Re: 4.0L basic Intro

["Jim Blair" <carnuck@xxxxxxxxxxx>]

All the years of XJ/MJ/TJ/ZJ and late YJ with 4.0L have their good/bad
points '87 to the end of 4.0L production (good points to know for for engine
swaps too). I also like the 2.5L with TBI (I'm about to find out what they
are like with MPFI) Piston slap during the '91 to '96 years is just noise
and not much of anything else. Chrysler just tried to assemble the AMC
motors with sloppier specs than AMC had and discovered this the hard way.
The '87 to 08/90 Renix EFI has it's good and bad points. It runs an EGR to
cut NOx and knock sensor to retard timing to keep the motor from pinging.
Trouble was that any internal engine noise would trigger the sensor and cut
the timing and power waaaay back to try and get rid of it (because the
computer thinks the motor is pinging)

   Renix is also a somewhat "dumb" system because it doesn't retain any
engine codes when the motor is shut off. (it starts off fresh each time you
start it) I have noticed that the engine temp sensor can also mess wih the
timing if you restart when the motor is still quite warm. Heat soak from
sitting can cause sensors to read higher than normal operating readings and
retard timing and other fun things till temps even out again. '87/88 models
have a large connector for the engine harness above the brake booster (right
where rain water dumps on it each time the hood is opened in the rain) that
tends to corrode and give false readings to the computer, causing it to do
strange things like rev the motor up when re-started hot or even stall when
the door is slammed or a bump in the road is just the right/wrong size to
move it slightly from inertia.

   HO ('09/90 to the end) comes in 2 "flavors". '91 to '96 are OBD1 and '97
up are OBD2 (last ones may be OBD3, but they defintely have 1 ignition coil
per plug and a different intake that other HO systems) They did away with
the knock sensor and EGR valve, and reprogrammed the computer for less spark
curve and changed the cam timing (more retarded) to cut down on cylinder
volume efficiency and engine ping, plus bump up the HP readings, albeit more
in the higher RPMs.

   The head was re-designed (intake ports were moved up slightly, allowing
better intake breathing due to a straighter shot at the valves) as well as
the intake (it hits the brake booster in a lot of conversions where the
Renix one doesn't) and ALL the sensors are different except the engine temp
(which they moved @93 to the thermostat housing)

   Both systems rely on the Crank Position Sensor (aka CPS, which is mounted
on the driver's side top of the bellhousing stock, or harmonic balancer in
aftermarket kits) to tell it when to spark and inject fuel. The CPS sensor
and flywheel/flexplate are system specific due to the signal/notches. (Renix
makes micro AC volts and HO makes DC volts) There is a MAP (Manifold
Absolute Pressure) sensor that checks engine vacuum (and causes poor
running/lousy fuel economy if the sensor is bad or the hose is cracked) that
may be the same for many years (It's a GM designed part, IIRC)

   The throttle position sensor tells the computer what your foot is doing
with the gas pedal. (it's different auto to stick) There are some other
sensors (engine temp, Oxygen, etc) that you need to read up on for better
understanding (I'm still in the learning stage myself)


   Auto Transmissions:
The AW4 automatic (All XJ/MJ and '93 ZJ) is very strong and as long as it's
properly serviced and not overheated, it keeps on going. The Mopar 4 speed
auto ('94 up ZJ and some TJs) isn't as tough. It needs serious upgrades to
work well. (I was going to do one with a hydraulic valve body for my 304
powered J4000, but it's a tow rig so I passed on it for a built AMC 727)
The 999 ('80 up 6 cyl FSJ, YJ and TJ) is okay unless you get really rough on
it. The 6 cyl 998 (early YJ and AMC Eagle) and 4 cyl 904 are pretty weak and
okay just for daily drivers that don't see much abuse. (the 6 cyl 9xx trans
can be swapped out directly for an AMC 727 or {with adapters} TH400 trans)
Note: the AMC 6 cyl and AMC 8 cyl trans share bellhousing, but not balance
of the flexplates. The 4 cyl auto changed several times. '80 to early '83
Eagle and CJ had a Chev smallblock patterned 904 4 cyl auto. late '83 up had
the AMC 4 cyl (which shared the 60 degree pattern of the 2.8L Chev engine
used in '84 to '86 XJs and a few '86 MJs) They went from the 904 to an AW4
type trans late in '90 till the end. (I haven't seen a 4 cyl auto TJ yet,
but there are several XJs running around yet)


   Standard Transmissions:
BA 10/5 was normal '87 to '89 (and some '90s) and pretty weak (it's actually
rated weaker than the AX-5 used by 4 cyls. I think the engineer
miscalculated metric to standard. Possibly with the same chart NASA used for
the early Mars lander that overshot it's target) Easy way to ID it is look
at the way the shifter is bolted on. A round collar with 3 screws is a dead
giveaway. Then came the AX-15. First ones were used as in service
replacements for the blown up BA 10/5s. They have 4 bolts on a rectangular
plate holding their shifter in (same as the slightly smaller AX-5) and were
21 spline on the output till 09/90. After that, the 6 cyl trans all got 23
spline (same as the 727 and 9xx trans, but a slightly different depth into
the tcase makes a spacer necessary for the swap) and 4 cyl stayed 21 spline
till the end (at least 95, as I have an AX5 from a YJ)
   You can easily swap the BA 10/5 for a 21 spline AX-15 (more work/parts
for a 23 spline swap) to run the earlier XJs. You just need the complete
trans to do it. After '96, the shifter was moved on the AX-15s (at least in
TJs) but the swap is still doable.

   Tcases:
I won't really get into these much, as it's partially a personal preference.
NP207 (used in early YJs and early XJs till @'86 with std or auto trans) is
okay for 4 cyl (if it isn't roughly used) and NP231 gives you locked 4x4
performance hi/low range as well as 2WD. NP242 started out with a skinny
drive chain that got bigger with HO motors and Mopar/other V8s. (generally
tagged NV242 HD) That one gives you all wheel drive hi or hi lock as well as
lo locked, but it's longer than the 231/207s. I like the FSJ NP208 (used '80
to '88 with stick and along with other cases in auto) to because it is the
big brother (always locked when shifted to 4x4 and no rear slip yoke) of
these cases. NP219 (used in '80/81 FSJs) was always 4x4 in hi or low. Eagles
used a NP119 which was always 4x4 and no low range. Case is externally
identical to the NP219 and swappable with minor external changes. NP228/229
(used in most automatic late '81 to '91 FSJs, '84 to '86 XJs with auto) has
2wd, 4wd full time and 4 low. Nice rainy/slippery condition case, but not
too strong. (I'll let you know how the '03 Rubicon NV241 Rock Lock with 4:1
low range is in a FSJ soon!)


   There are other issues regarding swapping, but they are kind of vehicle
specific. I started out in '01 to build myself the ultimate truck (economy,
load hauling, speedy yet a rock crawler if needed) and it's finally winding
down to the total assembly time. '84 J10 originally 4.2L/727/NP208 and
D44/Model 20 3.31 axles. I'm using a '90 4.0L block and head with my
original 4.2L crank and Renix EFI, AW4 auto ('95 XJ 23 spline), NV241 OR
tcase (you can see those specs on http://jbconversions.com or check out an
'03 Rubicon) running on propane (11:1 compression makes up for the lower
power potential of LPG since it's 120 octane equivalent and $1.41 a gallon
here) with Ford D44 front axle (instant 7" of lift), J20 Dana 60 rear axle
with 4.10 gears with lift leafs (not quite finished yet. I need to make a
rear shackle flip or buy the River Beast setup) Nice big tires (36" now, but
some 39.5" IROCs are calling me)
   I may just take my upcoming vacation time to finish the asembly as we are
getting our house ready to sell too. I'd sooner drive my project than drag
all the parts along! As it is, I need to get to the upcoming swapmeet with
my cube van full of spare parts!


From:
Subject: xj: Intro

Howdy, all.  Some of you may know me from the various FSJ lists I've  been
on
over the last 10 years or so.  I've begun to make the transition  from SJ to
XJ and have finally joined this list.  I've appreciated the XJ  from afar
for
several years but don't really know much about it.  I want to  purchase my
first XJ in the next year so I can have it ready to hand down to my
daughter
when she begins driving in a couple of years.  I was thinking I  wanted a
5-speed
so she could learn to use a clutch, but some  folks tell me the XJ manual
trannies aren't much good.

Here's my first question.  Which were the best years of XJs and  why?

Ben Williams