What could cause pinging other than carbon?

[SteveD2]

My 4.0 Jeep engine seems to be pinging under heavy load. It's got almost 200,000 miles on it. I gave it half a tank of premium today mixed with half 87. Pinging stopped. Also cost $20 for 8 gallons of premium.

Anyway...

I don't think there is much carbon buildup. I usually always use Chevron with techron, plus I decarbed it with seafoam in the TB about 1000 miles ago. It's getting almost 20mpg in the city, and that's just unheard of for this engine. Also the ignition system is brand new, with stock Champion plugs. What could cause pinging other than carbon or the wrong plugs?

 

[sbc350gearhead]

Ignition timing too far advanced. Excessive engine temp. Excessive intake air temp. Lean A/F mixture.

 

[SteveD2]

Timing on the 4.0 isn't adjustable, engine is running at 200-210 like it should be, and I have modified the air box to bring in cooler air.

 

[sbc350gearhead]

How old are your fuel filter and pump?

 

[SteveD2]

The filter is brand new, and as far as I know the pump is original.

 

[Chris142]

I was thinking of a partially plugged injector = Lean mixture.

 

[sbc350gearhead]

Try running FP for a while and see if it helps.

 

[Ken4]

Weak spark, insufficient spark duration (dwell), or incorrectly gapped plug can also cause pinging.

 

[cousincletus]

There are a few tricks to reduce or eliminate pinging. Use a colder sparkplug, run a 180 degree 'stat, use a higher psi rad. cap along with a 60:40 antifreeze/water ratio. I would do the radiator cap and antifreeze thing first, since this stopped pinging in my Dodge truck completely so far, but wasn't too bad to begin with.

 

[needtoknow]

Did you try checking the operation of the EGR valve if you have one. If the valve is not opening this could cause pinging as well.

 

[eljefino]

Running 75% water/ 25% antifreeze last summer in my cutlass ciera 3.3 seemed to reduce pinging. Possibly there were hot spots in the motor near water jackets that were cooled better. The car appeared to run at thermostat temp either way but I suspect in local areas there were differences.

Anyhow check your cooling like others have said.

 

[Patman]

I used to run 100% water along with Redline Water Wetter in my supercharged 87 Mustang in order to reduce the chances of detonation. Summertime only of course.

 

[Gary Allan]

Although there is no users adjustable timing for the 4.0 ..the dealer can flash the PCM with a new timing curve. The flash update runs about $24 (my son just had it done on his 00 Cherokee).

There is no EGR in the 4.0 and 2.5 (later models) jeep engines. It uses cam overlap to leave enough spent combustion material to cool the process.

Ours has done this since new. More in warmer weather. It's not excessive and only happens (typically) right after you shift gears and are accellerating ...especailly if you are either feather footing it ...or on the other end of it ..heavy footing it.

 

[SteveD2]

Hmmm...I like the idea of 75/25 coolant for the summer. Is that going to be more likely to rust than the normal 50/50?

 

[seotaji]

no, since you have enough of both.

make sure you only use distilled water though.

i'm planning on using 75 water/ 25 coolant when i service my timing belt/water pump.

 

[Drew99GT]

Also, if you overtighten spark plugs and crack the porcilen insulator, the plug will be rendered usless at removing combustion chamber heat, which will also cause pinging.

 

[T-Keith]

Things that contribute to knock:
compression ratio
boost level(if apllicable)
low octane fuel
high intake air temps
restrictive exhaust
engine temp
spark plug heat range
lean fuel mixture

-T

 

[Mitch]

Depending on the year jeep the camshaft angle sensor is adjustable. If it has DIS alot of them came from the factory anywhere up to 7 degrees off.The computor can not adjust the timing far enough then.

 

[jeepzj]

20mpg city? What model Jeep? How are you calculating? I have a 1998 4.0 Grand Cherokee and the best I can do in all city driving is 12mpg.

 

[SteveD2]

quote:

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Originally posted by jeepzj:
20mpg city? What model Jeep? How are you calculating? I have a 1998 4.0 Grand Cherokee and the best I can do in all city driving is 12mpg.

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It's a '96 XJ, stock with some intake modifications. I know it sounds ridiculously good, but I'm dividing the gallons on my gas receipt by the miles I drove. And my GPS agrees completely with the odometer.

Remember, it's got almost 200,000 miles too.

Does anybody know how to check the timing on this engine? Even though it isn't adjustable, I guess it could be off for one reason or another...