No spark at plugs

Tiny
TERRY BURCHFIELD
  • MEMBER
  • 1998 JEEP CHEROKEE
  • 4.0L
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 140,000 MILES
Coming home one night it just quit at an intersection.
It is not getting any spark. I have replaced the ignition module in the distributor, the coil, The sensor on the bell housing, and the PCM (main computer). I have checked the relays and still not spark. These were all parts that I was told to replace by a on line mechanic. This has cost me a bundle so far, but I am in too deep to quit. Car ran fine for the eight years I have had it only replaced a battery and AC unit in all that time and it is still in good shape. Am on social security so I cannot afford to take it to a shop.
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Saturday, January 21st, 2017 AT 1:14 PM

3 Replies

Tiny
DOCFIXIT
  • EXPERT
Try this, look at fuse box find automatic shut down relay remove find fuel pump relay remove and place in ASD slot. Then check for spark if there is replace ASD relay.
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Saturday, January 21st, 2017 AT 2:36 PM
Tiny
TERRY BURCHFIELD
  • MEMBER
Did the Swap still no Spark. What ever happened to the good old days of points and condenser. Well, any other suggestions short of match in gas tank. LOL
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Saturday, January 21st, 2017 AT 3:07 PM
Tiny
CARADIODOC
  • EXPERT
The first thing is always to read and record the diagnostic fault codes. Disconnecting the Engine Computer erased them, so that valuable information was lost. In particular, we are looking for a code relating to the crankshaft position sensor or the camshaft position sensor, (distributor pick-up assembly). The problem is codes related to them often do not set just from cranking the engine. They set when a stalled engine is coasting to a stop.

If there are no fault codes, the next step is to view live data on a scanner to see if those signals are showing up at the Engine Computer. If you do not have access to a scanner, you can at least determine if the automatic shutdown, (ASD) relay is turning on. Find the wire that is the same color at every injector, (usually dark green/orange), and back-probe that at any injector, the ignition coil, or either smaller terminal on the back of the alternator. Use a test light for this test. Digital voltmeters do not respond fast enough.

The test light should light up for one second when you turn on the ignition switch. You might also hear the hum of the fuel pump. What is important is if that twelve volts comes back during cranking. If it does, you have an ignition system problem or a fuel supply problem, but not both. If the twelve volts does not come back during cranking, you will not have spark and fuel, including injector pulses. That accounts for about ninety five percent of crank/no-starts.

If the ASD relay does not turn on only during cranking, you are going to need the scanner to see which sensor signal is missing. Be sure the distributor shaft is turning during cranking.

If you never see that twelve volts, including for that initial one second, there is a blown fuse feeding the ASD relay. Most commonly that is caused by a wire harness to the oxygen sensors that fell down onto hot exhaust parts, and the O2 sensor's heater circuit shorted to ground.
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Saturday, January 21st, 2017 AT 4:02 PM

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