Pinging or Detonation with the Grand Cherokee 5.9 Limited:
Most of this information also applies to the standard 5.2L, and some
can be applied to any engine.
By: Scott Mueller <mailto:email@example.com>
Q: I have a 1998 Jeep GC 5.9 Limited with about 20k and it started
pinging under load, especially in higher altitudes. Is there a fix?
A: Yes, there are several possible fixes which I’ll outline in this
First, some background: The GC 5.9L has a special premium fuel
computer calibration stock which has a full 15 degrees *more* spark
advance than Chrysler’s other calibrations for 5.2L and 5.9L trucks.
This mandates a minimum of 91 octane premium fuel. Spark advance is
further increased if you run the Mopar Performance replacement
computer, which increases the octane requirement to 92 octane minimum.
If you find the pinging only in high altitude environments, it may be
due to problems with the gasoline you are using. The gas you find at
the local pumps in high altitude areas will have reduced octane
ratings because in general the need for higher octane is reduced due
to the altitude (lower air pressure = less cylinder pressure = less
Unfortunately this can be a problem if you fuel up with this
low-octane gas and then drive to a lower altitude, or experience
higher temperatures which need a higher octane to prevent detonation.
In other words you may have difficulty finding high enough octane fuel
depending on where and what brand you purchase. For example, the
octane of “premium” fuel sold at higher altitudes will be much less
than the 93 octane I can purchase where I live in Chicago. Be sure
you are really getting a high enough octane fuel when you fill up.
In researching this problem I found several TSBs (Technical Service
Bulletins) from Chrysler related to detonation (knocking or pinging)
on Grand Cherokees.
The most important and easiest one to implement relates to spark plug
wires and their routing:
TSB NO: 18-48-98
DATE: December 30, 1998
SUMMARY: Ignition System Cross Fire/Secondary Ignition Wire Induction
This bulletin relates to cross-fire in the ignition and coil wires,
which can cause detonation and misfires. According to Chrysler, this
rerouting procedure should be performed before any other misfire,
surge, or spark knock repairs are attempted. The repair procedure
involves rerouting the coil wires and/or the plug wires to minimize
induction effects. You can see this TSB at:
If after rerouting the plug wires you still have problems, and
especially if you’ve noticed excessive oil consumption, then you
should check the following TSB:
TSB NO: 09-05-00
MODEL: All ZJ or ZJ (export) Grand Cherokee w/5.2L or 5.9L gas engines
SUMMARY: Engine knock and engine oil consumption due to intake manifold pan
gasket oil leak.
This bulletin relates to an oil leak through the intake manifold
which allows oil to be burned, causing excessive carbon deposits
which cause detonation. You can see a copy of this TSB at
<http://dodgeram.com/technical/TSB00/09-05-00.htm>. In the TSB is
detailed a procedure to check whether the intake is properly sealed
If your intake manifold seal is good, and the detonation you are
noticing has increased gradually over time, it is usually caused by
carbon deposits in the combustion chamber. This can happen in any
vehicle of course, but the 5.9L is perhaps more sensitive to this due
to the increased spark advance it runs, as would be any other high
The solution is of course to eliminate the carbon from the combustion
chambers. For this I recommend you use what is known as a “Top Engine
Cleaner” which is a chemical you either pour or spray into the
intake, or in some cases add to the fuel, to clean the combustion
chambers and valves of carbon deposits. Chrysler’s version of a Top
Engine Cleaner is the “Mopar Combustion Chamber Conditioner referred
to above. I’ve even used distilled water for this purpose, although
it’s not quite as effective.
Some of the better fuel injector cleaner type additives such as
Techron are also designed to reduce or eliminate combustion chamber
deposits, but they don’t work as quickly as the Top Engine Cleaner.
That’s what Chrysler refers to as “Mopar Fuel Injector Clean Up” in
the above TSB. They also have a product called “Mopar Fuel Injector
Cleaner” which is p/n 4318007 that performs a similar duty.
Here are several sites with instructions on how to use a Top Engine Cleaner
to rid an engine of combustion deposits.
<http://www.miata.net/garage/tsb/s004_93.html> Although these sites describe
procedures for specific automobiles, the procedures would be similar for all
fuel injected or carbureted engines.
There is a factory TSB that relates to this as well:
TSB NO: 14-08-97
DATE: DEC. 21,1997
SUBJECT: Poor Drivability With High DI (Drivability Index) Fuel
You can see this one at:
The pertinant info from this TSB is:
“If a vehicle is experiencing heavy spark knock on gasoline with its
designed octane rating, this may be an indication of excessive
combustion chamber deposits, or some other problem. Combustion
chamber deposits can be removed with Mopar Combustion Chamber
Conditioner p/n 04318001.”
“if fuel injector or intake valve deposits are suspected of
contributing to poor performance, occasional use of Mopar Fuel
Injector Clean Up p/n 04549613 is a much less expensive way to
maintain engine cleanliness than regular use of premium gasoline.”
Finally, if you want another way around the problem, and/or don’t
want to use premium fuel in the 5.9 Limited, then check out the
TSB NO: 18-28-97
GROUP: Vehicle Performance
DATE: Aug. 29, 1997
MODELS: 1998 (ZJ) Grand Cherokee
SUBJECT: Premium Unleaded/Regular Unleaded Fuel Selection
NOTE: This information applies to 5.9L engines
“The 1998 5.9L Grand Cherokee was designed to use Premium Unleaded
fuel. This selection was made to maximize the horsepower and torque
from the engine. Some customers may prefer using Regular Unleaded
fuel due to cost factors associated with using premium. If a customer
prefers using regular fuel, the software of the powertrain control
module will require flash programming to prevent drivability
concerns. The regular fuel calibration will reduce engine horsepower
“This flash program procedure will allow a technician to select
either a premium fuel calibration or a regular fuel calibration.
These calibrations can be re-flashed from one to the other at any
The bulletin goes on to describe the procedure for re-flashing.
OK here are my bottom line recommendations to solve the pinging
1.) First things first, make sure you are really using premium (91
octane or higher) fuel.
2.) Reroute your ignition wires as indicated by TSB 18-48-98.
3.) Test your intake manifold gasket seal as indicated in TSB
09-05-00. If the seal is bad then replace the intake manifold gaskets
replaced as indicated in the TSB. If you have the dealer do this, You
may also want to have them check for any misfire trouble codes, which
may indicate other ignition related problems.
4.) Clean your combustion chambers with the “Mopar Combustion Chamber
Conditioner” (Top Engine Cleaner) listed above. You can also use the
“Mopar Fuel Injector Clean Up”, “Mopar Fuel Injector Cleaner” or
something similar in a tankful of gas, although that will be less
effective than the top engine cleaner. The gas treatment products can
then be added to a tank now and then to control or eliminate future
5.) One of the *best* tips I can give is to recommend installing a
180 degree thermostat (stock is 195). This not only allows for
slightly more power production, but it will reduce the tendency to
detonate as well. I recommend the Stant “SuperStat” thermostat, which
is a high performance stainless steel version much better than the
stock unit. The Stant part number is 65358 for the 180 degree unit,
and they cost only $4.59 each at most parts stores like Trak, Pep
Boys, Western Auto, etc. Be aware that JET sells this same thermostat
for close to $20 if you feel like paying too much. <g> The thermostat
is very easy to change, especially if you are also doing a coolant
drain and refill at the same time (which should be done annually
anyway). For coolant I recommend the orange DexCool type (available
from Prestone and others), which although is rated for 5 years or
100K miles (or more), should still be changed *every year*. Dilute
with *distilled* water in a 50/50 mix for reduced corrosion.
6.) If after all this you still have a detonation problem, then you
may want to consider going with the 5.9L regular fuel calibration as
indicated by TSB 18-28-97. I’d consider this as a *last resort*
because you’ll end up losing some of the power and torque you bought
the 5.9 Limited for in the first place!
I hope this helps, and if so I’d appreciate any feedback on what
worked or didn’t work. Thanks, Scott.