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Stubborn Check Engine Light?


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Showing 1-14 of 14 posts in this discussion
Initial post: Feb 23, 2012 11:49:49 PM PST
mdarkpoet says:
Just looking for some feedback. I have a 1996 Mitsubishi Galant that keeps giving me the "Check Engine" light. Every time I read the code it's a p0303 cylinder 3 misfire. I changed the spark plugs and cables as a first priority because the previous owners I purchased the vehicle from hadn't changed them in quite some time. The problem had been fixed but now and then the code will return. I'm wondering if there's another underlying issue such as a fuel injector issue or coil. Thoughts?

Posted on Feb 24, 2012 7:25:40 AM PST
A. Good says:
try taking off the pos. battery cable for 30 to 45 secs. this should clear the code in the computer

Posted on Feb 24, 2012 6:26:53 PM PST
look closely for any sign of corrosion on the post on the ignition coil. also make sure you are using a high quality ignition wire set (i only use NGK in my shop, as long as it is available). to check the wires, try misting them lightly with water, and see if the vehicle begins to run rough. look closely for any arcing on the number 3 wire - try spraying it in the dark. a leak will light up like a christmas tree. that can also be used to check for a leaky coil. good luck!

In reply to an earlier post on Feb 24, 2012 6:51:59 PM PST
JackV says:
If it still has a distributor and rotor, replace those too. If it only has a single coil it would affect all cylinders.

But if it has coil packs, then yes, replace the coil first.

Fuel injector would be left.

That check Geoff noted in the dark is a very good way to detect leaks, but not a bad coil if it's internal.

Posted on Feb 24, 2012 7:10:09 PM PST
Carl G says:
Disconnecting the battery is not the recommended way to clear the trouble codes as it may cause other issues. The best thing to do is use a code reader to clear the codes. If the codes stay away then the problem is resolved. http://www.check-engine-light.com/reset

A code P0303 may mean that one or more of the following has happened:
Faulty spark plug or wire
Faulty coil (pack)
Faulty oxygen sensor(s)
Faulty fuel injector
Burned exhaust valve
Faulty catalytic converter(s)
Running out of fuel
Poor compression
Defective computer

If there are no symptoms, the simplest thing to do is to reset the code and see if it comes back.

If there are symptoms such as the engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders (i.e. spark plugs). Depending on how long the ignition components have been in the car, it may be a good idea to replace them as part of your regular maintenance schedule. I would suggest spark plugs, spark plug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.k.a. coil packs). In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors.

http://www.obd-codes.com/p0303

Posted on Feb 24, 2012 7:30:04 PM PST
Last edited by the author on Feb 24, 2012 7:47:35 PM PST
JackV says:
He has a reader and he says it "keeps giving" implies he's resetting the code.

The way I read it is that he sort of fixed the problem, just not completely. Which means that if the ignition coil is marginal, it would do exactly as described.

spark plug + wire (he's replaced that for all)

Coil pack, injector are next. Coil is easiest and cheapest and most likely

He can check for bad valves by doing a compression check. If bad, just keep driving :) Btw, that's identical to exhaust valve, so sort of redundant. Intake is much rarer.

The rest would affect all cylinders. It's more a generic catch all. It might be 3 and then 1 and then 4, etc. Sometimes these descriptions are not useful and border on nonsense. Running out of fuel? Don't see how a catalytic converter can cause just #3 misfire.

Assuming an accurate description, should be the coil or injector, otherwise replacing the plugs/wires would not have made any difference.

In reply to an earlier post on Feb 25, 2012 9:05:19 AM PST
Hi!
You should pull the #3 spark plug to see what it looks like. If it's black, it could be a cylinder problem(what's the compression reading for that cylinder compared to the others?) If the compression is OK, then you may have a leaky injector. If the plug is clean, then you may have a lean issue.
You should get a scan tool to check your fuel trim percentage. If it's high (above 10%), this means that the computer is adding extra fuel to compensate for a problem. It may be a bad injector, or even an intake leak.
The scan tool should give you freeze frame data(a snap shot of what the engine was doing when the code appeared). A low rpm reading from the data may indicate an intake leak. First things first...check the plug first.
Good luck!

Posted on Feb 25, 2012 10:09:34 AM PST
mdarkpoet says:
Thank you for all the imput. I had reset the code in the past before I changed the plugs and cables, now that the code has returned I can safely say the problem is elsewhere. When I took the spark plugs out they looked old and in need of a change but nothing abnormal. I'm going to replace the coil first and see if that helps, if not I guess I have to just keep going down the list to determine the issue. I wouldn't be surprised if I ended up replacing some of the fuel injectors as well seeing as the previous owners of the vehicle had left it sitting for a while. What I'm thinking now is it just needs to be given a thorough cleaning out maybe???

In reply to an earlier post on Feb 25, 2012 11:05:10 AM PST
My concern was what the new plug looked like?
If you think it might be an injector, you can swap out the # 3 with another cylinder. If the misfire moves to that new cylinder, then it's the injector. If the misfire stays, then it may be a cylinder problem.
With respect to the coil, if it's s single coil system, the misfire would affect all of the cylinders, no just #3.
Just my 2 cents worth.
Regards!

Posted on Feb 25, 2012 11:36:08 AM PST
Carl G says:
Other than the light being on, how does the engine run?

In reply to an earlier post on Feb 25, 2012 12:36:47 PM PST
Last edited by the author on Feb 25, 2012 1:03:44 PM PST
The vehicle's computer is looking for slight changes in engine rpm. If a cylinder is not contributing its fair share, there will be slight changes in engine rpm that you would not notice. The whole point of the strategy is to protect the catalytic converter. In your case the misfire is "slight", where an injector may be dirty or mechanically hanging up causing an intermittent "hiccup". The slight misfire could also be caused by an intake leak at that cylinder. That's why I recommended swapping the injector with another cylinder to see if the misfire moves to the cylinder that you just moved it to. If the code comes back for cyl #3, then a compression check for that cylinder is in order. If you find that the compression is OK, then I would look for an intake leak. This is why the freeze frame data from the scan tool is critical. If you want, I can get into how to check for an intake leak.
Just trying to help you from spending money.
If you want to take a gamble, you could try a bottle of fuel injector cleaner. You might get lucky!

Posted on Feb 25, 2012 1:20:05 PM PST
Carl G says:
Nicholas, you responded to my question. I am not the one who is having the issue. That would be mdarkpoet.

In reply to an earlier post on Feb 25, 2012 1:33:41 PM PST
Sorry!

Posted on Feb 25, 2012 5:26:12 PM PST
Taggert says:
Check the harness that plugs to the #3 injector. Look for oil, corrosion, any wire showing. I've had more than a few marginal harnesses that gave this symptom under heavy load or heat. With engine running and codes cleared, wiggle this connection and listen. See if you can get a miss of any sort.
I've also had oil buildup around a particular spark plug cause an intermittent misfire situation. Make sure plugs and the surfaces around them are clean and clear of debris and oil.
What about driveability? is it impacted at all? Can you feel this miss/misfire at idle? Under heavy acceleration? Never/always?
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Discussion in:  Automotive forum
Participants:  7
Total posts:  14
Initial post:  Feb 23, 2012
Latest post:  Feb 25, 2012

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