Hello again, here is an update on the things I have done to my 2001 Millenia with 149000 miles on the 2.5L engine since my 7-31-09 posting: I put in the spark plugs keninn as well as the owners manual said to. Keninn, you were right, by the way. O'Reilly's said "either one of these will work". I did not sway.
I also put in new top end plug wires, a new distributor cap, and a new rotor. I put in the double platinum plugs, and my engine is very, very happy - she now has *****.
My hold light no longer comes on. My car does not downshift on its own like a possessed beast anymore And man, she really gets up and goes. YET, it does still miss every now and then. One thing I forgot to mention is this: About 2 months ago after giving it an oil change my buddy insisted on pulling out his pressure washer and spray cleaning my clean engine. For two days it ran just horribly, then I figured the moisture inside the d. cap dried out. But come to think of it, things have never been quite same since then. Is this relevant? Duh. I need your wisdom please. This engine neither burns nor drips any oil and I want it around for some time to come.
Thanks for your help,
Chris

 

the 2.5 seems to have a lot of problems with the distributor. and i dont need to tell you where your "buddy" can stick his pressure washer.

 

Yes, I know keninn, but what is done is done. Yet....
Anyway, after reading hundreds of these blogs, I wondered if there is a sensor or a part that could be the source of this periodoc missing. I recall something called a "knock sensor" maybe. Sound right? The infrequent missing is overshadowed by the way she runs so smoothily the vast majority of the time, yet it just scares me knowing something just is not right. Is there anything you or anyone else recommends I do to remedy this situation? Or do I just leave'er alone?
I thank you again,
Chris

 

i'm gonna have to pass on this one. i have no experience with a 2.5. i generally dont like to post unless i have direct experience with the problem. i do know that washing the ignitor(cam angle sensor) on the 2.3 has caused all kinds of problems, from no start all the way to slight miss.

 

Keninn is dead right to be outraged by what your buddy did. Water driven in like that can hang around for weeks doing mischief to ignition, alternator, fuseboxes, even engine and chassis grounds. Worse still, it can precipitate arcing over insulating surfaces of the ignition system, carbonizing or crazing them such that the damage done is irreversible.
(The same applies to "gunk addicts" only more so; anyway who the hell in their right senses wants an engine to smell like a railway tie on a hot summer's day?)

I don't know the exact layout of your ignition HT wiring, but if it's a recessed well type with insulator tubes going from the point where the HT wires pass through neoprene sealing caps down into the plug wells, that's a prime suspect for your problems. The injected water lies trapped in bottom of the plug wells, then as your engine warms up, some vaporizes and recondenses in the insulator tubes, causing HT leakage, hence misfiring once warm.
To rectify this, pull everything off the plugs but leave them in place. Get yourself some wood alcohol and a compressed air source.
Soak the insulator tubes in alcohol, and pour about a tablespoon of alcohol into each plug well to capture any water, then blow out the wells with compressed air.
Finally, remove the tubes from the alcohol bath and blow dry them too.
When everything is thoroughly dry, put it all back together. Don't rush things before you start the engine though because if there's any residual alcohol around you risk finding your hood in your neighbor's yard.

"The automobile engine is the meticulously crafted result of over a century of painstaking and dedicated engineering, which, when entrusted to the care of an idiot, can be destroyed in a matter of minutes." --- Oldeng.

 

Hi all, this is cristofire1 replying. Thanks oldeng for replying. My bud feels bad
about it. I think he might be afraid to even ride in my Millenia now, though he is always welcome. He too owns a "classic" of sorts. A 1970 Ghia. Sweet little thing. My Millenia is really a VERY nice ride. Especially with the double platinums I put in her. Man i am telling you she is like an old hooker with a new hymen - full of juice and ready to use it.
Anyway, I do still get that occassional missing. I will try what you suggested oldeng - the back three are indeed recessed. Someone also told me my problem could be in the knock sensor. Dont know exactly what that does though. So, I will do the "alcohol dry out thing (first me now my wheels)" and let you know what happens. Thanks for taking the time to reply - it is appreciated much.
cristofire1

 

From your previous comments, you have made a fairly convincing case that your knock sensor is not defective. If the knock sensor were misbehaving, or if your engine was knocking, (a) you would get codes thrown to show it, one being random misfire DTC P0300, the other being engine knock detected, DTC P0325; (b) the probability is that one or the other or both would set the CEL on. (c) You would certainly note that the car would downshift on you, especially when hot.
My take on what you've got is plug related; Mazdas are ignition system bitches, this means among other things the plugs are reach, gap, and heat rating sensitive. That porcelain insulating cone around the center electrode inside the cylinder retains heat, and if the cone mass and geometry are such that it keeps too much, the engine will pre-ignite (hot plug). If it doesn't keep enough, you get late firing at high speed (cold plug), costing you torque, fuel economy, and potentially misfiring at high speed.
If the gap is not correct, high speed or high load misfiring results. Some of the high end performance plugs have preset gaps which cannot be reset, so you might want to check out whether the new plugs you put in are really the right stuff.
If you still want to go for the knock sensor, it's like a bolt with a small cable ending in a connector coming out of the head. It's screwed onto the block, buried under the intake manifold deep in the cleavage between the two cylinder banks. To access it, you need to virtually strip the inlet system off the top of the engine, and will need to replace the inlet manifold gaskets, a bunch of cooling system gaskets and O rings, possibly the EGR valve gaskets etc. etc. At a garage, labor alone is about $300.
Take Henry Ford's advice: "If it ain't broke, don't fix it."
If you want to mess with your engine, why not go to a dealer who's got the full kit scanner, and get a full OBDII hard copy printout of your car's state of health?
That way you'll know what if anything has to be attended to, and what to anticipate in the not too distant future. The cost of the scan is about the same as the cost of replacing one significant engine component which didn't need to be replaced in the first place.