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Eric, Automotive Repair Shop Manager
Category: Car
Satisfied Customers: 31064
Experience:  Automotive Repair Shop Manager, Technician/JA Mentor
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I have a P0305 code. Ive replaced a lot of parts and there

Resolved Question:

I have a P0305 code. I've replaced a lot of parts and there is still the same code. Any advice?
Submitted: 7 years ago.
Category: Car
Expert:  Eric replied 7 years ago.



It would help to know what parts you have replaced at this point, also were any of the parts tested before replacing them?

Customer: replied 7 years ago.
I already replace the following parts:

All Sparks - Motorcraft (Original replacement)
All Coils
Low Air Sensor
2 Fuel Injectors (without noice) (
Air Filter
Compression already checked and is Ok

Also the fuel Injectors where for pistons 5 & 6.
Expert:  Eric replied 7 years ago.



Ok, have you checked for injector pulse on #5 injector, and have you checked for #5 coil firing?

Customer: replied 7 years ago.
Yes both, I heard the pulse on th F. Injector, it's a new one.

Also there is a noice of the firing on the coil 5 when it's removed.
Expert:  Eric replied 7 years ago.



What was the condition of the spark plug on #5 when you pulled it? Have you pulled the new one to see if it is dry or wet? have you done an engine compression test on that cylinder?


Sorry for the questions, but as I cannot inspect it, I have to depend on as much info from you as possible. thanks for the patience

Edited by Eric on 3/11/2010 at 12:41 AM EST
Customer: replied 7 years ago.
No, that spark is dry.

The spark color is gray.

About a year ago I replaced the manufacturer ones with another with 3 lines.

By the weekend it was giving me the same code, I erase the code, replaced the sparks with the original ones, after that it was working fine, but today the code arrive again.
Expert:  Eric replied 7 years ago.



I havent asked yet, but with the code set, do you notice any driveability or performance problems, or just getting the check engine light on?

Customer: replied 7 years ago.
It has enough power, like new. It's just rough idle.

Today, sometimes after being on a road stop, the check engine start flashing and it presents some driveability performance, but after start moving it works fine.

Note: I haven't replaced the oxigen sensor, but I don't know if they can be related to this issue.

Also the Mss Air Flow sensor was cleaned using carburator cleaner.
Expert:  Eric replied 7 years ago.



While cleaning the MAF sensor with carb cleaner is not a good idea as it can damage it - always use electronic parts cleaner spray(auto parts store sells it), in this case if it did damage it you would have a code for the MAF sensor and more than likely a lean code such as P0171 or P0174. Also the Oxygen sensor would set its own code as well.


The grey on the spark plug indicates that it has good fuel/air ratio and burning the fuel good.


Just to eliminate a possible sticking valve or intake leak, I would suggest doing a cylinder compression test to see if #5 cylinder is 10% or more lower than the other cylinders.


If ok, I would next get a noid light and test for continous signal from the pcm to the injector. I have seen where the injector fires but erratically causing the misfire code.


Noid lights are about $10 at a parts store:



This simple plugs into the injector harness in place of the injector. crank engine and observe for steady pulsing light. If not present, then either a loose wire at terminal, open/short in wiring, or faulty pcm.


You can eliminate loose wiring at terminal by doing a simple wiggle test. Wiggle wiring harness and see if misfire smooths out.


If it doesnt, then physically inspect harness for nicks, cuts, frayed wiring insulation, or exposed wiring.


If ok, then the pcm needs to be tested with a factory level scan tool for proper signals going out to both the injector and the coil

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