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Another reason to change the spark plugs.

3K views 10 replies 6 participants last post by  6spd 
#1 ·
I've become somewhat used to the slight hesitation associated with my morning's commute - from the standpoint of slight roughness etc. for the first few miles, post cold start up.

Changing out the MAFS (every 30K IMHO), as in replacing them (cleaning is merely a placebo & worthless) certainly helped this roughness but did not eliminate it completely.

Changing the plugs completely eliminated any "cold start" roughness.
The car is w/o any hint of roughness, hesitation etc.

Just thought I'd offer this positive data point.:)
 
#2 ·
spark plugs

Do you have any pics of the old plugs? It would be interesting to "read" them to identify any issues. If I recall the service schedule correctly, the plugs should be due for a change at inspection II, so with your 55K miles, it looks like you should be right on target. Also, does your car drink alot of oil? I would suspect that the plugs should be changed more frequently if the car burns more oil.
 
#3 ·
verhagke said:
Do you have any pics of the old plugs? It would be interesting to "read" them to identify any issues. If I recall the service schedule correctly, the plugs should be due for a change at inspection II, so with your 55K miles, it looks like you should be right on target. Also, does your car drink alot of oil? I would suspect that the plugs should be changed more frequently if the car burns more oil.
The car uses very little oil.
I change out the Castrol 5W-30 every 6,000 miles & generally add 1/2 quart along the way. I'd not even do that if it weren't for discussions here associating low oil with the occasional "clack" upon start up, which appears somewhat accurate, only rarely occurring if oil levels are below the top reading line.

Plugs appeared fantastic; tan/brown, no build up- going to place them in the classifieds section they look so good :haha2: -Will try to post some shots if time allows...

What I did notice is that the center electrodes on these stock NJK plugs appeared slightly recessed, whereas the new Bosch +4 platinum's electrodes were clearly protruding up & over the insulator's surface.
 
#4 ·
I changed my plugs at about 65K miles and had the same experience - cured a slight roughness/bauble at idle. I now have 115K miles and I'm due to change 'em again, along with the O2 sensors. I have the parts - just haven't had the time. Maybe this weekend. I HAVE had that same ocassional rough idle lately; I'm expecting the new plugs to solve it. If there's anything worth seeing I'll photo the plugs when they come out.

/G
 
#5 ·
When the idle gets rough and replacing the spark plugs help, is that
misfire or pinging that has occured?

If so, why are there no fault codes?

David
 
#6 ·
I've always used Bosch Platinum +4's in my Vette and loved them. What convinced you to try them in the M5 over the NGK's?
 
#7 ·
Interesting question - never thought about it. You're right, the computer can throw fault codes for either. It is not pinging - the conditions that cause knock really don't exist at idle. So I suspect it is misfiring - but I'm not sure why the computer wouldn't catch it - depends how misfiring is detected. I am guessing the computer doesn't watch it at idle. I suspect this because the dreaded "low secondary airflow" condition (caused by carbon buildup in the secondary air passages as discussed widely here, and which I have) isn't detected at idle either, as far as I've experienced. Maybe detection isn't reliable enough at idle so the computer doesn't start caring until there is some load/elevated RPM?
 
#8 · (Edited)
A few things are happening(or Not)
During cold start the ECU is adding more fuel so it has a chance for some to burn. It needs to evaporate better to burn, which is harder when cold.
Worn sparkplugs don't like to fire, extra resistance to jump the gap(which also can be larger than spec).

cherrsagai

Sorry DavidS, Miss firing
 
#9 ·
6spd said:
A few things are happening(or Not)
During cold start the ECU is adding more fuel so it has a chance for some to burn. It needs to evaporate better to burn, which is harder when cold.
Worn sparkplugs don't like to fire, extra resistance to jump the gap(which also can be larger than spec).

cherrsagai

Sorry DavidS, Miss firing
Sounds about right!
The car's a different beast... but now, I've got an intermittent CPS cutting in / out rather frequently.....

(thanks BMW -got nothing else to do with my weekends
)
 
#10 ·
don't buy at dealer

For those of you wanting to change them, don't buy them at the dealer. My dealer wanted $17/plug (including my usual discount).

I went to http://www.sparkplugs.com and found the OEM NGK BKR6EQU plugs for $8.07/plug. My car is only at 26K miles, and is running perfectly without any hesitation, but at that price, I plan on changing them out during my upcoming DIY Inspection I. That will also give me a good opportunity to do a compression test using the information recently posted.
 
#11 ·
This is covered on another posting.
Make sure to blow the area out next to the sparkplugs before pulling them Just incase there is dirt in there.
We don't want the dealer saying they won't cover a engine change when a groove is carved into the cylinder.

:cheers:
 
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