Cant figure out missfire

[KB_GT]

Mustang GT MMR 750 shortblock (281c.i.) at 8.95:1, stock 2v heads/cams with Kenne Bell 2.1. Tuned via email by Rick @ amazon
The car is throwing P0316, and P0304. The car feels slightly shaky but the idle is steady. I replaced the #4 COP and tested the injector with a multimeter and it read 17ohms when the car was at operating temp. I tested another injector too and it read the same so I ruled that out.
I replaced that spark plug a few weeks ago when the car was very shaky, much worse than it is now (idle still steady) and throwing the same codes. That definitely helped but it didn't completely fix the miss apparently. However, I cleared the code myself when I replaced the plug a few weeks ago and it just popped back up. Picture of plug pulled a few weeks ago is below.

I will be pulling the #4 plug again later this evening to make sure its good.
I have them gapped at .032
I'm using NGK TR6's

I replaced the passenger side factory 02 sensor with an "OEM replacement" Bosch from autozone in July.

I can email a few datalogs if that would help.

Thanks in advance for any help you can give!

 

[KB_GT]

anyone?

 

[01yellercobra]

It's the weekend. Not everyone sits on the computer when it's nice outside.

First I would get rid of the Bosch sensor. Replace it with a Motorcraft. When did the plug close up? Were you just cruising or was it under WOT? My number 1 closed up like that on the dyno, but my tune was waaaaayyyyy off that day. I replaced it and never had another issue. And pull all the plugs. Make sure they're all ok.

 

[KB_GT]

It was hot out and I did a short WOT pull (smart I know) and that probably bent the old plug and that's when I started having problems.

Here is a pic of the plug I just pulled.

 

[KB_GT]

I logged missfires on all cylinders in livelink (not sure how accurate it is) and cylinder 4 is missing at idle. As soon as I start driving it stops.

 

[paulsauto]

missfire

what about compression, check compression pressure/leakdown but if it is missing at idle and clears up with rpm you might have a vacuum leak. but in my experience bent ground straps usually indicate engine damage.

 

[TVSCobra]

I see that you have already replaced the coil on cylinder 4 and the plug right? When did the issue start happening?

Could be anything causing those codes.

I see you have ohm'd the solenoid in the fuel injector. You could swap that injector to another cylinder and see if the fault follows the injector. Just becuase the ohms check out doesn't mean that the fuel injector is ok. It could be stuck open or closed, or just malfunctioning.

Like I said there are many things that can cause this issue. Have you performed a compression and leakdown with the engine warm?

 

[Ironhand]

Shaky at idle and a bent ground strap. I wonder if you have a loose rod cap and the piston struck the plug. Plugs will open in gap with boost not close down like that.

Do you have any metal in the oil pan?

Unplug the injector with it running? Does it still knock?

 

[KB_GT]

I see that you have already replaced the coil on cylinder 4 and the plug right? When did the issue start happening?

Yes they have both been replaced.

It started happening a little less than a month ago when I decided to do a short WOT pull when it was 100 degrees outside (dont know what I was thinking...). After I got out of it I noticed that the car was shaky. I got a p0304 and p0316 shortly after and I pulled that plug and it was bent in. I assumed that detonation caused it because it didn't appear to have any scratches/dings on the ground strap. I replaced the plug and cleared the code and it was still slightly rough at idle but nothing like before. The code popped up again after I got into boost last week. The idle isn't nearly as bad as it was when all of this started a month ago.

The vacuum at idle is around 17-16. Ive been thinking this was a problem but ive checked the vacuum lines and I dont see any holes or anything. Maybe im not checking them all?

I'll do a compression check this weekend but I'd like to try and rule all of the little things out first; I'm at school and I don't have many tools here.

Thanks for the responses everyone.

 

[KB_GT]

Unplug the injector with it running? Does it still knock?

I'll do that this evening and post back.

 

[KB_GT]

I unplugged the #4 Injector and the car got very shaky so I don't think that the injector is the problem. While I was doing that I did notice that the passenger side of the engine bay smelled like straight exhaust gas. I checked all of the hoses and everything looked
good. Could an exhaust leak cause the missfire?