can non mazda spark plugs cause a misfire?

K

knubile

Member
Hey all,

Dumb question I know. Here's the gist.

This past summer my Pro5 was idling very rough and achieving a miserable 450Km per tank instead of my usual 550.

I had the plugs and wires replaced ahead of schedule. It was the best my garage could figure that was wrong. This garage is owned by family so there's no concern about them.

That didn't fix the problem. I took it to a mazda dealership that said they couldn't figure out what was wrong but they said it could be the aftermarket plugs. They said they don't fit right.
I figured that was just a cop out and BS.

Recently my check engine light came on and the symptoms got worse.
Thankfully though an actual error code!
Random/Multiple misfire.

I tried new plugs(a different kind this time) and new mazda coils. The problem isn't fixed. My garage couldn't figure it out. They even removed the timing belt cover(is that right?) to see if its possible it slipped and the timing was off. My garage hasn't charged me a nickel yet. They said they'll worry about that once we solve the problem.
They told me to take it to the Mazda dealership and have them diagnose it.

My appointment is tomorrow(Monday). I fear they are going to blame it on my aftermarket plugs and/or wires again.
Is there any validity to their claim that aftermarket plugs could be the cause? All common sense to me says no, but I'm seeking the advice of the Mazda forums.

If its not the cause, what can I tell them if they tell me that again? I am just amazed that the Mazda dealership themselves couldn't figure out what was wrong with their own brand of car last time. My bet is the same will happen this time.

What also amazes me is the "trial and error" nature of automotive diagnostics and repair, all at my expense. I would think in this day and age they could pinpoint the exact problem and replace the part and voila!

Edit: Oh ya. I have 127,000 Km on the car. Its a manual Pro5. Maintained as per the owners manual to a tee by my garage. Even had the tranny fluid replace trying to figure this problem out.
 
Last edited:
I read the title, and the first few sentences.

Just wanna ask. Bosche plugs by chance? Bosche plugs DO NOT work in any Mazdas. I don't know of anyone, in any car, that doesn't have terrible misfiring problems with Bosche plugs.

Maybe they only work in german cars?

Pick up some NGK V-power (copper.. CHEAP) ZFR5F-11, or if they don't have those, the BKR5F-11. Problem solved, unless your plug wires are defective. My Sparkco wires went bad after a while, probably due to getting wet and stuff. I have belden wires now, they seem to be pretty decent quality. If any store carried NGK wires I'd get those. You can order them online though. I think the OEM wires are NGK, don't remember at this point though.
 
Don't remember the exact part number but both sets of plugs I tried were NGK. Nothing like V-power though. Just letters and numbers.

Could a new set of wires be the cause? All plugs, coils and wires are new. What are the odds the new wires are bad?

Plugs and coils are maybe 2 weeks old. Wires are 4 months old.
 
Well the "normal" plugs from NGK are the V-power.. there's just a groove (hence the "V") in the copper.

There really isn't a good chance that the new wires are bad. I've used the NGK iridium plugs (the more expensive ones) and they work fine with the car.. they're just a lot more expensive and didn't last any longer for me. Where are you located (I'm guessing Canada)? Maybe someone else from the forums lives near you and would be willing to swap plug wires with you.

You're at nearly the same mileage (kilometreage?) as I am on my p5, I'm at 124,700. I haven't had to do this just yet but I know other people have. You know how there's two plug wires and then two of the plugs just have the coil mounted directly on top of them, with no wire? Those do go bad eventually, they're a wear item much like a distributor would be on some cars.

Mazda charges a lot of money for the part, but auto parts stores carry ones that they sell for around 18.99USD a piece. I think from the dealership it is 70-100USD a piece, and you need two of them.
 
Ya I'm in Ottawa. The dealer i'm dealing with is Carling Mazda. I've personally boycotted Bank Street Mazda after my lease buyout fiasco. That's a whole other story. :)

I have had the coils replaced and the plugs and the wires. Does that cover everything you are referring to, or is there another part in there? I think the mazda coils were $150CAD a piece.

I went mazda coils to avoid any "its not a mazda part" BS from the dealership.

Really. Can they claim crap like that? I'm not under warranty so its not like i'm trying to get anything for free.
Aren't there any kind of standards or regulations for aftermarket parts? You would think if a plug is sold for a Protege5 that it would fit. How is there a variable there?
 
Yup, that's everything. Totally understandable about keeping it to the Mazda OEM parts, but yeah since you aren't under warranty, it shouldn't make a difference. So the Mazda dealership can't figure out what is going on at all?

Oh and if you have NGK plugs/wires don't worry at all about them complaining about aftermarket stuff. The OEM plugs on Proteges are either NGK or Delsing (they used both) and I do believe the original wiring was also NGK. NGK is top notch stuff, they won't complain about it.
 
They couldn't figure it out last time, but this time the check engine light is on and the error code means Random/Multiple misfire. So hopefully they can figure it out now.

I've got my fingers crossed. Good to know the OEM plugs are also NGK. Thanks
 
bad spark plugs *cough*autolite*cough* *cough*bosch*cough* can cause the engine to run rough... but seeing as you put in the good s***, there maybe other underlying issues.... you may have a vacuum leak or EGR valve stuck open... check the vacuum hoses for leaks... also check the intake manifold gaskets for leaks, higher mileage engines in our cars are known to develop gasket leaks... if they check out fine, then it's most likely the EGR valve as lots of people seem to be having
 
the random/multiple misfire code.. she and I are dear friends. At one point whenever it would rain I would get that code (there's a vent in my hood that allows water to settle around the spark plugs). I just needed to replace the wires and plugs and it was fine. I hope the dealership can figure things out for you, let us know how it turns out!
 
Wonder if my garage checked for leaks. I'll ask them tomorrow. Seeing as how they checked if the timing belt slipped, I'm guessing they did.
I'm pretty sure its not the EGR valve. I had that go on me while under warranty. I know how the cars acts with the EGR valve stuck. This is different. Unless it could die differently i guess.
I'll see what they say tomorrow. I'm just hoping I don't get the "its probably your plugs" crap again.
 
So it was the EGR valve. It was causing a "serious vacuum leak". Good call TheMan.

Too bad they couldn't tell this in the summer. I'll keep an eye out now to see if my mileage has gone by up to the usual 550.

Thanks for all the info everyone.
 
TheMAN said:
check the vacuum hoses for leaks...
Click to expand...

How exactly does one do that - thoroughly?

I can imagine exactly four scenarios where it would be easy for me to spot a vacuum leak just by poking around in the engine compartment: 1) the leak makes enough of a hiss so that it's audible; 2) there's a visible crack in a hose; 3) a hose is completely pulled off it's connection; or 4) a hose clamp is blatantly loose.

If the vacuum leak was not kind enough to be quite so obvious, what would the next step be?
 
pasadena_commut said:
How exactly does one do that - thoroughly?

I can imagine exactly four scenarios where it would be easy for me to spot a vacuum leak just by poking around in the engine compartment: 1) the leak makes enough of a hiss so that it's audible; 2) there's a visible crack in a hose; 3) a hose is completely pulled off it's connection; or 4) a hose clamp is blatantly loose.

If the vacuum leak was not kind enough to be quite so obvious, what would the next step be?
Click to expand...

someone will yell at me for this for SOME reason im sure, but you could spritz some starting fluid (ether) around the engine compartment sparingly and see if there is any variation in engine speed. the vacuum leak will pick it up and suck it into the engine causing the engine to rev slightly. this is what ive been told to do in such situations
 
qualityrockola said:
someone will yell at me for this for SOME reason im sure, but you could spritz some starting fluid (ether) around the engine compartment sparingly and see if there is any variation in engine speed. the vacuum leak will pick it up and suck it into the engine causing the engine to rev slightly. this is what ive been told to do in such situations
Click to expand...


Wouldn't that be considered a serious fire hazard? Why Not just replace then with new.... regualr black vac hoses are dirt cheap even at napa. I've replaced 18ft of hoses on a friends 80 monza for about 7 bucks. Grant it easier to keep track of which ones have been replaced when you have the fancy color crap.
 
You know, my distance per tank has been down to 450km from 550km as well, just in the last two months or so! And I don't have a clue what the reason is. My idle has been fine, though.

In the summer I put in some long reach spark plugs so I'll check those when I get the time.
 
long reach plugs dont do s***. actually iirc they are just as bad as puttin bosch plugs in.
 
redpr5 said:
long reach plugs dont do s***. actually iirc they are just as bad as puttin bosch plugs in.
Click to expand...

The long reach plugs work JUST FINE in our engines. It's what the JDM cars use. NGK ZFR5F-11 is the long reach part number gapped for our cars. It actually smoothed out the idle quite a bit compared to the stock (BKR5E/F-11 IIRC)
 
Use carb cleaner (not ether) to find a vacuum leak at a manifold or T/B.

The hissing is really quite loud - take a hose off with the engine running - you hear what i mean! Also- rev the engine - some vacuum ports get vacuum at idle - others at 1500+rpm depending on the function.
 
clicknext said:
You know, my distance per tank has been down to 450km from 550km as well, just in the last two months or so! And I don't have a clue what the reason is. My idle has been fine, though.

In the summer I put in some long reach spark plugs so I'll check those when I get the time.
Click to expand...

My mileage dropped before the rough idle was obvious. Not sure if there's a way to check the EGR valve before its completely shot. Anyone?
A drop of 100km per tank of gas is significant. Something is definitely up. I tried transmission fluid, oil changes, tires with no success(these changes we are due anyways).

My guess would be check the EGR Valve somehow. You're burning up a lot of cash in fuel. Might as well get it fixed. I hope yours is as simple as an EGR valve.

Cheers
 
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