Pinging....Knock Sensor?

[carvesdodo]

Originally Posted by Chaser

and on the next page:
"Light spark knock at low engine speeds is not harmful to
your engine. However, continued heavy spark knock at
high speeds can cause damage and immediate service is
required.
Poor quality gasoline can cause problems such as hard
starting, stalling and hesitations. If you experience these
symptoms, try another brand of gasoline before considering
service for the vehicle."
My apologies....

Nothing to apologise for ....

Petrol has become priced commodity ...

When its actually a fuel of various octanes which should be selected to suit a vehicles particular use.

Dodgy fuel supplies are probably a bigger issue than the octane ratings tho ... especially at this time of year.

Interesting that the JK info is almost word for word the same as a TJ manual I have.

Difference being ..... this is tucked away on the last page.

"when pulling a heavy load or driving a fully loaded vehicle when the humidity is low and the temperature is high, use a premium unleaded fuel to help prevent spark knock.

If spark knock persists, lighten the load, or engine piston damage may result."

Lighten the load probably means stop working the engine so hard ... rather than tossing out the kids school bags .....

[Chaser]

Originally Posted by carvesdodo

Dodgy fuel supplies are probably a bigger issue than the octane ratings tho ... especially at this time of year.

I agree completely. I reckon this might be the cause of my problem. Up until today I had been buying standard Shell stuff (not the ethanol crap) from the same servo each time. I think I should to try another brand.

It's a relief to know I don't have to spend another night on the garage floor chasing non existent rattles though.

[SeaComms]

Yeah, my experience with brands is acurate for this area, might be different in other areas. Funny though, the worst fuel I have found on the coast is the closest servo to me.. And its the newest of any servo I have used - go figure. The old Suby needed premium fuel from there just to act normal. So first I would be doing is changing servo for sure.

Should also be noted for anyone not aware, that the US 87 octane rating mentioned in the manual is equivalent to our 91 RON rated fuel.

[jklad]

Regardless of what service station I fill up at, my JK does noticably rattle under load when run on 91RON unleaded. There is also a noticable drop in power when under load (probably as the knock sensor tells the computer to retard the spark timing to reduce the pre-ignition), so I usually fill up with 95RON for this reason. There's also slightly higher fuel consumption on 91RON, but not enough to justify the extra 10cents per litre extra cost of the premium for this reason alone.

I've tried 98RON but don't notice any further improvement on the 95; I guess I'd need to get Superchips & run the high octane tune to get the full performance benefits of 98RON as our JK's don't have an octane sensor like some of the newer vehicles have.

I avoid running the JK on unleaded with ethanol, since on my old '95 Falcon the results were really bad; extremely rough idle, severe pre-ignition rattle and much higher fuel consumption (obviously these symptoms were exagerated as it was an older car with 200K KM on the clock so worn/malfunctioning components would naturally contribute to the deficiencies in performance of the low octane with ethanol).

[thermos]

Our JK does it also, to the extent that we fill it up with 95.
The KJ never did it and the TJ before it did also, but only with the A/C on.
It should run on 91 octane, my Holden 6L can run on 91 with no dramas and that is hardly hi-tech.

[thermos]

Took the JK for the 6 month service at a local Jeep dealer and I mentioned about the pinging. He mentioned that quite a number have come in for the same problem and the only suggestion is 95 or greater octane fuel. We will return to using 95- but we really shouldnt have to.

[Trigger82]

Originally Posted by jklad

I avoid running the JK on unleaded with ethanol, since on my old '95 Falcon the results were really bad; extremely rough idle, severe pre-ignition rattle and much higher fuel consumption (obviously these symptoms were exagerated as it was an older car with 200K KM on the clock so worn/malfunctioning components would naturally contribute to the deficiencies in performance of the low octane with ethanol).

Im surprised you had pre ignition rattle with ethanol, personally i think it was mixed with dodgy petrol as ethanol on its own has a higher octane rating then premium petrol.

Yes the car will use more fuel using ethanol as it doesnt have the amount of energy stored within itself as petrol does. When the gubment pull there finger out the cost should more thn make up the difference in usage (but the world revolves around oil companies).

With the rough idle, I would almost bet my lefty on it that that symptom was worse in winter than summer. A rough idle is a known side effect of ethanol the colder it is the worse the effect, tuning needs to be done to compansate.

Also for some that like to learn something new. The higher the octane fuel rating the slower it burns during combustion.