[johncrank]

I was wondering if anyone else had a similar experience with their 2000 Rodeo with the V6. I was getting about 20 mpg on the highway. After 35,000 a pinging/knocking sound appeared. I tried increasing fuel grade octane level, but still had the noise. The dealership re-programmed something, and the noise went away. Now the mileage is 17 at best on the highway

 

[Amigo-2k]

I have read one other post about how the reprogram had a neg effect on MPG. So I hate to say it, but there probably really nothing you can do now.

If you do the math now, you are still paying about the same per mile for gas now, but your distance per tank went down.

I'm planning on just using higher octane gas and skipping the new ECU update.

-Ryan
[edit]
Thought of one more reason. If it is getting cooler in your area, your MPG will go down, and also, maybe the winter gas (which typically), gives lower MPG may also, be causing this.

 

[wrenchmonster]

Howdy. John, there are a number of posts on the noise you are describing. I think this is the top end lifter problem that these Isuzus seem to have. Where is this noise and where does it seem to be originating from? The fix seems to be changing your oil, not the gas. As far as your dealer, first of all they should have known about this problem, and secondly, they are changing your LT and ST fuel trim numbers to mask a problem not related to fuel. This is not needed.

Guys, using a higher octane fuel on an engine not designed for a higher octane is just money down the drain, literally. Stick with the octane your engine is designed to use.

-Kevin

 

[eeZooZooJaz]

Hi Kevin. I found your statement about the octane fascinating. Could you elaborate on why you believe this to be so?

 

[wrenchmonster]

Howdy. Hey guys. Well, I get the feeling my buttons are being pushed :wink: but here's the deal with octane:

Octane is simply a rating of a fuels ability to resist knocking. To obtain an octane rating labratories match a fuels burninig characteristics with mixtures of iso-octane and heptane under specified conditions in a test engine. The test continues until pure hydrocarbons are found which gives the same degree of knocking in the engine as the fuel being tested. Hence the octane number of a fuel is the percentage of iso-octane in the matching iso-octane/heptane mixture.

For example, an fuel octane rating of 90 has the same burning characteristics of a 90% iso-octane and 10% heptane mixture. Therefore, if an engine is DESIGNED to operate on 87, having a higher octane fuel will not increase performance, starting qualities, volitility, etc. An engines tendency to knock primarily deals with compression ratio, and combustion chamber design to a lesser extent.

Back in the old days oil companies used lead to reduce knocking. Today oil companies use tetraethyl and butane to reduce knocking. If you look, old engines designed in the '50s and '60s are designed to run on 90 octane or higher, because lead was better anti-knocking agent. Engineers figured out they could tone it down to 87 octane, which most engines are designed to run on today.

The long and short of the story is that higher octane fuels are actually LESS explosive than lower octane ratings. Only if you have knocking issues should you switch to a higher octane gasoline. But doing this with modern computer controlled vehicles usually indicates that there is a deeper underlying problem with an engine control system.

Oil companies want you to believe that higher octanes and brand names are important to the quality of gasoline. The fact is that all gasolines need to meet certain standards set forth by the EPA, API and SAE. The greatest difference in gasoline has to deal with alcohol percentages and detergents.

So, if you like paying more money for the same performance, go ahead and buy a gasoline with a higher octane rating. I personally buy the least expensive gas with the minimum octane rating designed for the engines I own. No more is needed. My 2 cents.

-Kevin

 

[eeZooZooJaz]

No button-pushing here... :roll: ....I found your information very interesting, something I did not know about. It also seems that companies have jumped on the bandwagon of our ignorance and sell so-called "octane boosters" to quench our desire for higher performance... :?

 

[BRANDON]

The people that tell you that using higher octane fuel causes deposits in your exhaust, are the same people that will tell you to use the lwest possible octane rating, take the car out, floor it, and if you don't hear pinging/knocking your OK. The fact of the matter is that most newer vehicles, including Rodeos, have knock sensors, which sense when the engine is about to knock and retard the timing to prevent knocking. Thus many drivers of newer vehicles will never hear knocking. However, if the engine control system is retarding the timing, the vehicle performance (acceleration) may drop off a little. Switching to a higher octane fuel may improve vehicle performance slightly. Some vehicle owners manuals now state that the vehicle will operate on regular gasoline but may give better performance on a higher octane grade of gasoline. These engines are also eqiuipped with O2 sensors, which sense the air/fuel mixture of the exhaust just before, and sometimes after it reaches the catalytic convertors. If there is excess unburnt fuel in the exhaust, the computer leans the mixture being injected into the combustion chamber until the reading at the O2 sensor is within range.
Bottom line- If you can afford 93, don't think twice. If your strapped for cash, go ahead and get the 87, assuming that is the minumum required for your motor. Also have a look at your owners manual. Most of them will tell you to use higher octane for better performance right after they tell you 87 is the MINUMUM.
Brandon

 

[BRANDON]

As for the original question. The ticking noise that usually comes from these motors is a lifter problem, but that would not be corrected by enriching the fuel mixture. I would guess that you were probably experiencing slight detenation due to a lean condition, and with the re-program enriching the fuel mixture, it has been corrected. How a 2000 Rodeo would be running lean in the first place is beyond me, especially if it was so bad that running higher octane did not correct the problem, but that's the only thing that goes along with the problem, and apparent solution that you describe, and my 98 gets no where near 20mpg, although it is four wheel drive.
Brandon

 

[vinroc]

2000 Rodeos do not use a knock sensor...it uses an ion-sense igniton system to determine combustion quality and knock index. The "reprogram" that the dealer did was for an updated calibration labeled "fixes spark detonation". Although I haven't really noticed this to be an immediate fix, Isuzu techline has said that it will take a while for the noise to diminish due to an adaptive learn in the PCM and a higher quality gasoline should be used. As far as any lifter noise is concerned, the "problem" cars were the old 3.2L SOHC engines used through '97. The '98- current engines use a "shim and bucket" lifter which hasn't caused nearly as many problems. It should be easy to distinguish which noise you have....lifter noise should be heard at all engine speeds, spark "knock" will be heard on accell. when the engine is under a load. Hope this clarifies things.