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Swapped spark plugs. Car stalled at 1st stop light

JEDI

JEDI

Lifer
2005 mazda3 automatic

Back in Aug I bought new spark plugs (Iridium).
In Dec i swapped them out for new OEM sparkplugs. (unplugged battery each time.)

Yesterday (Feb) i put back the Aug spark plugs.
i drove 3 blocks then stopped at a red light. I saw my tachometer go below 500 RPM. WTF?!
Then the engine stalled. I turned off the ignition then restarted.

Drove fine for the rest of the day, plus today (~100 miles).

Why would my engine stall after putting back spark plugs that were in my car only 1/2 year ago?
 
Anything removed to change the plugs...? Possibly a sensor not plugged in or not secured all the way...? Possibly a leak on the intake side if you removed something there to put the plugs in...?
 
Bartman39 said:
Anything removed to change the plugs...? Possibly a sensor not plugged in or not secured all the way...? Possibly a leak on the intake side if you removed something there to put the plugs in...?
Click to expand...

only thing removed was the positive terminal on the battery, and the spark plug wires.
 
I'm curious...why did you go back to the August spark plugs? Was there something wrong with the way the car was running with the OEM plugs?
 
JEDI said:
only thing removed was the positive terminal on the battery, and the spark plug wires.
Click to expand...

Then with that said I agree it was still in learn mode and idle is the most finicky part of it besides fuel trim in cruise which gets the MPG`s up... Figure you have the positive off for several min so it lost the stored memory... First time you let off it was not sure what the heck to do...😵 (or more to the point just could`nt respond quick enough and properly) But the more you drove the better it would get as would the MPG`s as well...:thumbsup:
 
JEDI said:
so how did the car stalling affect the relearning process?
Click to expand...

It prob stalled while learning. Normally, you just let the car sit and idle for a few minutes to learn it's idle control. Usually with accessories turned off.
 
LTC8K6 said:
It prob stalled while learning. Normally, you just let the car sit and idle for a few minutes to learn it's idle control. Usually with accessories turned off.
Click to expand...

Yeah I wouldn't worry too much about it..after an ECU reflash my Subaru's idle will occasionally drop very low as well. Once it relearns everything, it's fine.
 
JulesMaximus said:
I'm curious...why did you go back to the August spark plugs? Was there something wrong with the way the car was running with the OEM plugs?
Click to expand...

gas milage.

original oem iridiums that came w/car had 36mpg hwy.
i replaced those w/compatible iridiums at 80k miles. (manual said 60k..😱pps ) but they only gave 34mpg hwy.

so decided to bit the bullet and buy oems to get back to 36mpg hwy.
to my surprise, it only gave 32mpg. 🙁

so i decided to go back to the compatible iridiums.
 
LTC8K6 said:
It prob stalled while learning. Normally, you just let the car sit and idle for a few minutes to learn it's idle control. Usually with accessories turned off.
Click to expand...

ahhh.. sit idle. next time...

but by stalling, it didnt affect anything? the ecu learning just left off at the point where i stalled?
 
JEDI said:
gas milage.

original oem iridiums that came w/car had 36mpg hwy.
i replaced those w/compatible iridiums at 80k miles. (manual said 60k..😱pps ) but they only gave 34mpg hwy.

so decided to bit the bullet and buy oems to get back to 36mpg hwy.
to my surprise, it only gave 32mpg. 🙁

so i decided to go back to the compatible iridiums.
Click to expand...

Are you calculating the fuel economy or are you going by what the computer says your fuel economy is?
 
JEDI said:
ahhh.. sit idle. next time...

but by stalling, it didnt affect anything? the ecu learning just left off at the point where i stalled?
Click to expand...

No, it wouldn't have bothered anything. It will learn properly even if you drive it, it just takes longer to get the idle correct versus letting it sit there.

Stalling won't "confuse" it or anything. 😀
 
This worries me. You shouldn't be swapping plugs on a whim like that, IMO. It's just not necessary. Threads, overall, are fragile. I hope you're at least threading them in by hand first.

Also, as someone else mentioned.. are you using new crush washers?

Spark plugs, overall, are cheap. You should have just installed new ones.

It IS possible that different spark plugs are causing different MPG numbers, but I'm skeptical in your case. There are just too many variables.

But like I said, it is possible. It most likely isn't due to the type of spark plug though. With the Insight, for example, the spark plugs are indexed. There is a stamp on the head for each cylinder, A, B, C or D. You buy the corresponding A, B, C or D plug, and this makes the ground electrode point towards the intake valve that opens all the time(the 2nd one only opens when VTEC is engaged, ~3,000RPM in my case). I have heard that the spark plug doesn't matter, and you're welcome to use the equivalent plug of your choice - but if you don't index them and the electrode happens to be pointing away from the intake stream, you could suffer up to a 10MPG loss, overall.

Anyway, my car is an extreme case. It makes sense that the equivalent for your car would be a couple MPG like you mention, but I don't know how you would practically measure the difference, without properly controlled tests.
 
Throckmorton said:
Are you using new crush washers each time?
Click to expand...

what are crush washers?
i didnt see any washers when i removed the original spark plugs that came w/the car

eli:
good point in that i should have just installed new spark plugs.
also, on the OEM ones i removed, there's alot of carbon around the threads. that normal for spark plugs that are 7k miles old?
 
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