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

blake182

New Member
Aug 12, 2020
1
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
 
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dr.zed

Member
May 17, 2020
14
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.