marky mark

which I thought might be the source of my suspected vacuum leak but I just can't tell where it's coming from. Sounds like air pressure bleeding off and it lasts only a few seconds. I did a brief intake manifold vacuum leak test and didn't seem to have one. This sounds as though it might be coming from the drivers side exhaust manifold but I can't tell for sure.Perhaps the exhaust manifold gaskeyt is blown? Definitely not coming from the vacuum resovoir cannister.

The symptoms are an unsteady idle: up & down 100-150rpm constantly. Won't stay at same rpm. Also, timing mark at idle moves up and down 2 or so degrees constantly. Also, left headlight is now very slow to rise: goes up halfway and then up all the way after driving a couple miles. Think the actuator is making a squeaky sound so this may or may not be related to the engine sound.

Car is a '69 427/390 4 spd. Any thoughts? Anyone heard of this before? I was thinking possibly a blown head gasket but there is no water in the oil and the car does not run hot. Any help is appreciated.

Regards, Mark :chevy


[Modified by marky mark, 3:22 AM 1/3/2002]

Les

You do have symptoms of a vacuum leak but a blown exhaust gasket wouldn't be the cause of that. I'd suggest letting the car idle w/ hood up & reaching in through the window to shut it off while standing next to the engine. You may be able to pinpoint the source better that way. I'm assuming you've made sure all the vacuum lines are in place but have you checked them for tightness & splits/holes? Carb base gasket would be my next guess.

Milest

I had the same problem and it turned out to be a loose vaccum hose on my wiper door actuator. I would check the headlight actuator for leakes, but then again it could just be slow because of lack of vaccum. Good luck.

Wrecked82

I had the exact same situation this past Monday. Could not figure where it was coming from. Would stop motor and jump up trying to hear where. Turns out there is a small plastic T coming off a vacuum port on the back left of the intake manifold lid. A 1/8" nipple had broken off and the connected hose fell down so it was not visible. A $.80 part. Car runs great now. Obviously was affecting performance. Going to recheck TBI balancing this weekend when warmer. So, check all the vacuum lines.

mrvette

Ifyou have that rounded square pillow steel canister like I had in my '72, you will maybe find that it had developed stress cracks over the years, and in fact has several stress breaks in the metal, on the flatsides, near the rounded part....I found that using one headlight relay and no cannister was the best option for my car....

GENE

marky mark

Thanks everyone,I'll keep looking.

Regards, Mark

73-454

I have the same problem on my 73, I think mine is comming from the brake power booster. If you have a vacume tester check the booster.

mrvette

Know how to check for leak operation, suck on the hose like siphoning gas.....not a natural operation for most guys....;-)))....and hold with tongue to see if leaking is loosing vacuum.....

GENE