[78PontiacB]

I have owned a factory stock one owner 1978 Pontiac Parisienne for the last 35 years, purchased from the original owner, body and paint remain excellent! It has been my wifes daily driver for the last 20 years....we run it through the summer and extreme winters of central Alberta...

Engine has been weak in performance for the last couple decades (rated at 150HP new..), but it always fires up and runs smoothly, decent gas mileage as well.

It was -32C this morning. It was plugged in and fired up as normal, let it warm and drove my wife to work, about 11kms each way.....ran as normal going, but coming home it began to loose power intermittently, like it was backfiring on itself at very little throttle load....

So I opened the hood and the engine she is a rockin more that normal....and i can hear a low banging/clanking....not a rod noise - more subdued....I held the engine at a high idle in neutral, seems no fuel or spark issues.....so I took it to check our mail, about 7 kms away....and well....barely got it home...can hear popping coming back through the carb....then it looses all power, then catches and runs for 10-15 seconds, repeat....

Plugs and coil and wires replaced a short time ago. Have never experienced this nature of hesitation/power interrupts on the highway with this car ever...

Please can some experienced Pontiac 350 gents comment and offer some advice? Is there any way to determine beyond a doubt if it is indeed a badly worn camshaft? Engine has 245,000kms on it, always changed the oil, never overheated or had the bag run off of it....

Thanks all - my wife loves this car....hate to take if off the road...!!

[Simple Man]

Timing chain?

[5th TA]

Not saying the cam couldn’t be worn, but if it ran decent going out and terrible coming back, not likely things changed that quickly with the cam condition. You could start with pulling plug wires one at a time from the distributor side while the engine is running. If pulling a plug wire doesn’t have an effect, you have a dead cylinder. On the other hand if you have an RPM drop then that cylinder is producing power. Pull the plugs on any dead cylinders and check the condition. You could also do a compression test on all cylinders. Any recent changes with fuel or fuel fill up before engine started running poorly? Large vacuum leaks or carb loosely mounted to intake?

Be careful when pulling plug wires if you have never done this before, you could get a shock. They make insulated pliers for this if you want to play it safe.

[78PontiacB]

Originally Posted by 5th TA

.......... Any recent changes with fuel or fuel fill up before engine started running poorly? .

I just filled up the day before I drove it.....yuup....at a cheapo gas station on a res....

so does that mean I have water in my tank or some other crap from that off the grid gas station....???

[Goatracer1]

I assume this is a Chevy engine. Dirt in your gas should not cause a noise. If it was water it would have frozen and not run at all. Try to locate the cylinder(s) causing the problem. If there is spark check compression. If compression is bad remove valve cover and check valve action. Bent push rod or bad rocker will be quite noticeable. If cam is bad rocker will move little or not at all.

[roger1]

Timing chain might have jumped a link.

[455dan]

Originally Posted by roger1

Timing chain might have jumped a link.

Could be, I think GM was still using the (silent) nylon coated cam gear. Many of the Buicks and Pontiac V8s seem to kill that Nylon toothed cam gear when they hit over 100k miles.
If that is a stock silent cam gear it is over due to jump time.

[78PontiacB]

So are the Pontiac engines using nylon in their timing assemblies? I know Olds was as our 71 Delta 88 455 needed that replaced at one point. When it went it would not even start. This engine starts at the touch of the key....I am hoping for a bad tank of fuel. Will fire it up once this -35 cold snap passes....
Thanks everyone!

[george kujanski]

Check the ignition timing.......if the chain is bad, the timing will be way off.

George

[455dan]

Originally Posted by 78PontiacB

So are the Pontiac engines using nylon in their timing assemblies? I know Olds was as our 71 Delta 88 455 needed that replaced at one point. When it went it would not even start. This engine starts at the touch of the key....I am hoping for a bad tank of fuel. Will fire it up once this -35 cold snap passes....
Thanks everyone!

Actually I think Pontiac dropped them around 1971? not sure on that.
I have bought a couple non runner Buicks cheap and they were Nylon gear failures.

I thought the Canadian Parisienne's were Chevy powered and I have seen small block Chevies with the Nylon over coated cam gear that were reportedly untouched- 2 were from 1978

[Half-Inch Stud]

sour gasoline, or water logged gas will cause rough run and hot-idle stall.

[roger1]

Originally Posted by Half-Inch Stud

sour gasoline, or water logged gas will cause rough run and hot-idle stall.

I thought that at first too but the car gets driven every day so it should be unlikely.

[Sirrotica]

Without taking a compression test, and a vacuum test, you're purely guessing. Doing both tests will at least give you the direction to move in a logical order of checking for the source of the problem.

Pulling plug wires is a good way to isolate it to one cylinder, if it is in fact only one cylinder that is causing the shake. This could be as simple as a bad plug/ plug wire, to all kinds of failures in the internal workings of the engine. In 78 Pontiac was about 7 years past nylon timing gears. My experience is 99 out of 100 the cam timing goes right away as soon as the teeth shear off, they get so far out of time they just quit running, not jumping one tooth. Shaking usually indicates an imbalance of one cylinder missing. Cam timing is usually just a loss of power all the time

Those are the steps I'd follow after 50 years of making my living trouble shooting anything with an engine. Your car, your choice.

[78PontiacB]

Thanks again to everyone who has posted. I am hoping for a tank of bad gas, since all of this started about 10 miles after I filled the tank right up....and these symptoms are intermittent. If it was a mechanical failure - would it not run like crap, hesitating and chugging all the time...?

[SRR]

Put some "dry gas" or Heet or what ever it's called up there and see what it does. It's supposes to suck up the water in fuel if that's your problem.

[78PontiacB]

Originally Posted by SRR

Put some "dry gas" or Heet or what ever it's called up there and see what it does. It's supposes to suck up the water in fuel if that's your problem.

Indeed yes I will add some gasline antifreeze and see if that helps.

Also since this is a 44 year old original 350 - it may be the fuel pump on it's way out....perhaps the diaphragm is now weak or torn and it is not able to maintain fuel pressure/flow....

Thanks everyone!

[78PontiacB]

Another question looking for assistance please....I have not ever checked the timing on this engine in the 27 years I have owned it. How do I check the timing, and how can I determine if the timing in terribly out, and or if the camshaft is terribly worn. Backfiring through carb under light - moderate load, low power, and intermittent hesitating at 60 miles per hour..

Could the timing be right out of whack? Or is the camshaft done in...

Advice please...! Thank you.