Replaced spark plugs and car won't run?

P

pbm

Joined
Apr 19, 2004
Messages
10,964
Location
New York
I finally got an opportunity to do some work on my daughters 2021 Mazda CX-30 as she's away on vacation (she lives an hour away from us and works a lot). The car has almost 88K miles so I changed the AT fluid for the 2nd time (D&R), oil& filter, air filter, cabin filter etc...I noticed her brake pads were nearly shot so I did a pad slap (I had the pads and the rotors looked good). I then noticed the rear brake pads were almost shot so I ordered pads from RA which surprisingly came the next day.
Yesterday I went out when the engine was cold and replaced the OE spark plugs with new NGK Rutheniums and then proceeded to replace the rear brake pads after putting the e-brake in 'maintenance mode'. When I went to start the car after finishing the brakes it stumbled and stuttered and sounded terrible. I assumed it had to be the new plugs as it ran fine after the 1st day's maintenance so I put the old plugs (which looked pretty good for the miles on them) back in but no change. I checked the wiring to the coil packs and all looks good. I disconnected the battery overnight and even touched the positive battery terminal to the negative for an hour to reset the ECM to no avail. I'm wondering if the 'ebrake maintenance mode' procedure caused the computer to get flaky? Any ideas from those more knowledgeable than I....I'd hate to have to flatbed it to the dealer?

PS: At first after changing the plugs I was able to drive it around the block with low power and stumbling etc...but now I can't even get it to run.
 
I learned my lesson about disconnecting a battery without a backup to hold the ECM settings on my old RAV4 when I changed the battery at 300k miles. The ECM must have adjusted settings so far from baseline over all those miles that it barely ran with baseline settings at 300k miles. It sputtered and stalled out until it got started and the ECM learned what to do. Your 88k miles is probably not enough miles to cause such an extreme response running at baseline settings. Do you have one them in-line spark plug tester things? Maybe the coils are not seated properly on top of the spark plug?
 
The E brake process has nothing to do with this. Assuming that you gapped the plugs properly before installing and torqued plugs down correctly...the only thing I can think of is perhaps a coil pack(s) lost the spring inside that connects to the plug top and carries the voltage or you bent pins reconnecting the coil plugs? Also check around the motor for any vac lines or evap lines that may have gotten knocked loose or cracked.
 
Did you umplug MAF? Is there a CEL?

How dirty is tb?

If one terminal is disconnected the length of time touching them together shouldn't matter. Discharged capacitors are discharged capacitors.
 
Leo99 said:
I learned my lesson about disconnecting a battery without a backup to hold the ECM settings on my old RAV4 when I changed the battery at 300k miles. The ECM must have adjusted settings so far from baseline over all those miles that it barely ran with baseline settings at 300k miles. It sputtered and stalled out until it got started and the ECM learned what to do. Your 88k miles is probably not enough miles to cause such an extreme response running at baseline settings. Do you have one them in-line spark plug tester things? Maybe the coils are not seated properly on top of the spark plug?
Click to expand...
I had the same on an '01 RAV4. Would initially not start after a new battery, then started but barely idled. In time it'll figure it out.
 
Pull the battery cable again and try to start it after a few hours. Also you're not giving it gas while cranking or worse holding the pedal all the way down like how some do thinking it'll make it start faster. That usually disables the fuel injectors and doing a full sweep will disable and enable then disable again. Did you get the rutheniums from RA? Those can be faked and can at times cause engines to barely run. I've never once had this issue in any vehicle i owned and i've let plugs go over 100k.
 
JavierH19 said:
Pull the battery cable again and try to start it after a few hours. Also you're not giving it gas while cranking or worse holding the pedal all the way down like how some do thinking it'll make it start faster. That usually disables the fuel injectors and doing a full sweep will disable and enable then disable again. Did you get the rutheniums from RA? Those can be faked and can at times cause engines to barely run. I've never once had this issue in any vehicle i owned and i've let plugs go over 100k.
Click to expand...
He said he put the old plugs back in but problem persists. Something else is being overlooked here
 
Step back and look at the specific actions you performed right before encountering the problem. Since it won't run properly with the new and old plugs, the issue is not with the new Ruthenium plugs. The e-brake servicing procedure should not prevent the Mazda from driving correctly unless they are still engaged.

Therefore, the deductive process leads you back to disconnecting the coils. I'd examine the condition of the contact spring terminals inside the coil boots and focus on the proper connection of each coil wire connector, including position. Also, scan for any codes (existing & pending) in case something failed coincidentally (such as a bad crank position sensor), however improbable.
 
I've tried most of the recommendations except 'examining the contact spring terminals inside the coil boots'....which I'll try today. I'm trying to get a friend to stop by with his (expensive) multi-tester. I'll keep you guys posted. Thanks for the replies.

PS: Just in case I damaged a plug installing it (which I doubt)....I took out the NGKs and installed brand new Autolite Iridiums that I had purchased before deciding on the NGKs (bought at RA). I had installed Autolites in my inlaws 2015 Mazda CX-5 (with the same 2.5 Skyactiv engine) about 100K ago and they still run flawlessly) Same stumbling with the Autolites so I dooubt it's the actual plugs but maybe the coilpack springs as some have suggested.
 
Last edited:
It's bound to be throwing some codes. I agree with the above posters, something to do with coils probably. Doubt it's the plugs as the old ones aren't working either.

Edit: If I remember right (I may be wrong) do you have to disconnect the fuel line to get to one of the plugs? Or, possibly reconnect the cables incorrectly (wrong order?)
 
Last edited:
GMBoy said:
...the only thing I can think of is perhaps a coil pack(s) lost the spring inside that connects to the plug top and carries the voltage or you bent pins reconnecting the coil plugs?
Click to expand...


1775831770789.webp



Exactly what I was thinking. When I changed plugs on my CRV the springs inside the boot were all loose.
 
Urshurak776 said:
It's bound to be throwing some codes. I agree with the above posters, something to do with coils probably. Doubt it's the plugs as the old ones aren't working either.

Edit: If I remember right (I may be wrong) do you have to disconnect the fuel line to get to one of the plugs? Or, possibly reconnect the cables incorrectly (wrong order?)
Click to expand...
If its never restarted will it throw codes? I am not sure it will?
 
KrisZ said:
It's likely the throttle body needs cleaning. I had that same thing happen on my old mazda 3, but it would just stumble and idle super low. i guess it's the compensation algorithm that got reset when the battery got disconnected. Cleaning the TB should fix the issue.
Click to expand...
Yep I’d try this first too. And put the NGKs back in!
 
You must log in or register to reply here.

Similar threads

HyundaiAbuser
Helping a coworker by servicing 2016 Honda HRV
Replies
15
Views
418
rszappa1
B
Thoughts on Maintenance Items for My 2017 VW All Track
Replies
12
Views
584
RobbS
T
2017 Fusion - Replaced NGK plugs-Issues
Replies
4
Views
196
tig1
N
NGK Ruthenium HX spark plugs in a 2025 3.5 Liter Ford Ecoboost
Replies
11
Views
496
charbaby
B
2009 Chevy Cobalt Low on Power
Replies
14
Views
192
379KITTY
Back
Top Bottom