"Jeep Cherokee XJ Trouble Shooting - My Jeep won't start!"
October 16, 2009
by Mike Strawbridge
Failure to start falls into two categories:
The engine will not turn over –
the starter motor will not run
Or
The engine turns over but will not fire and run.
This article will address the second cause.
If you engine will not turn over, see my other
article.
The Jeep Cherokee like other vehicles needs two things to run: Fuel and
ignition.
Fuel delivery can be easily checked with the use of a fuel pressure tester
connected to the test port on the injector rail.
In the event of an emergency, you can sacrifice a tire pressure gauge to
test for proper fuel pressure. The
correct pressure will be around 35 to 40 lbs depending on the vacuum state of
the engine.
If you suspect a fuel delivery problem, first listen for the fuel pump to
run. On most XJ Cherokees the pump
will run a couple of seconds and then stop when the key is first switched to the
on position. If the pump does not
run, check the wiring to the fuel pump. Start
to see if the proper voltage is present at the ballast resister located on the
left front fender. You can also
remove the fuel pump relay and use a jumper wire to energize the fuel pump.
If the fuel pump runs but does not produce the correct fuel pressure,
check for leaks in the fuel limes. There
is a rubber line inside the fuel tank that if it breaks will allow the system to
loose pressure without any visible leaks. This
one can be a real head scratchier to find.
If you have the proper fuel pressure and still the engine will not fire,
check the ignition source. The ECU
relies on two signals to determine the spark timing.
The Crankshaft position sensor and the camshaft position sensor.
The Crankshaft position sensor is located on the bell housing on the left
side of the engine. There is a
wiring connector on the manifold that sometimes corrodes.
Check for a good connection at this point.
Also, check the wires leading to the sensor as I have seen them damaged.
The camshaft sensor is located inside the distributor housing.
The most common problem with this sensor is the wiring again the
connector to the wiring harness. Also
note that there are several ground wires that connect to the back of the engine
block near the distributor. If these
grounds wires are loose, the ECU can malfunction.
Check these while checking the camshaft position sensor wiring.
If the distributor has been removed for any reason, verify the indexing of
the distributor. If the distributor
is even slightly off, the computer will not allow the engine to fire as a safety
precaution. See my other article on
distributor indexing.
Another part that can stop the flow of power to the ignition is the rotor
in the distributor. Remove the
distributor cap and verify that the contacts of the rotor are making contact
with the cap and the tip is not excessively burned.
if you have both correct fuel pressure and correct spark,
try the clear flood procedure.
Mike Strawbridge October 16, 2009