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Car runs rough after changing spark plugs and wires
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78merc
User
May 30, 2013, 10:22 PM
Post #1 of 21
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Car runs rough after changing spark plugs and wires
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Hello,
I have posted on this sight before and found people to be very helpful.
I recently had my mechanic adjust the idle speed on my 1978 Mercury Grand
Marquis with the 460 V8. He got it running great!. Never one to leave well
enough alone, I decided to give the car a DIY tuneup. I purchased some Autolite
spark plugs, gapped the spark plugs using one of those cheap disc shaped
gappers, used dielectric grease, and installed them one at a time so I wouldn't
get the plugs mixed up. I screwed them in finger tight, then screwed them in a
little more with the wrench. I thought I did everything correctly. After
driving it a while, I noticed that it seemed to run rough and shake,
particularly upon acceleration. I went to NAPA and purchased new wires,
carefully installed them one at a time, and still the same problem. I haven't
replaced the distributor cap and rotor yet. Any ideas what I did wrong? Any
input would be GREATLY appreciated!
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MarineGrunt
Enthusiast
May 30, 2013, 11:41 PM
Post #2 of 21
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Re: Car runs rough after changing spark plugs and wires
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Where did you put the dioelectric grease? I know you said you only did one plug and then one wire at a time but are you 100% sure you didn't get a couple wires mixed up? Are you sure the plugs are gapped properly? Check other connections and hoses that you might've accidently knocked off during install. Maybe you accidently knocked off a vacuum hose or something.
I'm not sure if on your engine you adjust timing by turning the distributor cap, but if you do, maybe you bumped the distributor cap while plugging in the wires and it through off your timing?
If nothing else maybe try reinstalling the old plugs and see what happens. Maybe the parts store accidently gave you the wrong ones.
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78merc
User
May 31, 2013, 9:09 AM
Post #4 of 21
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Re: Car runs rough after changing spark plugs and wires
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Thanks so much for the replies. I put a small amount of dielectric grease in the spark plug boot portion of the spark plug wires. I did not put grease on the distributor side of the spark plug wires. I was using the appropriate size socket for the spark plugs recommended by the parts store. One of the spark plugs made a very light cracking noise when I was installing it. I didn't think of it at the time, but perhaps it is causing the problem. I don't remember which one it was, so maybe I should just replace them all? Also....
Are the disc cheap disc shaped gappers accurate? Should I buy a different gapper?
If I decide to replace the distributor cap and rotor, do I need to put any grease or lubricant in any part of the distributor or rotor?
Thanks!!!!
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Hammer Time
Ultimate Carjunky
/ Moderator
May 31, 2013, 9:59 AM
Post #5 of 21
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Re: Car runs rough after changing spark plugs and wires
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You cannot use regular sockets on spark plugs.
As` i said, they make special sockets that have a rubber insert to prevent the plug from breaking. If you heard a noise, then you broke one or more of the plugs. They are only made of glass.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
May 31, 2013, 10:00 AM
Post #6 of 21
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Re: Car runs rough after changing spark plugs and wires
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Check that you have the right plugs. You just said you heard a "cracking" sound so that would totally explain it. You can't even drop the box they came in sometimes.
OK - Do you know how to cancel one plug at a time and see which one (probably just one) does not make it idle worse? The one that doesn't change anything is the one.
Hey - a 460 even in a monster car was still in need of proper plug removal/install tools such that you get a straight line of force as not to put any pressure of the porcelain to wire part.
Canceling plugs one by one: Safer is to shut off engine, pull one plug wire and with jumper clipped both end wire ground the wire to engine ground. Start engine and see if it's same or worse.
Long time ago now but think a 460 about then the back plug, closest to passenger's side firewall/heater box was the hard one? IMO if so that's the one to check first and don't even bother putting a used one back in the hard one.
Stuff happens: If you drop a plug, or question one going in mark that one is just crayon or something you can remove easily. Do that if the box was damaged on any so you know where that one went if problems begin instantly like that go there first.
If you are using one of those "T" handle plug things with a swivel those just are not good enough. Save that for a lawnmower and get better stuff that can take several things to get that straight line of force. You should also mark each plug coming out as to where it came from noting how each looks compared to the others especially as a DIYer,
T
T
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78merc
User
May 31, 2013, 12:58 PM
Post #7 of 21
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Re: Car runs rough after changing spark plugs and wires
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Thanks for the replies! I purchased the spark plug socket at the Autozone when I purchased the plugs. It has the rubber in the back of the socket that you mentioned. Its meant for spark plugs. I will try to find the broken spark plug and go from there. Also, its not impossible that I disconnected a vacuum hose somewhere. I'll let you know how it goes. Thanks!!
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Tom Greenleaf
Ultimate Carjunky
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May 31, 2013, 2:36 PM
Post #8 of 21
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Re: Car runs rough after changing spark plugs and wires
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OK - Read what I said or ask for a better explanation of cancelling plugs without needing wild equipment.
Note: Plugs and sockets etc: THERE ARE A ZILLION DIFFERENT SIZES FOR 3 fairly common sizes for cars + trucks. Common is 5/8th, then 13/16th and some older stuff was 7/8th. Of each they should hold the plug with rubber as you said. Now some are 6 point, 12 point, have swivels on them, lock to an extension or ratchet have hex tops to use a wrench and a 100 more differences I can't just recite right now.
Some and it was a 460 (in truck, 1978) was dang impossible without very specific socket + no room for a ratchet so need the hex end on the socket. This crap can make anyone go nuts! Neat trick to start some is use a rubber hose to start them in. They make a tool for that too.
They seem so silly but are the only things that spark the fuel! When I said ground out suspect ones especially handy with a tachometer hooked up you'll see which one or maybe more don't change the idle roughness, hence lower RPM. Do look for your vacuum hoses anyway and toss for new any that are the least bit hard, soft or cracked.
Plugs again and canceling them: The jumper alligator clip could be either at distributor or better at the plug - you ground it on purpose both so distributor, wires aren't stressed to find ground and so you don't get a shock. These silly things. $2 bucks for a pair at cheapo places...........
You just don't want sparks going random in distributor unseen or to another wire when one is unhooked to confuse it. YOU SAID YOU HEARD A CRACK so that about nails it that, that plug cracked, perhaps unseen. That or plain defective, mishandled by you or in shipping or who knows?
Sorry to beat the subject up that much. Treat plugs as if they were light bulbs in handling them - 
T
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78merc
User
May 31, 2013, 10:00 PM
Post #9 of 21
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Re: Car runs rough after changing spark plugs and wires
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Believe it or not, the plugs weren't too hard to get in and out. My neighbor had a nifty wrench that I attached the spark plug socket too. Its long and swivels back and forth at the head, so it wasn't too hard. That being said, I figured I would take the unscientific method of replacing all of the spark plugs on the side of the engine I remember hearing a crack, then drive the car and see if it runs better. If it doesn't, I would try the other side with the same new spark plugs. I like your method better because I could pin the broken plug down, save money, and be sure I haven't ruined any other plugs. Sorry I am such a novice, but could you explain it to me one more time? I didn't quite follow your explanation. Not sure where or how you ground the wires. Thanks!
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Tom Greenleaf
Ultimate Carjunky
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Jun 1, 2013, 12:46 AM
Post #10 of 21
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Re: Car runs rough after changing spark plugs and wires
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Again - just saves time. Put an alligator clip stuffed into and clipped to metal inside unhooked spark plug boot and ground it out of harm's way on something particularly on engine block. All that dang spark wants is to find ground whether making a plug do it or not.
Being new you can get just one new one and use an old one that works as needed till you get one. Makes a mess of stuff but save old parts like projects like this till all clear and working with the new stuff.
I'm writing/suggesting the low tech but effective approach that plain works for testing and finding which one as said, that all. I/we have to be mind readers as to what is available to you to do what while being realistic that wildly expensive approaches for something like this are not practical or cost effective.
What can stink is when you have new defective parts sometimes too common. You do have the right approach to do things ONE at a time so eliminating mixing things up either firing order or now vacuum lines where it's near impossible to get some diagram.
Back on something: When you gap new plugs they should be close right out of the box. If a lot is needed those plugs are wrong or plain suk.
Another redneck trick: Use some cheap clothes pins or something to mark wires and hoses and # them can help with order of some things like this. Using a piece of cardboard with punched holes for items that should go back in exact place and mark things.
T
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78merc
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Jun 1, 2013, 8:55 PM
Post #12 of 21
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Re: Car runs rough after changing spark plugs and wires
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Thanks for the advice! I went ahead and replaced all four plugs on the side of the engine that I thought might have the bad plug. Success! The car no longer has the miss and has a lot more power too!
An interesting side note. When I was gapping these plugs I did notice that they were a lot more accurately gapped than the first batch I bought. I might replace the other four just to be safe. I'm getting a lot of practice at replacing spark plugs.
Thanks again!
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Hammer Time
Ultimate Carjunky
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Jun 2, 2013, 4:50 AM
Post #13 of 21
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Re: Car runs rough after changing spark plugs and wires
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Just curious........................ what kind of plugs did you put in here?
Please don't say Bosch platinum or any for of Platinum for that matter
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Tom Greenleaf
Ultimate Carjunky
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Jun 2, 2013, 8:36 AM
Post #14 of 21
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Re: Car runs rough after changing spark plugs and wires
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Agree on that. Plain plugs that are called for. Quick look out there, these should be just fine..........
Autolite Copper/Spark Plug   Part Number: 26 (disclaimer - looks ups as shown might be wrong from where that came from) Playing with tricks with plugs doesn't work any better than what it called for. About one trick works to get one vehicle to a junk yard for it's last ride. If good they SHOULD be real close in gap to the spec listed and if not keep looking, T
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78merc
User
Jun 2, 2013, 8:03 PM
Post #15 of 21
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Re: Car runs rough after changing spark plugs and wires
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I purchased the Autolite plugs you mentioned. They are number 26. I am going to go to the same store tomorrow to purchase the other four spark plugs and make sure they are gapped close to spec like the four I just installed were.
One more question and I promise to wrap up this post. My mechanic likes to rev the engine while spraying carb cleaner down the carb throat to clean the carb and "blow out the carbon". A friend told me that this will gas foul the plugs. Will this gas foul the plugs? Is there a way to clean the plugs if they are fouled?
Thanks!
(This post was edited by 78merc on Jun 2, 2013, 8:28 PM)
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Tom Greenleaf
Ultimate Carjunky
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Jun 3, 2013, 1:17 AM
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Re: Car runs rough after changing spark plugs and wires
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Seems part look up was right. IDK why they were off gap the first round - dropped box or who knows? It's your biz but you shouldn't be paying for new plugs if all was as I see it - something went wrong but at least they are not expensive.
Cleaning carb like you mechanic like is fine but I prefer to do things like that BEFORE replacing plugs if just maintenance so if debris gets to foul up a plug it would be one you are about to replace.
As you know this is a real pig by that exact year even worse. It also helps to get carbon out by just a good long run and aggressive acceleration letting RPMs max (weak things could give out) out what trans allows at a safe, legal place like an on ramp to highway with little to no traffic. These were good tough engines and TMK '78 was the last year they put them in "passenger" cars, as meeting emissions and MPGs was tough to do with the humongous block engines.
Good luck with it,
T
(edit to add) "Is there a way to clean plugs when fouled?" If just a fleck to knock off one that is self grounded with junk just a pin. If really plain fouled from use or if now an oil burner just toss them for new. Heck, if you are there to check on them all put new ones back. Truly cleaning plugs with a machine was for things much older than this and can rough up surfaces such that they will collect junk faster so not advised.)
(This post was edited by Tom Greenleaf on Jun 3, 2013, 1:36 AM)
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Discretesignals
Ultimate Carjunky
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Jun 3, 2013, 4:54 AM
Post #17 of 21
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Re: Car runs rough after changing spark plugs and wires
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Probably wouldn't hurt to start reading your plugs to see what is going on in the combustion chamber.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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Hammer Time
Ultimate Carjunky
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Jun 3, 2013, 5:53 AM
Post #18 of 21
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Re: Car runs rough after changing spark plugs and wires
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He did read them............... they say Autolite 26
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Tom Greenleaf
Ultimate Carjunky
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Jun 3, 2013, 6:28 AM
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Re: Car runs rough after changing spark plugs and wires
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Beat this thread up some more. I think what was meant is looking at the plugs as a diagnostic of what is happening. Good info if the same one always has a problem type thing.
Can't expand this showing some common flaws vs normal........
Tom
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Discretesignals
Ultimate Carjunky
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Jun 3, 2013, 4:18 PM
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Re: Car runs rough after changing spark plugs and wires
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He did 
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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