Quote:
Originally Posted by StillRiding
I've spent a week looking for an answer so I hope you can help. 2001 Cherokee, replaced - coil rail, all injectors(4 hole), re flashed ecm $$$, new plugs, crank position sensor and shaft. I still get misfire codes and low pressure evap. leak codes. Starts good and idles good. When I accelerate hard engine starts missing and stumbling. Won't go past 2500 rpm until I turn the key off and back on. Then it runs great until I accelerate hard again(as in passing). restarting always corrects the problems. 195,000 mi. Uses no oil of radiator fluid. PLEASE HELP.


Codes:
P0305 #5 cyl misfire
P0302 #2 cyl misfire
P0303 #3 cyl misfire
P0300 random cyl misfire

Freeze Frame Data: (all 4 are the same)
Fuel sys 1 cl
Fuel sys 2 cl
Calc load(%) 59.61
ECT (F) 203
STFT B1(%) -0.78
LTFT B1(%) 4.69
STFT B2(%) -1.56
LTFT B2(%) 4.69
MAP(inHg) 0.00
ENG RPM 0
Veh Speed 35

Started eng cold and hooked up my scanner. I let the eng warm up to 210 deg F reving it up to 3000 rpm ocationaly to simulate excelleration. Codes did not appear untill I pushed on the gas peddle. when I turn off the key and then back on it runs smooth untill i excellerate.

I Originally posted this in the (Ask The Question Thread). Two weeks and no answers so I am trying here. I am a fair mechanic,but I am stumped.

 

Fuel filter? 195,000 miles is a lot......

 

1. Verify fuel pressure. It's the first thing I do when I see the P0300 random misfire. For an 01, you should have 49 psi, plus or minus 5 psi.

2. If fuel pressure checks out, I'd try reindexing your camshaft position sensor.

http://www.jeepforum.com/forum/f11/h...ensor-1145301/

 

fuel pressure at idle is one thing. Fuel pressure under a load is another. If it's an old filter, it needs to be changed anyway.

 

I have a new fuel pump/filter to install. If it is the filter would it reset and run fine by turning the ignition off and then back on ?
Cam sensor checked and rechecked.

 

You might want to check your catalytic converter, etc. You could have a clogged up exhaust.

 

I think JS is on the ball there. I didn't think of that...isn't there a pre-cat also?

 

The 01 I just got had the same problem. Removed the rear catalytic converter and found it pretty much in pieces. My front cats are OK for now but those COULD come apart and clog up the rear cat(i've seen it in other brand vehicles with similar setups). Its fairly easy to remove the rear cat and check it as long as your exhaust bolts are rusted horribly. You can even drive it with it loose and see how she runs.

 

Thank you for your suggestions. When it stops raining enough in WA. I'll replace my fuel pump and check the cat.