Please Help! Vacuum problem - 78 Monte Carlo

JK wrote in rec.autos.tech

Try going to

Thanks Dick... very helpful!

Yeah, I have my doubts too, but I figure I'll start cheap and easy and work up ;)

Your '78 may have a transmission-controlled spark advance system, especially if it is a California Emissions car. These systems prevent vacuum spark advance when the engine is at operating temperature and the transmission is in 1st or 2nd gear, allowing advance only once it shifts into 3rd. The presence or absence of vacuum spark advance would probably not kill the engine at 50mph, but if the system is improperly hooked up or has malfunctioned, it could throw off the ignition or fuel delivery enough to do so. You REALLY need a *factory* service manual to diagnose these '70s driveability issues.

DS

Unfortunately, they don't seem to grow on trees.... or much of anywhere else for that matter.

I do know it's not a CE car.

Oh, another comment about that... after I changed the filter, it ran great for a while. I actually drove it normally for about 50 miles. Then it started acting up again. I put another fuel filter in since it's only $2 and takes 5 minutes to do. If the tank filter were the problem, would it have even run right for that 50 miles? It's basically behaving the same it did before I ever even changed the filter. As for that port, the Autozone diagrams don't appear to indicate anything on that port. I don't understand why there's be an open vac port though.

A plugged up filter on the gas tank air vent and carb float bowl can act like that.

That is the emissions system charcoal canister and it is run from a ported vacuum line through the CTO valve on your thermostat. It looks like a coffee can with some hoses on the top.

The air filter is less than two bucks and stuffs in the bottom. You have to dig out the old one with a hammer and chisel, well I did anyway..., then the new one tucks in. Nothing unscrews or anything.

To test it drive with the gas cap loose or off and see what happens. If the problem goes away, bingo.

Also check where the carb float vent goes to to make sure they didn't disconnect and plug that too or something, it needs to be open.

No matter what, don't leave that line open on the CTO.

Mike

JK wrote:

JK wrote in rec.autos.tech

Glad to help. I only started reading these groups late last year, and have managed to find several interesting and helpful links. There is a lot of information on the web, if only you can find it. One of the big problems is that only a small portion of the info is referenced by Google or Yahoo, although autozone is. I am constantly looking for web sites that give good general information on car repair and trouble shooting. I have found some that make a start, but in general they make you dig, through many menus, make you log on, or bury you in ugly design and lots of ads.

JK wrote in rec.autos.tech

One thing you might try, is to put a hose on it and plug it up. Seems to me that if it is a vacuum and needs to be connected, that may solve your problem. Depending upon where you live, emissions may not be a problem, and much of the vacuum tubes had to do with emissions stuff in those years. So blocking the port may only disable some unneeded part. It could also be that there is problem in that device that is causeing it to have a vacuum when it shouldn't have one. Also, the way you worded the description made it sound like the thermostat housing has 3 vacuum ports, which does not sound right to me. Are you sure that they are not water fittings? According to an autoparts website the pictures they show have the regular hose fitting, and 2 more threaded fittings for other hoses, possibly emission or heater hoses. They also say that a plug may be needed. Or is this some device that is mounted on top of the thermostat. If so, it may be something that somebody added, and the connection is not needed. Good luck, and let us know what you found out.

Horsepucky. If I can find a factory manual for my '62 Dodge Lancer, you can find one for your '78 Chevrolet. They go by all the time on Ebay, and there are dozens of auto literature specialists listed in Hemmings. I would wager $50 you could pick up a copy of Hemmings and make 10 phone calls and come up with AT LEAST seven offers for a factory '78 Chev manual.

(I'd win, too...having just moused around on a few of 'em myself...)

DS

Stop, Look and Listen!

Would you like to save money?

Read my following disclosure and I am sure you will appreciate this information!

If the car was sold in the US, and if the decal is still there and intact, the car was sold with a US EPA Emission Control Information Decal with a tune up and a diagram of the Vacuum lines and components.

This was affixed to either of the fender wells.

Look preferably on the left side.

You should put together a website of good auto links.

Yeah, it's a vacuum port. It is something mounted to thermo housing and must be from factory because I know the lady who owned it before me and she wouldn't have changed anything. She's old. heh

Mr Stern is not worth the time and effort to convince him most posters do not care to argue.

If Mr Stern is such the expert, he could staff a General Motors 1-800 help line so we could call him at 2 AM EST with our problems and he could fax the small and finite plethora of information requested.

The basis to my post is due to my having a 1977 Caprice with a VECI label. The original poster only asked about the probable cause to his poor fuel economy maybe due to a vacuum line disconnected. Since that label is make, model, year, and engine specific there is no requirement for a rocket scientist. The original poster was not asking about a repair or tuneup.

Even though a 78 Monty is not a Chrysler product with a slant six, the Chevrolet engine specific VECI does have a picture of the vacuum operate emission control items with color coding of the different vacuum lines.

The 78 Monte Carlo owner could go to a metropolitan main library reference section and xerox the applicable Mitchell microfiche for his personal use.

Those labels can be purchased from various aftermarket vendors.

Who cares about a '62 Dodge Lancer with only a single vacuum line from the intake to the distributor vacuum advance on either a 170 or 225 cu. in. engine with a Torqueflite tranny.

It's a CTO valve. A coolant temperature reliant valve. The carb runs a ported vacuum through it before the vacuum goes to the EGR valve and the charcoal canister or gas tank air vent. Some run both ported and manifold vacuum through them to play with the timing vacuum advance too.

Basically it is supposed to not let the EGR or the canister turn on until the engine is heated up.

The missing line is likely going to the plugged up charcoal canister which is putting a vacuum on the gas tank bogging it out... See my other post in this thread.

Mike

Yes the sock filter can cause really funky problems. Get a fuel pressure gauge hooked up safely and let it lay on the windshield while you drive around and recreate the problem. If fuel pressure drops down you know what to do next.

There should not be an open vacuum port on the thermal vacuum switch. One port was manifold vacuum. One port was ported vacuum and the last went to the distributor. From the book " The thermal vacuum switch is designed primarily to help prevent overheating by providing full vaccum advance during prolonged idling periods or during unusually warm weather" It does this by switching the vacuum advance unit on the distributors vacuum source from the ported "normal" source to the manifold source.

The ports should be labeled "C" "D" and "MT" C=carb spark vacuum port. D=distributor and MT= manifold vacuum

I would try manifold vacuum to the distributor and take it for a run to see if it helps with the original problem. I don't think it will, but you need to get this straight to get the best gas mileage you can.

Hope this helps some.

Steve B.

JK wrote in rec.autos.tech

Little do you know what those little old ladys are capable of.:-). Anyway, try capping it off and see what happens.