shocks are a great thing. One minute you can be soft and
absorbent over the rocks and trails, the next you can be
cranked up to the max for high speed pre-running over the ruts
and rocks. As it turns out pre-running can be hard on a
stock ignition system. I found this out during a spring
trip into the
fern covered mountains
when some high-speed pre-running fun shook a bug out of
the ignition system of my 1978 Jeep CJ-7.
Several rounds of testing and troubleshooting yielded no
cause and no fix for the ailing sparkless stock Ford Duraspark ignition system. Before
spending too much time on it, I decided it was
time for an upgrade. Enter the HEI.
Why an HEI?
The AMC HEI distributors fits the AMC 290, 304, 343, 360, 390,
and 401 ci engines. They also make them for the 6
cylinder engine as well. They utilizing the durable and
dependable High Energy Ignition (HEI) system pioneered
by GM. The HEI distributors incorporate easily found
High Energy Ignition replacement parts. They're a
durable 1-piece design with the coil and module mounted
internally for an easy 1-wire hook-up. Plus by
eliminating the stock AMC ballast resistor, more ignition
voltage results and you get improved spark that permits a
bigger spark plug gap, resulting in more power and reduced
What is an HEI and
how it compares to the stock Jeep CJ ignition system?
When you look at a stock Jeep CJ-7 ignition system,
it consists of a few key components. First the starter
solenoid provides power. You also have a coil, the
distributor, a vacuum advance, a cap and rotor, below the cap and
rotor, an induction coil and a star gear that tells the ignition
module when to ground the coil, which in turn sends spark to the
rotor and out to the spark plugs. All of these main components
are in different locations under the hood and a bunch of wires run
back and forth to interconnect the components. My Stock Ford Duraspark ignition system had a few
minor upgrades. An MSD Blaster Coil built for offroad abuse, a
set of aftermarket spark plug wires, quality spark plugs and some
new stock parts, those being a new cap and rotor, a new pickup coil
under the cap, a new ignition module and solid, soldered wiring.
But something failed and to this day, I don't know what it was even
though I replaced and tested everything I could think of including
all the wires that run back and forth between the components.
Of course I didn't pour a lot of time into troubleshooting the old
system, I was soon to be acquiring an HEI setup to replace it
anyway. I did want to try to figure out what was wrong, just
so I knew but gave up after one go around testing or swapping out
each component with spares I had around.
HEI ignition system is a bit different. First, everything is
contained within and on the distributor itself. A single power
supplying wire coming from your starter solenoid / ignition switch is all that is
required. Another wire runs from the distributor to your
tachometer. It's simple and reliable. With most HEI
distributors, parts are readily available with lots of aftermarket
options. On the market there
are a few sources for HEI ignition systems for the Jeep AMC 360.
DUI makes a nice setup for a cost in the $400+ range. I also
found one made by CRT Performance for much less. Proform
Street/Strip also makes HEI Distributors for the AMC V8 engine. Ultimately I
bought one off of ebay from the seller qtip43 who converts GM Style
HEI distributors to work with AMC/Jeep V8 engines
290-304-343-360-390-401. I also picked up a Set of HEI spark
plug wires made by Live Wires. Here's the description of the HEI by
the Ebay seller qtip43 of Sterling Heights, MI, United States.
He also has HEI- AMC/JEEP conversion Distributor for 232-258 inline
AMC/JEEP (GM-STYLE) HEI Distributor 290-401
AMC/JEEP distributor conversion for 290-304-343-360-390-401.
Eliminate the original unreliable distributor with this 1-wire
hook up unit. Features 50,000 volt built in coil, low saturation
ignition module, and brass terminal cap. Engine will run much
smoother with added throttle response. Unit uses easy to replace
GM parts and HEI ignition wires. Also has provision for tach hook
up. Each unit tested before shipped. Add $15 for shipping.
Here's a breakdown of the GM Style HEI Distributor
that was installed on this AMC 360 Jeep engine. Everything in
the ignition system is contained within the HEI distributor.
All that is necessary is to supply 12 volts to the power plug
located under the rectangle sticking out the side of the HEI
Distributor. Next to the 12 volt power plug is a place to plug
in your tach.
Below the top
cover is the
50,000 volt coil.
Below the cap
is the rotor.
of the cap is
similar to the stock cap.
rotor exposes the advance curve precision weights and springs.
advance curve weights is the High-Performance low-saturation ignition
Vacuum Advance unit.
Wire harness and capacitor
Below the advance curve weights is
are inner and outer magnetic star ring. Not sure about
the exact naming of them but the inner star ring is
attached to the distributor shaft and when the shaft
spins, the points in the rings come within hundredths of
an inch, telling the ignition module its time to ground
the coil to produce a spark. When compared to the stock
magnetic trigger, this setup is much more precise.
Live Wires HEI Spark Plug Wires
Gear (in this case for the AMC V8) and oil pump slot
at the base
of the distributor shaft.
The HEI Replaces entirely this old, for the most
part, stock ignition system:
I also had a MSD Blaster Coil rated
for Offroad with an epoxy core.
An old Motorcraft distributor, cap
and rotor and all the guts of it. In my case I had
a few aftermarket parts mixed in including a set of MSD
larger than stock wires, 8.5mm I think they were.
The 2nd (or third?) Motorcraft
ignition module that I've gone through. When these
fail, they fail without warning. If you have one
of these, it's wise to carry a spare.
Below the cap
is the rotor. Simple and basic.
rotor exposes the induction coil, or magnetic trigger that has
the job of detecting when the star gear on the
distributor shaft passes. This in turn tells the
ignition module to ground the coil and create spark.
I've had these fail where the Jeep would fire up but
when the engine got warm, this coil would open up and
not work. the engine cooled (or the coil cooled)
and it would fire again. What a bitch it was to
figure that one out.
I had a whole slew of these plugs.
4 or 5 of them with 2 or 3 wires each. These
created a maze of wiring running back and forth across
the engine bay. When I was troubleshooting, I had
to check each wire for continuity and trace each wire
through from one side to the other. They're all gone
now. 2 wires with the HEI, 12 volts to the HEI and
a wire from my tachometer to the HEI.