misfiring... injector?

I've been battling heat soak for a few months... I think. I didn't really have it in the summer, but since the switch to the winter fuel blend, I've had the symptoms of heat soak pretty badly. After a hot startup I'd get OBD errors P0303 and/or P0304 and P0300.

This morning though, it started misfiring while driving home from work. Ambient temp around 25*F, intake manifold air temp 98*F, driving around 35mph when I noticed the CEL/MIL flashing. I didn't even feel it misfiring, however I did after a few seconds and it got worse until I made it home (1/4mi). Checked the codes when I pulled into my driveway and it only showed P0305 (cylinder 5 misfire). I thought it was just a fluke, a sign saying I should buy hood vents today. After a bite to eat and time to let the engine cool off, I started driving to the junkyard and after a couple minutes the misfiring was back. Continuous misfiring, only showing the error code for cylinder 5.

After chatting with a friend, it seemed that a bad coil rail was the most likely problem, so I spent the $105 for it and waited for the engine to cool down and swapped it out (and took the opportunity to put in new spark plugs). Went out on a test drive and as the engine started warming up, it started misfiring. Drove back home and checked the codes, P0305 again. With the engine still running, I started unplugging the fuel injectors (one at a time) and for all except injector 5, there was a noticeable change in the engine (misfire-ish). This leads me to believe that injector 5 is bad. Anybody have a different opinion?

Depending on weather tomorrow, I'll go out and buy a single injector and try it out. Unless anybody thinks a serious fuel system cleaner (or seafoam in the tank) would fix this. I'm thinking that 9 year old injectors with 115,000 miles might be due for a replacement, though.

Unplug the injector and see if it changes, if it doesn't thats the injector.

I'd say pull it out and check to see if its clogged with debris. I had a dodge dakota that would require fuel injector cleanings every year due to the rusting and delamination of the inside of the fuel rail.

If you take a long socket extension and put one end on the injector and your ear on the other you can hear the injector firing do this for each one and listen for a out of sync injector

You could try swapping the suspect injector with another cylinder and see if the code/misfire follows. If it does follow, then you have positive confirmation that particular injector is faulty. As you don't have a dist. cap or rotor on your 2001 and you've replaced the coil rail and the plugs, then the suspect is definitely the next thing to address.

If by chance you replace or swap the injector and misfire continues, then check compression.

Another thing you could do is check the resistance of the injectors with a multi-meter. I believe that there should be 8-12 ohms at the terminals.

Run a can of BG44K through the fuel before pulling and swapping injectors. Don't waste your time with the cheap crap, use BG44K.

Ive got 14 gallons left in the tank, at this rate it'll take 3 weeks to run cleaner through the tank.

x2 on listening to the injectors. unplugging an injector and seeing a misfire not change doesnt mean the injector is bad, youve just isolated the cylinder, which you already did with your scantool. like whats been said, id run some BG thru it and if that doesnt help move the injector to another cylinder. if that doesnt work id start to suspect internal engine failure

weebur said:

Another thing you could do is check the resistance of the injectors with a multi-meter. I believe that there should be 8-12 ohms at the terminals.

Click to expand...

Checking the resistance is a good idea. Compare it to another injector that you know is working. If it is different, just replace it. If it is the same as the others, that still doesn't mean it is good however. That would be the time to swap injector with another cylinder (as already suggested). If it moves the problem, replace it. If not, use a noid light to verify that the signal to fire is getting to the injector. If you get the signal at that point, check your compression.

Swap the #5 injector to a different cylinder and see if you still get the CEL codes.

been 5 months, but I guess the thread deserves an update. The injectors were all fine, I did buy a new one and compared the resistance to all of the oem ones, within specs. A week or two after this thread, it started blowing blue smoke out the exhaust, oil fill cap AND the side of the head. Additionally, the oil visible in the valve cover looked like creamy peanut butter. Poor 0331 head...

I bought a Dodge Charger and drove that for a while, got some extra cash and found a motor for cheap 2 weeks ago. Pulled the old motor at a friends place and took off the head, no visible cracks, but a lot of coolant in the #5 cylinder. Peanut butter oil gunk was a half-inch thick on the underside of the valve cover! That confirmed what I suspected after the blue smoke started marking my position to the Google satellites. :doh: