jgronho

I have a 2001 XJ. My check Engine light comes on and it throws a PO301 Code. My dilemma is that it only does it when it is cold outside. I live in Wisconsin, and all summer no issues whatsoever. Today temp was under 30 degrees. When I let off the accelerator to stop, and RPM's drop, Check Engine light flashes. When RPM's increase, light goes out. Scanner shows a PO301 code. Vehicle runs just fine. I have tried most of the fixes described, i.e. TPS, O2 Sensors, Sea Foam, Plugs, etc. Would really appreciate some input.

Diesel

PO301 is cylinder 1 misfire

jgronho

Thanks, I am aware that it is a Cylinder 1 Misfire. My issue is that it only occurs below 30 degrees, and only when the idle drops.

Diesel

Next step would be stop replacing and start diagnosing. Check cap/rotor/dizzy and make sure its firing at the correct time. Followed by cleaning the injectors. If you have access to a DRB that would pinpoint the problem for you.

413maxwedge

No dizzy on 00-01, check your first coil pack, and the ev-6 plug on injector #1, and buy yourself a chilton's haynes or fsm alot more in the book to look into.Also do some of Diesel's posting.

Diesel

Didnt even process that it was a 01. Apologies

jgronho

How would any of these things be affected only when the outside temperature drops below freezing? I drive the vehicle daily, and no problems since last winter without any mechanical changes to the vehicle.

Diesel

Jeeps are like women, very mysterious creatures.

mikepmiller

you should try the map sensor

tjwalker

Don't concentrate on the temp the code occurs so much as the code itself.

A single cylinder misfire on an 00-01 could be an injector, coil pack or the start of an internal engine issue (unlikely but possible)

I'd start with swapping the cylinder 1 injector with a different cylinder. If the misfire follows, you know what injector is bad.

413maxwedge

Well if you don't like the help people give to you, you can always do it by yourself.

99 Purple XJ

Def. try swapping injectors and when was the last time your spark plugs or coil was changed? See if you can have a shop hook up their expensive scanner theyll usually pull up other codes than a simple hand held one wont

jeepxj99

X2

jeepxj99

0900303 - 4.0L MULTIPLE CYLINDER MISFIRE
Date: 08/01/03
Model Year(s): 1999-2004

Description: NOTE: THIS BULLETIN APPLIES TO VEHICLES EQUIPPED WITH A 4.0L ENGINE. This bulletin involves inspection of all engine exhaust valves and a decarbonizing procedure if necessary.

Details: The customer may experience an incident of engine misfire during certain vehicle operating conditions. The misfire may occur when the vehicle is operated between 50 - 70 MPH and under light loading conditions, e.g. slight uphill road grades. This condition may occur at all ambient conditions, but is more noticeable when ambient conditions are less than 0 C (32 F).

If the vehicle is equipped with On-Board Diagnostic (OBD), a MIL illumination may also have occurred due to Diagnostic Trouble Code (DTC) P0300 - Multiple Cylinder Misfire. Various single cylinder misfire DTC’s may also be present. If the frequency of misfire is high the Powertrain Control Module (PCM) may place the engine in “Limp-In” mode.

The misfire condition may be caused by one or more engine exhaust valves that are slow to close. Late closure of an exhaust valve may be the result of no valve rotation and associated build up of carbon on the exhaust valve stem.

This condition may occur when the engine is not allowed to run at engine RPM’s that are greater than 3,200 RPM. At 3,200 RPM or higher the engine exhaust valves will rotate if not impeded by high carbon deposits. Low engine RPM’s and high carbon deposits are associated with short trip driving where the vehicle engine is not allowed to fully warm to normal engine operating temperatures. Cold ambient temperatures will increase engine warm-up time and add to the opportunity of carbon deposit build-up on the stem of the engine exhaust valve.


Just saw this....possibility???

tjwalker

Anything is possible but that bulletin that you posted is for a multiple cylinder misfire (P0300) and the OP has a P0301, cylinder 1. I'd still concentrate on everything relating to THAT cylinder.