I purchased a 1997 4x4 Ram from my neighbor. It has 111000 mile on the 360.
The truck starts just fine and other than the slightly rough idle (which I
am told is a pretty normal occurence in this engine) runs great while
sitting still and also has great accelleration and high speed (70+ mph)
performance. The problem is that while the engine is spinning at about
1700-2200 RPM, a miss can be felt which makes the truck, well, "shimmy" as I
run down the road. Not the shimmy you feel when a tire is out of balance or
round but the shimmy you feel when the engine is running sub-optimal. I put
new tires (265/75/16) on all four corners and had them balance them twice
and show me the readings as they did it so that I could eliminate a problem
with tire balance. I also notice that if I shift down while the shimmy is
occuring, it abates quite significantly but does not entirely disappear. I
took the truck up and had new dual exhaust put on (thrustmaster II) and
while in the shop they hooked it up to the diagnostic computer. While there
were no codes set, it was showing that the engine was running lean at those
RPMs. So here is my plan and I want to see if it makes sense.
I have already replaced the pcv valve, cap, rotor, plugs and wires. I have
a K&N drop in that has been cleaned and re-oiled. carb cleaner has been
used to clean the outside (and inside where possible) of the TBI.
Since it is running lean, either the computer is getting input that the
mixture is plenty rich and cuts back on the fuel even though, in reality,
the mixture is now off
The computer has no idea that it is lean and is putting the perfect mixture
through the manifold and the leak is occuring where the computer cannot
detect it and fix it.
My logics says I should:
First, start with the O2 sensor(s). Do I need to replace all three or is
there rhyme or reason to which one to try first?
Second, I thooght about the fuel system itself. Is it possible that the
computer is telling the injector to put in X amount of fuel into the
cylinder but the injector is unable to deliver it in the amount of time
specifed? Can injectors really be clean without removing them or is
replacement the only true option?
Third, The intake manifold gasket. It was replaced by Chrysler when the
truck had 36K on it for the vaccumm leak problem and I wonder if it could
have happened again.
I am up for suggestions since the O2 sensors are about 45 bucks each and any
of these option will eat into my precious "sit-in-my-chair-and-watch-nascar"
Thanks in advance for any ideas,