Good morning everyone. What should have been a 20 minute fix is now going on 4 days. Started as a leaking front fuel rail. I stopped the leak easy enough, but then it ran really rough at an idle. Checked the engine code and P0303 came up, cylinder # 3 misfire. Cut to the chase, I replaced plugs, wires, coil pack and even swapped the injectors between cylinder 3 and cylinder 6. Still it's a P0303 code. My son in law says that it didn't run rough before he parked it when he noticed gas leaking. While it was parked he checked the oil, it was about a quart low, so he topped it off and accidentally overfilled it just a bit. From what I gather that would not create a localized misfire code.

I am not smelling burning oil, it is not leaking oil, so I don't think its a head gasket. Someone said check your cam/crank sensors. I put a can of Sea Foam in the fuel tank with half a tank of fuel. If it was bad gas shouldn't I get more of a random misfire?

Also, I read somewhere that the P0303 code does not necessarily reflect the third cylinder, but the third cylinder in the firing order. Can anyone confirm which cylinder would be associated with a P0303 code?

ANY help or advice is GREATLY appreciated. Thanks for reading!!!

 

From my background , I have noticed Fords did from time to time indicate the wrong cyl with a misfire problem.
Everybody checks the plug, the injector , the wires,,but rarely look for a valve spring problem. Depending on where the spring breaks, it may not be easy to spot, but could still be producing a problem..
There is a function , Mode 6, that could be helpful in possibly providing some guidance to the problem.
That is where an experienced shop might be more helpful.

 

Thank you for the reply Hanky. I doubt there is a broken valve spring, the car only has 88,000 miles on it.

One thing I noticed is that it feels like only the front brakes are engaging. It's really hard to stop. I'm going to burn off the last 1/4 tank of gas and put in some Chevron or Shell gas and see if it's just bad gas.

Do you know where the crank and cam sensors are?

Thanks!

 

Checked fuel pressure at front fuel rail with ignition on ACC and it was less than 5 PSI. Checked it with the car running and it was about 40PSI. Shouldn't there be more fuel pressure in the rail with the key on accessory?

 

We're in a lot of fog here.
Fuel pressure IS NOT CHECKED with the key in the ACC position.

 

Thanks again. I usually connect my fuel pressure gauge to the fuel rail with the car off. Then when the gauge is attached I usually make note of what the pressure in the rail is with the ignition in accessory position and the fuel pump engages. I usually wait until the fuel pump stops making noise, note the fuel pressure, then start the car and note the fuel pressure again. I'm used to seeing more pressure in the fuel rail with the ignition in the accessory position before starting, but that's neither here nor there. I'm getting close to 40 PSI with the engine running and that should be plenty of pressure for those fuel injectors to atomize properly.

I took the fuel injectors from cylinders 1, 2 and three, and swapped them with their respective fuel injectors from cylinders 4, 5 and 6. Still it's a P0303 (cylinder 3 misfire) code. Tells me that the injectors are doing their job. So, to recap:

Replaced coil pack, spark plugs and spark plug wires.
Verified fuel pressure adequate at 38 PSI
Verified fuel injectors are all functioning
Replaced intake manifold gaskets
Verified alternator voltage 14V
Checked all vacuum lines

The EGR gasket did not come with the Felpro kit I got. It was not in terrible shape, but it was not in great shape. I did spray some carb cleaner around the EGR valve after reinstalling it and did not notice a change in RPMs.

The chances of an intake or exhaust valve faulting between the time the car was parked when it was leaking fuel and when we started it again after repairing the leaking fuel rail are virtually zero, but I am still considering mechanical failure a possibility. I think more likely something was already on the verge of faulting under the hood and it got bumped, jostled, or helped along the way to complete failure while we removed and replaced the fuel rail. What drives me nuts is that there isn't anything you need to remove to get at that front fuel rail. All we did literally is remove those two 8mm bolts holding down the fuel rail and lift. I suppose it's possible that a tiny amount of debris made it into the combustion chamber through the fuel injector holes, but we did blow it off with compressed air before we removed the rail, and that would be AFTER the fuel injectors so a trivial amount of debris making it into the combustion chamber should not have made any difference.

I'm wondering if while the car was parked overnight at the auto parts store someone poured something into the fuel tank(like water). We ran 1 can of Seafoam with the half a tank of gas, burned off all but 1/8 of a tank, then added 4 gallons of Shell gas. It seems to be running a little smoother, not trying to die so hard. My plan is to run the rest of the gas out of the tank and fill it up again. I don't know.

I don't see how it could be mechanical failure, but I am at a loss as to what else could be generating this P0303 code. I guess I could try getting some fuel stabilizer, another EGR valve gasket and a fuel filter to see if that helps. We took the fuel filter out and it was very easy to blow through so at the time the filter was good, but that was before we ran the Seafoam through the system so it could have dislodged buildup and gunked up the filter a bit. The car had been sitting for a year or so, but we have been driving it for a few months without any issues. Drives great, actually. Less than 90,000 miles on it. Was owned by an old guy who passed and stored in a garage.

Again, thanks for your help!

 

Just about all the things you have attempted apply to all cyls. You need to concentrate on 3 CYL ONLY.

You may need to do a compression check on a few cyls incl #3 and see if you can spot anything different. It could be a valve seating problem.

 

Is there a way to stop the fuel injectors from dumping fuel while I perform a compression test without disconnecting the fuel injector connectors?

Also, I noticed an oily buildup inside the intake manifold which I believed was from a bad PCV valve that was probably bad for the last 5000 miles. We cleaned the upper intake off the car with carb cleaner making sure to avoid the sensors. Then we sprayed Seafoam intake cleaner AFTER the MAF into the whole system through the throttle body. Changed the spark plugs during all this. Seemed to run better after that for a while, but still rough idle. But it does seem to have more power now.

Anyway, I want to do a compression test...do I have to remove the fuel injector connectors to stop them from dumping fuel while cranking, or can I just unplug a sensor somewhere?

Thanks again!

 

If you pull the fuel pump fuse while the engine is idling, it should run out of gas. Now perform your compression test. It won't inject fuel without fuel pressure.

Let us know what results you get, thanks.