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bobs94dakota
Dodge Dakota
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6/20/2003
17:55:31
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 Subject: 3.9 magnum cam timing
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Message:
I have a 94 Dakota with a 3.9 magnum, 135,000 miles on it. I'm going to change the lifters and timing chain, lifter tap. Does anyone know what would happen if I advance or retard the cam timing? How would the computer react? Could I change any sensor feedback voltage to counter-act the computer reaction? Details please. I would kindly appreciate them. Thanks, Bob
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J and J Auto
Dodge Dakota
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6/20/2003
21:14:29
|  RE: 3.9 magnum cam timing
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Message:
I don't know how it would react but I can tell
you this it will not even start unless you
re index the dist so the injectors know when to
paulse.
Larry
J&J Auto
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J and J Auto
Dodge Dakota
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6/20/2003
21:18:50
| RE: 3.9 magnum cam timing
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Message:
The intake valves open 8 degrees after TDC
advancing the cam 4 would make them open at
4 after.
You would have to look at the EXH open close
specs to see what you would be changing there
but I see no advantage to even doing that.
Here you can find the open close specs for
the cam
http://dodgeram.org/tech/gas/specs/3_9v6.htm
Larry
J&J Auto
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bobs94dakota
Dodge Dakota
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6/21/2003
09:10:33
| RE: 3.9 magnum cam timing
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Message:
Thanks Larry, Can you tell me the correct way to reindex the distributor. I know on older camaro's you jump a plug then you can set the timing. Also what's the correct way to reset the computer on my 94.
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J and J Auto
Dodge Dakota
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6/21/2003
19:23:24
| RE: 3.9 magnum cam timing
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Message:
Bob,
Setting the Dist index on the 94 is very easy to
do there are 2 ways.
1 with a volt meter but the accuracy on that is about
+ - 6 which will work to get it close.
You need 2 stick pins to push into the pick up wires
set the crank at 14.7 degrees after TDC compression
stroke, there is a V6 and V8 mark on the damper for
this. Now move the Dist back and forth you will see
a .5 volt reading. set on either side. setting it when
rotating it counter clockwise until you see the volt
meter pulse will get you on the + side and it will
run better on the + side.
2 put the damper on TDC be sure the rotor is pointing
at the #1 wire for both methods. Now remove the dist
cap you will see a line on the plastic pickup plate and
it says cyl. climb up and look straight down over the
rotor and center the button on the rotor over the cyl
line. and tighten down. I had an accuracy of + - 2 doing
it this way.
I know this because I now use a $2500 scanner to set them.
I checked ones I had set this way after I got the scanner
and that is what I came up with as far as accuracy.
Always rotate the crank clockwise when setting this if
you pass up the marks go around past them once and
than come up on them again.
NEVER turn the crank back to the mark it will be way off
from the play in the cam and dist gear and even with a
new chain there may be some play.
They are set at the factory anywhere from -6 to 0 but
they run better on the plus side. Ideally you want your
injectors to pulse right after the valve starts to open
which is 8 after, 0 is 14 after so they would pulse
after they have been open for 6 degree's a +6
would be right when the valves start to open.
I found most run best around +2 to +6 but no 2 trucks
will be the same. If you go past +6 you will get a mill
light in most cases.
You should always reset injector sync after you
replace a timing chain or add a tensioner.
To reset the computer just disconnect the Neg. battery
cable go in the truck and turn the key like you are
going to start it and hold it there for about 20 to 30
seconds. It will drain all the voltage out of the capacitors
and lose its learned settings and it will than relearn
everything for any changes you have made.
about 50miles for a short term 200 to 500 for long term
relearn than it will run nice. some times they run nasty
right after you do a reset depending on what mods
you have done.
Larry
J&J Auto
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bobs94dakota
Dodge Dakota
JOIN HERE
6/21/2003
20:46:25
|  RE: 3.9 magnum cam timing
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Message:
Thanks Larry, that is a big help. I understand. I'm a full time electrician in a steel mill but I also enjoy working on vehicles.
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