Multiple codes

Hello there!

About a week ago while running some errands in my 2001 Cherokee Sport, I was accelerating out of a turn and suddenly the transmission shifted really hard and the CEL started blinking. It ran fine the whole way home so I didn't think too much of it...maybe a misfire because I was gunning it. Stupid to ignore, I know.

My wife was driving it the other day and she's not nearly as lead-footed as I am. She was leaving a parking lot and the jeep started running really roughly and the CEL started blinking again. It blinked at her the whole way home.

I pulled the codes tonight and got the following:
P0204 - Cylinder 4 Injector Circuit Malfunction
P0300 - Random Misfire
P0302 - Cylinder #2 Misfire
P0304 - Cylinder #4 Misfire

I get that the 204 and 304 codes are linked and it sure looks like #4 injector went tits up, but what I don't get is the #2 misfire with nothing else accompanying it. Any ideas?

It's been my experience that OBD II misfire codes are
not all that reliable. I'd focus on the P0204 code. Try
pulling the #4 connector from the injector and spray
with some electrical cleaner, look for loose pins, etc.
The trouble could also be an open circuit in the injector
coil itself.

Once you solve the P0204, the other codes should
disappear.

As a shop owner I will tell you that step one for any misfire code is to replace the spark plugs...the public seems to have forgotten that they are wear items that must be replaced.

Runnin'OnEmpty said:

It's been my experience that OBD II misfire codes are
not all that reliable. I'd focus on the P0204 code. Try
pulling the #4 connector from the injector and spray
with some electrical cleaner, look for loose pins, etc.
The trouble could also be an open circuit in the injector
coil itself.

Once you solve the P0204, the other codes should
disappear.

Click to expand...

I'll try that. If the injector is bad, are the Bosch sets on ebay any good? At $60 for a set of 6 it's hard to pass up...

SuperB60ce said:

As a shop owner I will tell you that step one for any misfire code is to replace the spark plugs...the public seems to have forgotten that they are wear items that must be replaced.

Click to expand...

The reason I didn't immediately think plugs is that they were replaced about 5000 miles ago. I'll pop them out and double check them though since it's so easy to do.

engineerrol said:

The reason I didn't immediately think plugs is that they were replaced about 5000 miles ago. I'll pop them out and double check them though since it's so easy to do.

Click to expand...

What brand and number plugs are they?

Check the firewall wire harness(s) for breaks in the insulation, signs of rubbing, etc.

In my case, the plastic ties which hold the wire harness to the firewall broke (on either
side of the braided ground wire). The wire harness slumped down slightly (it was barely noticeable). Part of the wire harness rubbed against a metal bracket on the intake
manifold, and this caused a short to the fuel injectors.

Solder and heat shrink tubing fixed it all up.

SuperB60ce said:

As a shop owner I will tell you that step one for any misfire code is to replace the spark plugs

Click to expand...

Coil on rail can give you misfire codes with the wrong spark plugs. I constantly get misfire codes when I'm in low range and doing a lot of engine braking. My last set of spark plugs were the single platinum variety and not the dual platinum.

Firewall harness looked good and the plugs were Champions. I pulled them out and they all looked good, gap set to .035" and good coloring. I did see that #5 plug had that rubber boot that's in spark plug sockets left on it. I guess mine popped off while installing and I never noticed...

Anyway, here's a stretch...5 and 2 are on the same coil. Somehow the boot caused 5 to fire but not 2. Firing order has 2 fire before 4 so 2 having an issue meant 4 started throwing codes until everything could settle down.

BIG stretch, but I can't find anything else wrong. All injector connectors looked good and after clearing the codes the jeep drove just fine. Guess I'll wait and see if it happens again.