Hello all!

For starting.. I have a 2000 Jeep Cherokee sport, Auto, 4x4.

1- When I start the car up everything runs beautifully for the first 2-3 minutes or so, and when it starts warming up the injectors #3 and #4 stop working simultaneously. By checking up the PCM, no power signals was coming out for these injectors.

2- Leaving the car up for a longer time around 5-10 minutes or so the injectors #1 and #6 stop working simultaneously as well, and again no power signals come from the PCM to these injectors as well.

After that the car remains roughly running using only two injectors (#2 & #5) until I turn it off.

I took the car to a mechanic to check it and he verified the the PCM is fine and no code is coming up and concluded that the problem most likely in the wiring without given any specification.

Any ideas what might causes such a problem? I checked all the wirings connecting to the injectors and they same fine.

Thanks in advance for any input or suggestions.

 

Get a noid light to see injector pulses.
Possibly coil malfunction, maybe heat related.

 

The PCM does not provide power. It grounds the injector. All injectors get power from fuse 18 (15a) in the PDC. Note, there is a single wire from the fuse that then splices out to 6 wires.

You can use a noid light or a volt meter. Key on, start car, test for 12V at each injector (Dark Green/Orange wire). Wiggle the harness while you test.

Key off, you can then test for continuity/shorts from each injector to the PCM.

From the FSM:



So back to your symptoms. How do you know it's the injectors and which ones? Odd, there are no misfire codes.

 

I did not want the post to be too long so I did not go through some details.

Yes, I used a noid light to inspect all the injectors. When I start the car the pulsing light appears in all injectors connection harnesses. Then after few minutes the pulses stop simultaneously in the two injectors in the middle and after more few minutes stops in the two in the corners as well. This sequences occurs every time I start the car so it not random.

I went through some of the previous threads and I did some test before I started this thread including testing the wiring connections and resistances and I found that:
- Each injector has around 13v on the Dark Green/Orange wire (Car on) and a resistance around 12 ohm.
- There is a good connection between all the injectors and the PCM ( with resistance around 5 ohm).
- The grounding circuit or the pulsing received from the PCM disappears from the #3 and #4 injectors driver then after that from #1 and #6 injectors driver.

I was trying to check the wiring connection feeding the PCM but I did not know where to start. Here is some of my thoughts and questions I hope some one could help me with this:

1- Is it possible for camshaft position sensor/crankshaft position sensor or any other sensors to cause such problem?
2- Is it possible to any of these sensors to fail partially so it give a signal at specific point and time and not at the others?
3-Is it possible for any loose connections or damage wires before PCM to cause sending a bad signal to PCM which might cause for some injectors to stop working other than the other?

Sorry for making this too long. Any inputs or thoughts would very very appreciated

 

Sounds like a Closed Loop issue. PCM inputs:

• Air conditioning select signal (if equipped)
• Air conditioning request signal (if equipped)
• Battery voltage
• Crankshaft position sensor
• Engine coolant temperature sensor
• Extended idle switch (4.0L engine with police package only)
• Intake manifold air temperature sensor
• Manifold absolute pressure (MAP) sensor
• Throttle position sensor (TPS)
• Camshaft position sensor signal (in the distributor)
• Battery voltage
• Park/neutral switch (gear indicator signal—auto. trans. only)
• Oxygen sensors

However, the one thing that differentiates Open Loop from Closed Loop is input from oxygen sensors. How many you got, what do you have for testing/monitoring equipment?

Crankshaft position sensor is also thermally-sensitive. Any error codes?