New spark plugs, occasional misfire

Status
Not open for further replies.
A

avacado11

Joined
Aug 12, 2015
Messages
801
Location
NY
Replaced the spark plugs on my 2014 Maserati Ghibli 2 days ago. Used OEM plugs(Maserati specific NGKs). Checked the gap and they were all between 0.50-0.55mm. Original ones I pulled out were also the same. Factory spec calls for 0.5-0.6mm gap.

Car was running fine before the change. After installation, I got rough idle when I first started. Idle jumped 200-300rpm. Revved it alittle, sorted itself out. Idle is steady now. But on a cold start It'll misfire alittle, shake. Goes away once warmed up, but every now and then I'll feel and hear a misfire again, even at full operating temp. Exhaust also smells like it's burning rich, BUT car drives fine. It's just the idle.

I'm not getting a CEL and everything was put back together correctly. Plugs were torqued to spec. The only thing I might have missed was putting dielectric grease on the rubber boots of the coil packs, since I didn't have any on hand.

Would pulling the plugs and checking them atleast pin point the misfire? Is there anything I should look for?
 
Did you use a spark plug socket and gently guide the plugs into place? Or did you drop the plugs into the hole? Sometimes, dropping the plug into the hole (or having it fall out of the socket) will cause cracks on the plug.

Did you overtighten any bolts on the valve cover which may have led to minor cracks developing?
 
Originally Posted by avacado11
I'm not getting a CEL and everything was put back together correctly.


You don't need to have the CEL on to have set misfire codes. I'd scan the engine and check for pending codes and go from there. If you don't have any misfire codes, I doubt checking the plugs will show anything.
 
Originally Posted by The Critic
Did you use a spark plug socket and gently guide the plugs into place? Or did you drop the plugs into the hole? Sometimes, dropping the plug into the hole (or having it fall out of the socket) will cause cracks on the plug.

Did you overtighten any bolts on the valve cover which may have led to minor cracks developing?


Yup I used a proper spark plug socket. Only thing I had to remove was the plastic engine cover. Just 4 rubber boots that popped out. I put a small dab of aluminum antiseize on the new plugs because the factory ones(I assume, as this is the first plug change interval) were coming out alittle dry and sticking at points. Torqued them to around 10-15lbs, nothing crazy either.


Originally Posted by bionictony
where were the plugs ordered from? there's lots of counterfeit plugs if the cost is too low or bad supplier.


Ordered them from Scuderia Car Parts. They sell genuine Maserati and Ferrari parts along with other exotic brands. I doubt they are counterfeits, the part # is exactly the same except an extra "S" at the end. Assume it's designates the replacement part.
 
10 - 15 ft. lbs is a bit low. Any chance they are not tight enough?

Any chance you damaged a plug wire/boot and are getting an intermittent mis-fire? Happened to me and no codes were ever thrown.
 
What is the condition of the boots? I could see original boots tearing when you pulled them off for the first time causing a bit of a miss
 
Originally Posted by doitmyself
10 - 15 ft. lbs is a bit low. Any chance they are not tight enough?

Any chance you damaged a plug wire/boot and are getting an intermittent mis-fire? Happened to me and no codes were ever thrown.


I will pull the coilpacks once the engine cools down and check them over. The oe plugs had dielectric grease on them, I didn't put them on the new ones. not sure if maybe that's what's causing the issue.

That being said I did look over the coilpacks and there was no damage to them. Just took the car on a test drive and it drove fine. No misfire, no shaking, nothing. Only happens on cold starts.
 
That's a very tight gap. Must be high pressure turbo.

Tuneups require magic and years of experience.

Were you fastidiously clean with regards to the ceramic insulators an the coil pack towers?

NO sweat grease or grime on the ceramic?

White gloves or latex? ( I'm not kidding here)

NO improper force applied against ceramic when torquing?

you may have a wire terminal issue, or not fully engaged terminal.

Listen at either end of the AM radio band for spark noise, There shoudnt be any LOUD snapping,

You can use car radio or portable transistor radio (what's that?)

Look for aura in the dark.

You can also use a loose fluorescent flashlight tube to trace and pinpoint high voltage fields

If worse come to worse - just redo the job, but inspect the wires and coil towers carefully.
 
Originally Posted by Linctex
Any chance you damaged a plug wire/boot?

That is my first guess

Same here. I remember a time when OEM Ford ignition wires wouldn't survive the first spark plug change at 12K.
 
This is modern COP, no "wires" just coil "sticks".

Super easy plug swap. But completely not needed other than to scope the engine and read the plugs.

Part number -S purportedly has an improved crush washer over the -G version

[Linked Image]
 
Did you double check the gap for s&g? What cylinder is it on?.. move the plug(s) to a different cylinder that's not experiencing a misfire and see if the misfire follows. If it does, it's the plug. If it doesn't and the misfire stays on the problem cylinder, well then it's likely the CoP. If this leads you to suspect the CoP, you could repeat the process with the CoP to see if the misfire moves to the new cylinder. (you could further repeat this with the injector on the problem cylinder also).

Now you said it was intermittent and at cold start up, so you may need to go through multiple start ups/cool downs to get some "data" in re to the misfire moving/staying.
 
Last edited:
If you still have the old plugs, why not just stick them in and see if you still get the misfire, since you did not have it with the old plugs. Then go from there.
 
On coil over plugs you need to coat them well with Dielectric grease and don't be stingy with it.. The high voltage coil overs will arc across the boots and cause the problem described. Especially if there is any kind of contamination in/on them.
 
I'm betting you're getting an intermittent connection. Or else you damaged a boot. I always replace the wires when I replace the plugs on my 1991 F-150. Mainly because the boots are so difficult to remove without damaging them.

Even then the last time I did it I had a rough idle. Turns out I didn't have one boot all the way on. I know with coil packs replacing wires and boots is not always an option. At least not a cost effective one. Even with a LOT of dielectric grease, the things seem to weld themselves to the plugs over time.
 
Originally Posted by Kawiguy454
On coil over plugs you need to coat them well with Dielectric grease and don't be stingy with it.. The high voltage coil overs will arc across the boots and cause the problem described. Especially if there is any kind of contamination in/on them.


This^
 
Status
Not open for further replies.

Similar threads

T
Car jerking on acceleration
Replies
19
Views
2K
tookien
A
Vehicle feels slightly more sluggish after new spark plug change
2
Replies
29
Views
1K
apollo18
mosaud1998
Camry misfires and CEL P0301
2 3 4
Replies
66
Views
3K
joekingcorvette
S
Nissan Frontier VQ40 plugs changed at 100K miles
Replies
18
Views
989
GMBoy
C
Can anyone read these spark plugs?
Replies
10
Views
869
IndyIan
Back
Top