Deciphering Car Sounds and Gas Octane

This month, we open the mail bag.

I am the original owner of a 1976 Buick Regal hardtop with a 350-cubic-inch V-8 engine, four-barrel carburetor, automatic transmission, air conditioning and all power options. The car looks like new, inside and out, even though it has more than 140,000 happy miles on it.

However, for the last eight or so months, the car is hard to start, and when the engine does start, the car’s entire front end vibrates and shakes. The shaking is more severe when the engine is cold, and it continues whether the engine is hot or cold. I have taken the car to my local Buick dealer as well as several independent mechanics, who have not been able to correct this problem. Buick said the timing was out, but whatever they changed did not help. Also, the engine pings while accelerating (sounding a lot like a can of spray paint being shaken) and screeches. I have used premium gasoline since the car was purchased, and I have made every attempt to give the car excellent care. What can I do to save this beauty, or should I scrap it? What are your thoughts about a rebuilt engine? Any advice will be appreciated. Thank you.

ANNA F. CARLTON, Las Vegas

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Your description of the sound leads me to suspect a rod bearing rather than knocking from a fuel, timing or carbon buildup problem. But, descriptions of sound being subjective, let’s be optimistic for now. The dealer says the engine timing is out, but it didn’t remedy that. There is a possibility that the timing chain has slipped a tooth, which would throw the timing off. If the dealer doesn’t want to tackle whatever is ailing your car, find an independent shop, preferably one that specializes in older GM vehicles. If a new chain and related parts are needed, it won’t be cheap, probably $250 to $400, depending on required parts. But if you love the car and it’s in otherwise good shape, it’s still cheaper than a new vehicle.

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Please help me with the answers to the following questions concerning my 1995 Jeep Grand Cherokee. (2-wheel drive, 6 cylinder).

First, my neighbor insists that running premium (92 octane) gas in the car will make it last longer. He claims that fuel lines and fuel injectors will remain cleaner and require less service. He says that the engine will burn cleaner. He got this information from an automotive tech class at a local community college.

He also claims that the automobile manufacturers would rather that we did not know about using higher octane gas because they have a vested interest in servicing our cars and selling replacement vehicles. Thus the old conspiracy theory.

The manufacturer recommends that I run regular unleaded 87 octane or higher gasoline. I am not experiencing any knocking or pinging, and my engine is running perfectly. However, my neighbor insists that spending the extra money on premium gas is worth the additional benefits and the engine longevity that is to be derived. I understand that higher octane gasoline is recommended for automobiles that have knocking and pinging problems, but what about my neighbor’s concerns with cleaner fuel lines, injectors and combustion? I have always purchased unleaded 87 octane gasoline for my vehicle. Should I be spending more and pumping premium gas into my car?

Second, I replaced my spark plugs at 30,000 and 60,000 miles, as recommended by the manufacturer. Because my Grand Cherokee has electronic ignition, nothing else was done besides replacing the plugs. Does the on-board computer automatically make the adjustments? Does my car need to be placed on some kind of scope in order to see if it is running according to specifications? Are there manual adjustments that can be made, as in the old days, or do I just have them install the plugs and have the on-board electronics do the rest? Caps and a rotor are still there (aren’t they?) and are easy to replace. I was just wondering about the need for making tune-up adjustments. The automobile runs just fine with the latest replacement spark plugs.

JOHN M. KOCHIAN Jr., Via the Internet

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First question is easy, and the short answer is, no, higher-octane fuel is no cleaner or less likely to cause fuel system components to collect deposits than fuel of a lower octane. Octane describes one characteristic of gasoline: its resistance to knock.

That said, regardless of octane, it’s a good idea to use a bottle of injector cleaner. A number of automobile manufacturers recommend Chevron’s Techron. I’ve used it, and products by Castrol and Red Line. Your owner’s manual should offer some guidance about what to use and how often, but if not, every oil change should be sufficient. And, as always, RTFD (read the fine directions)! Some products are a half-bottle in the tank for 10 to 12 gallons of gasoline; some call for using the whole bottle.

As for your second question, yes, the on-board computer is capable of compensating for small imperfections in tuning and octane. A vehicle with electronic ignition doesn’t have points and newer models don’t have a rotor. Timing will drift a bit with engine wear, so it’s good to check it when the plugs are changed. If your car has timing marks, you can check this yourself with a timing light. Track down a shop manual for your vehicle’s year to get full directions. Or, if you don’t want to get under the hood, have it checked by a mechanic. Also, the new smog test in California includes a check of the ignition timing.

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Two items.

In the first Highway 1, you used the term “pre-detonation” for the premature firing of the gas/air mixture in the cylinder. More correctly the term should be “pre-ignition detonation.” The gas/air mix explodes before the igniting spark, the ignition, hits the spark plug.

The second item relates to pre-ignition by way of low octane rating.

Since the appearance of the first Highway 1, I drove into the Rocky Mountains and discovered regular gasoline is 85 octane. The middle grade is 87 octane. My car normally uses 87 octane and, to play it safe, that is what I filled up with. I think the high altitude is a factor in 85 octane. Would it have been OK to use the lower octane?

MIKE HATCHIMONJI, La Palma

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OK, yes, strictly speaking it is pre-ignition detonation.

As for Rocky Mountain gasoline, octane ratings are lower at higher altitudes because octane requirements go down the higher up you go. You would have been fine with the 85 octane as long as you didn’t travel to sea level on a hot, humid day.

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A great deal of vehicle engine wear is supposed to occur during the initial start-up, when the engine is cold and the oil has not circulated.

There are devices on the market that pump the oil with pressure before the engine starts. Cost: about $250.

Are these devices worthwhile in prolonging engine life?

I plan to keep my truck a long time, so I would not mind the investment if they are helpful. One opinion in a magazine says they are, but that they cost too much for mass car sales.

Your opinion and information would be appreciated.

FRANK W. SUMMERS, Santa Ana

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Properly set up, a system that pre-oils the cylinders should prevent much of the wear that occurs when you start the engine. Sure, $250 sounds like a lot, but it’s what some people spend in a couple of years on oil additives that do not prevent start-up wear.