.5%) indicates a lean misfire. In either case thsi could cause the emission failure. But id the CO is between the numbers above, I would look elsewhere for your HC failure.

Hydrocarbons (HC) is unburned gasoline. It caused by incomplete combustion in one or more cylinders in the engine, so the unburned fuel goes out the tailpipe as pollution. Either there is to much fuel going into the engine and not enough air to burn all the fuel (i.e. carburetor over fueling); or you have too much air (i.e. vacuum leak) and not enough fuel (lean misfire) so there is not enough fuel to be ignited, so the unburned fuel goes out the tailpipe.

Without the gas readings it is difficult to say which problem you have. I would start by checking all vacuum lines (i.e. PCV valve hose) and hoses again (espeically the exhaust gas recirculation valve hose)to make sure they are routed correctly, and do not have any cracks or breaks. There should be an underhood label somewhere with a vacuum hose routing diagram.

I suspect that the oil may be from the PCV valve being blown out of the valve cover when the throttle stuck open, letting the oil vent to the air.

Common causes for HC smog failures are:
1. Ignition misfire (spark plug or wires, distributor cap, rotor, etc.)
2. Overfueling/underfueing carburetor
3. Vacuum leak
4. Evaporative canister contantly purging into the engine (not likely)
5. Bad PCV valve
6. Burnt valve (usually exhaust valve)
7. Bad Head gasket
8. Worn or broken piston and/or rings
9. Worn valve guides

I would do a very close visual inspection (e.g. hoses, wires, etc.) before condeming the carburetor.

Does the engine idle smoothly? and does chug/jerk on acceleration from a stop light? If it does do either one of these, and there is no visual problems, then I would start with a compression test to ensure that the mechanical part of the engine is sound. All cylinders should be within 15-20 pound of pressure of each other. If that test proves OK, then the next thing I would look at is the ignition system - if OK, then finally the carburetor.

Hope this helps.
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