P0303 issues - JeepForum.com
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post #1 of 6 Old 03-26-2014, 08:34 AM Thread Starter
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2000 XJ Cherokee 
Join Date: Mar 2014
Location: Oxford
Posts: 4
P0303 issues

Hey guys. Your forum has been helping me so far in my quest to fix my jeep but I'm running into a brick wall here. I have a 2000 cherokee sport 4.0 with 161k mileage. I'm going to assume it is an XJ since it's nothing but problems. Now mind you, as much as I hate these problems, I love my jeep.

Due to antifreeze and overheating issues since I've had her, which blew my radiator apart last spring, I opted to not install a thermo this past summer and it did pretty well. Water pump was replaced and thermo changed to a 190 last fall. Still antifreeze went missing and the amount I needed to replace kept growing. Last week, after the head gasket blew, she had a full top end with a heavier head casting (old one was full of grease, forget oil, and was lighter so here again I have to assume it was the 0331). This fixed my missing antifreeze problem. We also did 2 oil changes, plugs, #2 rod (banana).

She ran like a queen for 4 days and sounded like a jeep should. I didn't push her so she could break in so to speak. Then, I noticed a slight hesitation, which in all honestly I know I've experienced before but now that she is quieter it's obvious. By the time I got to my friends house she was bucking more or less and the engine light came on. Blinking then steady. I counted 20 CEL blinks before each pause. Computer Code was p0303 (which I've gotten in the past as well)

We then changed the coil and #3 plug. Same. Every time she would warm up. Although, I did pick up on a slightly not so right startup. It felt a little less calm but not noticeable to those who don't drive her.

Then it seemed my injectors sprung a leak so we changed them out. #3 and #6 were cracked. #2 was leaking due to o-rings. We even changed #3 plug again. We threw the heat coil aside seeing I have never had a leaf in my manifold and opted to individually wrap each injector as one of your forum threads showed.

Now, I'm a sensitive person and an observer so I pick on on small things and notice off the wall stuff. During a test drive, as she shifted downhill and my ears popped, her tone and handling got better and she seemed to start getting shakier as she switched going uphill in the same dang spot on the hill. We took her through the same spot and each time she did the same thing giving me the p0303 but this time I get 17 blinks on the CEL. For ****s and giggles I tried the 'on off while holding the trip down' thing which only checks gauges and lights (I know I have the oil gauge sensor issue too but it's not a full time thing) and upon restarting her, she sounded better and no blinking but cel is still on. There is a little black unit under the hood on passengers side next to the ac in the back that clicks non stop when she starts acting up.

I'm at a complete loss and I'm completely broke after this. I'm looking at the TPS, map, etc etc etc etc etc etc. I'm thinking it's something that has not been changed causing all these issues as well as the possibility of something breaking during the top end, but she was perfect for 4 days which confuses the heck out of us. HELP!

Note... When I first got this vehicle in 2009 it was obvious it had been overheated. Stained with anti freeze on the underside of hood. A shop took the engine out, cleaned it, replaced freeze plugs, replaced water pump, hoses, radiator etc etc.

Last edited by Quinni; 03-26-2014 at 09:54 AM. Reason: Forgot mileage
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post #2 of 6 Old 03-30-2014, 02:09 PM Thread Starter
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2000 XJ Cherokee 
Join Date: Mar 2014
Location: Oxford
Posts: 4

3/28 3rd oil change

Replaced EGR (the thing that was clicking)
Test drive
Symptoms gone: bucking and stumbling.
Symptoms still present: hesitation and p0303 misfire

Replaced TSP
Test drive
Symptom gone: none but 'tighter' and smoother
Symptoms still present: hesitation and p0303

Replaced MAP
Test drive
Symptoms gone: all and much 'tighter' than last time.

7 miles between apartment and friends house
No issues on way home.

6 miles into driving to friends house... P303 going up steep hill
Compression test A-ok
Replaced Bosch plugs with NGK V-Power ZFR5N 3459
Test drive
Pulsating going up hill at roughly 1700 rpm and 2200 rpm and at idle/reverse.
4 miles no light yet.
Sat for about 20 mins and headed back
On steep incline again: Hesitation, p0303, and a self correction with light gasping at next shift (if that makes sense) 2000rpm.

Anybody? Bueller?

Last edited by Quinni; 03-31-2014 at 07:46 PM.
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post #3 of 6 Old 03-31-2014, 07:40 PM Thread Starter
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2000 XJ Cherokee 
Join Date: Mar 2014
Location: Oxford
Posts: 4
Cam possibly just took out #3 lifter. Cling clang.
I'm surprise no one has responded to my pleas for assistance.
I can't afford to be a lab rat, to be without a vehicle, or to even think about affording a new engine.
If I'm in the wrong place, just tell me.
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post #4 of 6 Old 03-31-2014, 07:57 PM
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2000 XJ Cherokee 
Join Date: Oct 2008
Location: Sumware Inn
Posts: 3,000
If the little black box you're talking about is right beside the AC accumulator (black bullet at firewall) and has a couple vacuum hoses hooked up to it, then you are referring to the Evap System Solenoid. If it's clicking, then it's trying to purge fuel vapours.

Check the lines going from it across the back of the firewall - make certain they are still intact and attached.

P0303 is an injector misfire (as you know) but may be misleading you.

Be patient and if you're frustrated, take it to a mechanic -- people don't wait at home hoping to answer a thread because they have nothing else to do.
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post #5 of 6 Old 03-31-2014, 09:05 PM Thread Starter
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2000 XJ Cherokee 
Join Date: Mar 2014
Location: Oxford
Posts: 4
Problem is, I can't afford a mechanic. I have a good friend helping with it. Already changed the ERG Solenoid out the other day along with TSP and MAP. In 2nd posting down. I know I may be a little impatient but relying on others to pick me up, drop me off, and crashing out on couches isn't something that is sitting well with me. People are getting annoyed with me as well.
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post #6 of 6 Old 04-01-2014, 08:19 AM
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2001 XJ Cherokee 
Join Date: Oct 2011
Location: Somewhere in the middle
Posts: 594
I was having similar problems last week. But I was getting a P0351 along with a couple of misfire codes. I changed the coil rail (probably wasn't bad because they usually don't go bad) and then I changed the Crankshaft sensor (CSS638 from Napa ~$80). It got a little better after changing the Crank sensor but still had episodes. What actually fixed it (at least so far) was I unplugged all the connections to the ECU (under hood drivers side by the factory air intake) cleaned the connectors and plugged them back in, making sure they were tight. Apparently the connections can corrode and/or loosen over time and just need to be refreshed a bit. I would try this before you throw anymore parts at it. Also try this: with it running open the hood and wiggle all the wiring harnesses under the hood to see if the misfire happens, this might tell you if you have a wire that has been rubbed and is grounding to the frame when you go up a hill.

2001 XJ build thread --
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hesitation , rough start , xj

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