I pulled this off of the alt.autos.dodge.trucks newsgroup for those of you
who don't have access. The post is from Mike Simmons, a Chryco Service
Manager. I've been following the newsgroup for a coupla years now, and Mike
seems to be a straightforward, trustworthy guy, judging by his past
postings. The following is his post:
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I just returned yesterday from a Chryco Tech Workshop where the ongoing
spark knock problem was discussed in detail. Since this has been a hot
topic on the NG, I thought I would share the info with the group and also
offer some insights.
The long promised TSB relating to spark knock on MY '98 vehicles will be
released sometime this month. The TSB relating to MY '99 vehicles will be
delayed until the 3rd quarter of this year.
Why the delay? The above referenced TSB's will allow the dealer to
reprogram the vehicle PCM and retard the ignition timing by either a 2,4 or
6 degree increment based upon the severity of the spark knock. Now, before
anyone goes off the deep end regarding this fix, keep in mind that the spark
advance value on your truck currently is NOT a fixed value. The PCM varies
spark advance based upon inputs from vehicle sensors and thus is constantly
varied to match conditions. This variance however is transparent to the
driver. The fix merely allows the PCM a wider latitude regarding the spark
advance curve.
This fix could not be released until it was approved by the EPA to ensure
that there was no impact on air quality. Further, accelerated long term
testing had to be done by Chryco engineering to ensure that no long term
negative effects would be encountered by this fix. That is also why the
release date for MY '99 vehicles is being delayed until the 3rd quarter of
this year.
Will this fix have an impact on my vehicle's horsepower? Yup, sure will,
but before you go off the deep end again consider that if any other strategy
(i.e. knock sensor, etc.) was employed this too would have reduced your
vehicle horsepower, but since the change is transparent, you the driver
would have never noticed it. Also, testing has indicated that unless you
are towing a heavy trailer the effect on horsepower and fuel economy is
minimal.
Is this spark knock a defect in my truck and will it damage it in the long
term?
No, the spark knock problem is a complex issue caused by several external
factors, some of which are:
1.) Stringent EPA reg's regarding air quality. Engines are running so lean
that they are on the threshold of spark knock.
2.) Highly oxygenated (reformulated) fuels that increase combustion chamber
temps.
3.) Higher sulphur content in fuels which results in accelerated carbon
buildup in combustion chambers
Regarding potential damage to the engine, several engines from vehicles that
were bought back by Chryco were torn down for evaluation and no damage was
noted due to the spark knock issue. It appears that the spark knock issue
is an annoyance and not potentially damaging to your engine.
Chryco recommendations:
1.) If the spark knock occurs only during heavy load conditions (i.e.
trailer towing) the use of premium fuel is recommended during these
conditions.
2.) If the spark knock occurs during "normal" driving, Chryco recommends the
following repairs in this order to correct the situation.
a. perform TSB 18-48-98 which involves rerouting of the plug wires
b. check for intake manifold leakage per TSB 09-06-99
c. Clean combustion chambers with MOPAR combustion chamber cleaner.
Make sure engine is hot before starting and let cleaner soak in for at least
two hours.
d. perform soon to be released TSB for MY '98 vehicles or TSB to be
released in the 3rd quarter for MY '99 vehicles.
Finally, a potential fix for the spark knock problem has been bandied about
on this MG for sometime that involves replacing the stock t-stat with a
cooler one. While this fix MAY temporarily "fix" the problem there are some
negative consequences by using this approach.
1.) Increased fuel consumption due to the coolant temp sensor returning a
low value to the PCM.
2.)Premature cat converter failure due to excessive internal temperatures
resulting from an over-rich fuel mixture.
3.) Failure to pass state emissions tests due to an over rich mixture
4.) Increased carbon buildup in the combustion chamber
I hope this info proves helpful. If anyone has any questions regarding the
above, please direct them to the NG and I will try to post the answer for
everyone's info.
Chryco Service Manager
Member SAE
This archive was generated by hypermail 2b29 : Fri Jun 20 2003 - 11:49:31 EDT