Engine falter

My car is 1976 Chevy Impala.
Recently, a strange thing happened while the engine was idling and my foot on the accelerator pedal and depressed about an inch and without warning the engine began to falter , the ammeter needle dropped almost all the way down, akin to turning off the ignition key for a moment, then turning it back on. Why did that happen, anyway ? Something to do with the carburetor, choke mechanism, or what ? Got me worried and mystified. Any way to find out on this forum.
My mechanic says he's too busy to check for the rest of 2014.

Hi, Chevy.

Is the problem repeatable?
Does it heppen every time or is it random?
Does it happen under certain weather conditions?

There are many possibilities to consider.

It could be fuel pump, carb icing, loose wiring connection, fuel contamination, temporary fuel blockage, etc., etc.

Did the fault clear itself or were you able to clear it by revving the engine perhaps?

More info please.

Ken.

>> Is the problem repeatable ? Yes
>>Does it happen every time or is it random? Random
>>Does it happen under certain weather.. ? No

>>Did the fault clear itself? Yes, definitely. The needle goes back to normal, but returns to slightly abnormal.


To perform the test, I idled the engine continuously for about 27 minutes keeping my eyes on the needle, the ammeter needle, I suppose.

The ammeter is only showing a result, not a fault. When the engine stumbles, it slows down and makes less current. The ammeter measures the current flow, ergo, less current, lower reading. Does your car have points or electronic ignition? If it's points, you probably need a tune up. If it's electronic (this was built when all the car companies were going with HEI) you may need a tune up.

If the cap and rotor have been on there a while, I'd replace them. I'd also pull the spark plugs and look at them. With HEI, you can go quite a while between changing them. If you have points, you need to replace them twice a year. You also have points and condensor to replace.

One thing you can do is wait until dark and find a place away from lights. The darker the better. Now open the hood with all the vehicle lights off. If you see sparks or phantom flashes sliding along the plug wires, you need new ones. I suspect you just need a tune up from age.

My car has HEI. As for the plugs, I hardly drive the car, maybe 10 to 15 miles per week.

The way the car is behaving, (read post #1) I first suspected a new fuel filter should fix the problem, (No ?)

Edit:
Current odo reading 58010.
Plugs/wires replaced at 51376 mi. in 2007
Carb o/haul 51107 mi. in2007

Tune-up 47929mi. in 2004

Chevy, ten to fifteen miles a week hardly gets the plugs hot enough to burn off the contamination from the previous run and the 'choked' start fuel regime. I would suggest taking the car for a good, high speed, thirty to fifty mile run to clean the plugs up and boil off any acid and water in the oil. Grouch's suggestions of checking out the ignition electrical components and giving the car a 'tune up' would be a good precursor to a nice long run which would also help clean up the combustion chamber and the exhaust system. Cars that are little used, like yours, require more frequent attention than cars that are regularly given good long distance commuting runs.

Ken.

[QUOTE=Ken;139506]Chevy, ten to fifteen miles a week hardly gets the plugs hot enough to burn off the contamination from the previous run and the 'choked' start fuel regime. I would suggest taking the car for a good, high speed, thirty to fifty mile run to clean the plugs up and boil off any acid and water in the oil. <<

Would occasional fast idling in place help, instead of taking it on the highway? I'd hate it in case something goes wrong and the engine dies , requiring me to call a tow truck.
I idled it for about 35 minutes, simulating increasing the speed time to time and several times the engine wanted to die but never did but it did decrease the RPM slow enough to turn the GEN light on momentarily. I suppose it's safe enough to go shopping a mile away and back. What do you think?.

[QUOTE=ChevyMan;139507]

Quote:

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Originally Posted by Ken

Chevy, ten to fifteen miles a week hardly gets the plugs hot enough to burn off the contamination from the previous run and the 'choked' start fuel regime. I would suggest taking the car for a good, high speed, thirty to fifty mile run to clean the plugs up and boil off any acid and water in the oil. <<

Would occasional fast idling in place help, instead of taking it on the highway? I'd hate it in case something goes wrong and the engine dies , requiring me to call a tow truck.
I idled it for about 35 minutes, simulating increasing the speed time to time and several times the engine wanted to die but never did but it did decrease the RPM slow enough to turn the GEN light on momentarily. I suppose it's safe enough to go shopping a mile away and back. What do you think?.

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Maybe, but I doubt it. The first thing I would check would be inside the distributor cap. Being near the ocean (on an island everyplace is near the ocean) you may have corrosion inside the distributor cap. You say you replaced the plug and wires in '07. 8 years is long enough for a hairline crack to form in the cap. It's just plastic after all. If it WASN'T replaced, it's way past time. Moisture getting in because of a crack can cause arcing and this wil show up as a falter like you describe. If you replace it, be sure to get one with brass or copper electrodes. These can make better connection and get a hotter fire to the plugs.

You said, and I quote " Maybe, but I doubt it." You were referring to fast idling, in place, or to "I suppose it's safe enough...........". ?

[QUOTE=ChevyMan;139507]

Quote:

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Originally Posted by Ken

Chevy, ten to fifteen miles a week hardly gets the plugs hot enough to burn off the contamination from the previous run and the 'choked' start fuel regime. I would suggest taking the car for a good, high speed, thirty to fifty mile run to clean the plugs up and boil off any acid and water in the oil. <<

Would occasional fast idling in place help, instead of taking it on the highway? I'd hate it in case something goes wrong and the engine dies , requiring me to call a tow truck.
I idled it for about 35 minutes, simulating increasing the speed time to time and several times the engine wanted to die but never did but it did decrease the RPM slow enough to turn the GEN light on momentarily. I suppose it's safe enough to go shopping a mile away and back. What do you think?.

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In my experience nothing beats a proper run, with the engine working hard, in the car. Carry out the checks that Grouch recommended, then, if everything checks out take the car for a good run. You may find that you have a much sweeter running car afterwards. Don't get worried if after about ten hard miles you see clouds of black smoke and crud coming out of the exhaust as the rubbish gets burnt off.

Ken.

Ken

In contrast to yesterday's (Wed) test, today, not once did the engine faltered within a 20-minute time frame. Will repeat the test tomorrow . Will report the result.

Larry

Quote:

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Originally Posted by ChevyMan

Ken

In contrast to yesterday's (Wed) test, today, not once did the engine faltered within a 20-minute time frame. Will repeat the test tomorrow . Will report the result.

Larry

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Well, I repeated the idling test this morning. In FAST and NORMAL idling for at least 30 minutes, not once did it faltered like it did a couple of days ago. Ken, what do you think? Should I still have a tune-up performed and also replace the plugs and wirings as a preventive maintenance?

Quote:

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Originally Posted by ChevyMan

You said, and I quote " Maybe, but I doubt it." You were referring to fast idling, in place, or to "I suppose it's safe enough...........". ?

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I was refering to idling in place. An engine under load performs differently than one at idle. The vacuum advance has different setting on your type of system. I'm thinking your issues may have to do with humidity. The age of your distributor cap is what I think is the source of your problem. There are only 4 clips holding your cap down but flipping the cap up for an inspection can be problematic on your engine. I've got a Camaro with a similar setup and sometimes the positive wire slips out. I've worked on these since they were new so I know what to plug where.

As I mentioned on my previous post, I idled the engine for almost 30 minutes and NOT ONCE did it falter. I will do it again tomorrow for the last time and see how it will go, but I plan to replace the wiring, distributor cap and plugs. I will be 92 in April 2015 and no intention of switching cars, for obvious reasons.

Larry.

Certainly replace the plugs, cap and wiring, Larry. I still reckon you should take the car for a good run, though. 92 eh?, man that's a good age, I thought I was getting on at 81 but I still enjoy the occasional 120 mph thrash in the car or on the Yamaha.

Keep on truckin' Larry and all the best for 2015.

Ken.

Sakes, here I am looking at 60 and I now feel like a young pup. My mother was active until she passed away at 93. She drove until she was 90 but managed to stubborn herself into a broken hip and that was the end of her driving. Her aunt Clara lived to 98 and drove until she was 96. The only reason she quit was she needed the moeny and sold her car.

Quote:

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Originally Posted by Ken

Certainly replace the plugs, cap and wiring, Larry. I still reckon you should take the car for a good run, though. 92 eh?, man that's a good age, I thought I was getting on at 81 but I still enjoy the occasional 120 mph thrash in the car or on the Yamaha.

Keep on truckin' Larry and all the best for 2015.

Ken.

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I'm using 87 octane gas. Will switching to a higher octane help engine performance ? Available are 89 and 91/92 octane.

Edit:

Car is equipped with QuadraJet 4 bbl carb.

Changing the octane rating won't cure any actual problems that exist. The car may run slightly better on a higher rating but check the car's manual for the recommended grade which I believe, for your car is (US) 91 Octane or better. I think your US ratings are different from ours over here in the UK.

Ken.

I think it's certainly true about the ratings between UK and US. Although I no longer have the original owner's manual, I distinctly remember the manual saying regular 87 is fine.

Quote:

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Originally Posted by ChevyMan

I'm using 87 octane gas. Will switching to a higher octane help engine performance ? Available are 89 and 91/92 octane.

Edit:

Car is equipped with QuadraJet 4 bbl carb.

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Not really. A higher octane can actually cost performance. Octane is the resistance to ignition ping, or knock. It slows the combustion to prevent preignition. That's when you get spontaneous comustion and when the two flame fronts meet, it's a knock. The higher the octane the slower the burn. This allows a higher compression for more power. higher octane in itself won't help performance unless you have really high compression. Pure octane is rated at 100.

The opposite is cetane. That's what you want with a diesel. The lower the cetane rating the easier it is to combust from compression. There you want a lower number.