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Missing or Knocking under a load, HELP!!

Morris 04 GTP

Morris 04 GTP

New member
I changed the plugs in my 04 GTP w/ 98k. I put in autolite platinum 605's. At an idle it used to have a periodic miss which annoyed me, it's gone not, great. During normal driving it's nice and smooth again, great. But now if I put a load on it to pass somebody or going up a decent hill, it boggs down skips and misses. Any clues as to what would cause this? the one heat level cooler should do that right? It's bone stock.
 


TB and MAF might need a good cleaning. ('04s are drive by wire right?)
Otherwise it might be the following (for starters, or your problem is further down the line):
Bad plug wires
Clogged injectors
Bad coils
 
Many people say you are better off with a copper plug in a boosted car.

Can you get a scan of what is misfiring? Most likely a coil, plug, or wire as stated above.
 
605's are just a hair cooler than stock... what did u gap the plugs at? im assuming u put new wires on too? what kinda wires did u get?
 
Were you having knock issues with stock heat range plugs (indicated with a scan)? Or just threw a colder plug on for the heck of it? The Army's got a saying: "If it ain't broke, fix it 'till it is." You may have only needed fresh stock plugs to fix your problem, not colder plugs.

Though, at 98k, could be a clogged fuel filter (should change this anyway - it's $15), if your MAF sensor and throttle body are clean.
 
I had similar issues recently:

http://www.grandprixforums.net/f18/installed-plog-dp-now-issues-w-32045.html

So far the wires seemed to be the problem. I found a hole in the #4 wire. Exactly like you I would get skips and misses under load. Since I replaced the wires on Saturday, the problem has not returned. I'm running the exact same plugs as you and have been for about two years.
I will continue to monitor and see if the problem stays gone.

VictorSmalls said:
Many people say you are better off with a copper plug in a boosted car.
Click to expand...

I've heard this as well but so far no one has been able to tell me why. I don't mean to jack the thread but I'm curious to know if anyone has any insight...
 


I didn't replace the wires at the time due to low funds, but that was my first thought was the wires are doing it seeing they gave me a hard time coming off. Once I have the money I'll try some new wires. I didn't have it scanned to see if it had knock before, but I plan on doing a fwi and some other mods in the future and wanted to be safe so I went a hair cooler for these plugs. I didn't gap them because they are platinum and if you gap them you will crack the coating and at that point there is no benifit. I'm going to take them out and check the gap though, they're supposed to be pre-gapped at .060" but you can't rely on them I guess. The cooper cores are better for performance because they expell the heat quicker which will help with more power, the platinum/iridate plugs are designed to have a longer life. 100K versus once a year. matter of preference, this is my wifes driver so it doesn't need to be a hot rod. If I'm wrong about the reason most go for the cooper core please correct me. I'm only going off of what I remember from a thread on this matter. Thanks for the help guys. I'm gonna pull the plugs and wires this weekend (weather permiting) check the gaps and see if there is any obvious damage to the wires, maybe i'll find one isn't completely snapped on or something. I hope I can get this straightened out, Even not running right I can feel a big increase in nut since the new plugs.
 
So...

Platinums = longevity
Coppers = performance

Right?

Let us know how it goes with the plugs and wires and if you see a diff - I'm curious.

If I find out my wires weren't the problem, I'm going to look in to plugs and coils next.
 
Copper has less resistance as well.

I had this issue when trying to get past 3 PSI of boost and it was my ICM.
 
I love write-ups.
From Side Gapping Spark Plugs by SyntheitcShield:
There is yet another source of resistance we have not yet considered. The resistance of the spark plugs themselves. Have you ever heard the term resistance spark plug. There is a finite amount of resistance built into the spark plug, though no where near the amount found in the plug wires. However, the very construction of the plugs, the materials they are made of, can be a huge hindrance to the spark voltage.
Today you can buy plugs made of all sorts of things. Copper, Platinum, Iridium and so on. The exotic metal spark plugs have become all the rage in recent years primarily because of reduced maintenance. Platinum and Iridium do resist erosion or wear quite well. But the combustion chamber of a normal engine is quite the violent place and presents an extremely harsh environment to spark plugs. I have pulled platinum plugs (the so called 100,000 mile plugs) out of customer vehicles before as a result of a complaint of a lack of power and hesitation with 70,000 miles and found the gaps on the plugs were nearly two and a half times the recommended gap.
If you look at the resistances of various metals you will quickly see just what a hindrance some exotic metal plugs are. Lets take a look at a few.
Aluminum - 2.65 Micro Ohms per centimeter
Gold - 2.24 Micro Ohms per centimeter
Copper - 1.67 Micro Ohms per centimeter
Silver - 1.58 Micro Ohms per centimeter
Platinum - 10.5 Micro Ohms per centimeter!
Iridium - 4.7 Micro Ohms per centimeter!
As you can see, platinum has over 6 times the resistance that copper does, Iridium is nearly 3 times higher. Only Silver comes in with a lower resistance than does copper. In the effort to maximize ignition system efficiency, copper rules. Couple the lower overall resistance of copper plug and low resistance plug wires with side gapping, you will make the most of your ignition systems capability.
Click to expand...
 
Great info, thanks! So my next question (again, pardon the thread jacking) is what kind of replacement schedule are you committing to with copper plugs? Yearly?
 


I've seen anything from 10k miles to 30k miles. I would probably stick with 25-30k unless I noticed a decrease in performance (then change sooner). My guess is that these things start getting pretty worn out past 30k - they're less durable than the expensive plugs, and besides, by 30k, they'll probably start going out of gap. I mean they're fairly soft copper just hanging out in a chamber full of explosions for like two years. I wouldn't bother re-gapping when you can get a new set for $12, and you're going to have to take them out anyway.
 
I spent $12 for my set of autolite platinums at Wal-mart. I figured for the same price I'd just get the platinums and they would last longer.
 
I went out and checked my wires and found a couple that didn't seem like they were completely "snapped"on. I re-installed them and took it for a ride. For the first part of the ride it was great, plenty of smooth power. after a minute or two it strated again. progressively getting back to how it was. I think it's just work out plugs not keeping a tight enough grip. I'm gonna try to get some wires this weekend. I'm debating whether or not to spend the $30 on wires or save more for the $100 for my window regulator for my truck that has tape holding the window up. I didn't forget one thing and wonder if anyone knows what it it. While doing the plugs, I slipped and hit one of the two sensors (with my arm) that are mounted onto the bracket just above rear valve cover. The plastic clip holding to the bracket broke. I used a zip-tie to keep it place and it hasn't moved. Does anyone know what these sensors are?
 
Same thing happened to me with the wires. I tried fiddling with them and it worked for like a whole hour and then slowly came back.
 


Morris 04 GTP said:
I went out and checked my wires and found a couple that didn't seem like they were completely "snapped"on. I re-installed them and took it for a ride. For the first part of the ride it was great, plenty of smooth power. after a minute or two it strated again. progressively getting back to how it was. I think it's just work out plugs not keeping a tight enough grip. I'm gonna try to get some wires this weekend. I'm debating whether or not to spend the $30 on wires or save more for the $100 for my window regulator for my truck that has tape holding the window up. I didn't forget one thing and wonder if anyone knows what it it. While doing the plugs, I slipped and hit one of the two sensors (with my arm) that are mounted onto the bracket just above rear valve cover. The plastic clip holding to the bracket broke. I used a zip-tie to keep it place and it hasn't moved. Does anyone know what these sensors are?
Click to expand...

Does anyone know what those sensors are?
 
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