P0303 code

FORDHOG

MEMBER
2002 FORD EXPLORER
4.0L
4 CYL
2WD
AUTOMATIC
150,000 MILES

Check engine light came back on after changing the spark plugs, wires, coil pack, number three cylinder fuel injector. The obd codes were 303 and 316, misfire in number three cylinder and misfire on first 1,000 revolutions. Reset code but engine still runs rough and check engine light is still on. What next?

4 Replies

FORDHOG

MEMBER
2 POSTS

I have reset the computer to clear, started the car, ran it for a minute, shut down, then rechecked codes. Still got a PO303 and PO316 for a misfire in #3 cylinder and a misfire after the first 1,000 revolutions. Check engine light still on and still runs rough.

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Friday, October 4th, 2019 AT 8:06 AM

SCGRANTURISMO

MECHANIC
4,897 POSTS

Hello,

This might be a problem with the compression in cylinder #3. Could you please do a compression test of your vehicle's engine for us. Here is a link below explaining how to do this, if you are unfamiliar with the procedure:

https://www.2carpros.com/articles/how-to-test-engine-compression

Please go through this guide and get back to us with the results. We can go from there.

Thanks,
Alex
2CarPros

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Friday, October 4th, 2019 AT 11:48 PM

SLYJACKSON

MEMBER
1 POST
1999 FORD EXPLORER
6 CYL
2WD
AUTOMATIC
13,900 MILES

I've changed the wires, plugs and the coil. The engine still runs rough at startup and I get the PO303 code. I have also check the valcuum line as well. This is really getting annoying. Do you think it may be the EGR valve? I'm told that it may also be a head gasket problem but I don't seem to have lost in water in the radiator or reservoir. Any help is appreciated.

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Monday, December 21st, 2020 AT 1:48 PM (Merged)

MERLIN2021

MECHANIC
17,250 POSTS

If you have done a vacuum check, and no leaks found. Test the injector at cylinder 3. Use an ohm meter on the other injectors to determine what the reading is, then check #3. Use a noid light on it to test the harness, they are cheap, and sold at part stores.

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Monday, December 21st, 2020 AT 1:48 PM (Merged)