zacschmuker

Mazda forums are pretty inactive, it appears this isn't.
hopefully you can help me out a little bit. Since it's the same motor. Among other things I guess. I'll get to the point.
My sister has a 93 626 V6 auto. It wouldn't start the other day. Put a new fuel filter on, it was a cheap guess. Started right up. So I was warming it up, making sure it was OK. I went through the distributor issue already, and didn't want to tow it again.
I walked out of the garage while it was running. When I came back less than 5 minutes later, it was knocking. Checked oil, not low. It's coming from the rear cylinder head. Sounds like cylinder 5, but hard to say for sure.
Is there any common weak point up there? Just looking for ideas before I tear in to it.
Almost forgot, it's got about 165k miles on it.

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R.S.LOGAN

When you say " knocking " do you mean the big ends knocking or top end knock ?

zacschmuker

It's not a rod knocking. I pulled plug wires one by one with no change. Not an injector. It's definitely top end though. Maybe you could call it a tapping type noise. It's a loud tap, or a quiet knock. Six of one, half dozen of another. I thought maybe, for example, valves bend. Or lifter problems are common. It's too cold here, so I won't be getting to it for a couple weeks. But if when I do get in there, there's something I should look for. It would be appreciated.

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R.S.LOGAN

May be a hydraulic tappet / lifter sticking .Could try an oil and filter change or an additive for clearing sticking tappets or both .

zacschmuker

Going to try that. But I had a thought today. Are there any sort of baffles on the valve cover? I'm thinking, if there are, it may have come loose, and the cam lobe is hitting it.

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CatSkinner

Never seen baffles in them, but I've not seen them all.

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R.S.LOGAN

As Cat says , most are just lids . But I'm sure some have other bits and bobs underneath , just cant remember which ones . Something like this for example ,

CIMG3367.jpg Photo by nevik78 | Photobucket

zacschmuker

That's what I'm talking about. There's that extra plate on there. It appears to for the pcv valve in the pic. But does the rear one has something similar? Do you know?
Also, I just a compression test. I don't know if my gauge is correct, but I got 125-130psi on all 6 cylinders. So I don't think it's a valve issue.

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R.S.LOGAN

Psi's are all even , not bad for year and mileage , wont be a valve .Never known or heard of any plate on cam cover coming loose or causing knock .But there's always a first .If it's at the top end , I would think it's more likely to be a hydraulic tappet / lifter sticking .Remember and use a good synthetic oil if changing oil and fliter .