2015 gt all stock. 24k miles. A few weeks ago I had my AC compressor fail. Got it back and probably 200 miles later I got a check engine light.

Autozone printout says p0300 random cylinder misfire as well as 6 of the other 8 specific cylinder misfires. I had just put a few gallons of gas in it probably 20 miles before this happened. Drove around to burn it down and then refuled with new 93 and code went away. 2 days later the on my way to work this morning I got a flashing check engine light. I haven't pulled the codes yet. In neither instance did I feel any misfiring or sluggishness or anything abnormal.

I'm aware of the IMRC issue on these intake manifolds but if that were my issue wouldn't it only be cylinders on one side? I have at least 6 cylinders throwing codes. Could this somehow be related to something with the new AC compressor or something during the install? The autozone printout references doing a PCM reprogram alongside the p0300 code - is that a practical viability? I tried disconnecting the battery for a few hours but that didn't discharge the system. Will resetting the keep alive charge possibly help? How is that done? I'm really not trying to take this to the dealer out of warranty and have them troubleshoot everything under the sun.

 

Anybody????

The question I REALLY need answered is if the IMRC failure would cause misfires on both sides? So far I've logged individual misfires on every cylinder but 1 and 8. Im trying to figure out if I should start there to troubleshoot this but my rudimentary understanding of the intake I'd only be seeing misfires on one side of the engine unless both sides broke.

 

Hi.

After doin' a little research on them intarwebs, the answer is 'yes, the p0300 may be caused by IMRC failure'. There are TSBs for this issue, but the real deal thing to do is get a scan tool that can read the valves while driving so you can get them properly diagnosed. It could also be coils or the plugs, or something else like a temperature related intake crack opening and closing, crazy as that might sound, but stuff happens, y'know? Could also be injectors, fuel pressure regulator... vacuum leak... computer's goin' south... chafed/eaten wires... If you don't have the scan tool that can do this diagnosis, or the shop manual and TSBs involved to guide, you'll need to take the car to a mechanic who does.

It is unlikely that this has anything to do with the A/C compressor, except for if wiring was bumped, but the location of the compressor is in a place that's unlikely (lower right side bolted direct to engine with three bolts and one unrelated connector.) If it were the 4.6L the crank sensor is located behind the compressor, but on the 5.0 Coyote the sensor is relocated to the rear of the engine reading a reluctor off the crank back there, so it's unlikely to be a timing issue.

The IMRCs are controlled one per side, but the entire intake manifold has to be bought to fix the problem should one or both shafts be messed up. The easier thing to do is delete the IMRCs, but that may change performance on the car, as they're there to compensate for low end torque issues and better fuel economy, so beware of what you delete. And yes, both can get messed up, it does happen.

Again, all this is solved, as far as 'what' is concerned, by a scan tool and proper diagnosis.

Hope that helps, good luck, and welcome to the forums. Sorry we didn't get back to ya in less than 2043 microseconds, we'll try to do better next time, k?

 

Hi Houten, thanks for the in depth reply. i know that the IMRC runners are a very likely culpritnfornthe p0300, what I'm still trying to discern though is that since I also have p0302, p0303, p0304, p0305, p0306, and p0307 (every cyllinder except 1 and 8 has logged a misfire) wpuldnt it take two both runners breaking at the exact same time to get these codes? Or would one runner cause misfifes on both sides?

 

Yes?

I'm goin' with yes. And I know that's not an answer, but it is. Both are valid scenarios: They both break, or one side is causing such a ruckus that the other is ticked off. If you get a misfire, it yanks things around, y'know.

This is why you need the scan tool. Less guess, more info, better result of answer to fix the thing and be done with it.

 

What sort of scan tool would you suggest? Obviously I'm trying to troubleshoot likely scenarios before being at a dealers long and drawn out diagnostic mercy without a warranty.

 

I don't have any recommendations. The Ford scan tool is the best because it has all the tricks needed to diagnose such things for sure. However, you could look into the Forscan software (Google that) and it will recommend the proper OBDII cable to get that'll maybe be the thing to do. You also want the *actual* Ford shop manual for your car to go with it, so buy that.

Then you're talking generic scan tools and they may be good may not. Eric O of South Main Auto (go watch some of those videos) uses various scan tools from Snap-on, Autel, Maxxis? and others depending on whatever works. Brian at BSG/FordTechMakuLoco uses some scan tool I'm not familiar with, but it's for Ford and it does some really good stuff.

Myself, I don't even have any of those, except I did buy the OBDII cable for the Forscan software, and I've downloaded it. I just haven't put it on a computer and played with it.

You sound like you have a (siphoning with large negative pressure) dealership. You don't have to go there. You can go to any other mechanic who knows these cars. Ask around, or do some googlin'. Might be surprised at what you find.