P0203 and P0303 code question

Brian Nuttall

Brian Nuttall

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Joined
May 25, 2018
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47
Location
Southern Illinois
So, my wife borrows the TJ and all heck breaks loose. I had to have it towed home because it was running rough and had a CEL. I had two codes, P0203 and P0303, when I finally got a chance to check it.

I’ve checked the injector Ohms and they were all the same. I ended up buying an injector to install because I thought it had to be the issue. It wasn’t. I have spark for the cylinder, but haven’t figured out the best way to test the wiring going to the injector.

What really has me stumped is that I cleaned the throttle body and disconnected the battery to reset everything. It was runnning great as I test drove it around town. The next morning it was back to having an obvious miss. I can take the connector off of the cylinder 3 injector with no change in the way it is running.

I have read as much as I can find before asking for help. I don’t think this is a heat issue because the rough idle/miss is constant. Any suggestions from this point would be greatly appreciated.
 
Sorry, should have mentioned it’s a 2000 with the 2.5L with a manual transmission.

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Simple way to check if its an injection problem. Swap number 3 out with number 1.

If it moves to number one its the injector. If not then you can trouble shoot deeper.
 
Boinked said:
Simple way to check if its an injection problem. Swap number 3 out with number 1.

If it moves to number one its the injector. If not then you can trouble shoot deeper.
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I already removed the #3 injector and replaced it with a new one before I read that suggestion on another thread.


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Brian Nuttall said:
I already removed the #3 injector and replaced it with a new one before I read that suggestion on another thread.


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Click to expand...
If it was me i would be looking at the wires.

You should be able to read 12v on the injector with the key on. The PCM pulses the ground to activate it.
 
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Well, the volt meter was showing 5V for that injector so I checked the #1 injector to compare. I got the same reading for this injector.


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My 01’ Sahara was running the same codes. Little over a month ago I replaced all spark plugs (needed them), new coil rail, new heat shield, new #3 injector, new insulator boot for said injector and it ran smooth as could be afterwards.....yesterday I cranked it up to leave my hunting land and the check engine light came on and I’m throwing the P0303 code again. I’ve decided to light it on fire and run.
 
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Cal said:
My 01’ Sahara was running the same codes. Little over a month ago I replaced all spark plugs (needed them), new coil rail, new heat shield, new #3 injector, new insulator boot for said injector and it ran smooth as could be afterwards.....yesterday I cranked it up to leave my hunting land and the check engine light came on and I’m throwing the P0303 code again. I’ve decided to light it on fire and run.
Click to expand...

After reading how much of an issue these codes are, probably not a bad idea.


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So, I couldn't find a noid test kit locally but I was able to use a test light to see if the harness was cycling on and off at the #3 injector. It appears that it is cycling and I confirmed this by using the same method on another cylinder. So the search continues for the cause of the codes.
 
Very strange...... i wish i had a simple answer.

The injector code has me scratching my head.

When you reset the code how long till it returns?
 
This last time it took about 5 miles through town before the light came back on. And it was running like crap the entire time. It’s almost like it is trying to run on all four cylinders some times, but it can’t. It will be smooth for just a second and then back to struggling. When I read the codes this last time it only had the cylinder 3 misfire code.


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Brian Nuttall said:
This last time it took about 5 miles through town before the light came back on. And it was running like crap the entire time. It’s almost like it is trying to run on all four cylinders some times, but it can’t. It will be smooth for just a second and then back to struggling. When I read the codes this last time it only had the cylinder 3 misfire code.


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Ok that is a good sign.
Next thing I would do is pull the #3 plug and see if there is any bad signs. (Burned/covered in fluids/carbon build up) Check the gap of the plug and replace (all) if necessary.
 
Well, I’m kind of wondering if this hasn’t all been caused by some bad fuel. I was talking to my wife about what happened while she was driving it and found out she put gas in it just before heading home. So she gassed it up and before she made it to the next town and wasn’t going highway speeds, it was running rough and the light was on.

I put some Heet in the tank and it’s running a little bit better, but still not 100%. I think as soon as I get a break from work I’m going to drain the tank.


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I wanted to wait a few days to see what happened before posting again. After putting Heet in the tank and putting new fuel in after it was almost empty, it’s running smooth again. I hadn’t cleared the check engine light either and it went off by itself today. So it seems bad fuel can also cause the codes I had. Who would have thought?


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The problem is probably the P0203 code only (injector wiring Failure). The P0303 code is normal if you have a P0203. The P0303 means that the computer has seen a variation of crankshaft speed between firing of two cylinders which is normal if you have a fuel injection failure for cylinder 3. The P0203 means that the computer sent a signal for firing the cyl. 3 injector but did not detect the expected currrent change in the circuit. Maybe someone can suggest a tool (oscilloscope type) or other method that can display the current pulse at the injector to help troubleshooting the electrical circuit.
 
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Just to update on my status, it’s still idling rough after a few tanks of good gas. I’m not getting any codes currently, but it clearly still has an issue. I’ve checked the wiring the best I can and have not found anything noticeable. At this point I’m thinking it’s either a cam positioning sensor or maybe a clogged fuel filter. If I have to drop the tank to get to the filter, I figure I might as well change the pump. I have 127,000 on the Jeep.
 
With all the rain, water in gas is likely....and water can make an injector fail....it kills em on diesels.
 
Brian Nuttall said:
Just to update on my status, it’s still idling rough after a few tanks of good gas. I’m not getting any codes currently, but it clearly still has an issue. I’ve checked the wiring the best I can and have not found anything noticeable. At this point I’m thinking it’s either a cam positioning sensor or maybe a clogged fuel filter. If I have to drop the tank to get to the filter, I figure I might as well change the pump. I have 127,000 on the Jeep.
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Sorry to resurrect. What did you figure out? I have the same problem and now it’s getting bad. CEL flashed today.
 
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