I bought this beautiful 72 Cutlass a couple months ago. It has a 350. It has ran beautifully, not a single problem.

Last weekend I filled up with premium unleaded gas. Prior to this, I had always used regular unleaded.

Shortly afterward, it started missing and having major hesitation. The missing and major hesitation is not constant. THe majority of the time it still seems to run great, but then it seems to slip into missing and hesitating for a few minutes and then will go back to running fine.

It usually starts missing and hesitating under load.

Any ideas????? Thanks.

 

Water in the gas?

- Eric

 

Sounds like you got some bad gas!
Put some HEAT in the gas, or go to a busy station and add more premium!
Could be the fuel filter, too!

 

Going with H2O fuel on this one too. Maybe put some 'Heat' in the tank, change your fuel filter, and find somewhere else to buy fuel. Part of the problem, I believe, is that with the cost of fuel keeps the premium tanks full. The lack of movement builds condensation in the holding tanks. Bam, bad fuel.

 

My bad..........Yeah, what Rickman said

 

Could be water, could be a load of gas that got dosed with too much or the wrong additives. As much damn ethanol as is in gasoline now, you'd think all that alcohol would absorb any water. Trouble is the solvent action of it can break stuff loose and plug the fuel filter. Hesitation under load makes me think that may have happened.

I've run inline filters on the fuel pump suction side for many years and I don't have near the fuel filter problems I used to- plus that filter is a lot simpler to change out than the carb filter, and you don't worry about stripping out fuel inlet threads.

X2 on buying your gas at a station that runs a lot of gas thru their tanks.

I've had cars that actually got worse mileage on premium. The computer vehicles get 87 since I've seen no difference in running it vs premium in them. The wagon wants 89- it will ping and hard start on 87, but I see no difference in performance or mileage between 89 and 93 octane on that car.

Bottom line, if it runs fine on 87 octane, use it.

 

X2 on what Glenn said. If the car runs fine on regular, why use premium? Are you not spending enough on gas? And yes, all else being equal, you usually WILL get worse mileage with premium than regular. Premium is more difficult to burn. Bottom like is always use the lowest grade you can get away with without pinging.

 

I used premium because the guy I bought it from told me it ran better on premium and didn't ping when using premium. So I decided to try it. Not a good decision apparently. Especially since I never could hear any pinging, although I have no idea what the hell pinging even sounds like.

So I'll try putting some HEAT in it. Is that something I can buy at Autozone?

I'm also going to check the plugs for fouling and maybe check the timing. Even before this problem, the car had a really strong smelling exhaust. Might be a little rich?

Thanks so much for all your imput.

 

The best analogy I've ever heard is that it sounds like the rattle sound the little ball makes when you shake a can of spray paint. It's not a very deep sound. Just light little clicks like marbles bumping into each other. I always thought that the word "pinging" wasn't good because, to me, a ping is a high-pitched sound almost like a bell being tapped with a small hammer. "Knock" is a better word.

 

So should I be listening for the knocking coming from the exhaust or from the engine? What if I open the hood, can you hear it then?

 

You will hear it under load while your driving, like up a steep hill!

 

The pinging will occur in the engine when you are driving the car and place a load on the engine. A good example will be if you start to climb a hill and you give it just enough throttle without it causing the transmission to drop down into a lower gear. If it is going to ping, you will hear it then. It may help to have the windows up to hear it.

So to the second part of your question, for your safety and that of other motorists, I would strongly encourage you to stay in the car with the hood closed while driving it to hear this pinging!! Just couldn't help myself with that one.

 

As the others have said, you hear it under load such as going up a hill or hard acceleration to merge on a freeway. It will sound like it's coming from the top of the engine under the hood just in front of you. If you haven't heard this, your engine is not knocking, and you'll know when you hear it. All the more reason not to be putting premium gas in it when all that's called for is regular. Why try to fix what ain't broken?

 

I'm curious as to see if the car runs OK after you get it back on regular. It could be something else has crapped out and just happened at the same time.

 

pinging is most apt to be heard in high gear, low rpm, under light acceleration up a slight incline.

my C5 Vette "recommends" premium but after two tanks of bad gas from the premium pumps I've started using the 87 with no adverse affects. The ECM adjusts.

I think the premium isn't sold as much because of the price so it sits longer in the underground tanks, having a better chance of becoming contaminated.

 

HEET is a water remover and fuel de-icer that has been around for years. It works. You should be able to find it at AutoZone or probably even WalMart. It's in a yellow bottle.

Y'all have brought up interesting points about premium gas sitting in the tanks long enough to go bad. I've read that current fuel formulations will sour in as little as 30 days. Somewhere like a Sheetz or other high-volume gasoline retailer would probably not see it as much as say a neighborhood gas station.

 

Put in the HEET last night. Still not running any better. The tank is still about 1/2 full of the possibly bad premium.

I'm going to check all the plugs and the wires to make sure no loose wires and no fouled plugs.

 

If your tank is down to 1/2, I'd go fill it back up with the regular grade of gas you had been using all along. That would dilute the possibly bad gas enough that your engine would likely run better, perhaps as well as before the premium was put in.

Then, the next time you fell this overwhelming urge to fix what ain't broken, simply lie down until the urge passes.

 

So I filled the tank back to full with regular unleaded. Drove around for about 10 minutes, it was still running like ****. So I took it out for a drive on the freeway at 70 to 75 mph. After about 10 miles, it finally started running like a champ again.

Thanks so much for all of you for your advice I love this car and this forum!!!!!

 

Glad to hear it.

After all the advice-giving above, I have to say that I actually think you probably really did run into a load of bad gas. Yes, the car might not run as well on premium when it's designed for regular, but I don't think the use of premium should have caused the degree of problems you experienced. Particularly since you were probably, what, a quarter full when you filled up? That means you were running on a mix of premium and regular, not pure premium. I wouldn't have expected the severity of problems you did with that kind of gas mixture.

I think that, some time in the future, when you get your courage back up, if you really want to see if premium gas makes a difference, you might try this again with a different brand.

 

So you gave it the old "Italian tune-up" Glad to hear it's back to running well!

Reference: http://en.wikipedia.org/wiki/Italian_tuneup

If you do want to try this again, here's a sure fire way of getting known good premium fuel.

Step 1 - Find the local drag strip.

Step 2 - Figure out which night is "Test & Tune night" (Typically Thursday nights)

Step 3 - Fill up with 3/4 regular unleaded and 1/4 of the highest octane "race fuel" they have on hand.

Step 4 - Have fun!

If you're feeling REALLY froggy, take it for a blast down the track & see what She'll do. At the very least, stop in and watch for a night. Walk around the pits til you find someone running a similar car (Preferably a 1965-1975 Oldsmobile with a 350/400) and see if they're amicable to chatting about how theirs is set up.

Without knowing the exact compression ratio on the engine, I would not put more than 1/4 of the tank of race fuel in it. Once you can verify it runs better on premium (and I bet it does!) You can start researching how to set the timing properly for premium vs. low-octane if you want to become more knowledgeable about how it all works.

Older cars are a much different beast than the newer cars. They don't have any of the following:
-ECU (engine computer)
-Fuel injection
-Knock sensor
-Oxygen sensor(s)
-Catalytic convertor
-Crank sensor
-Cam sensor
All of which are designed to give you the best mileage possible and reduce the emissions to the lowest possible pollutants. Back then, ALL these settings had to be made manually. Mechanics were a different breed then. It's a totally different game now and carburation is becoming a lost art unfortunately.

p.s. Got any pics of her to post? We all love to see these old cars, no matter what shape they're in.

-Jeff

 

Glad it work out, sometimes blowing the cobs out, is all it takes.

 

Here ya go!!

 

Thanks, and damn! That's a sweet ride! LOVE the color combo.

-Jeff

 

Thanks Jeff. And thanks to everyone for their assistance.

 

What self respecting person would have a color combo like that?!?

I still can't figure out whether I like SS1's or SS2's better & your car just makes it harder to figure out! It's beautiful.

 

Turn off your radio/music !!!!!!