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Unread 07-14-2013, 07:59 PM   #16
dellis
Registered User
1998 ZJ 
 
Join Date: Feb 2013
Location: Vienna, VA
Posts: 313
First let me double check some of what you write.

(1) When you turn the key "on", the voltage at the injector jumps from 0 to 2.5V, and then drops back to 0 after about 2 seconds. Correct?

If so, then you either have a resistive short or a slow response on your multimeter. I'll assume a resistive short. Let's find it.

(2) Let's check for good voltage into your ASD. First, temporarily remove your ASD relay. With Key "on", probe at test point #4 in the original diagram. I am assuming you have 12V on both sides of Fuse 18, correct? Now assuming you do, then clean the contacts of your ASD relay and reinsert.
(3) Disconnect the two wire plug going into the coil. Did the injector voltage ramp up to 12V with key "on"? If so, your coil is bad. If not, leave it unplugged.
(4) Disconnect the plugs to your two O2 sensors, one at a time. Each time, check the voltage to the injectors. Did the voltage increase from up to 12V when key is "on". If so, you have a bad O2 heater in one of your O2 sensors. If not, leave them unplugged.
(5) Disconnect all of your injector wires, but make sure they are labeled or identifiable because you don't want to mix them up. When you do this, does your injector voltage ramp up to 12V with the key "on"?



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Unread 07-15-2013, 03:44 PM   #17
ZJMatt
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1998 ZJ 
 
Join Date: Jul 2012
Location: Weare, New Hampshire
Posts: 485
I got the jeep to start! But it will not stay running. The new ECM has AB at the end of the part number whereas my old one was AD. Could this make a difference? The guy at the junk yard said it did not matter as long as the numerical part was the same which it is.
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Unread 07-15-2013, 04:25 PM   #18
dellis
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1998 ZJ 
 
Join Date: Feb 2013
Location: Vienna, VA
Posts: 313
Quote:
Originally Posted by ZJMatt View Post
I got the jeep to start! But it will not stay running.
Sounds like an security system issue.
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Unread 07-15-2013, 04:40 PM   #19
Oldfrog
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1997 ZJ 
 
Join Date: Feb 2008
Location: Louisiana/Texas
Posts: 3,627
dellis....does the 5.2 PCM also shut down the fuel system if it doesnt get a CPS signal within 3 seconds after the engine begins cranking like the 4.0 does?
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Unread 07-15-2013, 08:51 PM   #20
dellis
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1998 ZJ 
 
Join Date: Feb 2013
Location: Vienna, VA
Posts: 313
Quote:
Originally Posted by Oldfrog View Post
dellis....does the 5.2 PCM also shut down the fuel system if it doesnt get a CPS signal within 3 seconds after the engine begins cranking like the 4.0 does?
We all know the PCM is a huge mystery, right?

When key is turned "on" (no cranking), the ASD and the Fuel Relay will activate for 2 seconds and then shut off.

If cranking begins, I have some PCM operating logic in my notes based on the 93-95 PCM operation at start-up (that I'm modifying slightly for 96-98). When the key is turned to crank:
  • ASD and Fuel Relays are engaged
  • Pin # 12 (Connector 3) sees voltage change from ASD relay.
  • Cam sensor is sampled and seen prior to crank signal.
  • Crank signal must seen and properly aligned with Cam signal, within x degrees.
  • Primary ignition signal is seen (on coil driver)
  • Injector signal is turned on.
  • With this in order, the PCM sees everyone is OK and allows the engine to run.
If anything is not properly running, the PCM shuts down the ASD and Fuel Relay after two sparks!
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Unread 07-15-2013, 09:01 PM   #21
ZeeJay1997
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1997 ZJ 
 
Join Date: Dec 2008
Location: Sweet Home, Alabama
Posts: 6,215
In addition to what dellis said the FSM for a 97 states:

ENGINE START-UP MODE
This is an Open Loop mode. The following actions
occur when the starter motor is engaged.
The powertrain control module (PCM) receives
inputs from:
  • Battery voltage
  • Engine coolant temperature sensor
  • Crankshaft position sensor
  • Intake manifold air temperature sensor
  • Manifold absolute pressure (MAP) sensor
  • Throttle position sensor (TPS)
  • Starter motor relay
  • Camshaft position sensor signal
The PCM monitors the crankshaft position sensor.
If the PCM does not receive a crankshaft position
sensor signal within 3 seconds of cranking the
engine, it will shut down the fuel injection system.
The fuel pump is activated by the PCM through
the fuel pump relay.
Voltage is applied to the fuel injectors with the
ASD relay via the PCM. The PCM will then control
the injection sequence and injector pulse width by
turning the ground circuit to each individual injector
on and off.
The PCM determines the proper ignition timing
according to input received from the crankshaft position
sensor.
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