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2005 Grand Prix 3.8L suddenly doesn't want to run then shoots a P0300

G

Grindal

New member
So, I have been looking all over and I haven't seen anything too close to my problem. I'm new, so forgive me if I forget something.

I have a 2005 Base Grand Prix ... no ABS, no TCS, just me and the road. (I hate this car, didn't want to get it but I had to get something to drive.) Yesterday I was driving @ work and for no reason it lost power, for a little while before the power left it, it was making a strange whining noise that I noticed was new. I live in the Bay Area of California and we've been dealing with a heat wave, but up until this point it had been fine. The thing is totally gutless on hills, and won't rev over 3400 RPM, doesn't even hit the limiter anymore. Idle is rough and bounces between 600 and 800, but seems fine when you put throttle to it when in park and under no load. It is spitting out a P0300 (Random/Multiple misfire) code and I have tried unplugging the MAF/MAP with no change. I have seen a lot of people talking about the ICM, but those were all on older cars. I have about 96k on this car, and it just has to last me another 2 weeks until I can finish the work I need to do on the 98 GTP I just bought.

I love the Grand Prix, 97-03 GT/GTP body style and I used to own a 2002 SE, this 2005 Grand Prix has been a nightmare from day one. I have to leave for work now, but I will try to check in on this on my break. Thanks in advance for anyone that can lend some insight. @ least my job is letting me use a company car this week.
 


I would try and figure out what is causing the misfire.

Might be plugs or a coil pack, very possible its a ICM too. You might be able to just do a straight swap with your 98's ICM just to test it out and see if it fixes the issue.
 
my first guess would be to check the connection for the coil packs make sure its good. then would look at coil packs to see if they are shorting out on you. then lastly check your dam plugs. if they are bad they cause knock.
 


I was looking @ part numbers, looks like those are the same. The ICM looks the same on both. I will try the O2 sensor tonight when I get off work. The plugs aren't that old in it either. I put Bosch +4 platinum plugs in it about 30k miles ago and they've been great so far.
 
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The wires and connectors going to the ICM look good. I am going to try swapping the ICM from the 98 tomorrow. Thanks for all the ideas.
 
Those platinum plugs are supposed to be 60,000 mile plugs. Are they really so bad in these cars that they live a half life?
 


The life of the plug does not matter, its the fact that they are Platinum.

Our cars hate those style plugs, they are known to cause issues after being in the car for a while.
 
I typed in Google...'platinum plugs in 3800 a no no'..this is what I got

Bosch acknowledges a problem with using their Bosch Platinum spark plugs in engines with ignition systems that employ 1 coil for each pair of spark
plugs (also known as a "waste spark ignition system").
In cars with conventional (1 coil, distributor/rotor) ignition systems, there
is no problem.
The problem that Bosch has acknowledged when using their Platinum plugs
in engines with waste spark ignition systems stems from the tendency of
electrode metal to get transferred depending upon the polarity (direction
of current flow) of the spark. In waste spark ignition systems, 1/2 of the
plugs always see reverse polarity sparks. Given the very narrow platinum
center electrode of the Bosch Platinums, performance will be degraded more
significantly when reverse polarity sparks will cause material to be
transferred from the large ground/outer electrode onto the narrow platinum
center electrode's exposed end surface.
In cars with conventional (1 coil) ignition systems, every spark is of
the same polarity, for which the Bosch Platinums are optimized, leaving
them to deliver their designed-in advantages, which include:
o reaching self-cleaning temperature faster ("than any other plug")
o maintaining the spark gap and low firing voltage requirement throughout
their service life. While there remain some cars with conventional ignition systems which
do not seem to get along very well with Bosch Platinums, which seemingly
no one can explain (maybe all their sparks are of the 'wrong' polarity
in some cases).
 


So, I swapped out the plugs for a new set of Autolites, and it's still running really rough. I am getting the 98 later this week so I can try swapping the ICM's.

The plugs don't look that bad, there is a strange cross mark on 4 of them where the 4 electrodes were working. One does look darker than the others, but the computer never gave a cylinder for the misfire, said random/multiple.
 
Since it's a little cooler today, I was able to do a little more trouble shooting today. Took my laptop outside and plugged in the Autotap and this time I went looking for the misfire directly. Turns out only 2 cylinders are misfiring and it's 2 & 5. Blown coil pack, thanks for all the other ideas tho ... I'm canning those Bosch plugs since it's only a matter of time for them anyway.
 
I am having this exact same issue. Number 2&5 coil not firing. I replaced it with a new coil and still didnot fix the issue. I changed my plugs 6 months ago with iridiums. Any insight would b appreciatd. I'm stuck without a car.
 
08 gp lvr said:
I am having this exact same issue. Number 2&5 coil not firing. I replaced it with a new coil and still didnot fix the issue. I changed my plugs 6 months ago with iridiums. Any insight would b appreciatd. I'm stuck without a car.
Click to expand...


does it fire, ( the coil?) or does it misfire? maybe you got the plug wires on wrong.

plugwires.jpg
 
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