XJ Cherokee's and caravan towing

[jake]

dont worry Junglejuice mines a '96 and pings its head off unless I run pulp. I can get away with ulp in winter but my way of thinking is for the extra $6 or there abouts per tank I might as well run pulp as I normally tow the boat down the ramp most weekends and I hate that "rattling" noise from the pinging and surely it cant be helping the engine doing that.

I am actually glad to hear mine isnt the only jeep that needs pulp, as I thought I had some sort of problem.

[hillsjeep]

I just read up on pinging as I've never experienced it and wanted to know what caused it.

A couple of sites mentioned that it can be caused by timing too advanced and engine running too lean, as well as everything mentioned above. Assuming your engines are well tuned, I wonder if your 02 sensors might not be reporting accurately causing it to run too lean.

[jake]

funny thing hillsjeep I was thinking that on the way to work this morning as I have done 175,000km on original 02 sensors and have not changed my spark plugs for over a year. slack eh

[Steve F]

Mine used to ping and PULP was the answer, until I fitted a snorkel, the reduce intake temperature got rid of the pinging altogether even in deep soft sand at full throttle, previously if I planned a day on the sand then PULP was a requirement and even then it wasn't perfect.

Cheers
Steve

[hillsjeep]

This is what one site said, another site mentioned running the engine to lean or using the wrong spark plugs can be a cause too.

Engine Pinging
by David Schwarze


--------------------------------------------------------------------------------


"...The piston can overheat and knocking can and will occur. This knocking is caused by ignition of the gas/air mix in your cylinder before the spark of the spark plug. This causes temperature and pressure peaks that will melt your piston, crack your cylinder head, and drop one of your exhaust valves. You have heard about those abrupt deaths of air cooled engines..."
Pinging sounds like rocks being thrown around inside your engine. It will never happen at idle, may happen at part throttle, but is most likely to happen at full throttle. It is usually accompanied by a small amount of smoke out of the tailpipe, but don't rely on that.

Pinging is like... taking a cutting torch to your combustion chamber. Your engine can stand anywhere from less than one second to perhaps minute of pinging before it suffers permanent and serious damage, depending on conditions.

The hotter your engine is, the more likely your engine is to ping. The farther your timing is advanced, the more likely your engine is to ping. The higher your compression ratio is, the more likely your engine is to ping. The lower the octane of gas you use, the more likely your engine is to ping.

So, in order to minimize the risk of pinging, do the following:


Make sure your engine doesn't over heat!
Make sure your timing is not too far advanced.
Make sure your compression ratio is not too high (< 7.5 to 1)
If necessary, use higher octane gas.
If you take care of the first three, you shouldn't have to worry about the last one.

[jake]

according to that post I must have no internals left in the engine
that explains the crap fuel economy..the fuel is just falling straight through the motor

mine doesnt exactly sound like rocks but more faint metallic rattling unless I give it more throttle then its a loud metallic rattle, once im off the hill its gone. Then I put in pulp and it's gone

[Grant]

I am just wondering how many if any of the people who have a pinging problem have added throttle body spacers or bored out the throttle body. Jeeps have a compression ratio (high output) of 8.75 to 1 and all fuel management systems are designed around that figure, if you add throttle body spacers and or bore out the throttle body itself then you are effectly altering what has been the factory default. Bearing in mind that if you bore the throttle body and go into the venturi then you will alter the air flow dynamics of the air through the venturi (venturi's are not a straight through hole) but actually have a slight convex surface right at the butterfly (slight restriction), so unless you have a milling machine that is CNC capable you will not get the inner face to match the correct curvature thereby altering the airflow design criteria (aerodynamics comes into play "high velocity = low pressure", "low velocity = high pressure") A throttle body spacer adds to the length of travel of the air from the butterfly to the intake valves and even this changes the airflow characteristics thereby affecting the default settings.
Only safe way that I know to alter any of the above factors is if you have a programmable chip (Eprom).
Like I said just a querie or thought