Bought an Alero...bought a p0303...need help.

[Markline]

My wife and I bought a 1999 3.4 Alero. The car looked great inside and out with only minor interior and exterior flaws. At the time, the engine ran very good, we test drove it 15 or 20 miles...ran great. We purchased the vechicle then drove it another 40 miles home with no problems. The next morning the check engine light came on before it got out of the driveway. Ran a scan for codes and came up with P0303 (Misfire on #3 cylinder). Then the search began, here's what I did:
Changed out #3 spark plug wire.
Switched out #3 and #2 plugs.
Swithed out coil packs.
Tested module with test light on #3 cylinder coil pack terminals while spinning engine over (Test light blinked brightly and consistantly).
Compression check #3 (135) #2 (130).
Decided to replace #3 fuel injector, and as I pulled out the injectors I noticed #3 injector intake oring was missing. I thought it might have fell on the valve(valve was closed) but with a bright flashlight I could not see the oring. I could see the valve and around the valve plainly but no oring. I blowed compressed air in the #3 injector intake hole several different times hoping if the oring was in there it would move in a position where I could see it, but it didnt so I assumed it was not on the injector from the start. Maybe this is my problem..sucking air around the injector. So I bought new orings for all the injectors and checked resistance on all which ranged from 12.6 to 12.9ohms. #3 injector check out at 12.6. Checked the new injector to compare with, it check at 12.6 also. I also tested injector wire from injector plug to another larger plug on top of the engine with a test light, it was fine.
To save $85.00 I gambled and reinstalled the #3 injector, but moved it to #2 cylinder so if there was something still wrong with that injector the next scan would follow it. So I started engine, it ran for 5 mins. and you know whats next...lights on. Ran a scan, came up with P0303 again...now this could get exspensive. Whats next? Intake gasket? Head gasket? Wire harness?
Can anyone please help? THANKS!

[blazes9395]

I was going to say injector for sure,....but you diagnosed that already. From here I would get the coolant system pressure tested, see if its holding proper pressure.

[Markline]

I will definately try that coolant pressure test. Thanks.

[Markline]

Well I finally did a coolant pressure test. Borrowed one from Autozone but the adaptors would not work on my surge tank (threaded), and could'nt find one eleswhere that would work so I T'ed to the bottom radiator hose.
On cold test it held well at 10 and 15 lbs. for about 15 mins. I then realeased air pressure, cranked engine and with HOT pressure test it took around 13 to 15 mins. to reach operating temp. with NO signs of dramatic air pressure jumps indicating a blown head gasket on a water jacket.
While the engine was running I pulled #3 wire off coil pack and there is a noticable difference in the way the engine runs and has a very good spark, not only visually but I felt it if u know what I mean lol.
The engine runs smooth when cold but as it warms and the hotter it gets the worse it runs.

Could it be the Converter clogged?
If it's the Intake Gasket, is there anyway to know other than just replace it and hope for the best?
Please read my thread above to see all I've done so far.
Thank you in advance for any help you can give!

[BNaylor]

To test the CAT converter just run an automotive vacuum gauge (0-30 in-hg) and run the rpms up to a range of 2K-3K rpms and see what vacuum does. Connect to the upper intake manifold. If the gauge decreases below 15 in-hg and towards zero there is excessive exhaust backpressure or a clogged CAT. The problem with misfires is it will cause the CAT to heat up and may damage it.

What brand ignition wires and spark plugs to include heat range are installed? Most misfires are secondary ignition related.

[Markline]

Plugs are AC DELCO 41-940.
Plug wire brand is Packard.

[BNaylor]

How many miles do you currently have?

The Delco 41-940 double platinum spark plugs are the OE (original equipment) plugs and same for the Packard wires. I bet you still have the cylinder numbers on them which are only on the OE wires.

[Markline]

Yes, the wires do have the cylinder #'s on them. I don't know how many
miles the plugs have on them but visually they look good.
If you will notice above in a previous posting I did switch out the #3 wire which had no effect. Would u recommend these plugs in this vechicle?

[BNaylor]

Hard to say on your issue without running further in depth diagnostics using a more sophisticated full function odb-ii scan tool like a GM Tech 2. The misfire history counters have to be looked at to see the inter-reaction of weak or bad secondary ignition components like spark plugs and ignition wires to include coils. That is the one of the problems with DIS "waste spark" systems although they are fairly reliable. One coil fires a pair of spark plugs that are opposite each other in the firing order.

You didn't say how many miles you have. If these are the original spark plugs then replacement may be over due since they are supposed to be replaced NLT 100K miles. Also, look very closely at the ceramic part for cracking or carbon tracks. The ignition wires should be inspected at 100K miles but very closely. You can run a resistance check with a DMM on each one just to be sure. As far as the Delco 41-940 plugs they are excellent but finding them may be hard to come by. You can use other suitable alternative plugs. The current recommended AC Delco plug is now the 41-101 Iridium. Gapped at .060". These are made by NGK for GM. We use NGK TR55IX Iridium which are similar to the 41-101 and Taylor Spiro Pro Silicone 8mm ignition wires in our '02 Alero GL2 versus the recommended AC Delco Premium Silicone 7mm replacement wires which are made to replace the original Packard brand.

[Markline]

First of all thanks for all the good info. Nice pic also. The odometer reads 160,000. I know this is alot. Dont know if these are actual.
I just purchased this car and what really caught my eye was how clean it was under the hood including the engine. Not as nice as the one u posted, but clean. Before buying I removed the valve cover fill cap and looked in...it was very clean, no sludge (maybe the oil has been changed regularly). I know this doesnt say much for rest of the engine, or the heads may have been off recently, but that had a big influence on me buying it.
The car really looks great inside and out. Well worth I think to get back in good running condition as long as my funds hold up...lol.
You are mentioning wires and plugs. I'm getting a P0303 (misfire on #3).
I did switch #3 and #2 plugs and wires (like a trade off). I did move the coil packs as well.
Are u saying I need to replace all plugs and wires?
I may be a dumb but I thought I eliminated wires and plugs as I explained in my opening post. I guess that shows how much I know...Thanks again!

[xeroinfinity]

One other thing you might check is the injector wire harness. These tend to get damaged over time and cause shorts in the pulse signal which fire the injector(s).
When the lower intake gaskets get changed is when the wires are most likly to get damaged.

I find it very strange that 75-80% of misfires are always on cyl #3.

You can also goto a stealership and request a repair history report, its free. This would tell you what, if anything, was ever repaired under the warranty or by a dealer.

[Markline]

Thanks xeroinfinity. I did check #3 injector wire with a test light from injector plug to another larger plug on top of the engine. Seemed to be fine, at least the part of the wire thats underneath the upper intake manifold. You reminded me of an oil change sticker inside the windshield from a shop thats run by someone I know from years ago. I bet they could probably tell me some things the previous owner was tight lipped about.
Or maybe didnt know. No disrepect intended. I know if I keep digg'in, and with good help like you guys we will fix this thing. Thanks again for the info.

[Markline]

I'm going to replace wires and plugs. I did find the AC DELCO 41-940 at Autozone. What is a good wire at a parts store normally stocked that I can purchase now rather than have to order?

[xeroinfinity]

I personaly dont know of any good wire sets from part stores, maybe napa has a 7.5-8 mm wire set.
One other thing I forgot was the ground for the injectors is on the LI , make sure its tight.


Those Taylor wires are nice Bob.

[BNaylor]

Thanks JC. Best part although 8mm wires is they still fit in the stock wire loom holders and the cost. $44.00 through PFYC.com.

The only other plug wires I would use are the AC Delco Premium Silicone 7mm wires.