Check Engine light code PO303
 

Hello Ford Enthusiasts, could use your help with this one. i have a 1997 f-150 4.2L v6 190,000 miles first time my check engine light has ever come on since ive owned it. i took it to auto zone to scan for a code it showed a P0303 code which according to them was a miss fire in no.3 cylinder. So i changed the spark plugs and wires, problem still there, im not sure that it is a missfire because the only time it shudders or misses is at 1475-1525 rpm. This is what i have narrowed it down to, possible a fuel injector or a ignition coil maybe, would like to hear some opinions on this if it could be this or possible something else.

Check Engine light code PO303
 

Hey Dawg. Have you ever changed the coil pack? I would start with the coil pack, given the miles on your pickum-up We have a few f-150s
that have high miles on them with no problems with the injectors. Have changed the coil packs. Let us know what you did.

Dave Powell:-X15

Check Engine light code PO303
 

Just to let you know hoss i'm going to change out my coil pac later today and ill get back with you then to let you know if that worked or not. until then have a wonderful day.

Check Engine light code PO303
 

>Just to let you know hoss i'm going to change out my coil
>pac later today and ill get back with you then to let you
>know if that worked or not. until then have a wonderful day.

Check Engine light code PO303
 

My 3.8 Windstar dropped a cyl, it was the coil pack too. I dropped #2 cyl.

Check Engine light code PO303
 

I know this is an old post but with the engine idling apply vacuum to the EGR valve. If it starts to miss then the EGR ports are clogged. If they are all free it should die. To get to the ports you have to take the upper intake off. This is a common problem with 4.2 and 3.8 split port engines

Check Engine light code PO303
 

I have the same problem on a Chev. Lumina 3.1 P0303 misfire on cyl 3. The engine sounds fine, can't detect a misfire. After clearing the code it will appear in less than 20 miles later. Did the coil replacement solve your problem? Whne you changed it out did you have to cleart the code or did it clear itself?
smilie(':-fire')
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Check Engine light code PO303
 

i changed the coil pac out the check eng light went out it came back on the next day went and got code retrieved again same po303 missfire no. 3 cyl. finally got tired of trying to fix it so i took it back to dealer to see if they could fix it they retrieved the same code he said that i left the spark plug loose which ive checked a couple of times he said they had it fixed when i got in my truck the light was out but soon as i pulled on the highway it came back on so i went had code pulled again same thing po303 still not fixed so im left to believe it possible an injector but if it was an injector stoped up it would set a code for it any suggestion would still be greatly appreciated.

Check Engine light code PO303
 

test for clogged EGR ports like I explained a couple of posts earlier. Common problem with the 4.2

Check Engine light code PO303
 

Could a cloged EGR valve only effect cyl #3 with code P0303? I swaped coil packs... same error code, plug wire 4.6k ohms OK. This engine 3.1 6 cyl Chevrolet Lumina shows no signs of a misfire it seems to run OK....But I feel I am not getting good gas mileage around 17mpg. This code comes on after about 2 to 3 trips and 25 miles.
Could the injector for cyl #3 stick open forcing occasional too much fuel and cause a intermitent misfire?
How does this ODBII system detect a misfire?

:-X09

Check Engine light code PO303
 

I said EGR ports, not a valve. What happens on the 3.8 split port and 4.2 is every port except one gets clogged so all the EGR gases go into one cyl leaning it out.

Check Engine light code PO303
 

My son replaced the plugs and wires about 8,000 miles ago, with no problems at all during that time. Then about 1,000 miles ago, the "check engine" light came on and stayed on. I rechecked the wires and checked for vacuum leaks, and found nothing wrong. AutoZone ran the codes and we first got a code P0300, which is a "random multiple misfire". Not much to go on. They reset the computer and a couple weeks later the "check engine" light came on again. A code P0303, "plug 3 misfire" popped out of the computer. I checked plug 3 and found nothing wrong. The weird thing is that this afternoon the "check engine" light went out, and has not come on again after about 50 miles of driving.

My son-in-law, a Ford mechanic, had previously told me to run some injector cleaner through the engine because he thought the number 3 injector was clogged. Turned out he was right. I ran Lucas injector cleaner through three tanks of gas and the "check engine" light mysteriously went out this afternoon. This may be of help to you if your "check engine" light comes on again and you get a code P0303.

I checked the #4 and #5 plugs and no fouling was noted.

The "check engine" light came back on today!

Code P0303 was stored. Misfire plug #3. Guess I need to look at that plug too?

misfire #3
 

hello, first time here... I had the same problem with my 2002 f150 2wd 4.2L. It has 85000 miles 40 of it in last year alone. I had been fighting the misfire for 3 months, my p0303 code accompanied by various other codes, multiple recommendations by ford, might of been my ultimate demise, but I hung in there and after changing spark plugs 2 times the plug wires once, all the o2 sensors that would be 4 of them. multiple fuel injector cleanings, mas air flow sensor, air temp and iac, I still had the same problem, misfire would come and go, and yesterday the truck couldnt take it anymore, it started sputering, jerking when driving. so I went online to read what everyone had to say. I took the suggestion and checked the egr valve, and ports. found that the egr wasnt getting a vacume pull even at high rpm. checked and found the vacume silinoide was not operating at all. $25 later truck is running great no codes no check engine light.. so check if you have a vacume at the egr vacume port connection.. it just might work