Thread: Misfires after having new spark plugs & cat put in.. *yay* (+ hard starts)

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  1. #1 Misfires after having new spark plugs & cat put in.. *yay* (+ hard starts) 
    SE Level Member wickedfrisone's Avatar
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    I know there's quite a few threads already on misfiring issues but none (to me anyway) seem to be close enough to my situation. Just for some background, my '04 Comp G has 132k mi right now. (131k when this service was done, and had check engine on since I purchased in October due to bad cat)
    On May 15th I had someone at a nearby shop that my dad knew/suggested do my oil change and put in Bosch double iridium plugs (I was having some minor starting issues and figured I'd start with new plugs to see if it helped). The next day, I noticed Pumpkin was having REALLY bad misfires during acceleration and going up hills. We took him back to the shop and the mechanic who did the work asked if there was a check engine light on, which there was but that was always there since he needed a new converter. We were hoping maybe there was just a loose plug wire or something since he just worked on them...right? Well he said it's not possible because that would show up in their scan tool (not sure if that's true as I'm not too familiar with them). He said it was just because of the bad cat, engine wasn't getting enough air and whatnot.
    So... we ordered a new OEM fit catalytic converter and had it replaced on the 30th by someone at a different shop that specializes in exhaust (but mainly were charging less than this dude). Maybe about two days later the misfire seemed to improve - the car isn't stuttering and struggling to accelerate nearly as badly as before, and the check engine went away. Yay, but still not really yay.

    I want to say maybe two weeks ago we went somewhere else to see if they could pinpoint the culprit and we were told we needed a new MAF sensor and ignition control module (because I've been having hard starts - engine would sometimes turn over but then appear to want to die, and needed to either give it some gas or shut it off and try again a couple of times). They said they cleaned out the MAF sensor a bit but that I would need a new one anyway. We ordered a new one (well not brand new but still functional) and not really much improvement from there either. I haven't gotten to the ICM yet because at the moment I can't afford even the cheapest I can find at around $65.
    Now I just wanted to add that two separate times now when getting on the freeway and having the usual misfire(s) during acceleration on the on ramp, I did get a flashing check engine light once the misfire subsided; so I did have to pull over and shut the engine off for a couple of seconds. I noticed today while getting on the freeway the misfire occurred as usual, but I noticed maybe five seconds into it you could feel one of the cylinders snap out of it and the engine regained some power - but not completely. Again the flashing check engine light began after the misfires subsided, but this time before being able to pull over the check engine went away by itself within a few seconds.

    So...I'm in the process of finding some throttle body cleaner so I can clean it out and see if that helps at all..but I'm not too hopeful. I've also tried checking in the case of the hard starts to see if I can hear the fuel pump whine when turning the key to the On position but not cranking it - however I can't really make out the sound of it priming unless its thanks to the chime every time I put the key in that doesn't shut up soon enough for me to listen closer. I do know that the previous owner had bought a new fuel level sensor two years ago, so I don't know if the fuel pump in general could be having other troubles :/
    Aaand speaking of fuel level, I have also noticed some time ago that the fuel gauge behaves a little odd in my opinion... I've had times where I drive around for a bit and when we come to a parking lot and park for a while, engine still running, the fuel gauge will slowly start creeping up a bit and go a couple of notches fuller (I've seen it go from 1/4 of a tank to just one notch away from half a tank). I have no clue as to whether or not that is normal or one of the symptoms of whatever issue Pumpkin is having. I know that my mom's Bonneville definitely has something up with the fuel system as you hear a loud compressor sound coming from the pump almost all the time kicking in, and the fuel gauge definitely does not accurately mark the fuel level. (Maybe when you first start the car it will show you the true fuel level, but once you put it in drive and move a bit it will go straight to either full or empty).

    Anyways, this is one of the few things bugging me lately that I can't seem to figure out. It sucks having what was once a fun supercharged engine that now feels like the exact opposite. Can't even get onto the freeway without being an embarrassment to the GP family...
    2004 Grand Prix GTP Comp G, aka Pumpkin
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  2. #2 Re: Misfires after having new spark plugs & cat put in.. *yay* (+ hard starts) 
    GXP Level Member GTPpower's Avatar
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    Ignition wires would be my first guess. You can also try cleaning the maf and see if that helps.

    You also should get a fuel pressure gauge on the car and check it.


    2001 GTP Drag Car - XPZ, Tischler heads, Upsidedown M90 IC'd, e85, Gen V, 2.3 w/ 5%OD
    2005 F350 6.0 - studded, deleted, tuned
    2001 GTP - cam, headers, nitrous, stock trans - 11.83 @ 116 <$2k in mods - sold
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  3. #3 Re: Misfires after having new spark plugs & cat put in.. *yay* (+ hard starts) 
    SE Level Member wickedfrisone's Avatar
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    I'll have to see if I can find one of those gauges to check fuel pressure for sure, as I'm highly suspicious something's going on in that area... as for wires, I guess I will try and check as well, even though that lovely mechanic swore there could be nothing wrong in that area because it would show up in his scanner... I do believe if I remember correctly from checking the service records the previous owner gave me, they bought the wires and coils that are currently in the car sometime around 2010. They're by MSD and funny thing is when I looked up the part numbers on their website and even called them, I found no indication that these coils and wires were actually designed/tested for this year and model. What just bothers me is that the only problem I ever had before was the hard starts, never any actual power reduction/misfires before simply having the spark plugs changed. Unless like I thought the guy screwed up one of the wires or something while he was working on it...
    2004 Grand Prix GTP Comp G, aka Pumpkin
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  4. #4 Re: Misfires after having new spark plugs & cat put in.. *yay* (+ hard starts) 
    GXP Level Member GTPpower's Avatar
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    Are the coils and wires red in color?


    2001 GTP Drag Car - XPZ, Tischler heads, Upsidedown M90 IC'd, e85, Gen V, 2.3 w/ 5%OD
    2005 F350 6.0 - studded, deleted, tuned
    2001 GTP - cam, headers, nitrous, stock trans - 11.83 @ 116 <$2k in mods - sold
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  5. #5 Re: Misfires after having new spark plugs & cat put in.. *yay* (+ hard starts) 
    SE Level Member wickedfrisone's Avatar
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    Quote Originally Posted by GTPpower View Post
    Are the coils and wires red in color?
    Yup. (and I apologize for how filthy he is, haven't gotten the change to really start cleaning things up )

    2004 Grand Prix GTP Comp G, aka Pumpkin
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  6. #6 Re: Misfires after having new spark plugs & cat put in.. *yay* (+ hard starts) 
    Killa Bee Scottydoggs's Avatar
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    them coils might just be the issue. get some stock coils on there. should be better.

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  7. #7 Re: Misfires after having new spark plugs & cat put in.. *yay* (+ hard starts) 
    SE Level Member wickedfrisone's Avatar
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    I wondered if maybe it really was just the coils and not the ICM like they told me at the last shop...think spraying each once with some water with the engine running to test them would help confirm or not? lol
    But I will definitely keep that in mind and probably buy coils first anyway before spending money on a new ICM. I did just get the TB cleaned out and let Pumpkin idle until the RPM's were back to normal - I did feel like he sounded better when I started the engine. Just haven't gotten do actually test driving yet. We shall see.
    2004 Grand Prix GTP Comp G, aka Pumpkin
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  8. #8 Re: Misfires after having new spark plugs & cat put in.. *yay* (+ hard starts) 
    Killa Bee Scottydoggs's Avatar
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    those coils are known to cause misfires. they kinda suck. best coil you can use is the stock one. hell snag a few from a junk yard, they tend to last forever unless they are cracked.

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  9. #9 Re: Misfires after having new spark plugs & cat put in.. *yay* (+ hard starts) 
    GXP Level Member GTPpower's Avatar
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    Those coils suck. Get some ac delco coils.


    2001 GTP Drag Car - XPZ, Tischler heads, Upsidedown M90 IC'd, e85, Gen V, 2.3 w/ 5%OD
    2005 F350 6.0 - studded, deleted, tuned
    2001 GTP - cam, headers, nitrous, stock trans - 11.83 @ 116 <$2k in mods - sold
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  10. #10 Re: Misfires after having new spark plugs & cat put in.. *yay* (+ hard starts) 
    SE Level Member wickedfrisone's Avatar
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    Haha, will do. Too bad they won't match anymore, but what the heck XD Yeah I remember when I called MSD the rep (who seemed like he was having a long day and his battery was like at 10%) said they dont have ANY products for an 04 GP. It just boggles my mind why they bought those from some local parts store (which has since then closed) if they say they're for like 90's GM engines (I don't recall the specifics).
    Oh, and when I took him to the dealer sometime in February I think for the diagnostics the guy did say that "whoever did those MSD coils and wires didn't do them properly" which is what made me look into them in the first place, thus I found out they weren't even made for this car.
    2004 Grand Prix GTP Comp G, aka Pumpkin
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  11. #11 Re: Misfires after having new spark plugs & cat put in.. *yay* (+ hard starts) 
    Killa Bee Scottydoggs's Avatar
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    you can paint the new to you stock coils red. clean em up, then scuff em or lightly sand, tape off the bottom and tips. then have at it.

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  12. #12 Re: Misfires after having new spark plugs & cat put in.. *yay* (+ hard starts) 
    SE Level Member wickedfrisone's Avatar
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    Quote Originally Posted by Scottydoggs View Post
    you can paint the new to you stock coils red. clean em up, then scuff em or lightly sand, tape off the bottom and tips. then have at it.
    I literally was thinking about that hahaha

    I actually found the link to the coils I have right now
    MSD 8224 GM Coil Pack, 2 Tower Style - MSD Performance Products

    definitely not an 80's-90's GP...lol
    2004 Grand Prix GTP Comp G, aka Pumpkin
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  13. #13 Re: Misfires after having new spark plugs & cat put in.. *yay* (+ hard starts) 
    GXP Level Member GTPpower's Avatar
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    Zzp sells red coils for cheaper than new ac delco, if you wanted to go that route instead.


    2001 GTP Drag Car - XPZ, Tischler heads, Upsidedown M90 IC'd, e85, Gen V, 2.3 w/ 5%OD
    2005 F350 6.0 - studded, deleted, tuned
    2001 GTP - cam, headers, nitrous, stock trans - 11.83 @ 116 <$2k in mods - sold
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  14. #14 Re: Misfires after having new spark plugs & cat put in.. *yay* (+ hard starts) 
    SE Level Member wickedfrisone's Avatar
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    Quote Originally Posted by GTPpower View Post
    Zzp sells red coils for cheaper than new ac delco, if you wanted to go that route instead.
    Is that so? Didn't think they would offer anything cheaper haha, then again AC Delco can get pretty pricey in some areas... I was just checking pricing for my local junkyards, and one place will sell individual coils for $6.99 but the pack for $35.99 - not too bad I guess. I just have to look at one other place that's closer and maybe Wednesday we will go hunting for coils... (shh...be very, very quiet..)
    2004 Grand Prix GTP Comp G, aka Pumpkin
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  15. #15 Re: Misfires after having new spark plugs & cat put in.. *yay* (+ hard starts) 
    SE Level Member wickedfrisone's Avatar
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    So I don't mean to double post but the forum won't let me edit my last one for some reason...

    Anyhow, took Pumpkin for a drive and I noticed right off the bat the engine sounds a lot better/stronger and seems to feel better cranking it too. The misfire is still there, BUT - it only lasts about 2-3 seconds before it corrects itself and he's able to accelerate a lot better because of that. I'm quite happy with the result from just cleaning the TB, and I wish I could clean a little further inside past the TB but not sure how to tackle that safely... I will probably be looking for replacement coils soon in hopes that that will fully correct the issue (and that I won't need the ICM). Also I think I finally noticed I can hear the fuel pump whine prior to starting the engine, so at least I know that isn't completely bad. Still have yet to figure out why the gauge acts a bit weird, though.
    2004 Grand Prix GTP Comp G, aka Pumpkin
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  16. #16 Re: Misfires after having new spark plugs & cat put in.. *yay* (+ hard starts) 
    SE Level Member wickedfrisone's Avatar
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    Sorry for double posting again... but I'm really annoyed now. Recently the misfires have been occurring only when cruising at around 1,500-2,000rpms and when trying to speed up a bit from there. From a full stop, usually way more responsive with the exception of what feels almost like the trans slipping for a split second when you hit the gas. Anyways, was just on my way to bring lunch to my boyfriend at work when of course getting on the freeway there was some hesitation, and I got the dreaded flashing CEL (meanwhile I was on the left lane nowhere to pull over into, all I could do was put my hazards on and let him slow down a bit on his own) however before I could eventually pull over I realized I now have a fixed CEL again. I'm kind of ticked off now, not sure yet if it's the NEW cat we put in a couple of months ago that is shot again or what, I have to wait until I get home to plug the OBD into this guy.
    I am not a happy camper and just really annoyed we haven't been able to figure out what's been causing these misfires since that shifty mechanic did my spark plugs. Just my luck I guess...trying to fix this car up and when we get one thing resolved something else gets screwed up..
    2004 Grand Prix GTP Comp G, aka Pumpkin
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  17. #17 Re: Misfires after having new spark plugs & cat put in.. *yay* (+ hard starts) 
    Turbo is the way to go. BillBoost37's Avatar
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    Seeing your thread for the first time and buzzing along through it, the first thought I had on post one was get the Bosch plugs out of the engine. Put in either an NGK or AC Delco plug, our cars seem to dislike Bosch spark plugs and bosch o2 sensors very quickly.

    The moment I saw the picture with the MSD coils, I completely agreed with the others... those coils break down fast in this ignition system and stock coils do a much better job.

    At this point, I wouldn't 100% rule out the cat and I wouldn't swap a new one on either. I'd do the plugs and go from there.
    I drink..so consider that when reading my posts.

    2010 Audi A6 Dual IC's
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  18. #18 Re: Misfires after having new spark plugs & cat put in.. *yay* (+ hard starts) 
    SE Level Member wickedfrisone's Avatar
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    Quote Originally Posted by BillBoost37 View Post
    Seeing your thread for the first time and buzzing along through it, the first thought I had on post one was get the Bosch plugs out of the engine. Put in either an NGK or AC Delco plug, our cars seem to dislike Bosch spark plugs and bosch o2 sensors very quickly.

    The moment I saw the picture with the MSD coils, I completely agreed with the others... those coils break down fast in this ignition system and stock coils do a much better job.

    At this point, I wouldn't 100% rule out the cat and I wouldn't swap a new one on either. I'd do the plugs and go from there.
    Ah, I didn't know that about them not liking Bosch, haha. Actually the day before we got the new plugs put in, my dad also had Bosch plugs put in his car (he has an '06 base) and he hasn't had any issues at all...lucky for him.
    I still definitely have been wanting to try getting original coils on him because I have been suspicious of the MSD ones as soon as I called MSD and they told me these weren't designed for this engine nor did they have any options for it. That, and that from the service/part purchase records the previous owners gave me, it looks like they bought these coils and wires 8 years ago so might've been enough time for them to start failing maybe.
    I did go into Advance yesterday and ordered a fuel filter through them (they were out of stock but another store had them) so hopefully I can get that changed out soon and see if it helps at all.

    When I got the OBDII back on him after the CEL came on it turns out its not the cat again (thank goodness) and just a P0300 random / multiple misfires code. Apparently the computer JUST now realized the engine has been misfiring, lol.

    I was wondering if it turns out there is low fuel pressure causing the misfires and replacing the filter does not help, what would be anyone's next guess as to what needs to be looked at to resolve the low pressure?
    Just because even if this may not be Pumpkin's problem, I have a feeling my mom's Bonneville is having low fuel pressure problems among other things. The Bonnie does have a code for bad cat but also another for bank 1 running too lean, plus the engine often shuts off two seconds after it turns over requiring one to try again and give it some gas to get it to not die. This often happens at the gas pump too after filling the tank a bit - acts as though there's no fuel at all. Not to mention the fuel pump starts making loud noises (think of a mini A-10 Thunderbolt firing a mini 30mm cannon - I guess not 30mm anymore) quite often when driving the car at random. That and I'm pretty sure the fuel level sensor is bad in the Bonnie too as usually the gauge shoots straight to either full or empty while the car is running, never the actual correct fuel level.
    (if anyone is wondering the Bonnie is the 3800 series 2, NA)

    So many problems, not enough solutions (not to say everyone on the forum hasn't been helpful, because you definitely have)
    2004 Grand Prix GTP Comp G, aka Pumpkin
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  19. #19 Re: Misfires after having new spark plugs & cat put in.. *yay* (+ hard starts) 
    Turbo is the way to go. BillBoost37's Avatar
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    Hold on a second.. you still have the MSD's on the engine?

    Here's how I fix problems and it's fairly well proven itself ....every single time.
    1. Replace the known bad parts. In your case go to a junkyard with a 5.5mm socket/nutdriver, then pull a set of coils from any Bonneville, Park Ave, GP, Lucerne, Riviera... basically any car that has the same looking coil. Second, order some fresh NGK plugs and get those items installed.
    2. Take it for a drive and see what has changed
    3. Did you mention there is a newer maf sensor in the car? if it didn't come from GM, pick one of those up at the junkyard while you are there. In this case there are a couple different ones, so take yours out and snap a picture of it or the number on top of it. Install and see where that puts you.

    P0300 can be caused by a bunch of differing things. Personally I prefer to have one cylinder misfiring so you can go after that specifically. I'm betting between the coils and plugs that you fix the misfires.
    I drink..so consider that when reading my posts.

    2010 Audi A6 Dual IC's
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  20. #20 Re: Misfires after having new spark plugs & cat put in.. *yay* (+ hard starts) 
    SE Level Member wickedfrisone's Avatar
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    The MAF sensor was ordered online and came off a Malibu I believe, but is the same exact model as what was in there before. I did wonder if the new one was faulty as well since there was no improvement but I wasn't going to harass someone about it for an $8-ish refund haha..
    I have noticed several weeks back that sometimes when moving the car around in the driveway (as we have to play musical cars here sometimes) he will start normally and as soon as I put him in reverse, even if I'm not moving yet the engine would start to idle funny - rpm's fluttering a bit but oddly enough only on those occasions when in reverse and moving slowly or not at all.
    Anyways the coils have definitely been on my list but just haven't had a chance to go out to the scrap yard again..and this week's been awful hot too.
    Now I just got the idea just to be sure I could temporarily borrow the Bonnie's coils which are oem I believe and take Pumpkin for a drive with those on and see if there are any improvements, if so I will obviously give them back to my mom because I'm not a jerk and make it a point to go to the junkyard sooner than later lol.
    2004 Grand Prix GTP Comp G, aka Pumpkin
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