MaxDog

I have had some problems with my 72 Olds Cutlass 350 4bbl the last few weeks. I put premium in it and it almost immediately began missing. THe missing got progressively worse. So I put some HEET in it. The HEET didn't really make much difference.

Once the gas tank was about 1/2 empty, I filled it with regular unleaded gas from a busy gas station and took it on a 10 mile freeway drive and it was running smooth again.

It ran smooth for a while, but then started missing again. Last night I pulled seven of the spark plugs (couldn't get the one on the passenger side nearest to the firewall). All the plugs had a short gap of about 30. So I increased the gap to 40ish.

Most importantly, the plugs all looked great except for cylinder 8. That one looked like crap and was wet with oil.

Any thoughts? Thx.

oldcutlass

My guess is the one that looked like crap is not firing. With the engine running, pull that wire and see if there is a change in the way the engine runs. If there is none, then I would replace that wire and possibly that plug.

Thats where I would start!

Good luck!

72 cutlass455

Wet with oil is not a good thing. The seal on the piston or the seal on the valve stem is letting it in. Also a hotter plug might help but as said above it could be the plug is not working.

jaunty75

I also wouldn't put premium in it unless that's what's called for in the owner's manual. An engine not designed to run on premium won't run better with it and will likely run worse.

Junkman

I have seen this statement more than once, and I would like to hear the explanation as to why the engine will run worse on a premium fuel than on regular fuel. I will agree that it might not run better, but worse... I can't comprehend why.

MDchanic

I have already responded to this on a different thread - I'll keep it off of this one so as not to derail it.

- Eric

jaunty75

Because engines that require premium fuel do so usually because they are higher compression engines. Premium fuel is designed to ignite at a higher temperature and higher compression than regular fuel.

The compression occurring during the compression stroke of the 4-stroke cycle also raises the fuel/air mixture temperature. The higher the compression, the higher the temperature. Premium fuel is designed to ignite at this higher compression/higher temperature.

Using premium fuel in an engine not designed for it (a lower compression engine) means that the fuel is being ignited (by the spark plug) before it has reached the temperature and level of compression it would in the higher compression engine. It will not burn completely, leading to carbon deposits and fouling and generally lower power output.

By the same token, using regular fuel in an engine designed for premium means that the fuel/air mixture will reach its combustion temperature BEFORE the top of the stroke and ignite prematurely, resulting in lower power, knocking, and generally more rapid wear to the engine.

That's why people whose engine is knocking will "fix" the problem by putting premium fuel in instead of the regular called for. Their engine is likely knocking because it's old or is out of tune or something similar and thus has carbon build-up, reducing the volume of the cylinder and, in effect, raising the engine's compression. But using premium fuel doesn't fix the problem, it just masks it.

So, yes, use regular fuel if your owner's manual calls for it and premium if it calls for that.

jaunty75

How does this derail it? The OP mentions putting in premium fuel. He brought it up. It might not have been his main point, but it's not irrelevant, and the conversation might prove useful to him.

MDchanic

Okay.

Here's what I said:

- Eric

jaunty75

I would qualify slightly that very last statement:

Check this page:

Why use premium gas when regular will do?

http://www.usatoday.com/money/autos/...emiumgas_x.htm



For the most part, the article is about people who go the other way and put regular gas in an engine that calls for premium in order to save money and whether or not they are doing any harm to the engine.

For the most part, it agrees with you in that using premium in an engine designed for regular won't hurt the engine but gives you no advantage, either.


But there is this passage:

Premium, in fact, sometimes is worse fuel than regular. It resists knock because it's harder to ignite than lower-octane fuels. As a result, some engines won't start as quickly or run as smoothly on premium


Admittedly, that's not a hugely serious warning against using premium if it's not called for, but why take any chance, especially if premium costs more?


In fact, that's the constant refrain from Joe Padavano. "Isn't gasoline costly enough already? Why do you want to spend more than you have to?"

Junkman

I thought that I had deleted my post in this thread before I started the other one. Don't know how this happened. Possibly a moderator can delete my post, and merge the answers into the post that I started called Fuel Choice..
thanks Junk

oldcutlass

Back to the problem at hand, Premium fuel will not cause this problem!

MDchanic

Sorry, but with all due respect, I absolutely do not believe that statement.
(and, frankly, if a USA Today "journalist" told me it was raining out, I'd look out the window to check). I can see that the author quotes "Lewis Gibbs, consulting engineer and 45-year veteran at Chevron oil company... chairman of Technical Committee 7 on Fuels, part of the Society of Automotive Engineers (SAE) Fuels & Lubricants Council," but I would bet that the quote was inaccurate (anyone who's ever been quoted in the press knows what I mean ).

It goes against everything that I have experienced. I would like to see some sort of evidence.

- Eric

jag1886

Sorry to hear that, so something else did crap out and it was just a coincidence that it happened at the same time as the gas fill. You should get a cylinder leak down test done to try and determine where your leak is coming from. I'd also set the plugs back to .030 if you are using a stock point ignition.
Again sorry to hear about your misfortune.

MaxDog

I definitely will not use premium again.

I did change out that one oily plug. Runs fine now. Once the engine cools down in a few hours, I will pull the new plug and take a look at it and see if its starting to foul again.

Thanks for everyone's comments.

MaxDog

Thanks. I do have a stock point ignition. Can you please explain the reason for setting the plugs back to .030?

MDchanic

If you set the gap larger than specified, then the spark will be unable to jump the gap under high resistance conditions (high combustion chamber pressures, such as acceleration), causing misfires, dirty plugs, hard starting, and crappy running.

The reason to use HEI is to be able to set larger gaps (and to be able to avoid adjusting your points periodically).

- Eric

MaxDog

I just pulled the new plug. It already has frickin oil or fuel on it. Its actually hard to tell whether its fuel or oil. In any event, i'm not happy.

Can this condition be caused by too rich timing? Too rich choke setting? Or too rich carb settings? Again, all the other plugs looked good. Only this one was wet-fouled.

The exhaust has had a strong gas smell since I bought it. I was thinking it might be running rich. Its just been to damn hot outside the last two months to go out and spend four or five hours tinkering.

Junkman

You have a serious problem with that one cylinder. I suggest that you pull all the plugs and do a compression test on all cylinders. From what you describe, you have one dead cylinder, and 7 live ones. Now it is time to find out how much life you have in the other 7. It could be rings, or it could be valves, but you will get a better handle on it when you know the overall condition of the engine. No matter what, I have a feeling that you are going to have to pull the head on that one side to determine what is actually going on.

MaxDog

Well once I replaced that plug, the car was running very smooth, and was clearly firing on all 8 cylinders.

Certainly the cause of the plug fouling could very likely be a ring or valve problem. But, before I get to the point of trying to repair a ring or valve problem, I was hoping hoping hoping there might be some other cause like timing, carb setting, or choke setting. What do you think?

Junkman

A new plug in a bad cylinder will always run better, but it won't fix the problem but for a short time. This isn't a timing problem, a carb problem, choke setting, or anything like that. It could be a totally dead spark plug wire, but you can either change the wire, or do the compression check. If you change the wire, and the problem goes away, then it was the wire. A quick method would be to switch the plug wire that is next to it with the suspect one.. Make sure that you also switch them correctly at the distributor cap. If the problem follows the plug wire, then you have solved the problem, it is a bad wire. If it doesn't, then you are still left with having to do a compression test. The only reason that I can think that there is resistance to doing a compression test, is that you don't have a compression tester. If you don't have one, possibly a friend might. You are just chasing your tail if you don't find out the compression of the engine. It is like going to the doctor, and him/her not checking your blood pressure.

MDchanic

Look, "timing, carb setting, or choke setting" affect ALL of the cylinders, but this problem applied to only ONE cylinder, so it is not any of those problems.

You have two choices:
1. No spark / weak spark, so plug doesn't get hot, and gets dirty
2. Bad mechanical seal, involving valves / piston / rings, allowing oil to get into the cylinder, fouling the plug.

Your choice: check whatever you'd like, but sooner or later you've got to check 'em all.
I'd start easy by switching the plug wire, then check compression once the engine's warmed up after you switched the wire.

This is a common old worn-out engine problem. Fact is, unless you've rebuilt it, likely as not, all of us have old worn-out engines.

- Eric

MaxDog

All good advice. I'll try switching out the plug wire tonight. I will go buy a compression tester too.

Will the compression tester be able to tell me whether the problem is a bad mechanical seal vs. valves vs. piston vs. rings?

Thanks.

Junkman

The compression tester will tell you the pressure in each cylinder when you crank the engine. If the compression is low on one cylinder, then you should put a teaspoon of motor oil into that spark plug hole, and crank it over for a few seconds. The reinstall the compression tester, and check the compression again. If it reads higher, then it is bad rings. If no change, then it is in the valves, bad head gasket, hole in the piston, etc.. You never mentioned if there is much blow by from the crankcase vent. If there is, this is a good indication that the rings are worn. What is the mileage of this vehicle? Do you know if it has had routine service and oil changes?

jag1886

A cylinder leak down test will and you can't do that yourself. In a cylinder leak down test the cylinder is put on TDC an then they inject air and the gauges read the percentage of leakage in a cylinder, in a bad cylinder you can generally hear the leak either up the carb or from the crankcase fill tube. One of the shops I worked at did it regularly to find which end of the engine was causing the problem.

MaxDog

I don't know how to determine if there is blow-by from the crankcase vent.

The mileage of the vehicle is 125,000 (supposedly it had a rebuild at 80,000 miles - who really knows for sure though)

It did have routine service and oil changes, at least for the last 6 years. Unknown prior to that.

MaxDog

Do I put the spark plug back in prior to cranking it for a few seconds?

Junkman

take the cap off where you put the oil into the engine, start engine, and observe if you are getting a lot of "smoke" or fumes out of that hole.

MaxDog

How much does one of those leak down tests cost generally? Would I get that done at a valve shop?

Thanks.

MDchanic

I don't agree with that.

You can get a spark plug thread air chuck at the auto parts store and pressurize the cylinder, and you can even plumb a gauge onto it if you want.
Then just run it up to pressure and time the leakdown and check it against specs.

... and this sort of problem should NOT be a surprise at 125,000 miles.
That "rebuild" 45,000 miles ago could have been a filter change for all you know.

- Eric

MaxDog

my thoughts exactly

MaxDog

Thanks, I would much rather do it myself if possible.

jag1886

Ok someone always has some home brewed way! Personally I'd call a good garage and let an expert diagnose it, but I guess that's just me.

MDchanic

I really don't see what's so complicated about setting the cylinder to TDC with the valves closed, applying a specified amount of air pressure to the cylinder, closing an air valve, and looking at the second hand of my watch while I watch a pressure gauge.

And I would MUCH rather do it myself than let someone I don't know, who may literally have half my IQ, do it for me.

And if "home brewed" methods are not good enough for you (and, yes, I do take offense at your pejorative reference), then he can spring for $35.00 for this one, which is far more complex than what he needs.

I see this site as a place where people can share information about how to do things, not about how to take things to other people to do for them.

- Eric

MaxDog

Thanks Eric. I agree. I love this car so much that I really don't want to entrust it to anyone else. To the extent there is a way to do something myself, I will always rely on me, and not some stranger that doesn't give a rat's *** about the car.

Plus, it is really rewarding to try and do the work myself and figure out the puzzle. I love the fact that while I am working on the car, or researching how to solve a problem with the car, I am focused on the task and not thinking about anything else, especially not work. It is a truly an enjoyable distraction.

That is why this site is so great. Because, thanks to you all, it is a tremendous source of information that allows me to attempt to do all the work on the car myself.

MaxDog

So I cleaned the fouled plug and switched two of the plug wires and took it for about a 20 minute drive.

Just pulled the plug out and its again fouled with oil/fuel. The other plug that received the switched wire was dry as a bone. So clearly not a wire problem.

I'll have to go get a compression tester like the one linked in Eric's last post. I don't have an air compressor, so I'll have to find one that works without a compressor, if such a thing exists.

I forgot to check for blow-by as suggested by Junkman. I'll try to do it tomorrow night and update this thread accordingly.

Again, thank you all for your assitance.

oldcutlass

We all learned by doing things ourselves thru trial and error!! My belief is that I can screw it up myself and if all else fails, pay someone to educate me in the error of my ways!

MDchanic

Sorry. You will need something to compress the air.
EVERYONE should have an air compressor, so maybe now is your chance .

Considering that this requires a very low volume of air, though, you might be able to get away with a high-pressure bicycle pump - just pump it up higher than specified, grab your watch quickly, and start counting when the gauge passes the initial reference pressure. (Now THAT's home brewed!)

- Eric

oldcutlass

Good ol American enginuity at its best. He will need some cheap beer tho!!

MDchanic

The day isn't complete without it!

Unless he prefers HOME BREWED !!!

- Eric