Check Engine Light Flashing....Injector circuit open?

[penberth]

So my CEL is on and flashes occassionally. I took it to Autozone and had it read. They said that it was fuel injector circuit open? Or fuel injector stuck open. I can't remember which.

Anyways, how do I diagnose this, and fix it. Dealership wants $85.00 to just look at it, then how much $$$ more to fix it. Or do you guys think it's one of those things that you have to take it in for?

The Jeep is a 2000 Cherokee with 4.0L.

[jneary]

was it just one injector or all injectors? if it is wiring related it is almost impossible to diagnose over the internet.

[bottleworks]

A flashing MIL indicates a misfire.... Did you get a misfire code?

[jneary]

i may not be an acura tech, but i know that when the CEL is flashing it means there is something causing a fault right now. if it is just on and not flashing there ia a code stored. that doesnt mean it is a misfire, it could be an injector fault or another sensor failure.

[penberth]

The last two codes I got were:

I am pretty sure they (Autozone w/ the code reader) said that "Injector stuck open on cylider 6.

Someone on JeepsUnlimited, said that it was more likely "Injector circuit on cylinder 6 stuck open. (Bad wiring) So now I don't remember.

Then the second code was misfire detected on cylinder 6. (as a result of the first code.)

The kid at AZ erased them....but they came back after 15 minutes or so.

SO the XJ sat all day today. So I took it for a ride, and it was fine for about 30 minutes, then it started acting up and the CEL blinking. Any ideas on why it would take a while?

Anyways, I was planning on pulling out injector 6 and trying to clean it....or just replacing it. Any thoughts on this?

I just posted this thread...any thoughts?
http://www.naxja.org/forum/showthread.php?t=30285

[jneary]

it could be the injector, however it could be a wiring problem or even the pcm. the pcm controls the ground for each injector. if the driver circuit for #6 injector is bad, it is a bad pcm. chech the wiring harness between the injector and the pcm for continuity between the injector and the pcm to rule out wiring prob.

[penberth]

Originally Posted by jneary

it could be the injector, however it could be a wiring problem or even the pcm. the pcm controls the ground for each injector. if the driver circuit for #6 injector is bad, it is a bad pcm. chech the wiring harness between the injector and the pcm for continuity between the injector and the pcm to rule out wiring prob.

How do I do this?

[penberth]

I think the circuit is bad. I did like you said and checked the continuity between the two and it looks like there is a break in a wire somewhere. Now to find out how much the harness is....it looks like its all one piece. Yikes....

[bottleworks]

Originally Posted by jneary

i may not be an acura tech, but i know that when the CEL is flashing it means there is something causing a fault right now. if it is just on and not flashing there ia a code stored. that doesnt mean it is a misfire, it could be an injector fault or another sensor failure.

Your right. I should have added in a "usually". However, I would have also expected a misfire code with that injector code too.

To make sure it's the injector, you could connect a test light to the #6 injector wiring. With the engine running, it should pulse lightly (ie the test light will act as the injector). The difference of resistance between the test light and the injector coil will be minimal and won't be a problem.

[penberth]

The FSM said that you can check the injector by checking the resistance through it. I have a test meter, and it said 12.5ohms...which is what the FSM said it should be. So I chalked up the injector as good.

I then checked continuity through the look to the PCM, and i got no continuity. So after doing some digging, etc...still didn't see anything. I put it all back together, and it is running fine now.

So I am going to hold out. I am guessing it will act up again sometime.

[jneary]

maybe the connector was loose at the injector and by reinstalling it is on tight now.

[penberth]

I knew it was too good to be true. I started the truck up yesterday, drove less than 2 miles, and the CEL came back on, and the truck is running like crap again. So I am right back to where I started.

I haven't re-tested the continuity again...but I am guessing that's what the deal is.

[Matthew Currie]

Here's one way you can test whether the fault is in the harness or the injector itself. Usually there is enough slack in the injector harness so that you can swap plugs between adjacent injectors. Wait until the problem starts to occur, if it's intermittent, and then, while idling, pull each injector plug, one at a time. If the injector is working, the engine will slow slightly and then recover. If the injector is not working, there will be no change in idle. If you find one bad one, turn engine off and swap its plug with the nearest adjacent one, then restart and test again as above. If the fault follows the plug, the problem must be in the harness. If it remains with the injector, it's the injector.

Remember that on the Chrysler system the injectors get their positive current from a common circuit coming off the ignition, and the negative is switched by the PCM. Low voltage on the positive side will prevent the injector from firing. The positive branches to the plugs through a number of splices in the harness. You can use an ohmmeter to measure the harness for resistance. It's not that hard to open up the harness and bypass bad splices in the positive side.

[Craig]

Thank goodness for the forums! My 2000 Cherokee Sport was having similar problems - CEL coming on and rough running. Sometimes it would clear up by itself, or if I disconnected the battery, the CEL would reset and everything ran fine.

Recently, the problem got much worse. I thought it might be the O2 sensor going bad, but I bought a code reader and found: P0202 - injector circuit open and the "misfire" code. Thanks to Matthew's post above, problem solved.

Notice that Matthew said the pos(+) circuit to the injector comes of a common circuit and the neg(-) is switched. That means when your ignition is on, one of the wires going to the injector is actually hot and the other is switched by the PCM to the battery neg(-).

So... if the hot wire gets shorted out, it will probably burn a wire, blow a fuse, or fry the PCM - and the injector will always be OFF. If the "other" wire shorts out (and completes the circuit), then your injector is ON all the time! (STUPID Chrysler engineers!!!!) Which might make your engine run really rough, flood the engine, and give you really crappy mileage.

I didn't have a multimeter, so I used a 12v LED from Radio Shack and a 9v battery to check the injectors. All injectors good. Now, with the engine running, check each injector connector with just the LED. (note that LEDs are polarity sensitive) No light on #2. I traced the harness off the back of the engine where it bends over the fuel rail and guess what - the fuel rail had worn through the cheap plastic flex covering and had worn against some of the wires inside. The light on #2 started flashing! (STUPID Chrysler engineers!!!!) Problem solved!

Hope that helps someone else out there.

(Search words p0201 p0202 p0203 p0204 p0205 p0206)

[mcnamaag]

Okay, I know this thread is old but it's the only one I've found while searching that matched my issues. I'm not new to troubleshooting and I'm very familiar with jeep electrical systems. This is on my;
2000 XJ, 4.0, 4WD, AUTO, 160,000 miles
I've already pulled the codes and have a P0203. I originally had both a P0203 and P0303 but after troubleshooting I've been able to get the P0303 misfire fixed by replacing the coil rail. I've switched injectors (new), checked continuity on the yellow white tracer wire from the number 3 injector and have it, also checked continuity on the green pink tracer (power supply) to the coil and it's good. I have power to the number 3 injector and have verified by checking all injector connection readings (same across the board). Now, I'm not ready to say it's the PCM, but I'm running out of ideas. The only thing that doesn't seem right, and I almost missed it, but for a split second and I mean quick, when I check the yellow white tracer for ground I get a reading. I'm talking unplugged from the injector, negative probe into the female plug on the harness and then touch the positive side of my multimeter to ground. Engine off, battery disconnected. No other injector connections do this, just number 3. So yeah, that's where I'm at. I've already pinned the harness from the PCM to the number 3 injector and have verified continuity and from the pin on the PCM harness to ground and it's not grounded out. Again, sorry for reviving an old thread but I'm running out of ideas. Thanks in advance!!