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1998 Mazda 626 ES
07-05-2010, 03:36 PM
Post: #1
1998 Mazda 626 ES
My 1998 Mazda 626 ES sedan has a misfiring #2 cylinder. It causes very noticeable abnormal vibrations at all times including idling, but especially when accelerating uphill.

I have taken it into a mechanic several times and feel like I am getting the run-around. The first time, he said it was a clogged fuel injector. After he cleaned it (not replaced), the ride was smooth but that lasted about 200 miles before the vibrations returned and the check engine light came on again.

I then had my oil changed and asked the shop to take the distributor wire off the #2 cylinder and show me the spark plug. He showed it to me and he examined it. He said it was worn, but not shot and that it shouldn't be the cause of my problem.

So I took it into the mechanic again again and he said it was an issue with the spark plugs. He replaced it and the car seemed fine for another 100 miles before the vibrations returned again.

I am a grad student on a very tight budget. I cannot afford going back and forth like this. I need some help!

If you have any suggestions or happen to know a good, honest mechanic who will properly diagnose and repair my car in the Baltimore, MD area, I would be much obliged.
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07-05-2010, 11:47 PM
Post: #2
RE: 1998 Mazda 626 ES
Repeat problems usually have a root cause and I don't think we have quite enough info to go on here.

The plugs have been out but no mention of fouling or obvious discoloration. If they are marginal it might be wise to replace them anyway. (plugs are cheap and labor is expensive) While the plugs are out it's also a good idea to check the compression just to make sure the 12 year old engine is ok otherwise. If the check engine light was on there are codes in storage that we need to know. Have it scanned, post the codes here, clear the codes, and see what codes may come back in a few days with a second scan. Post those codes here as well because the most recent code is going to lead us somewhere. Many parts stores will do a scan for free if you ask nice.

BTW, how many miles on this car? Does it use any oil or coolant? How is the fuel economy when it runs ok? Is it hard to start? Any unusual noises?
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07-06-2010, 03:53 AM (This post was last modified: 07-06-2010 04:00 AM by psu lions.)
Post: #3
RE: 1998 Mazda 626 ES
The guy who changed my oil showed me the plug. The plug when removed had a little bit of oiliness to the exterior portion. The terminal that sparks was black and soot colored (like the inside of a chimney). He sniffed the plug and said something that I forget, but he proclaimed that the plugs were worn but not shot and he didn't see anything glaringly wrong. He's a guy at a retail shop, not a mechanic, but I took it at face value.

After that, the sparkplugs were replaced by my mechanic on the second visit and the problem has begun again.

If it helps identify some possible causes, the misfiring also gets worse with use. Right now, I have driven it about 150 miles since the last visit with the mechanic so the misfiring is not constant. But based on past experience, in about another 300 miles, it will be fairly constant misfiring.

Mileage: 120,000
Oil: No abnormally large loss of oil. Its generally towards the low end when I hit the 3000 mile oil change mark. If I postpone the oil change, I add a quart.
Coolant: My dad has told me that there is a small leak in the coolant system (unknown location), but again, not a large amount by any means.
Starting: No problems, quick start.
Noises: No abnormal noises other than the thumping caused by the misfire.
Vibrations: I can feel the misfire as the car shakes and I can feel it in the accelerator under my foot as well.

I was told that the code was for a misfiring #2 cylinder. But I'll go to Autozone tomorrow and get the codes read so I can post the specific code and have it cleared tomorrow.

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07-06-2010, 10:06 AM
Post: #4
RE: 1998 Mazda 626 ES
OK, this is more helpful.

The fact that there's oil on the outside of the plug may be a clue that the plug wire is also covered with oil on the end, which may be breaking down the insulation, which causes a misfire, which eventually fouls the plug. Recalling this engine has the plugs through the center of the valve cover with long plug wire ends and at that age / mileage it would not be unusual to need both a valve cover gasket and a set of wires.

Let's see what the codes are and if that gives us any more clues.
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07-07-2010, 12:13 AM
Post: #5
RE: 1998 Mazda 626 ES
The error codes are:

P0302 and P0304 - both are cylinder misfire codes.

Something new started happening today while on my way to Autozone to have the codes read. One of the distributor plug/wires was popping out of place causing more misfires in that cylinder (middle cyl on the front of the engine). I am guessing engine vibrations from the misfires are causing it because these are fairly new distributor wires (less than 18 months old).
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07-07-2010, 09:39 AM
Post: #6
RE: 1998 Mazda 626 ES
The first code is #2 and the second code is #4 cylinder.

With no other codes to go on it could be a number of items getting marginal (coil packs?) or something in common. (ignition module?) I'd start comparing the problem child with the others if the compression is ok and there are no other mechancal issues. If it's got weak spark then maybe you can get away with a single coil replacement. Hard to say from here. If the coils are interchangable you may want to try a swap with another cylinder and see if the problem moves. That may pin point a bum coil without spending any money.
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07-07-2010, 11:29 AM (This post was last modified: 07-07-2010 11:30 AM by psu lions.)
Post: #7
RE: 1998 Mazda 626 ES
I'm sorry. All of that was way over my head. I dont know what coil packs (or how to swap them) or the ignition module are, and I have no idea how to test the compression. Could you explain that to me?
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07-07-2010, 11:37 AM
Post: #8
RE: 1998 Mazda 626 ES
That does present a problem because this forum is geared toward do-it-yourself types looking for ideas and willing to do the work or finding someone who is willing to do it for you.

BTW, as expensive as dealers seem to be they are also the experts in their given field and may be able to solve your problem is half the time of a local garage. You could also ask freinds and neighbors who they have had good luck with for repairs.
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07-08-2010, 10:29 PM
Post: #9
RE: 1998 Mazda 626 ES
okay. thanks for your time!
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07-12-2010, 01:45 AM (This post was last modified: 07-12-2010 02:14 AM by psu lions.)
Post: #10
RE: 1998 Mazda 626 ES
So I made a fairly long distance trip this weekend and noticed other trends with the problem.

1) There is little to no misfiring at high speeds ( >60 mph)
2) If I accelerate slowly on a highway, I dont get any misfiring. By slow I mean it might take me a 1/2 mile to get up to high speeds.
3) Accelerating up a hill causes rapid misfiring

Does that help eliminate possibilities?
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