I posted this review to the Durango forum - I guess I should have posted it
here as well.
***
Well, I finally had a chance to get out this weekend and do some miles and
testing with the performance PCM on my '98 5.9 D. The weather was good with
low humidity and temps around 80, so the engine was in a good temp zone.
As far as idle is concerned, there was no noticeable difference. The exhaust
tone was the same, and the idle smooth. However, appyling the throttle with
the tranny in Park and revving to higher RPMs, there is a definite "perky"
feel to the response. I also noticed that there was much more rumbling in
the exhaust when the throttle was released quickly after revving. This
exhaust "knocking" on throttle release was also very perceptible while
driving.
The first thing I noticed after driving a bit and fully warmed up was that
the OverDrive shifted in the same RPM/MPH range as it had with the stock
PCM. I was really disappointed with this finding because the OD shifts too
early IMO, and I was hoping the PCM would resolve the problem. Looks like
I'll have to continue to drive with the O/D off.
On the road, doing normal driving, there was no evident difference in
throttle response, acceleration, or shifting. The shifting probably would
have been different, but I have a TransGo shift kit installed, so the shift
points are already overriding any PCM control.
During Wide Open Throttle, a slight increase in power was definite. I
normally break loose the tires for a certain duration under WOT before
launching, but I noticed now that it was somewhat easier to break them
loose, and that they were spinning longer. Acceleration felt about the same,
so I'm guessing the power increase was there, but not overwhelming. I will
dyno with/without the PCM very soon, so I'll have some hard numbers to
correlate.
I tested the rev limiter removal, and yes, it is gone! Well, at least to
about 6000 RPMs. With the shift kit, I can hold first gear to any RPMs, so I
opened it up on a nice long stretch of open road, and wound out to about
5900 before I backed off and let it shift. My MSD 6AL is set to a 6000RPM
limit, so I still have that protection. I did find that I was still pulling
strong over 5000, so it looks like the Crower rockers may have given me some
more upper RPM power.
Surprisingly, there was absolutely no detonation in combination with the
supercharger. The air/fuel mixture was consistently rich under WOT, and the
revs very smooth at higher RPMs. The combination of larger fuel rails, 24#
injectors, and good pressure may have helped to eliminate potential
starvation, and thus detonation. I still wonder just how much the timing is
advanced. It seems that I should have had some detonation at 5500+ rpms. If
it wasn't for the removal of the rev limiter, I was beginning to think that
maybe I got the stock PCM by mistake! BTW, does anyone have the part numbers
for a stock, California, and Federal PCM for a '98 5.9? I know they have
been posted, but I didn't save them. I just want to be sure. ;)
After driving a few hundred miles over the weekend, I didn't notice any real
change in performance. I'll give it a few more hundred to see if there is
any "learning" going on that changes the PCM mixtures.
I hope to have some dyno numbers real soon. I've been trying to schedule an
appointment, but the shop has been busy with other work. Seems they'd rather
work on engines then watch my D perform!!?? Go figure!
My D mods: 5.9L, Powerdyne 6psi supercharger, JBA headers, Gibson 3"
cat-back, MSD 6AL/BTM/8.5mm wires, Crower 1.7 roller rockers, 24# injectors,
Intense Performance fuel rails, 180 degree t-stat, TransGo shift kit, DOC
sticker ;)
>>From: Stlaurent Mr Steven <STLAURENTS@mctssa.usmc.mil>
>>Subject: RE: DML: What to do with stock PCM?
>>Chuck, describe how it feels with the new PCM or did I miss the e-mail.
>>Kick butt? No speed limiter? Higher RPM etc...
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