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Misfire - Plugs or coil pack?

88K views 80 replies 39 participants last post by  Long 
#1 ·
Hello all,

Ever since I got my car with 5xk miles it has had a slight miss, but 3 different dealership visits told me there was no miss. I recently got a check engine light that required warranty replacement of the secondary water pump. I had just started getting the miss much more noticeably, and they assured me, somehow, this would fix the miss (still popping no codes for that). Well, picked it up, miss remains, took it back and they inform me though the car is giving ME no codes, it did show them it had a miss due to plugs needing replacing (now at 8xk miles). I went on home and a few days later and now I am getting a violent miss and finally popping a code on cylinder 6. It increases in severity with temperature. In the 30s it is really bad, 50s and 60s like we will have this week ease it greatly.

My question is, is there any way to deduce whether it is a coil pack or wires? If not, should I change plugs and hope or is it much easier to go ahead and replace packs while I'm at it and what is the cost? or maybe all plugs and just the coil pack on the cylinder in question?

Thanks in advance.

-Ryan
 
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#62 ·
Had 92,000 on my stock plugs. I bought it used so I thought the 1-2 WOT upshifted delay was programed in .. Well then it threw a cylinder 6 misfire .I Replaced plugs, simple job and WOW it runs way smoother HA HA. Now I have to reset the check engine light. I thought that after 50 miles it would reset.. I do not have a scanner for it and the auto parts stores will not reset due to Texas having testing stations. So now to research the best way to rest I do not want to buy a scanner.. I hate working on my own stuff..
 
#63 ·
it has been discussed here about using other than AC Delco parts, from my experience 50+yrs
backyard mechanic, it is best to use nothing but, everything including spark plugs. Now days
it's very easy I use Amazon plug in my vehicle type,yr,etc. and up pops the parts and you can
compare AC Delco with other brands and the price isn't that much different. The trouble with
Advance Auto, O'rielly, and other stores is they don't always carry AC Delco and if they do it's
double the price of Amazon even if you have to pay shipping, most stuff on Amazon you can
get free shipping. The trouble with Amazon is you have to wait a few days to get your parts.
thanks, douglas
 
#65 ·
Hi Guys, I also have a misfire and purchased the D501C from amazon. However I now found out that they only fit engines with the VIN "V". I am unsure now if I purchased the right coils. I have a 2008 3.6 DI. The 8th digit in my vin is "V". Can someone tell me if I got the right one?

Please and thanks in advance!!
 
#67 ·
Hello. With the plug change being an excellent precautionary move everything else you said was right on the money. It is rare to get really concise help here sometimes as there just isn't anyone who has any real world experience, with most of them extolling what they "think" or "thought" they heard and soo much of it is just a complete waste of time. I drove home one day and the next morning I warmed it up and whern I left I was "missing" a cylinder. The car has always had a little pre-warm up piston skirt slap\knock since I got it at 72,000 mi and at first I had though that had finally gotten MUCH worse{my luck] [I had a '87 buick 4 cyl that had twice the skirt knock as this and I flogged the s*** out of it on a regular basis and the skirt thing never got any worse}never the less it was a somber drive into work thinking that My northstar was Kaplooie. So imagine my happiness when I read your advice and presto it is just a coil pack!! Thank You!
 
#69 ·
I have a 2008 CTS 3.6L DI with 90,000.
Since @ 50,000 I have intermittently experienced a rough idle - not too bad but noticeable at times when idling in park and mostly with cold temperatures.
Last week the check engine light lit (steady) for a few hours.
I took the car to my local auto parts store and they ran a computer error code diagnostic.
Result: #1 cylinder misfire - bad ignition coil. I have a plug replacement scheduled and decided to buy all 6 ignition coils. My mechanic will be in there anyway so do 'em all.
OEM AC Delco Ignition Coils (D-501C) sell for $89 each. I got 6 online for $170 (includes shipping). So you gotta shop around for the best buy.
I read on this forum that is the way to go. Since last week, the check engine light no longer is lit. Plug/Coil changes still on maintenance schedule for next week.
My mechanic says he will ONLY USE OE Replacement Parts on this engine.
Anyway ... I agree with the above ... probably a bad coil ... but the car is probably under warranty ... let the dealer deal (no pun intended) with this.
 
#72 ·
Follow-up to my Jul 05 2017 Post
I received the ignition coils from the seller. Six coils for $170. Turns out though AC Delco OEM D-501C was for a "V" vin code engine. My engine is a "7" and the replacement coil for the vehicle is D-515C. Oh well. The D-501C coils were returned for a refund. I told my mechanic to replace all the spark plugs (OEM AC Delco plugs) and #1 ignition coil (OEM-price $85 locally). The old plugs were worn and definitely needed to be replaced. I would not recommend trying to get to the manufacturer recommended 100,000 miles before a spark plug change. Looking at the original plugs 90,000 was pushing the limit. Car runs well, better performance and better fuel mileage is noticeable. No rough idling.
 
#73 ·
Good catch on the coils! We have had others post saying that replacement of the coil did not clear the misfire; I'm curious if they were given an incorrect application as you were and did not pick up on the discrepancy. Are they physically the same in outward appearance or are they visibly different?
 
#74 ·
Long

The ignition coils looked similar to me. My mechanic caught the difference. I surmise the staff dealt with this before and / or verified the replacement parts needed prior to my appointment.
I intended to change all six igniton coils as I have read on this forum it is always best to replace all the similar parts (within reason) when one goes bad, but I wasn't about to spend $85-$90 each for six coils (just not in the budget). The cost for a spark plug change (with one ignition coil OEM), labor and state tax was $350.
My latest tale of wow @ 91,000 miles the DIC showed to Service Brake Assist / Service Stabilitrak / Service Traction Control.
The car runs / handles / brakes / performs normally.
According to this forum, I have a bad wheel bearing hub (magnetic sensor) which will cost probably another $350 parts/labor for one.
I shouldn't complain as this is what I paid for one car payment when the car was new ten years ago.
As a long time Cadillac owner I was once told that you do not want a Cadillac out of warranty, but I figure it is better to spend $1,000 to repair a ten year old Cadillac a year than $6,000+ a year for a new car. I guess I could drive a less expensive (new) car but as an old Cadillac owner once said to me before I bought my first Caddy: "Once you drive a Cadillac, you don't want to drive anything else".
 
#75 ·
Long:

One last thought on the ignition coils: Always double check and maybe double verify with multiple OE vendors the replacement part against the VIN #.
The website I bought the "V" coded coils was very unclear but said the D-501's were the correct part. The vendor refunded my money minus a 10% restocking fee.
The refund money will now go toward the wheel hub bearing repair.
 
#77 ·
I'm sorry, but I would raise hell over that restocking fee. I provided accurate information on what my vehicle and engine combination are. YOU sold me the wrong part. You said the part number was correct, but it is NOT correct, so YOU made the mistake here. Now I'm supposed to pay return shipping and give you a 10% fee for being wrong. OH HELL NO! I'd have insisted on they pay return shipping and refund in full.

If anything, report them to the BBB and see if you can obtain any additional satisfaction that way. I hate to see vendors screw people like this. Especially now that you need a wheel hub. I just did mine. Got a Timken off Amazon for a good price, then it took the shop 4 hours to get my old one off the car. For want of $.02 of antisieze compound, or just plain grease, I could have done that job myself.
 
#76 ·
Thanks for the update-I'm willing to bet that those who have stated new coils didn't solve their misfire condition purchased improper coil applications as well.
Your new problem does sound like a wheel speed sensor/bearing. Unfortunately, they don't make wheel bearings the way they used to and now are almost to the point of being regular maintenance items like brakes.
My father told me "once you own a Cadillac, you'll never want to be without one". He was right :D
 
#78 ·
2007 CTS: Same problem here. No start, rough start, misfire and four trips to the dealer service who could not find anything wrong and no codes given. Last week the car had a rough start, started rocking under the hood, rich fuel smell and it barely ran. Misfires were random however. I took it to a different dealer service center who found a bad coil and plug. It was coming up with codes at this time They replaced two coils and all the plugs and it runs fine now. QUESTION: If you replace all the plugs, is a best practice to only replace the bad coil or replace all the coils? I am thinking that might be excessive and expensive to replace all the coils but a family member disagrees with me. I’m hoping someone can advise.
 
#79 ·
Welcome, SethSeth.

Replacing only the defective coils is sufficient.
No need to replace a coil if it is functioning properly.
 
#81 ·
NP.
Lots of knowledgeable people here to help--
That was a fairly generic query, but keep in mind to post specific questions in your Gen I CTS ('03-'07) subforum for best results.
Enjoy the forums!
 
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