2000 Mustang GT 4.6L Code P0302 (misfire on cylinder 2) CAN'T SOLVE!!!!!!!

blake182

New Member
Aug 12, 2020
2
0
1
25
San Jose
Hello SN95 community!

I recently bought a 2000 mustang GT with the 4.6 and I have been chasing a misfire since I got it. OBD shows P0302 and sometimes P0303. The car came with an OE replacement intake manifold, step colder plugs, bigger injectors and a chip tune from Kenne Bell. Here is a list of everything I have tried:

1. Swapped all the plugs to brand new stock spec
2. Swapped back to stock injectors
3. Removed the tune from the ECU (chip on the ECU)
4. Swapped coils from other cylinders to cylinder 2 and 3
I took the coil off while it was idling and plugged in an old plug to see if it was sparking and it was and then I did the same thing with the spare injectors to see if the injector was
getting power and it was also.
5. Replaced cam position sensor
6. Replaced O2 sensor before the cat on that side.
7. Compression tested cyl 2 and compared to 1 (both 150 psi cold)
8. Checked for vacuum leaks and even fixed a couple minor ones I found while smoke testing
9. Cleaned MAF sensor
10. Finally gave up and took it to the dealer who then repeated a bunch of this stuff. They started it and confirmed it was always misfiring on 2 and sometimes on 3 then took it for a drive. When driving both misfires went away. When they returned to the shop, they let the car idle and the misfires were gone. They let it sit for a couple hours, started it again and the same thing, misfire always on 2 and sometimes on 3. They suggested vacuum leak somewhere in the intake manifold that potentially went away as the car got warm. They also re-flashed my ECU
11. Bought a new ford performance intake manifold and installed with factory torque spec
12. Leak tested cyl 2 and compared to 1. Both were leaking about 10 psi (80 psi to 70 psi)
13. Took it to another dealer who suggested it was the ECU
14 I bought a new ECU off ebay and got it flashed by the dealer (SAME P0302 RETURNED)
15 I checked battery voltage both with the car off and running and checked a whole bunch of grounds near the suspect cylinder. They all looked good (12.8 V everywhere off and 13.6V everywhere running)
16 Got the battery checked at O'Reilly, it was fine
17 I pulled the valve cover on the cyl 2 side to check the cam shaft and valve springs and they looked fine
18 I stuck a scope in the spark plug hole on cyl 2 to see what the piston looked like and it looked good

Also, I should mention for every one of these changes, I cleared the code and it always came back the same within 1 or 2 days.

It definitely seems to be related to the warm up cycle or something when the engine is cold because the car runs great when I am driving it. It is also consistently on cyl 2. Like when I start it, I can unplug the cyl 2 injector and nothing changes with the idle.

Another thing I noticed yesterday was that my gauges sweep on start up and they are not supposed to. Apparently that means the dash is getting low voltage or something but I thought it was normal. Not sure if this is related or not but just something else to note.

The dude that owned it before me also unplugged the air bag and moved the battery to the trunk. It seems like it is an electrical issue at this point. That is the only reason I wanted to mention this.

I really hope someone comes up with some new suggestions. I am out of ideas on my end so anything helps!

Thanks for taking the time to read through all of this and I hope you have some idea of what I have going on here.

Thanks again!
Blake
 
  • Sponsors(?)


dr.zed

Member
May 17, 2020
15
6
13
70
Nova Scotia
A buddy of mine moved the battery to the trunk in a 4th gen Camaro, nothing but problems if I recall.
The obvious solution to me is to move the battery back to the engine bay, ensuring the positive isn't hacked apart for the transition and the negative grounds all remain like stock.
 

McFly2

New Member
Nov 21, 2020
5
0
1
63
Cincinnati
An intermittent wire or connector plug on damaged injector circuit. Check plug (loose pin) or wire (bad insulation) going to injector # 2 and 3.

" The catalytic converter may cause the P0300 random misfire code to show up due to the inability for the exhaust to properly breathe, which can cause un-burnt exhaust gases to reignite inside the catalytic converter. A clogged or failing cat can cause the vehicle to have poor fuel economy. " Apparently that would be bank 1 cat if you still have one?
Since you swapped coil 2 with 3 and problem has been detected at both 2&3; you might swap coils and injectors 2 & 3, with 5 and 6. Sometimes new injectors can be bad. Not positive you had the P0302 code before you changed all the parts. Just double checking.
If you have any fuel trim data at Idle and 1500 rpm and 2500rpm STFT and LTFT and under load at 3000 rpm, that might give you another set of clues to go on.
You might ask why. You actually might have more than 1 problem going on besides electrical. - Loose fitting electrical connectors and broken or disconnected vacuum hoses are often overlooked.
If you have determined that your ignition system is operating correctly, there may be a problem within your fuel system that is causing the random misfires. The following should be checked to ensure the engine is getting the proper amount of fuel: Check fuel pressure. Low fuel pressure can cause intermittent misfires on multiple cylinders (I know you are not getting multiple misfires- but that is not written in stone.) When the pressure is below the specification, the engine does not receive the proper amount of fuel and will start to lean misfire. The fuel pump or fuel pressure regulator could be the source of the low fuel pressure. (How to check fuel pressure). Check that the fuel injectors are functioning properly and activating. Random misfires can be a sign of faulty or clogged fuel injectors that need to be replaced.
If you have repaired the car already, please share results.
 

blake182

New Member
Aug 12, 2020
2
0
1
25
San Jose
Hello @dr.zed and @McFly2

Thanks a bunch for the reply! I really appreciate the input/help.

So crazy ending to this story. I bought a whole new injector harness off of ebay, I went to install it and it was slightly different. The one that was on my car was basically 3 separate harnesses where the new/used one I bought was a single harness. I checked all the pins on the main connector and it seemed to match the current one so I said screw it and tried it anyways. I removed two of the three current harnesses from the car and replaced them with the new one. I left the third one and just didn't plug those connectors in from the new one (it seems like it is the same it is just all wrapped up into a single harness. The new harness basically combined the injector harness, the alternator harness and another one into one neater/cleaner one. I am not sure which one is supposed to be stock but in the end they were the same).

Anyways, I then drove it a couple days waiting for the IM readiness or the check engine light to come on. I got to work one day and the IM readiness was good to go on all the important checks to get it smogged so I didn''t even shut the car off and went straight to smog. I left it running there too and got it to pass which was great because that was all I was trying to do in the first place. I then went to work. After work on the way home, the light came back on but I didn't really care because like I said all I was really trying to do was pass smog. The car runs great other than the little misfire when idling cold.

I then saw your reply @dr.zed and thought I would move my battery back to the front. I disconnected it and started to do it, but then got distracted so I just put it back together how it was (battery in the trunk). Disconnecting it cleared the code again and the light hasn't come back on since!!! I have been driving it for 2 months now and it hasn't come back which is super strange. I thing the problem was power related from the battery/alternator plus just a crusty old injector harness. I think moving the battery to the front actually would have also helped/solved the issue but since it went away after all that, I haven't touched it.

Also just for reference @McFly2, I did try swapping other coils and plugs (from cylinders on the left side) and that didn't help either. The misfire stayed on cylinder 2 and sometimes 3. I was also checking fuel trim constantly. When it was cold and felt like it was misfiring, it was adding fuel (STFT). Then when it was warm, it seemed to level back out.

There is still a little issue because the gauges still sweep on start up which apparently means the dash is not getting power but honestly the car is running great and the check engine light is gone so I don't even care. I still think I will move the battery to the front in the near future and see if that helps anything but if not I am happy and it is time to start adding some forced air!

Thanks again for your responses! I really appreciate the help!

-Blake