Cylinder 1 Misfire Under Throttle
 

Stock engine, 68k miles, new OEM sparkplug and Ignition Projects Quad Spark coil pack about 5k miles or so, E85 tune with Zack, was on 91 gas at the time.

I was driving on the freeway in 6th gear at about 75ish MPH keeping speed with throttle. I gave the pedal enough to start accelerating probably like 30% or so, basically normal driving, and noticed the car felt off. Felt like there was lack of power and hiccups while accelerating. Thought it was weird since it should accelerate since I was at 3k rpm so I gave it more gas probably around 50% or so throttle and held, that's when the CEL started to flash, but did not stay solid. Ran code and it was cylinder 1 misfire.

Car felt great when I started driving out of the garage, but feels like it got rougher when warmed up completely. This usually happens, but I always assume it's me being paranoid over the smoothness of the engine since I have Cusco engine and stiffer transmission mounts, and no codes are ever thrown so I ignore it. It was hotter day today, about 90 degrees, but this was the first time I got noticeable symptoms. What should I check in addition to swapping coils?

Thanks!

no check engine light? very odd. Misfires under load are a major catalyst damaging action and thus, newer obd2 cars are mandated to turn on the CEL in that situation.

I'd look to see if there are any stored codes and/or pending codes. Specifically misfire related.

This will let you know what cylinder to focus on.

Then you can find out if its spark, fuel or compression causing it.

For spark you can swap the plug to another hole and see if the misfire follows it. Same for the coil. Do them one at a time, as you want to isolate each part.

Compression is easy, it needs to be roughly the same as the other cylinders and above about 120 as a bare minimum. I know it will probably run ok down to about 90, and yes, it should be well higher, probably 220 or so, but check it.

Fuel is trickier with these platforms as they are both DI and PI. You can use a stethoscope to hear the injectors and see if one isn't sounding the same as the others, but its tricky. You can put a 'noid light on the PI injector harness and see if its flashing.

If you have a good scan tool, you can read various PIDS on it that will help you isolate whats going on.

Swapped the coils and logged using ECUTek. Don't know what I'm looking at so can't tell if any of the parameters are out of spec. Did not get any readable misfires, but the car does feel hiccupy when accelerating under load sometimes. Repeated yesterday's scenario on the freeway and it accelerated fine at 6th.

Are you logging this and sending logs to Zach for review?

I have not, but let me contact him. Can't seem to replicate the misfire issue today, but car does feel a bit off.

He can't magically wave a wand and produce a diagnosis.

Get a log, and send that to him with notes. :thumbsup:

What? Is Zach’s crystal ball still on back order?

Zach thinks its the injectors that needs cleaning and that the misfire was localized in cylinder 1. I could see that, but I just got misfire in cylinder 4 so it's not the plugs or coilpacks. I could see one cylinder's injectors that may need cleaning but two? I guess, I'm no mechanic, but there are many owners that have higher mileage than me that have never cleaned their injectors that aren't getting misfires so trying to cross out what is likely and unlikely.

I'm dropping my car off at the mechanic's tomorrow and want to give him a list of things that may be wrong. I can't nail the misfire to one specific cylinder. So far, I pulled codes for cylinders 1, 3, and 4 misfires so 3/4 injectors may be bad. I can't say it's injector seals since I don't seem to have the common popping noise symptom but could be a possibility. The car smells abnormally of gas when I start it up, and I got a really bad misfire when I left work today, cylinder 3, but both smell and misfire CEL flashing went away once the rpm dropped. The car prefers to misfire at lower rpm to where the torque dip is, accelerates fine from 4k to redline. High negative STFT around -14%, LTFT hovers around 0 to -4%, o2 voltage at 1.3v, but I know the flex fuel kit unplugs one of the o2 sensors so not sure if bad or good. Wished checking common things wasn't such a chore with this car. Meh just ordered a Tesla, need this car to run till December.

Vacuum leak?

Maybe, but I think it's the DI seals. The car just took a dump today, got a hard misfire code on cylinder 2 when I started it up this morning. It stopped misfiring after the rpm dropped and was driveable, but doesn't feel as smooth so it's still misfiring intermittently. Got the common DI seal symptom of popping noise when I stab the throttle so I'm leaning towards that.

https://i.imgur.com/QuiFTZN.jpg
https://i.imgur.com/EeJPUMZ.jpg
https://i.imgur.com/NTUWm8z.jpg
https://i.imgur.com/Oeb5Q67.jpg

An update for those that are interested. Mechanic did a leak down test and it showed good leak down on all cylinders. Tried swapping coils/new spark plugs and no improvement so those are out of the equation. Looked at the valve area with the manifold off and no crazy carbon build up as well. Currently, cylinder 2 has been consistently misfiring. He pulled the injectors which is pictured. They don't look too bad I think. The 3rd photo is injector 2. They're off to being cleaned and new seals installed. Possibly switching to e85 dislodged some gunk and clogged the injectors. Hopefully, that will fix the misfires.

OP, did you see any LTFT / STFT being very negative during idle?

High negative STFT when starting from cold. Averaging -14% or so but once it finishes the warm up idle, it goes to around -4%. Not sure if it's the flex fuel tune, I think I read flex fuel tune has high negative fuel trims at start up idle.