P0456 Evap Small Leak P0303 Cylinder 3 misfire 2001 XJ

So my CEL came on again the other day.

Pulled the codes today with a

P0456 EVAP emission control system leak: very small.

P03030 - Cylinder 3 misfire.

So I did a little searching and it sounds like I need to examine some lines but I had not seen both these codes occur simultaneously.

Any suggestions. I'm starting to think this vehicle is beginning to hate me between having crappy fuel mileage and codes coming up lately.

The evap leak could be the gas cap. When does the cylinder misfire happen? Search for "heat soak" for the misfire.

Cylinder misfire happens on cold start.

Cold start, as now, when it is warm out, or in the winter? The reason I ask is that there is a TSB for a PCM reprogram for misfires on a cold start, but IIRC cold in the TSB is stated as 60* or below.

Whats your fuel pressure?

Let's call it like 80-90 degrees out. I'm not really sure what my fuel pressure is as I don't know how to measure it.

I don't think the PCM reprogram TSB will help you. There is another TSB for a heat soak hot start which puts a heat shield on the #3 injector. While it isn't exactly your issue you may want to try it. Basically all you need is some form of insulation to put around the #3 injector.

Also, check your fuel pressure.. buy or rent a fuel pressure gauge and attach it to the injector rail.

Also, I doubt both codes are related.

Well I've been getting the evap leak more often now. I'm thinking it's time to buy a new gas cap. The code cleared itself once then it came on a couple of days later. No misfire, but it was a cold start.

I got the evap. code on my '00 twice. 'First time it was the gas cap.

Second time, it was the o-ring for the fuel pump. Dealership ended up charging me $240.00 to tighten the lock ring(without changing the o-ring).

Well I've been tightening the gas cap down more for the past month and haven't gotten the evap leak code at all. So that problem feels solved.

I still have a CEL for misfires.

How is the spark plug in the #3 cyl?

When does the misfire happen?

have you done a tune up lately? thats where ide start terrible mileage and a misfire could be related...

Do not buy the crappy autozone gas cap or you will just have to replace it again in about a year. Get the mopar one at stealership for ~$20. well wort it.

I've replaced all the plugs, air filter, doing another oil change today since I'm due, changed all O2 sensors.

Misfire happens on cold start and occasionally happens on a hot start.

The evap leak code is gone so I think it was just an issue of tightening down the gas cap.

Put a fuel pressure gauge on and observe what happens what you shut the engine off. If it drops rapidly it's most likely the fuel pump check valve, which won't cause your concern. However there is a chance there is an issue with #3 injector hanging open dumping fuel into that cylinder causing the misfire. To check for that lift the fuel rail up out of the intake manifold, cycle the key and watch for drips.

So when you lift the fuel rail you just literally lift it up??

Misfire on no. 3, lets talk heat soak.

Late models, after the fuel return line was eliminated and the manifolds redesigned (especially with the CA dual-CATs), have problems with the no. 3 cylinder.

Now, before you dismiss the thought because the problem is there when cold, if you have heat soak one of the symptoms is that fuel is getting out of the no. 3 injector and causing rough hot restart followed by a rough idle/acceleration for a short period--often picked up as a no. 3 misfire. What happens for the cold issue is when you shut it off for an extended period the fuel simply pools and is there to screw up the cold start.

That is my SWAG, actually a WAG as there isn't a whole lot of science involved.

The suck-a** Chryco TSB "fix" (I had to hold my nose typing that) is insulate the no. 3 injector.

Do this, if your living arrangements allow. When you get home and park it for the night open the hood and let it cool for 30 minutes or more. If it seems better in the morning that would be an indication. Second, drive it a little hard and get it good and hot, then park and open the hood for 30 minutes. If on restart it is better, then you have got yourself a full-blown case of heat soak.

Also, on the later models there was a change to recommending an NGK spark plug.

What is this chryco TSB fix and how do I get one? I think that could be possible. I've gotten cylinders 1 and 2 to misfire as well as 3 on occasion. Which NGK plugs do they recommend? I have standard champions in right now.

That's what I'm saying Joe, a leaking injector. Yes, you just unbolt the rail and lift it up. This is a two minute check to actually verify what's causing the problem before proceeding with the TSB.

The TSB by the way is a joke. Everything else out there that does that gets a new injector. Problem is Jeep decided some insulation was a cost effective (warranty pricing here) way to bandaid the problem which is crap injectors incapable of sealing at high temps. I'd just replace the culprits instead of wrapping junk around them- IF you verify first that they're leaking.

JJacobs said:

That's what I'm saying Joe, a leaking injector. Yes, you just unbolt the rail and lift it up. This is a two minute check to actually verify what's causing the problem before proceeding with the TSB.

The TSB by the way is a joke. Everything else out there that does that gets a new injector. Problem is Jeep decided some insulation was a cost effective (warranty pricing here) way to bandaid the problem which is crap injectors incapable of sealing at high temps. I'd just replace the culprits instead of wrapping junk around them- IF you verify first that they're leaking.

Click to expand...

Agreed. :cheers: