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Old 03-18-2015, 07:15 PM
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4.0 with one lean cylinder from reading plug

Hi all,

I started my error hunt from a P2098 and P2096 code in my 2005 4.0 with the auto that is new to me with 194k. The jeep seems to be running fine although lugs a bit when the trans shifts into overdrive, but I figure that may be normal with slightly bigger tires (31 in) and stock gears. I just cross-countried 8000 miles with the code.

My #3 plug looks lean I think. (It is very white and crusty). I figured it may be a bum fuel injector, but after swapping the fuel injectors the problem did not follow the old #3 injector. I think the injector is getting a good signal, as my multimeter showed similar values on the #3 and other suspected good cylinders. I have not checked fuel pressure yet, but plan on it soon once I get the correct adapter to measure it on the 2005 that doesn't have a test port. Any thoughts on the cause? Is it normal for the #3 cylinder to look any different?

I understand that the original error code could be caused by bad O2 sensors or maybe even an outdated PCM, but I am currently fixated on my plug-reading. I don't think I have any vacuum or exhaust leaks.

Thanks,

Doug

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Old 03-18-2015, 07:50 PM   #2
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Unfortunately your multimeter isn't telling you the whole story. To accurately diagnose an injector you need a lab scope. Moving the injector was good but won't rule out wiring or other related items as you know. Personally I think it would be worth the diagnosis time to get it hooked up to a scanner.

A few simple tests you can run though:

With a long screwdriver or mechanics stethoscope you could listen to the injector with the engine running. See if the opening and closing on cylinder three is different than the others. If you don't hear a click you either have a bad injector(ruled that out I believe by switching) or possibly a weak PCM Driver.

Are you getting a steady 12 volts on the control wire? I assume not since you are running lean-if you are though that isn't correct. Open control wire or open PCM driver.

If you have a steady low voltage or no voltage on control wire you have an injector solenoid issue, short to ground in control wire(this is where I think your problem lies)or shorted PCM driver.

To test for shorter control or shorter driver hook up a test light to battery positive and touch to control wire. If it lights that will tell you that you have a short in either control wire or driver

To verify which it is: with test light still hooked up as noted above unplug PCM connector-if the light stays on you have a short in your control wire. If it goes off short is in PCM(don't immediately condem PCM-look at connections, pins, ground, wiring etc)

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Old 03-18-2015, 09:11 PM
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Thanks AUJeeper.

I can do a couple of these before I get back home. Just to confirm, by control wire, do you mean the ground side of the injector wiring harness at each injector?

Thanks
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Old 03-18-2015, 10:20 PM   #4
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Control wire is the wire going to the PCM. In this case on injector 3 it would be Brown with a Light Blue stripe.
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Old 03-18-2015, 10:32 PM   #5
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Quote:
Originally Posted by dmpowell View Post
Hi all,

I started my error hunt from a P2098 and P2096 code in my 2005 4.0 with the auto that is new to me with 194k. The jeep seems to be running fine although lugs a bit when the trans shifts into overdrive, but I figure that may be normal with slightly bigger tires (31 in) and stock gears. I just cross-countried 8000 miles with the code.

My #3 plug looks lean I think. (It is very white and crusty).
Check TSB #18-028-06, there is a reflash on the Powertrain Control Module (PCM) for P2098 & P2096.


On a side note, are you certain the #3 plug discoloration is from a lean condition? Could it be oil? Take a picture of it and post it if you get a chance.
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Old 03-19-2015, 07:32 PM
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I checked the voltage between the brown control wire with the blue stripe at the injector connector and the positive battery terminal. I measured 11.5 Volts with the ignition on and off. On the other terminal within the connector, I measured 12.5 Volts between the positive terminal. I repeated the measurements on good suspected cylinders and measured the same values. I don't have access to a test light right now.

I attached a picture of the plug below. This is what a new plug looked like after about 3000 miles. I pulled it again at about 8000 miles, and the buildup was much worse. After a bit more, it may have bridged the side and center electrodes. After looking at a plug reading guide, this image does look consistent with oil contamination. As a FYI, the previous owner of the Jeep was motivated to replace the head, though I am not sure when or why.

Thanks,

Doug
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Old 03-19-2015, 08:09 PM   #7
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I should step aside here as c.d.c is one of the best trouble shooters on the forum. I always learn a ton when he and Digger get involved in a thread

Personally based on what I see with that plug I would do a quick compression and leak down test on all cylinders

Voltage looks good unless you are getting a steady 11.25 on the control wire. If so inputs from crank or cam sensor could be the culprit, pin problem for injector 3 at PCM

Oil fouling though may be the issue. It usually is something simple. Keep us posted
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Old 03-20-2015, 11:37 PM
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Thanks. I can do compression and leak-down Easter weekend.

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