2001 Nissan Sentra 1.8L P0303

Ok..... I know that cylinder 3 is misfiring. I thought that it was the coil pack. I switched coil packs from cylinders 3 and 4. P0303 came up again. When I have the car running and I pull up the coil pack off of the cylinder 3 plug my car does not bogg down like it does if I were to pull the others. I changed my spark plugs about 3 months ago so I don't think that's the problem. I put one of the old plugs in just to check and it didn't make a difference. Car sputters and shakes when I drive. Shakes bad when i'm in 4th gear at about 1500rpm - 2000rpm. Please Help!

Switch injectors from cylinders 3 & 4 and see if the code changes.

Also, perform a compression test.

Good luck and keep us posted.

Thanks. I'll give it a try when I get out of work. It's snowing like a bastard here! I'll keep you posted!

Ok.... I switched the fuel injectors from cylinders 3 & 4 and P0303 still came up. I also got the code P0300 right after I put the fuel injectors back on. I erased it and it didn't come back. I figured it had something to do with it needing a second to refill the injectors with gas. I'm stumped!

And the compression test...?

Also check for vacuum leaks on the intake gaskets in the area of cyl. #3. Make sure you do this when the engine is cold.

Do you do alot of city, stop and go driving?

How do I do a compression test? I checked the gasket and it looks like a have a very little leak. I do a lot of stop and go driving.

Just a bit of info for those of you that are getting a misfire code PO303 on a 2001-2003 Sentra with the QG18DE 1.8L motor.

One of the possible causes is coolant leaking into #3 cylinder . I have worked on two cars this week with a PO303 code. One is a 2002 Sentra and the other one is a 2003, both with the 1.8L engine. I did the usual checks (Vac leaks, plugs, coil, injector) and everything checked out o.k.. Both customers stated that the engine would run rough for a few seconds when starting the car after it had sat overnight. I duplicated the problem on both cars.

The next step was to pull the #3 coil and spark plug and apply pressure to the cooling system. After sitting with pressure for about 20 minutes I looked into #3 cylinder with a light and notice some liquid collecting on top of the piston. I determined it was coolant and realized that this is the cause of the misfire. I have not taken apart either engine yet so I don't know if the problem is a bad haed gasket or a cracked head, but I hope to get into the repairs soon??

So keep this in mind if you find yourself with a PO303 code on one of these Nissan Sentra 1.8L engines. I hope this helps someone out there.

chasr212r
"...I have not taken apart either engine yet so I don't know if the problem is a bad haed gasket or a cracked head, but I hope to get into the repairs soon??..."

Any conclusive info re these sentras with the PO303s?

My sentra is an 02 w same reading and symptoms - suspicious of similiar problem.

Check the # 3 ignition coil harness connector.
Does it has voltage supply ?
Are all the wires ok ?
Check for shorted, damaged or broken wires, on the entire harness.