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Old 11-21-2013, 04:33 PM   #1
frodojj
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Misfiring 2009 Ford Focus Perplexing Problems

Hey all, my car is having some weird problems. I was wondering if I could get some advice please. A few days ago, the check-engine light came on, and the car started misfiring. Sometimes it would stop misfiring, other times it would. A few times the check-engine light was blinking at me. The error codes were:

P0171 System to Lean (Bank 1)
P0202 Injector Circuit Malfunction - Cylinder #2
P0302 Cylinder #2 Misfire Detected

Some history: This car is a 2009 Ford Focus. It does need an oil change and probably a new screen. It has over 155,000 miles on it - mostly highway. I just moved to Los Angeles a year ago from Pittsburgh, PA, so it's seen a lot of stop-go traffic out here too. This started happening on a work trip from San Diego to Las Vegas to Los Angeles.

Work done:
1) Initially, I stopped in Barstow, CA. There, I replaced the spark plugs. I noticed the cylinders #3 & #4 were full of oil, so we let that drain. It worked to get us home to LA, but then it started happening again. This suggests to me that it wasn't the spark plugs or oil (although that was a problem).

2) A mechanic changed the valve cover gasket, in case that was allowing oil into the spark wells. He also suggested changing ignition coil #2. I did so; however, the error came back later that day. I returned the initial coil to cylinder #2 and there was no change. I don't think it was the ignition coil.

3) I checked the resistance on the fuel injectors with a multimeter. All of them are consistently around 12-15 ohms.

4) I hooked up the diagnostic machine, took some data, and averaged out about 3 minutes 24 seconds each of fuel trim values.

- At about 0.75k rpm (idle), I get a Total Fuel Trim of positive 21-25%
- At about 3K rpm, I get a fuel trim of positive 15-21%

This is pretty weird. What do you think could cause the lean condition and misfiring of cylinder #2, if not the coil or spark plug? To be on the safe side, I put in a bottle of Techron, a full tank of Chevron gasoline, and I've cycled through about half of it now. I'm trying to finish the gas tonight.


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Old 11-21-2013, 06:24 PM   #2
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You have a bad injector or damage to the injector wiring harness like the connector is not clipping in properly. It all makes sense with that.

It's true that oil in the spark plug tubes will cause misfiring, so you're not too far off from that issue with what happened to you. However with these codes, I'd be checking the resistance of the injector, and the wiring to the injector on #2.
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Old 11-21-2013, 06:42 PM   #3
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a compression test wouldn't hurt IMO

did you check the gap on the new spark plugs before installing them ?
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Old 11-22-2013, 01:12 AM   #4
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You have a bad injector or damage to the injector wiring harness like the connector is not clipping in properly. It all makes sense with that.

It's true that oil in the spark plug tubes will cause misfiring, so you're not too far off from that issue with what happened to you. However with these codes, I'd be checking the resistance of the injector, and the wiring to the injector on #2.
Thank you so much! I moved the fuel injector to cylinder #1 (and cylinder #1's injector to cylinder #2). The error moved to cylinder #1, so that means the injector is bad. I'll order a replacement and come back to report whether it worked. Thank you for the advice!
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Old 11-22-2013, 05:10 AM   #5
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Good mechanicing there bro. I was hoping for a bad connector, but bad injector it is.
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Old 11-25-2013, 06:27 PM   #6
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My roommate and I replaced the injector yesterday. It seems to work now after about 70-80 miles of travel (my work commute is long)!!! However, I have 3 questions:

1. Someone recommended that I replace all four fuel injectors. I only replaced one. Should I replace the others?

2. I checked the Fuel Trim. The Short-Term fuel trim is between 0 to -5, but the long term fuel trim is about 10. Is this normal? It doesn't seem to change when I rev the engine or when it's idling.

3. I had a hard time moving the fuel injector retainer c-clip. Here's a pic before we moved the c-clip.



The new injector is on the left, the old one is on the right. We used a screw driver to pry it off and install it on the left injector... but I'm worried about deforming the others c-clips. I would like some instruction please! Thank you guys so much for your help so far. I really appreciate it.

Last edited by frodojj; 11-25-2013 at 09:42 PM.
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