Hello I have a Mazda Millenia S (2001) with a 2.3L Miller Cycle Engine. The engine is missing (sounding like a rumbling diesel) when in drive and at idle. It is worse when the air conditioner is on, and it is really bad when braking to a stop (such as slowing down and gliding into a parking spot - it rum rum rumbles like the engine is going to stall).

My brother had me put it in drive and I popped the hood and held the brake while he looked at the engine. I could see the engine through the windshield and it POPS! like it's going to come out from under the hood.

I had the dealer run a diagnostic and the dealership suggests replacing left and right catalytic converters, and we did replace a broken Tee Valve (this seemed to improve acceleration but did not fix the missing).

My brother is an amateur mechanic and believes it is not the cats.

Keninn replied to my last post (https://www.mazdaforum.com/forum/maz...lenia-s-26390/) and suggested coils. We did not check them yet but I do know all 4 plugs were recently replaced (yes the mechanic could have dicked them up).


Thanks in advance guys/gals for any of your help.

Ryan

 

well, the millenia is a 6 cyl. so if 4 plugs were changed, 2 more need to be done. and it has a coil on plug system, so no ignition wires. but if the motor is jumping, your motor mounts are fubar, very common on the 2.3. and very expensive. and dont but the ebay mounts, they are junk. the missing is not related. you need to rescan your codes and repost them. and the precats are also common on this motor. but again, precats generally dont die on their own. a missing engine will kill the cats real soon

 

ok keninn, will do

 

Thank you Keninn.

Your info has been invaluable, and I appreciate your expertise.

My bro and I are going to be checking spark plugs this weekend for correct gap and wear this weekend. Do you have info on how to trouble shoot coil packs?

I don't know if this is legal or not but have you ever heard of anyone removing the precats and leaving the main catalytic converter on? Would performance be affected?

Thank you Keninn.

Ryan

 

the precats are part of the exh manifolds. you would have to run headers, or something similar, then you would have a huge problem with oxygen sensors, since they are also in the exh manifolds. then there is the emissions problems, and if you are in a state where emissions testing is mandatory, it will not pass the visual. the feds could come and take you to jail. then you end up with a bf cellmate named bubba.
the only plug i know of that comes from the factory with the correct gap is the ngk 3741. do NOT get a plug with an 11 or -11 after the part number, that gap is way too big. and you do NOT regap plugs with precious metals tips, like platinum, iridium, yada, yada.
you should mark the coils, and switch the rear bank coils to the front. the fronts get less heat, and last longer.

 

Ive found this site ( www.milleniatech.net ) very helpful. I do most of the work on my 1996 millenia S myself thanks to the service manual AND Kennin

milleniatech.net - Documentation

milleniatech.net - KL-ZEM (2.3L V6) Vacuum Hose Routing Diagram (1996+ Models)

These cars are ALOT of fun to drive but can be a pain when they're not running right. Hope these help

 

thank you rockoe, i appreciate it

 

@Keninn Thank you once again, I believe what we will do is core the pre cat (my bro says we'll only need to do one of them) - again I do not know if there are legal concerns for coring, but it appears that this supercharger burns these precats out. Keninn if you have any tips or pointers about coring, please let me know.

We got 4 of the coil packs off (the last two are kind of a pain - it looks like we'll have to remove some bolts and wiring to get to them).

The last owner did replace the spark plugs. They are this model: NGK.com - Application Search Results Keninn, this is the exact model you suggested, I believe, but they are however double platinum, which I thought you said was a no no. Please let me know.

Question: Can a clogged (it's clogged! a hole was literally burned through the block so air could pass!) precat cause missing (the diesel effect I described)? Or does it have to be a coil?

Thank you once again, Kennin. My bro and I like your blunt, direct style and appreciate it.

Ryan

 

iirc, the plug should have pzfr5f on it. if you want to gut the cats, then you should go to the other forum, Mazda Forums : MazdaWorld.org Mazda Owners Forum, you will have to register. then go to the millenia forum, and look for yel-low. he can gut them for you, but you might have to wait. if there is a hole burned thru, then you may have bigger problems. this place has aftermarket precats, and can probably make you one with no brick inside:
Mazda Millenia S Manifold Catalytic Converter 97-02 | eBay

while it will pass the visual, depending on where you are, it may not pass the sniffer
and i would not do just 1 side, the engine will be unbalanced as far as flow goes. afa the diesel sound, i would think it would be a hole in the exhaust.

when i do the plugs, i also pull the rear intercooler. that gives me access to the #5 coil and connector, which i have a hard time getting to. however, to pull the rear intercooler, the battery has to come out, and some of the wiring harness has to be moved. also, there are a couple hidden nuts that hold on the ic piping

 

Hello Folks:

So here's what we've done to the car:

1. Replaced all oxygen sensors (they were carboned out and it was too hard to tell if they were working, plus they were due to be replaced)
2. Checked spark plugs (they are the size and brand Keninn suggested) I will be honest we did not check the 6th (the hardest one to get to but I have documentation that says the shop replaced them and I believe they did)
3. cored the precats - they are cored and the temperature reading on both of them is even

After we took these steps the car was not doing the missing problem I described. It sat there idling for 30 minutes fine, then we drove it a mile and a half and it started doing the stuttering (missing) again.

I am at a loss.

I will say it does not miss when you slow down the car like it did before. And it seems to be running better, but it is still missing in a sort of lurching sluggish motion. What is going on?

Thanks for your suggestions.

Ryan

PS - The car seems to do better when it is cold. My bro also wanted to know if the supercharger may not be kicking in when it needs to. There is no smoke from it but could the supercharger not be engaging properly?

Car just gets bad when it heats up.

Thanks,

Ryan