911 PLEASE HELP! P203 code- injector 3 fault/ missing on #3 - JeepForum.com
 
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post #1 of 11 Old 09-28-2019, 03:03 PM Thread Starter
Seanjiggityjeep
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911 PLEASE HELP! P203 code- injector 3 fault/ missing on #3

Hey guys,
I'm in a bit of a pickle and really need some help/opinions/advice...
I have an '01 4.0 XJ Classic.
I started getting a p203 code (missing on cylinder 3/ faulty injector circuit) about a year ago, but was running fine for a week, then a week later it started running on 5 cylinders and engine light flashing instead of solid. It would also "redline" or cutoff and rpm gauge bounce at 3500 rpm, which I'm assuming was the computer detecting an issue and protecting the motor from higher rpm's? At first I was able to unplug injector 3, plug back in and then would run on all 6 and engine light go solid for a day or 2. I had good voltage at that harness, was getting a good connection and there was good continuity through that pair of wires. I decided to reset the ECU and see if that fixed my issue. It did for a week and engine light went off and ran normal. After a week, engine light back and a day later flashing and running on 5 again. At that point, the unplug the harness to cylinder 3 and plug back in trick was not working and didn't do anything. I reset the ECU again and engine light went off and ran on all 6 for a day, then back to flashing trouble light and running on 5.
At that point I decided to take to a shop, as I didn't want to just start guessing and throwing parts at it that it may not need. I figured they could diagnose further and and get to the bottom of the issue without having to replace every part concerning that injector circuit... So they gave it back and said they found a fuse out, which a few days earlier I thoroughly checked every fuse not just visually, but for continuity even (I'm an electrician not mechanic, but can turn s wrench) and they were all good. They also said they reprogrammed the ECU to "normal running conditions", which from my understanding, the ECU programs itself over its first 50 starts and I didn't even know that it was programmable. Whatever they did, it was running on all 6 again and engine light off, so I paid and was satisfied enough.
Fast forward to a week ago and one day engine light comes back on and later the same day, before I could even check codes, she starts running on 5 again, flashing light and all same symptoms. So I do the reset the computer trick again and engine light goes off and runs fine for the past week, so I thought maybe a fluke and it was okay again. Then last night I'm driving my girlfriend to Portland for a convention (I live outside Seattle) and halfway there engine light comes on solid and then 2 mins later flashing and running on 5. I pull over, reset the computer, engine light goes off and I get back on the road. 5 mins down the road, lights back on, flashing and back running on 5. I decided to criss my fingers and just keep going. Found a sweet spot between 70-80 mph and the shaking and vibrating from running on 5 would stop. It also sucks a lot more fuel running on 5 (I'm guessing fuel is just dumping info that cylinder and not firing?) and would run slightly warmer and oil pressure seemed to go up a little.
So now I'm kind of screwed here in Portland for the weekend, auto shops are closed, I don't have the extra $ to start just guessing at replacing parts myself (I have my electrical tools, as well as a basic socket set and some wrenches with me). I disconnected the positive cable last night when we got to the hotel and rested on the starter bolts overnight to fully drain the capacitors and fully reset the computer and when I started it this morning, the reset dis nothing and immediately started on 5 and engine light came on and flashing within 30 seconds.
Please help! I don't know what to do and really don't want to risk driving 4 hrs back with it running like that and risking doing permanent damage to my baby's heart and soul... or the motor. Any help, opinions and advice would greatly appreciated! I have to be back at work Monday morning and am supposed to be driving back tomorrow and I'm sweating it and don't know what the truck to do!
Sorry for the novel of a post, I just wanted to give as much detail as possible in hopes someone could lead me in the right direction.

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post #2 of 11 Old 09-28-2019, 03:34 PM
mukluk
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If you're getting good power to the injector and both wires ohmed good, then it sounds to me like you most likely just have a bad #3 injector. Normally I'd advise swapping the injector with #2 to see if the problem follows the injector before replacing it to be sure, but it doesn't sound like you have much luxury of time to do so. One last check I'd recommend if you have the means to do so would be to disconnect the injector and PCM connectors then see if you have less than 100ohms continuity to a chassis ground at the YL/WT injector driver wire -- it's a known common problem for the wiring harness to chafe on a valve cover stud at the rear of the engine between it and the firewall.

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post #3 of 11 Old 09-28-2019, 04:18 PM Thread Starter
Seanjiggityjeep
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Okay thank you very much for your response and I appreciate the advice! I'm confused as to why resetting the computer wold occasionally fix and why it worked fine for a year? Maybe I'm overanalyzing and just need to throw a new injector at it. Is there a special tool needed to remove the fuel line? It looks like it would take something like a sharkbite (plumbing fitting) tool to remove possibly? And do you know if I would ever need to "program" the PCM after resetting it or could the issue lie with a faulty PCM itself?
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post #4 of 11 Old 09-28-2019, 04:41 PM
CJ7-Tim
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The OBD-II diagnostics is pretty good at focusing your diagnostics. Follow the trouble codes. PCM failure is only considered after a thorough and in-depth diagnostics and trouble shooting of the more common and more logical causes for the symptoms.

The shop is probably pulling your leg, all that can be done without a $3000 DRB-III Scan and Program tool is to delete the PCM adaptive memory. The problem is ignored until enough adaptive memory is stored and then the CEL is triggered. If there is massive amounts of excess fuel, the O2 sensors will likely report that and trigger the CEL.


I would start with suspecting wire harness issues, chafed/melted wire insulation, or other damage first. I do not recommend random new parts without any diagnostics, but if you can scrounge up a compatible used injector from a local Jeeper I would try it. A special tool is used to disconnect the fuel line fitting but I find a strip of sheet metal from a soup can or coffee can also works. If you do pull the fuel rail or injectors, have spare brand new injector O-rings on hand, and lube all the O-rings before you re-install them.


P0203 JEEP - Injector Circuit Malfunction Cylinder 3

Possible causes
  • Faulty fuel injector 3
  • Fuel Injector 3 wire harness is open or shorted
  • Fuel injector 3 circuit poor electrical connection

.

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post #5 of 11 Old 09-28-2019, 05:11 PM Thread Starter
Seanjiggityjeep
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Tim, thanks for the advice.
My main wire harness by the back of the valve cover looks good and ground running to it is good.
The harnesses to the injectors look okay... I broke the brittle little red clips on half of them about a year ago, but I put zip ties on them to hold in place, which seems to hold them even tighter than the silly little clips.
I love the soup can hack! I had just called auto parts store and was about to drop the 20 bucks they wanted for one, so yeah, thanks for that!
And good idea on a used injector. I'm going to go on Craigslist and see if I can find one local somewhere. I saw online for twenty bucks (which i don't have time for) , but the local auto parts places wants 60 bucks for a remanufactured one, so ill look used first.
I'll keep you guys posted and keep the advice coming, I appriciate it everyone!
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post #6 of 11 Old 09-28-2019, 05:31 PM
jtec
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with the accompanying P0303 the flashing CEL, I am thinking driver side of circuit is grounding out, the wire from #3 to PCM.

Using A noid light would be a good easy test of the circuit.

If money is an issue - swap # 3 with say #1 and see if issue follows injector to new 'home'.


this was mentioned by mukluk - check the harness at rear of cylinder head - Not an easy area to insp but I wanted to mention that area also....might want to wiggle shake and tug harness as you use the noid light, see if that causes a steady light.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #7 of 11 Old 09-28-2019, 06:20 PM Thread Starter
Seanjiggityjeep
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I visually inspected that main wire harness by rear of cylinder head and valve cover and it looks fine. No chafing or damage to any wires. I don't have a noid light with me, but have my multimeter and can do the same thing, however I don't know what wires do what at that harness, so not sure what to look for there.

Another question for you guys: So I have a steady 14.1V to that injector harness when engine on, which I'm assuming would tell me that the PCM pulses the ground to open and close the injectors? And if that's the case, does anyone know what range in ohms I should be looking for with that ground pulse? And for how long the pulses should be (if its other than just a quick millisecond, which then a multimeter wouldn't even read...)? And has anyone ever tried to test both the injector and that circuit going to it, at the same time, by removing the injector, plugging back in to the harness, turning over the motor with starter and just visually seeing if the injector opens as closes? I'm assuming that would diagnose both to see if the PCM is working and telling it to open/close and actually seeing it open and close?
And if that is a okay way to troubleshoot, I'm assuming my only precaution wold be to unplug the fuel pump so that gas doesn't spit out of the disconnected fuel line... am i missing anything? Does that sound like a legit way to test to you guys?
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post #8 of 11 Old 09-28-2019, 06:42 PM
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Injectors are pulsed in milliseconds, so you're not going to see that with a digital meter. You're correct in your assumption that the injectors are provided a constant power source (via the ASD relay in case you're curious), and the injector pulse is controlled via the ground leg by the PCM. As I mentioned earlier you can see if the control (ground) wire is shorting to ground and causing a problem.

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post #9 of 11 Old 09-28-2019, 06:49 PM
jtec
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the inj circuit activation is in milliseconds,
above I suggested swapping inj to test the injector - cheap, somewhat easy, fast- compared to checking with injs out.

TRY jumping the inj connector with a test light - did the light flash - stay on bright- not stay on or flash?

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #10 of 11 Old 09-29-2019, 06:51 PM Thread Starter
Seanjiggityjeep
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So I limped it home on 5 today... it kicked back onto 6 for a few mins twice. Made it though.
Back to all my tools and everything now...
Last night I did ohm out the control wire on that injector circuit and it was good, no shorts in that circuit, PCM has good ground too. I didn't pull the injector yet.
Jtec, you're saying with a light on that circuit, I should see it flashing if the PCM is doing its thing and working correctly, right?
I did ohm out all the injectors too and had around 12 on all of them except that one I had 7. I don't know if that's even a way to diagnose them or not, I couldn't find anything about it on a search.
I'm about to go try a light on that circuit now and then probably just go grab a new injector at O'Reilly (just remembered they price match internet prices - woohoo! ) and cross my fingers that takes care of it
Thanks for the 2 cents everyone. I'll keep you posted.
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post #11 of 11 Old 10-01-2019, 10:30 PM
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A flashing CEL means stop and shut off the engine. Raw fuel will destroy your cat very quickly.


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