Just a story you all might find interesting. I bought a JET module for
my 97 Dakota, and had nothing but problems with it. I found that with
the module , the check eng. light would come on and my 3.9 V6 would no
longer idle. Further, I could be cruising at 65 MPH and the engine
would die. Mashing the accelerator seemed to get it going again,
sometimes right away and sometimes not. The fix was to unplug the JET
module and plug it back in again or disconnect the battery. I quickly
got tired of this and returned the thing to the shop to have it sent
back to JET and replaced. JET was prompt in getting me a new one. Just
one problem. The new one did some of what the old one did. I again
returned the unit and had my truck analyzed and found that it indeed
is healthy. The third module arrived and the truck ran great. No
dieing or rough idle or check engine light. Now there was a whole new
problem. This module didn't even improve performance. I was a bit
puzzled and not sure I got what I paid for. I figured that I wasn't
going to get one ofthese things that worked, and I wasn't going to
get my money back. So I carefully disassemled it. I used an exacto to
cut all arround and seperated the two plastic parts. I then seperated
the header on the interface card from the PIC16C711 microprocessor
board and drew out the complete schematic of both the interface card
and the board. I then went to the Chrysler deeler and looked at the
servise manual to find out the pin out of the 97 Dakota 3.9 V6
computer. Pimarilly the pins that the interface card connected to.
By the way, none of the pins are interrupted by this circuit. I simply
piggy backs or inother words is in parallel with the existing wires.
It turns out that not all of the pins they tapped were sent to the
PIC16C711 and not all of the inputs/outputs on the module made it to
the vehicle computer. However, +5 volts, +12 volts, and ground did
connect.The following is what was available at the interface card...
pin 2=fused B+
pin 8=crankshaft position sensor
pin 23=throttle position sensor
pin 4=sensor ground
pin 17=+5 volt supply
pin 27=manifold absolute pressure
pin 16=engine coolant temp sensor
pin 15=intake air temp sensor
pin 31&32=ground
I can't go into great detail about how the software works, but
basically the microcomputer is supposed to look at different sensors
and compare the reading to a programmed look up table that only JET
know the contents of.depending on the code feeding a cheap digital to
analog converter, a buffer amp hammers on the correct pins with a new
voltage based on the look up table. They use the same pin onthe
microconputer as an input and an out put. All bit to zero=
digital-analog converter to turn off and allows the microcomputer to
sample the real reading and then compare to the lok up table and then
the buffer is told to hammer on the existing voltage with the new
voltage again. This all sounds good except for one thing. There are
two resistors labled as R7 and R2 there is also a capacitor labeld C10
C10 is no big deal just a filter, but R7 and R2 are in series with the
traces from the module to the only pin being sampled or changed. These
two resistors are not even present on my third module.there is no way
it can do anything ! I do believe that the folks at JET thought that
they would send me an incomplete unit to see if I would still
complain. Sure enough, here I am. I am not even sure that there is any
code on the PIC16C711 because you can't read these once the lock pins
are set. I would appreciate it if JET would work with me on this, but
a call to them resulted in me being accused of removing these two
missing risistors myself.What a joke. I can't tell you not to puchase
one of these, but beware.Also, one of the claims of this devise is to
improve the shift of the auto trans. It doesn't even connect to the
trans pinws located on a different plug of the vehicles computer.
Hope someone enjoys this.
John.
Cat, the OTHER white meat.
Keith R. Phelps
This archive was generated by hypermail 2b29 : Fri Jun 20 2003 - 12:10:46 EDT