I'm sure this car was traded in for a reason and the longer I have it, the more I've got to believe this is true. I just finished replacing the starter motor on my 05 GXP and I drove the car the next day with absolutely no problems with it running (except SES light on for P0128 code). I go out on Saturday and start driving it and not only is the SES light on, it's now flashing and the car acts like it's missing badly. I give up. Just pulled the codes and I have P0128, P0136, P0137 and P303 cylinder 3 misfire. I was extremely careful with all the injector wires when doing the starter job and like I said, it ran just fine on Friday. The P0128 may be coming from the cooling fans running all the time as someone has run a jumper wire from the underhood fuse box to the fans. Double checked all injector connections and they seem to be snug. I also just serviced the K&N air filter but doubt that has any connection to these problems. I'm perplexed...........

It means you have air entering post MAF most likely. P0136 and 137 are low voltage for the post-cat HO2S's. If they're low, that means they're running lean, which is indicative of air intrusion post MAF, which in order to replace the starter, you removed intake parts...

_________________


Retired Bonneville Owner and former GM Tech:
2004 Pontiac Bonneville GXP: Black/Ebony *SOLD*

Summer Toys: Combined 827 RWHP / 877lb/ft RWTQ
2004 Pontiac GTO: Impulse Blue Metallic/Black/M6: lots 'o mods, 415 RWHP / 405lb/ft RWTQ!
2006 Cadillac STS-V: Light Platinum Metallic/Light Gray/A6 - Spectre CAI, Magnaflow exhaust, Speed Inc. tune, 412 RWHP / 472lb/ft RWTQ

Daily Drivers:
2019 Chrysler Pacifica Limited: Mommy's new RGC
2015 Chrysler Town & Country Limited Platinum: Kids new RGC
2007 Chrysler Town & Country Limited: Sold to neighbor
2009 Pontiac G8 GT: L76, Sport Red Metallic
2003 Chevrolet Suburban 2500: Doeskin Tan - 8.1L Big Block... new plow truck
1999 Chevrolet Suburban: Sunset Gold Metallic - Daddy's winter beater and plow truck

The intake on the N* engine is very prone to air leaks.
The gaskets to the ports and the large rubber and metal
coupling gasket from the intake to the throttle body should
have been replaced with new when you removed the intake.
Also the plastic tube and rubber hose that is part of the PCV
that runs under the intake to the back cam cover endures
a lot of heat and can leak air if old.
Like Lane said, you messed with the intake, that would be the
first place to look. Unmetered air will make cylinders run lean
and eventually misfire.

_________________
Black 95 SSEi (original owner) 238K miles
Black 05 GXP (some idiot put the first 12K on it)186K miles
Black 04 Tahoe (original owner)310K miles
Black 16 Traverse (original owner)90K miles
Black 15 Lacrosse (some nice lady put first 15K on it)43K miles


"You can have one in any color as long as it's black" - H. Ford

Installed new seals to the intake ports on the bottom side of the plenum, set it down very straight and carefully, torqued in 2 steps to 89 inch pounds. Replaced the rubber between the throttle body and the plenum. Not sure about the hose you mentioned that runs under the intake for the PVC system?? (I'm assuming the one on the passenger side end of the plenum runs partially under the plenum?) I removed the plastic hose and rubber from the front cam cover and the one that runs from the passenger side of the plenum to the rear cam cover (I only pulled the tube out of the rubber and not the rubber hose off) and the small vacuum line from the top of the throttle body to the small vacuum pot on the rear fuel rail and that was about all. I cleared all the codes yesterday and the car still had a misfire when I started it. Didn't let it run long enough to set any more codes. What drives me crazy is the car ran fine all day Friday and I drove it a bunch.............

There was another guy on a different GM forum having the exact same
codes and problems with his GXP. He was taking it to a dealer and they
weren't permanently correcting the issues as he was going back to them.
I read the entire thread but he never posts about resolving the issue.
He did mention exhaust emission problem was part of the diagnosis.
I'm wondering if you may be having catalytic converter issues.

Also you need to find out what temperature the engine is operating
at when fully warmed up. If it is actually running too cold, from maybe
a stuck thermostat or something, you need to correct that first, and
get rid of the PO128.

Do you have a scan tool that will show operational parameters so
you can watch what the O2 sensors are doing and read the voltage?
Also a scan tool can tell you what the coolant temp sensor is reading.

_________________
Black 95 SSEi (original owner) 238K miles
Black 05 GXP (some idiot put the first 12K on it)186K miles
Black 04 Tahoe (original owner)310K miles
Black 16 Traverse (original owner)90K miles
Black 15 Lacrosse (some nice lady put first 15K on it)43K miles


"You can have one in any color as long as it's black" - H. Ford

I do have a reader that has 'Live' information on it. As I said above, the fans run all the time as there is a wire running from the underhood fuse box to the fans and they start running as soon as you start the engine. I'd assume that this was done because possibly the fans weren't coming on when they actually should have. (Or maybe not at all.....)

Since Pontiac is no longer in business, would the best place to take this thing if I decide not to fool with it, be a Cadillac dealer since it has the Northstar engine? I'm just not sure how long or how much I want to fool with this car............or does anyone know a good place to take it in the Frederick, Maryland area? Thanks.

Hopefully the fans weren't jumped as some asinine method of trying
to fix an overheating engine. If the engine was overheating, it could
have other major issues.
If you use the scanner you can find what the computer "thinks" the
engine temp is. You should also watch the o2 sensors. They should
be cycling between 100mv and 800mv. I have forgotten some of this
stuff as it has been a while, but do some internet searches on how an
ECM controls fuel mixture and all the correct parameters needed.
It's actually fascinating stuff, and really helped me get my GXP
running good.

Some others might add some thoughts on some easy things to look for.

And yes, use a Cadillac dealer to fix the Northstar, but bring Vaseline and
your checkbook.

_________________
Black 95 SSEi (original owner) 238K miles
Black 05 GXP (some idiot put the first 12K on it)186K miles
Black 04 Tahoe (original owner)310K miles
Black 16 Traverse (original owner)90K miles
Black 15 Lacrosse (some nice lady put first 15K on it)43K miles


"You can have one in any color as long as it's black" - H. Ford

Since I don't have a shop manual for this car it's tough to try and find the fixes. Since someone jumped the power to the fans and they run all the time, can someone tell me how they should be triggered to go on and off? I know most GM cars when you turn on the A/C then the fans will come on but when the A/C is off there is usually a temperature sensor or thermal switch that controls them. Any one know where I can find a service manual?

I don't have a service manual for my GXP. They are hard to get and
expensive. Ebay is where I purchased one's for other vehicles.
I've just used this forum and other internet sources to fix it.
There are a lot of Caddy's out there with Northstar engines so
the internet is full of sources of information.

I would disconnect that jumper and see what the fans do and what
temperature the engine is running at using the scan tool and not
the gauge. Then go from there to find the misfire. It could
be a coil causing it just by coincidence and not a lean fuel
condition.

_________________
Black 95 SSEi (original owner) 238K miles
Black 05 GXP (some idiot put the first 12K on it)186K miles
Black 04 Tahoe (original owner)310K miles
Black 16 Traverse (original owner)90K miles
Black 15 Lacrosse (some nice lady put first 15K on it)43K miles


"You can have one in any color as long as it's black" - H. Ford

Guess I'll start there..............

Spent about 20 minutes searching for air leaks using brakleen around all hoses and connections and the intake plenum and did not find any leaks. The small PCV system elbow off the front end of the plenum appears to have been replaced already and showed no sings of sucking the brakleen into it. Since I cleared the codes the other day I only have the P0303 cylinder 3 misfire and of course #3 is underneath whatever that big thing is bolted over #3 & #5 plugs. I guess my next thing to do is pull the coil and check the plug. Does anyone know the electrical specs. for the single coils? Thanks

After looking at Rock Auto site for coils, I checked mine and they are all black epoxy so I assume by that, that I can replace the coils individually and not have to replace the whole rack of 4? (If 1 is bad)

I think you're referring to the seconday A.I.R. system. Typically if it is an ignition system fault, it is a constant cycling misfire. Meaning, not erratic or sometimes there, sometimes not.

I'm not saying a coil module can't go bad, but it is highly unlikely. GM doesn't publish specs on them that I've ever seen, just figure at a minimum, around 40k volts. When they do go bad, it's not the coil itself on these, it's the spring connector in the base that makes contact with the plug (this module is a one piece setup that simply mounts over the plug).

Could be a cracked plug...

_________________


Retired Bonneville Owner and former GM Tech:
2004 Pontiac Bonneville GXP: Black/Ebony *SOLD*

Summer Toys: Combined 827 RWHP / 877lb/ft RWTQ
2004 Pontiac GTO: Impulse Blue Metallic/Black/M6: lots 'o mods, 415 RWHP / 405lb/ft RWTQ!
2006 Cadillac STS-V: Light Platinum Metallic/Light Gray/A6 - Spectre CAI, Magnaflow exhaust, Speed Inc. tune, 412 RWHP / 472lb/ft RWTQ

Daily Drivers:
2019 Chrysler Pacifica Limited: Mommy's new RGC
2015 Chrysler Town & Country Limited Platinum: Kids new RGC
2007 Chrysler Town & Country Limited: Sold to neighbor
2009 Pontiac G8 GT: L76, Sport Red Metallic
2003 Chevrolet Suburban 2500: Doeskin Tan - 8.1L Big Block... new plow truck
1999 Chevrolet Suburban: Sunset Gold Metallic - Daddy's winter beater and plow truck

It seems to be mis-firing all the time right now at all RPM's. I assume that the secondary AIR thing can just be unbloted and moved slightly out of the way to get to #3 plug without damaging it. (It has a ribbed metal pipe that runs out the bottom of it?) On the question of the coil, is there a specific resistance I should be looking for between certain terminals?

That tube bolts to the exhaust manifold. Two 10mm nuts.

As to resistance, I don't think I've ever seen any published specs as they're simply R&R if not good. The quickest way to troubleshoot it, is to move it to another cylinder and see if the misfire moves with it.

_________________


Retired Bonneville Owner and former GM Tech:
2004 Pontiac Bonneville GXP: Black/Ebony *SOLD*

Summer Toys: Combined 827 RWHP / 877lb/ft RWTQ
2004 Pontiac GTO: Impulse Blue Metallic/Black/M6: lots 'o mods, 415 RWHP / 405lb/ft RWTQ!
2006 Cadillac STS-V: Light Platinum Metallic/Light Gray/A6 - Spectre CAI, Magnaflow exhaust, Speed Inc. tune, 412 RWHP / 472lb/ft RWTQ

Daily Drivers:
2019 Chrysler Pacifica Limited: Mommy's new RGC
2015 Chrysler Town & Country Limited Platinum: Kids new RGC
2007 Chrysler Town & Country Limited: Sold to neighbor
2009 Pontiac G8 GT: L76, Sport Red Metallic
2003 Chevrolet Suburban 2500: Doeskin Tan - 8.1L Big Block... new plow truck
1999 Chevrolet Suburban: Sunset Gold Metallic - Daddy's winter beater and plow truck

That's what I'm going to do. Got it out and am replacing the spark plug while it's out and will move it to a front side cylinder. Here's hoping...........

UPDATE: Put back together and started it up. Could tell it was still mis-firing so I pulled the connector for the #3 cylinder fuel injector and could tell the engine sound changed. Then I pulled the injector connector for #6 (where I swapped the #3 coil to) and there was no change in engine sound so I've got to imagine the coil is bad even though resistance figures between the two were very similar in numbers. It also set a P0206 injector code for cylinder #6. Will order a new coil and install when I get back from vacation........

The issue I bet is the spring loaded connector within that whole unit that actually makes contact with the plug. That is why it tests out to equal/similar resistance.

_________________


Retired Bonneville Owner and former GM Tech:
2004 Pontiac Bonneville GXP: Black/Ebony *SOLD*

Summer Toys: Combined 827 RWHP / 877lb/ft RWTQ
2004 Pontiac GTO: Impulse Blue Metallic/Black/M6: lots 'o mods, 415 RWHP / 405lb/ft RWTQ!
2006 Cadillac STS-V: Light Platinum Metallic/Light Gray/A6 - Spectre CAI, Magnaflow exhaust, Speed Inc. tune, 412 RWHP / 472lb/ft RWTQ

Daily Drivers:
2019 Chrysler Pacifica Limited: Mommy's new RGC
2015 Chrysler Town & Country Limited Platinum: Kids new RGC
2007 Chrysler Town & Country Limited: Sold to neighbor
2009 Pontiac G8 GT: L76, Sport Red Metallic
2003 Chevrolet Suburban 2500: Doeskin Tan - 8.1L Big Block... new plow truck
1999 Chevrolet Suburban: Sunset Gold Metallic - Daddy's winter beater and plow truck

I guess that wasn't one of Fords 'Better Ideas' that GM stole.............

Well, good news. Replaced the coil unit and it's now running on all 8 again!! Hoo-rah. No codes have re-appeared again (yet) so we'll just wait and see what happens next............

What was? GM was one of the first to use C-N-P/C-O-P ignition systems. GM, toyota (gawd I hate to say that), and BMW were some of the first to utilize this setup. GM didn't steal anything from ford.

However, glad you found the issue.

_________________


Retired Bonneville Owner and former GM Tech:
2004 Pontiac Bonneville GXP: Black/Ebony *SOLD*

Summer Toys: Combined 827 RWHP / 877lb/ft RWTQ
2004 Pontiac GTO: Impulse Blue Metallic/Black/M6: lots 'o mods, 415 RWHP / 405lb/ft RWTQ!
2006 Cadillac STS-V: Light Platinum Metallic/Light Gray/A6 - Spectre CAI, Magnaflow exhaust, Speed Inc. tune, 412 RWHP / 472lb/ft RWTQ

Daily Drivers:
2019 Chrysler Pacifica Limited: Mommy's new RGC
2015 Chrysler Town & Country Limited Platinum: Kids new RGC
2007 Chrysler Town & Country Limited: Sold to neighbor
2009 Pontiac G8 GT: L76, Sport Red Metallic
2003 Chevrolet Suburban 2500: Doeskin Tan - 8.1L Big Block... new plow truck
1999 Chevrolet Suburban: Sunset Gold Metallic - Daddy's winter beater and plow truck