Error Code PO303, suggestions needed please on how to fix. :(

[yadfgp]

Hey guys :)

About a month ago or so, my check engine soon light came on, took it to a local gas station, they said it was code PO303 cylinder misfire detected. He recommended a couple of things, check the spark plugs and the coil pac assembly, and to also try some fuel additive. He said the spark plugs looked fine, so he said that the coil pak assembly should be fine to. I tried the fuel additive and no go, the light is still on. So anyways, the car drives fine. I have a 2000 Grand Am SE btw. It's got 62,000 miles on it. Also I checked the gas cap, and its nice and tight. The light stays on all the time. Except for after a week or so, it will go away for a day or so, but then it will come back on for a week or so, then it will go away again for a day or so etc... Also sometimes when I start it, every once in a great while, the light for the traction control will be on for a couple of minutes, and then go away on its own.

[SE2000]

Thats a big problem with the V10 engines, unless you got the diesel. I assume you have the 4 cyl. I would replace the plugs and tighten up the connetor that attaches to the plug. Otherwise, the coil pack is probally the culprit. There are no plug wires so that should do it.

[yadfgp]

Ok, great, thanks alot for the help. I do have a 4 cylinder. So even though that 1 mechanic I took it to said the spark plugs were fine, I should get them replaced anyways do you think? He's not a certified Pontiac mechanic or anything like that, just a guy at the local gas station. Just wanna make sure were on the same page before I go through with this. Any ideas on an estimate for the plugs, connector and coil pak? Thanks again for the advice so far :)

[MantaGreen97]

Originally posted by SE2000
Thats a big problem with the V10 engines, unless you got the diesel.

WTF??? V10? Diesel??? He's talking about a Grand Am here, not a Dodge Ram, lol...

[SE2000]

Could not pass up the V10 crack, too many people leave important details out when they ask for help. The plugs will be less then $10 for the set, The connector is part of the the coil assembly on top. Have no idea the price, but not cheap. The plugs are electrical but they wear like a mechanical part and 6 years and 62k means they paid their dues. Mine looked fine and I have more miles,same year. The platinum plugs should last as long as you own it.

[rixGAphx]

Originally posted by SE2000
Could not pass up the V10 crack, too many people leave important details out when they ask for help.
:D :D Phew, had me goin' there for a while, too!
The plugs will be less then $10 for the set.
On which planet??

More like $4-7 EACH.

For the GA, ALWAYS use ACDelco Platinum

[/B][/QUOTE] The connector is part of the the coil assembly on top. Have no idea the price, but not cheap. The plugs are electrical but they wear like a mechanical part and 6 years and 62k means they paid their dues. Mine looked fine and I have more miles, same year. The platinum plugs should last as long as you own it. [/B][/QUOTE]
Well, all engines manufactured in 2000 were certified by the manufacturer to the EPA to be emissions-clean for 100,000 MILES (~160,000 km).
This includes plugs.
62,000 km/~40,000 miles) is well within the range that plugs *should* still be VERY servicable: Tips not very worn/burned, gap still within specs (~0.050", IIRC).
AND, the mechanic LOOKED at them; can't ask for much more IMO.

Unless he truly IS "just a guy at the local gas station", in which case he should never even be looking under the hood.
Not to say there aren't many qualified mechanics at local gas stations; there are.
Only you can assess his qualifications.

Go ahead and throw $20 or so at a set of plugs, but it's doubtful it will make any difference or solve your P0303 problem.
* * *

P0303 = Misfire detected cylinder #3.
Misfire = failure to fire, caused by EITHER:
1. Faulty ignition (coil, plug, plugboot/wire, ignition module, or rarely the PCM);
OR
2. Faulty fuel injection causing mixture too rich or too lean for ignition (injector bad or not firing (NO gas in mixture), injector clogged (lean mixture), injector needle stuck partway open (rich mixture).
Also, partially-clogged fuel filter (lean mixture, but usually on all cylinders) or weak fuel pump (again, lean mixture but usually on all cylinders).
Finally, a faulty front O2 sensor can be giving bad signals to the PCM which then causes a rich or lean mixture (but on all cylinders).

You've heavily-examined the ignition-related possibilities.
Time to take a look at the fuel-related causes of P0303.

IMO, if the P0303 were caused by a RICH mixture, the O2 sensor would be sending you a code.
Have you run a bottle of name-brand off-the-shelf FI cleaner thru the tank?
Cheapest thing to do, and has a good chance of solving the problem.

Hope this helps.
-Rick

[yadfgp]

That does help Rick, thanks! I did try the fuel injection cleaner and it didnt do the trick. Sounds like theres just way to many different things it could be! The guy at the gas station is a mechanic, hes been there for 15 years or so, so he seems very qualified to me. It's just that it's not a bigger more service and repair oriented garage is all. I'm wondering what I should do next though. It'd be great if i could just take it in and say "I need this done" and be done with it. Should I just take it to an aforementioned shop that does all kinds of major service and repairs and see what they say? I can just see it now... "You need a new this, this, and this, and for parts and labor for all that your looking $1000.00" :(

[Triolent]

I had a similar problem a few months ago. I had a real bad shudder in my engine (2.4) and it was generally running bad. However, I did not have the SES light come on at all.

Anyways, I took it to a mechanic, who put it on their computer. He was able to tell me exactly what the problem was, which turned out to be cyl #4 misfire. Then they proceded to tell me that it was most likely a coil pack going bad, or ignition control moduel, so I might as well replace all of it while they were at it.

Well, that was fine. However, the prices they quoted were off the wall. Now I know that shops make some money off these parts, BUT

quoted $250 for a igntion module - $139 at Autozone
quoted $50 for each of 2 coil packs - $32 at Autozone
no wires, no rotor, but AC Delcos ran $7 or so each

ALSO, certain Autozone stores are able to test your ignition module in-store! I had a fellow hook mine up and it tested bad. This meant I didn't have to deal with buying parts that I didn't need, etc. He also checked my coil packs and let me know that they were OK ($100 savings!). He stated that the resistance should be around 4 Ohm, IIRC. So you may want to give that a try as well.


Fuel injector cleaner doesn't do much, IMO. I have, however, put it in an old Toyota and watch it chase away the SES light from time to time. But that's not a car that I really care about either...