“But the plug should be pulled to see if it’s causing the misfire.” ???
“I don’t know about anyone else, but when I get a misfire code for a cylinder the first thing I do is pull the plug.”
The first thing I do is diagnose the cause of the misfire. I know there are many DIY’ers on this form and for a guy with more time than equipment I can see doing it this way, but for a pro in a shop I can’t see this being efficient. Why would I pull a spark plug (that may or may not be easily accessible) if the misfire is clearly fuel related or caused by a mechanical condition in the engine?
I’m not against replacing plugs. I’m against replacing plugs when there’s nothing wrong with them. And OBDII will let you know if there’s a problem with a plug with a misfire code.
Example: In order to replace the three plugs at the firewall on some Ford 3.8 liter engines, the upper intake manifold has to be removed. If there’s no Check Engine light on indicating a misfire on those cylinders, who’s willing to pay me $500.00 just to replace those three plugs when there’s no indication of a problem with those plugs?
But if someone insists that they want the plugs replaced when there’s no indication of a problem with the plugs, I’m more than happy to relieve their wallet of that money.
As much as I hate to disagree with Tester, I have to in this case simply because any spark plug may misfire without even causing a noticeable symptom or setting a code.
There’s also the much more difficult issue of trying to read a spark plug on a modern car; especially if it’s a Platinum or Iridium.
A plug may look brand new and yet it may belong in the garbage bin.
I’m afraid that I just don’t get the logic behind this.
I’m confused. You say the first thing you do for a misfire is pull a spark plug. And you also say you pull intake manifolds to change spark plugs? Why? You get a Ford 3.8 with a P0302 and you pull the intake without even knowing what the cause of the misfire is?
Everyone has their own diagnostic process, but in this day and age I think removing and looking at a spark plug is a little dated. You’ve already got your scan tool hooked up for diag, why not just use all the info there for your diag and keep your hands clean?
Well. Is it a spark plug, COP, or a plug wire. The scanner doesn’t tell you that. It tells you there’s a misfire on that cylinder.
I just went and looked at the data base I have on customers who have brought their vehicles to me since they were purchased new and went out of warranty, or were purchased with less than 50,000 miles on them where I’ve serviced them in that time. All these vehicles have never had the spark plugs replaced. Though misfires were caused from other circumstances.
Let’s start with my vehicle. A 1995 Nissan pickup. This vehicle is OBDI so it doesn’t detect for misfires. But I do remove the plugs every 30,000 miles to check for condition and if they need regapping. 186,000 miles and the plugs have never been replaced since I’ve owned it with 90,000 miles.
1998 Honda Civic. 214,000 miles and the plugs have never been replaced.
2001 Toyota Camry. 172,000 miles and the plugs have never been replaced.
2001 Infinity QX4. 156,000 miles and the plugs have never been replaced.
2004 Monte Carlo, 240,000 miles and the plugs have never been replaced.
2001 Chrysler Town and Country. 184,000 miles and the plugs have never been replaced.
This is just a sample. But these vehicles don’t leave my shop with a Check Engine light on from a misfire.
I have a friend who has a 2007 civic, plugs were not replaced until 200k miles, they were working perfectly, he just got nervous and decided to changed them.
I think every 30k miles for plugs is a bit much, even for standard cheapo plugs. If you put in new platinum plugs and change them every 30k miles, you are crazy.
An old mechanic friend of mine used to put customers used discarded plugs into his own personal car, If a car was in for an oil change and the oil still looked clean, he was also known to collect the used oil in a special container and put it in his car. Now thats thrifty.
“Well. Is it a spark plug, COP, or a plug wire. The scanner doesn’t tell you that. It tells you there’s a misfire on that cylinder.”
That’s my point, just in different words, or not as many words. I know I have a misfire. Why would I pull a spark plug, or look at/test a wire, COP, coil if the misfire is being caused by a fuel delivery or supply issue, or an internal mechanical issue, or a vacuum leak, or an oxygen sensor? The scan tool has all this information for you to interpret before even opening the hood. And if you narrow it to an ignition problem don’t you scope the system to determine if it’s a COP or a plug or a wire?
As for your customer’s long-lived spark plugs, I hope you didn’t spend too much time looking up service history. I’m sure you have better things to do with your time. Good for them that they’re still running on original plugs. Most of my customers expect me to maintain their vehicles according to manufacturer recommendations, and that includes replacing spark plugs at specified intervals, be it 30K or 100K.
" . . . used to put customers discarded plugs into his own personal car."
Some people would use another word to describe your mechanic friend
I won’t say what that word is
I will say this, though
At my previous job, we were legally forbidden to reuse car parts that were removed, replaced, etc.
We were legally forbidden to take stuff from the scrap metal bin
In other words, if it went into the trash, waste oil, bin, etc. it stayed there . . . until it was picked up by the appropriate people to be discarded, recycled, etc.
Our service manager also said that it looked very bad to be reusing parts. It gave people the idea that they were sold parts that they didn’t need.
BTW . . . it is company policy in lots of places that the items in the trash are “company property” until they are picked up for disposal, recycling, etc.
I’m not hammering you or your friend
I’m just pointing out that, in many cases, trash needs to stay trash
I wonder what the attitude of a passenger in a Cessna 172 would be if the engine started sputtering at 8000 feet up followed by the pilot stating that the spark plugs were 500 hours overdue…
@Wheresrick, I have no problem with making do or performing workarounds in most cases but the time expended installing used spark plugs is simply not worth it. If your mechanic friend wants to do that to his own car then have at it I suppose.
While I don’t know if they’re still around or not, there used to be a chain of quick tune shops in OK City that ran ads all the time for tune-ups on the cheap. My understanding is that they had a barrel or two of used spark plugs present. The car would enter the shop, get slapped on the oscilloscope, and if a firing line on any cylinder was a bit higher than the others they would root around in the barrel and find a similar looking plug to install. Brand name, heat range, etc was all irrelevant.
I’ve seen some 4 and 6 cylinders come from that place with 4 different brands of used plugs in them. Even the length of the shanks and type of tip was irrelevant…
I supposed valve lash is another issue not worth worrying about…
