2014 Mustang GT - Code P0302 - Second Cylinder Misfiring
 

Hi all,

I have a 2014 Mustang GT that I bought in July. It has about 9100 miles on it. I took it out this morning and noticed it was running a bit rough out on the highway. It was shuddering/choppy when accelerating and backfiring when I shifted/let off of the accelerator. Turned around and took it straight to Grapevine Ford (where I bought the car), but they haven't been much help so far.

I have a Steeda CAI, BBK 85mm throttle body, BBK ceramic long tubes, a custom catted H-pipe, and MBRP race series cat-backs on the car, and a Bama tune. The tech at the dealership basically refused to even look at the car with all the after market parts on it, told me he couldn't help me since I wasn't throwing any codes. Suggested I call the place I had the mods done (Dallas Mustang) or the place that did the exhaust (B&G) and get them to check it.

B&G found no leaks, but while they were checking the car, the check engine light came on. The tuner showed it was code P0302, second cylinder misfiring. Turned around and took it back to GF and showed them the code and they still said there was basically nothing they could do, since they don't know if the coil is throwing the code or the after market parts are generating the code and making it look like a misfiring cylinder (if that's at issue, wouldn't checking the coil tell you? It's either bad or it isn't.).

I still have my factory airbox kit and throttle body, so they asked me to bring those up and let them put those back on the car and test it. Already felt like I was getting the run-around (I know after market parts can cause problems with diagnostics, but seriously, refusing to even look at the car because of it?) and felt even more like it when they quoted me two hours of labor to put the stock parts back on (no way that's a two-hour job. Took about 30 minutes to have it done, initially). Seriously concerned they're going to do the swap, spend a few minutes driving it and tell me they still can't tell what it is because of the headers and exhaust mods and hand me back the car and a $200 bill.

Any thoughts on what the problem may be or how I should approach the dealership? I'm really surprised. Grapevine had treated me really, really well up until today.


Thanks,

C-

A little additional info: I've seen code P2626 (O2 Sensor Pumping Current Trim Circuit/Open) intermittently, as well. I know high-flow cats are prone to throw codes, so I wrote it off to that, but am now thinking I should have had it checked. The car started idling hard at startup a few weeks ago. I thought it was the colder weather, but I'm starting to wonder if the O2 sensor is bad. All the symptoms seem to fit bad O2 sensor.

Try a different Ford dealership....sounds to me like that one is just being lazy. Ford soldme my car with all kinds of stuff on it...CAI, aftermarket X pipe and axle backs and still gave it a 100k warranty certification...

Being lazy or trying to cook up things to charge me for. The coil in particular should be an easy diagnosis: Swap it with another cylinder and see if the code moves with it. No reinstall of stock parts needed.

The only thing that bothers me about taking it to another dealership is that I'm leery to drive it much with the cylinder misfiring.

Thanks for the reply.

Just drive it like an old lady and you should be ok

Was looking online, and with LT's the code P2626 was on one side. The suggestion was to switch sensors and see if the code follows. The car in question turned out to be a bad O2 extension.

Are you using a mail order tune with TB and longtubes? No way I would trust that. I'd give HPP a call and ask them for help if you can't get it figured out.

Update: Dealership put a new coil and plug on cylinder 2 and the code switched from P0302 to P0300 (random misfire). Took the car to Dallas Mustang, where I had the mods done. They were to start data logging it this afternoon, so hopefully I'll know something by tomorrow morning.

Update: Data logging didn't turn up anything, so they ran a compression test today and compression tested fine in all cylinders. That's good news, but the crew at Dallas Mustang is pretty stumped as to what it might be at this point. My car already has the O-ring fix from the TSB, so they don't think the crank position sensor is involved. They're going to text the injectors tomorrow. Prime suspect at this point is the tune, but they're really just guessing right now.

Ruled out: Low compression, bad/dirty throttle body, coils, plugs, vacuum leak, O2 sensor.

Hope they find an answer soon.

C-

I've heard nothing but complaints from people about Bama tunes...even mine throws a MIL occasionally for Fuel to Air ratios on the driver side....

I don't see why guys do mail order tunes when the best Mustang tuner around is right here in the DFW area. There are reasons there are month long waits.

They can be good, though. My dad had the Steeda intake, Roush exhaust, and a Steeda mail order tune, and it worked great. I trusted them as they do a lot of work for Ford.

I think type of mods should play a factor in deciding.

I have a bama tune no problems here. It would stumble a bit at idle so I sent them a Data log and now its like driving a factory car.....well except for the awesome sound of my cams :) .

Nice. Who installed the cams?

I installed them myself.

Turned out that the driver side bank was running lean. The problem was traced to the O2 sensors installed when the headers were done. Car is fixed, but I'm planning to have the extensions removed and F-150 O2 sensors installed instead (THEY'RE LONGER AND WON'T REQUIRE EXTENSIONS). Too many folks have had MAJOR problems with those extensions for me to leave them in.

Awesome on installing the cams yourself, I bet it sounds amazing. How much power did you pick up?

Wonder why the extensions are made bad? Seems to be hit or miss.