'96 pinging under load with 87 octane

For some reason my '96 XJ seems to be pinging under heavy load on 87 octane. I put in half a tank of premium, and it stopped. It's got almost 200,000 miles on it. I don't think there is much carbon buildup, I use Chevron gas with techron and it's recently had a good dose of "Seafoam" down the throttle body. All the ignition parts except the coil are new, and the spark plugs are OEM Champions. Any idea why is causing this? I can't afford to keep this pig full of premium... :bawl:

AAA had a good article on octane levels, & its conclusion is one of the few things all the engineers/car nuts in my family have ever agreed on: "run the cheapest gas your car doesn't ping on".

Higher octane makes engines run cooler, so a car that's generally ping-less on 87 might need higher octane when towing/climbing or in hot weather.

Take this for what it's worth: I don't know a monkey wrench from a baked potato. But I've always been surrounded by car people/car talk & I listen well.

Try mid-grade (89) before you spring for premium.

My 95 pings too, and as noted above by Churchlady, the quickest solution is to put in higher grade gas. But if you have a lot of miles and it's getting worse, you might try a carbon cleaner like GM Top Engine cleaner. GM dealers sell this. It works well. It will burn off built up carbon, and improve the pinging, at least for a while.

my '95 was pinging until i took it to my mechanic and had him flush the engine with one of those machines that flush the engines of all the deposits. I deal with a lot of bad traffic and it was pinging and had a lot of lifter noise at 80K miles. After I had it flushed it was surprisingly quiet and the pinging still has not returned.

I couldn't find the AAA article itself, but found this good summary of it on the Brickyard Volvo site.

Monday, 28 June 1999, at 12:24 p.m.


89 octane gas will not do any harm to your or anyone else's engine UNLESS the car pings on that grade of gas. In fact, if you are buying any higher octane than the car doesn't ping on, you are wasting your money. AAA had an article on gasoline octane and how oil companies use consumers' ignorance to sell them premium gas when in reality only very few cars on the road today require it. Basically, the jist of the article is this. The octane number is a measure of gasoline's combustobility. The higher the number, the less combustable the gas. To make the gas less combustible, impurities are added to the gas. Yes, this is counterintuitive, but the higher octane gas actually has more impurities in it to raise the octane number. Most of the time the additives are ok, but sometimes (and in most states oil copmapnies aren't required to disclose the content of the gas formula) the additives are wood- or grain-alcohol based, which can be bad for your engine in the long term. Also, in many states there is no way to know that what you get is what you paid for. In other words, surprise inspections revealed that many gas stations (even big name ones) sold regular grades at premium prices. So, AAA's advice was to buy the cheapest gas that the car doesn't ping on. I personally put 87 (regular) into my cars and my motorcycle and every few months I pour a bottle of good quality fuel injector cleaner into the tank, since regular grades usually have less cleaning agents in them. So far, I had no problems with any of my cars that were fuel related. My last car was a turbo (Mazda 626) and I fed that car regular, too. The performance is insignificantly effected, but not nearly enough to justify $0.20/gallon price difference. Premium gas was developped when many cars pinged or knocked going uphill in the older days. This occurs from pre-ignition, i.e. the fuel mixture ignites before the spark and before the valves are in the appropriate positions. The force of premature ignition opens the vales "against their will" and this produces pinging sound. If you don't hear this sound (and you shouldn't -- with today's sophisticated engine management this problem is all but elliminated), there is no harm being done to your engine. Keep in mind that regular grades typically have less detergents in them (but they don't completely lack them), so if you are worried about that, throw a bottle of fuel injector cleaner when you fill up once a couple months and save your money for other things. You Volvo, as well as most electronically managed cars on the road today will adapt to any octane in the range specified in your owner's manual (I think the lower limit is 87).

A friend of mine that builds competition race heads told me that he runs cheap Arco gas (here in Los Angeles) and adds a 1 - 1.5 cups of Toluene to
a full tank. He told me toluene (which is a thinner/reducer) is the same thing as octane booster. I tryed this a few times on my older 4 banger toyota carolla which had a pinging problem with 87 octane gasoline and it actuallly worked. But it became a hassle, and probably a hazard hauling around a container of toluene every where with me.

Scott S.

RisingSun said:

A friend of mine that builds competition race heads told me that he runs cheap Arco gas (here in Los Angeles) and adds a 1 - 1.5 cups of Toluene to
a full tank. He told me toluene (which is a thinner/reducer) is the same thing as octane booster. I tryed this a few times on my older 4 banger toyota carolla which had a pinging problem with 87 octane gasoline and it actuallly worked. But it became a hassle, and probably a hazard hauling around a container of toluene every where with me.

Scott S.

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Can anyone else tell me more about this?

Sounds like a cash cow to me.

Cut and paste from the Chrysler TSB archive. You will need to go to a dealer for this. It applies only if there is a slight spark nock. Make sure everything else is operating normally, including running th GM top cylinder cleaner as mentioned above. I did thid TSB on my own vehicle with good results. The engine controller must be updated to the most current software level to be able to adjust the timing with the factory DRBIII scan tool.

Bryan

T.S.B NO: 18-24-98
SUBJECT: Light Spark Knock Timing Retard Feature
DATE: Jul. 31, 1998
NOTE: THIS INFORMATION APPLIES TO VEHICLES EQUIPPED WITH A 2.5L, 4.0L, 3.9L, 5.2L AND 5.9L LIGHT DUTY GASOLINE ENGINES.

SYMPTOM/CONDITION:
Some vehicles may exhibit light spark knock with a warm engine under load.

DIAGNOSIS:
Determine when the customer exhibits this condition and verify it by driving the vehicle in similar conditions. If the vehicle exhibits light spark knock with a warm engine under load perform the flash update procedure. Once the flash procedure is completed, spark advance/retard may be adjusted.

NOTE: THE DRB III® MUST BE OPERATING AT RELEASE 25.5 OR HIGHER.

Select DRB III® stand alone, current model year diagnostics, engine, and miscellaneous. When in miscellaneous, spark advance will be available. Use the arrow keys to retard timing in 2o increments to a maximum of -4o. When the DRB III® screen reads 0 the vehicle will be set at maximum advance and when at -4 it will be set at maximum retard.

NOTE: THE IGNITION KEY MUST BE CYCLED FOR THE CHANGES TO TAKE EFFECT.

After performing the spark advance/retard feature, drive the vehicle to verify that the light spark knock is gone.

This feature will not compensate for heavy spark knock conditions. If heavy knock is experienced, further diagnosis and testing will be required.

So how many million will the dealer charge me to do that, Bryan?

Figure an hour's labor to just read it.

Not to mention that alot of owners had MORE problems after the comp was flashed....

I've been mechanicing for 40 years and sold commercial fleet fuel additives for a while. There are several things that can help ping. Getting rid of the carbon deposits and cleaning the injectors will be the most effective. I recommend running a can of BG44K cleaner through as a first step. It is by far and away the best cleaner out there. It runs about $18 a can. If cleaning the carbon doesn't do the trick, then you are faced with the octane problem. The additive that makes premium gas is a combination of toluene and xylene. The amounts you need are about 2oz of each per tank. Its a heck of a lot cheaper than buying the off the shelf octane booster. Those were the main ingredients of the additives I sold, along with stoddard solvent.

Bottom line is that if the engine is healthy and the carbon under control, you shouldn't have ping problems on regular gas. I run a 4.7L stroker with 9.6:1 compression and I don't get ping on any of the gas around here. I run a can of BG44K through every vehicle I own every 10k miles.

old_man said:

I've been mechanicing for 40 years and sold commercial fleet fuel additives for a while. There are several things that can help ping. Getting rid of the carbon deposits and cleaning the injectors will be the most effective. I recommend running a can of BG44K cleaner through as a first step. It is by far and away the best cleaner out there. It runs about $18 a can. If cleaning the carbon doesn't do the trick, then you are faced with the octane problem. The additive that makes premium gas is a combination of toluene and xylene. The amounts you need are about 2oz of each per tank. Its a heck of a lot cheaper than buying the off the shelf octane booster. Those were the main ingredients of the additives I sold, along with stoddard solvent.

Bottom line is that if the engine is healthy and the carbon under control, you shouldn't have ping problems on regular gas. I run a 4.7L stroker with 9.6:1 compression and I don't get ping on any of the gas around here. I run a can of BG44K through every vehicle I own every 10k miles.

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I know about using toluene and xylene, but you need to use a few GALLONS in a tank to have any effect. 2oz will do absolutely nothing. I really don't think carbon is the problem, I allways use Chevron gas and that techron stuff really does work good. I have also sprayed some seafoam down the throttle body, which is basically the same thing as the GM engine cleaner. I'm thinking about removing the head and cleaning it out that way, it would be nice to take a look at the cylinders anyway.

Does anybody know if there is any way to slightly retard the timing without having the dealer reprogram my computer? I know it's not adjustable on the 4.0, although I know there are a few tricks to increase it. (like a high altitude CPS)

RichP said:

Not to mention that alot of owners had MORE problems after the comp was flashed....

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I really don't agree with that statement. While PCM software updates fix numerous things, I haven't noticed any more problems once it was done. My own personal 96 XJ didn't have any extra problems. Most customers have a positive experience after the software update.

Figure about 1 hr labor to have it done.

Bryan