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My baby is making bad noises ...

dmention7

dmention7

Hater
I also posted this here: http://www.mazdas247.com/forum/showthread.php?t=123773862


Quick backstory: About a week ago, I started noticing a momentary hesitation that would randomly pop up when I was around 8-12 inHg vacuum. I pulled a P0171 code (system too lean, bank 1 O2 sensor). Did a bit of reading on causes and decided to throw some seafoam in the gastank in the meantime. For the next couple days the car was running great, without a hiccup in sight. Then yesterday I had about a 3-4 second episode of misfiring while accelerating slowly from a stopsign. Threw a P0300 code for the random misfires, but nothing else for the rest of the couple miles home.

Then this morning, I fire up the car to go to work, and I'm greeted by a moderately loud rhythmic ticking that sounded like it was coming from the passenger end of the motor (not sure if that's #1 or #4, haha). It came and went if I gently revved the motor, and faded away after about 2 minuted of idling. I took the GF's car to work just to be safe. When I got home, it was the same thing.

At this point I don't really know what to think... if I had a rod about to give up the goat, I don't think the noise would go away as the motor warms. Sounds too loud and regular to just be spark knock. I also don't know if the prior symptoms are part of the same problem, or if they were indicators of a problem about to happen. I know how hard it is to play internet mechanic, but I'm hoping I someone can get me pointed in the right direction, or at least narrow down the possibilities.


Right after a cold startup:


After a minute or so of idling:



EDIT: a few other (possibly) helpful bits... 108k miles on the motor. I've been running 7.5psi for the last year or so (spikes as high as 9 though) but I don't really beat on it. Never had a lick of trouble with anything mechanical or electrical on the car in the past.
 
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dmention7

dmention7

Hater
So, I'm just planning ahead here for the worst case scenario. If I do have to go ahead and do a rebuild, how prudent is it to only replace the pistons, rods, and rod bearings on a motor with over 100k miles? I'm pretty confident about going that far in my garage (and not having to bogart one of my parents' cars for too long), since that can be done without pulling the motor. But if we're talking about dropping the crank and having to yank the motor, that's where I'm inclined to take it to a shop. And also where the price starts to more than double over just doing pistons/rods.


Also, thinking about the next-to-worst-case scenario, having caught the rod knocking while the engine still runs normally, can I expect to get away with just doing rod bearings?
 
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mndsm

mndsm

I'M OFFENDED!
Yeah, if I had to take a guess, I'd imagine either the rod bearings are on the way out, or you have a cracked piston ring.... other possibility includes a failing oil pump. Have you checked the pan for shavings? That will tell you right away how bad it is.....
 
dmention7

dmention7

Hater
I plan to drop the oil pan tomorrow and take a look.

As far as a failing oil pump, I do have an oil pressure gauge that I eyeball religiously. At startup, it's sitting around 55psi at idle. Clogged passages are a possibility I suppose, but I change the oil in this thing religiously with good oil, and I haven't heard of that being a weak spot on this motor. Though, the design of the oil pan is such that oil pressure can tail off during hard cornering at high rpm. But I really don't flog the car very much either.
 
dmention7

dmention7

Hater
When I fired it up this morning, the noise was far less noticable, but still there. I got under the car for a listen, and I don't think it was coming from the bottom end (hard to say for sure though) so I decided to work from the top down. Pulled the valve cover and checked the clearances on all the lifters, and they all checked out okay.

Anyone else got anything I should look at in there before I run out for a new valve cover gasket? Otherwise, I'll report back once I get it buttoned back up and take another listen.
 
D

DrWebster

Guest
Not sure what to suggest looking at next, but that certainly sounds like something in the top end.
 
dmention7

dmention7

Hater
Actually I just heard from a dude on 247 who was certain it's a timing belt tensioner. He suspected my earlier symptoms were from some slack in the belt causing intermittent timing issues (hesitation/misfire). I've been meaning to do that this spring anyways, so I guess I'll park the MSP for this week and tackle that next weekend. No dyno for me :(
 
Big Nate

Big Nate

Chaos Engineer
Timing belt sounds right to me. I mean the noise comes from the timing cover so sure swap it.

Or it could be your motor just getting pissed at you for not cleaning it..............I mean you have to try to keep your motor that dirty.
 
dmention7

dmention7

Hater
LOL Actually, when I pulled the valve cover I was surprised at just how clean it was in there. But you'll also be happy to know that while I had it off, I gave the cover a good cleaning on the outside as well.
 
M

Matt D.

Guest
Is that engine an interference engine? With mention of the timing belt tensioner have you bothered checking the timing marks? Line the crank up at TDC and check the marked on the cam gears to see if they line up.
 
dmention7

dmention7

Hater
It's funny, Matt. I have heard just as many reputable sources claim the FS-DE is an interference motor, as claim it's not. Which causes me to go on the safer assumption that it is, and leave it parked until I check all that out.

But when I was checking the lifter clearances, I did indeed line up the timing marks on the cam gears several times, so it hadn't skipped a tooth or anything (yet). Also, it was running way too smoothly to have had the timing off measurably. With the exception of the few infrequent symptoms I mentioned, it was running great.
 
dmention7

dmention7

Hater
Timing belt, tensioner and water pump have been replaced; mystery noise persists. Though it's still quieter like before... I haven't heard it as loud as in the video except that one time.

Someone on 247 suggested piston slap, which is sounding like a good guess to me... thoughts?

Or does anyone have a plausible idea of a catastrophic problem this could be? Otherwise I'm probably going to go on the assumption that since it goes away after a minute or two of idling, it's just a sign of an aging motor, and keep on driving for the meantime. Though, I'll start saving my pennies for a rebuild later this fall/winter...
 
Workdawg

Workdawg

NARWHAL
My only thought is...


I slapped your mom with my piston.

Okay, fine. Not my ONLY thought. I don't know much about engines, but I'm willing to lend a hand if ya need.
 
dmention7

dmention7

Hater
Not yet. I plan to try that some evening this week.

The noise was coming and going (as loud as the original) on my way to work this morning... same thing on the way home. blargh
 
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