Hello,

I just had my engine rebuilt by Northstar Performance in Ontario. For the last couple of weeks since I got it back it's been running great but today I was driving and slowed down at a stop light and it began running rough. I put it in neutral and revved the engine a little bit and at higher RPM it went away. When it went back to idle it started running rough again. I took off from the light and it seemed fine driving it but when I got to the next light and slowed down same thing. This time the SES light came on. I pulled into a parking lot and let it idle (roughly) for a minute and then the SES light began to flash which seems to indicate a misfire.

I got home and read the code and it was a P0300 with no followup code so it's just random misfire. Everything that I've been reading so far tends to indicate a vacuum leak more than anything else because it's only happening at an idle. I don't have a fuel pressure gauge to test the pressure on the fuel rail but if I need to buy one I will.

As far as vacuum lines I wonder if someone has an image of the engine compartment that they could edit and outline the location of all the lines? I don't know where all the vacuum lines run to check them. I see a few but I don't know how many there are.

I have checked all the connections on the coil packs on the front bank and the fuel injectors as well. I'm not sure how to get at the rear bank to check those connectors.

Jake said he put in all new spark plugs so not likely a plug.

Any ideas or help is appreciated - or a methodical approach to diagnosing this issue is good too!

Thanks,
Rich

In my experience, I'm 99% sure its a coil. Get a scantool on there that reads live data and find the misfire. Simply swap the coil around with another to confirm that's the issue.

_________________
Andrew - owner/operator of Bonnevilles Unlimited

2004 Bonneville GXP | 60k | White Gold Tricoat | custom built supercharged 3800 hot rod | garage queen
1997 Corvette | 55k | Silver Metallic | Z06 wheels | Date-night Hauler/Parts runner
2014 Town & Country Limited | Cashmere Pearl | 95k | Family Hauler
2002 Ram 1500 Quad Cab Sport | Black| 260k | Official Bonneville Hauler

Ran the engine this morning with Torque Pro running and the SES light started flashing. Pulled the code and got cylinder 6 misfire... then it went back to P0300 random misfire. I'm guessing start with Cyl 6... but I don't know which that is... I'm guessing in the rear bank?

All the coils on this engine have 160k on them. Maybe I should replace all?

Rich

#6 on a Deathstar is front bank, second from the drivers side. #8 is the first on the drivers side. Swap the two coils. If your misfire moves to #8, then you know it was the coil.

Anytime a misfire trips the counter, P0300 will generate. Some GM PCM's and the tool you use will also indicate P030x where the "x" is the affected cylinder(s). Otherwise, you need to monitor, under engine data, the misfire menu and look at current misfires. If nothing there, look up history misfires. At least on a Tech 2 anyway. I am not familiar with this program you're running so I am not sure where that is at. But the same methodology would apply regardless.

_________________


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

#6 coil is easy to deal with, should only take a few minutes to swap them around.

_________________
Andrew - owner/operator of Bonnevilles Unlimited

2004 Bonneville GXP | 60k | White Gold Tricoat | custom built supercharged 3800 hot rod | garage queen
1997 Corvette | 55k | Silver Metallic | Z06 wheels | Date-night Hauler/Parts runner
2014 Town & Country Limited | Cashmere Pearl | 95k | Family Hauler
2002 Ram 1500 Quad Cab Sport | Black| 260k | Official Bonneville Hauler

I just found a two-pack of 4 coils (all 8) on Amazon for $130 so I think I'm just going to replace them all since it's got so many miles on it.

Next question is can someone give me some advice on how to do the rear bank? I have the alldata subscription but often there are better procedures than the shop manual has to get it done.

Thanks,
Rich

Most people don't like doing this job because of the obvious tight access. Since you plan on changing the bank, there really isn't an easier way. The manual suggests you can replace an individual coil (which you'd need to of course do four times over) and it may save a couple of steps. Part of the problem here is that since the service manual was written, GM changed something with the coils. When my right bank was replaced under warranty, they had to change the entire assembly. As I recall, the existing harness on the cassette will not plug into the new design coils. So... basically, just go through the steps and replace the bank as a whole. There's unfortunately no real way here to get around moving things that are in the way.

There are some tools that would make life easier but aren't completely necessary. Mostly, a set of 1/4-inch drive deep magnetic sockets. These are very helpful when removing and reinstalling the 10mm nuts deep behind the engine where the intermediate hose (pipe) connects to the manifold from the bottom of the solenoid (mounted on top of the cam cover).

There's also a gasket between the manifold and intermediate pipe which the manual says needs to be replaced when taken apart. I'd bet most people don't, but just letting you know ahead of time. It's GM P/N: 12564682.

_________________


Bose Luxury Sound System w/Touch Screen Navigation, Addition of Factory XM, 2005 MY Antenna, OnStar Upgrade (3G),
RainSense Wipers, Backup Camera, '00 Style Door Panel Courtesy Lights, Heated Washer Solvent, 2X Remote Trunk Release,
Turn Signal Mirrors, Center Console Courtesy Lamp, Rear Outboard Heated Seats, PVD Chrome 18" Factory Rims, Upgraded
Carbon Fibre Appearance Interior Trim, Highly Modified Main Body Harness, Instrument Panel, Door, Door Panel & Headliner
Wiring Harnesses, Custom Fuse Box & Tire and Loading Information Decals, Additional Acoustic Insulation

I had to do this (replace a coil on the LC3), this weekend as I had a random misfire on #4. And working on an LC3 is a heck of a lot harder than an LD8 in this facet. I too like to pull the whole "Cartridge" as GM calls it), it just makes life so much easier, especially with the tight, nearly inflexible wiring harness and obstinate plug release mechanisms.

LC3 work constraints;


#4 out of the cartridge;


New #4 in the cartridge;

_________________


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

OK I have replaced the front bank coils. Made no difference. I may try to tackle the rear bank tonight but since I got the cyl 6 code and cyl 6 has been replaced I'm not sure if it's a coil issue.

Rich

It's not likely a plug based on what you say, but things happen. It may be worth pulling it to have a look and perhaps swapping it with Cyl 8 as well.

_________________


Bose Luxury Sound System w/Touch Screen Navigation, Addition of Factory XM, 2005 MY Antenna, OnStar Upgrade (3G),
RainSense Wipers, Backup Camera, '00 Style Door Panel Courtesy Lights, Heated Washer Solvent, 2X Remote Trunk Release,
Turn Signal Mirrors, Center Console Courtesy Lamp, Rear Outboard Heated Seats, PVD Chrome 18" Factory Rims, Upgraded
Carbon Fibre Appearance Interior Trim, Highly Modified Main Body Harness, Instrument Panel, Door, Door Panel & Headliner
Wiring Harnesses, Custom Fuse Box & Tire and Loading Information Decals, Additional Acoustic Insulation

All back together with rear bank replaced now. Still getting P0300 and it's misfiring... it seems to be running a little better but it's still missing. I still am not getting any specific cylinder codes - just the P0300 so likely something else maybe?

Are you saying pull the plug for cyl 6? Not sure what good swapping will do if I am not getting a specific cylinder code - I don't know how I would tell if the problem moved.

Could this be a bad EGR valve?

Rich

Based on your earlier posts, I was kind of under the impression you had reason to believe it may be cylinder 6.

According to the service manual, if a crankshaft position sensor relearn was not completed (which may have been the case here, and after pretty in depth engine work), it can result in setting P0300. One of the first diagnostic steps is to complete this procedure. You absolutely must have an appropriate scan tool to perform this function.

Getting back to a misfire (should this be the ultimate cause)...
I've had some instances of receiving a generic P0300 DTC but was able to quickly identify the culprit cylinder this way. Otherwise, you're just guessing. If everything comes up clean, then I'd start looking elsewhere.

_________________


Bose Luxury Sound System w/Touch Screen Navigation, Addition of Factory XM, 2005 MY Antenna, OnStar Upgrade (3G),
RainSense Wipers, Backup Camera, '00 Style Door Panel Courtesy Lights, Heated Washer Solvent, 2X Remote Trunk Release,
Turn Signal Mirrors, Center Console Courtesy Lamp, Rear Outboard Heated Seats, PVD Chrome 18" Factory Rims, Upgraded
Carbon Fibre Appearance Interior Trim, Highly Modified Main Body Harness, Instrument Panel, Door, Door Panel & Headliner
Wiring Harnesses, Custom Fuse Box & Tire and Loading Information Decals, Additional Acoustic Insulation

The engine work was done by Northstar Performance out of Ontario Canada. All he does is works on Northstar engines so I would be very surprised if he didn't do the required learn procedure but stranger things have happened.

Also the car has been running fine since I got it back for about 2 weeks and then this popped up so it's like something failed or came loose or something like that. I went ahead with the coil packs since the old ones had so many miles on them anyway but aside from getting a scan tool to watch the data I'm not sure what I can do. Maybe I may need to take it in to the dealer to diagnose... I hate the thought of that though.

Oh and the cylinder 6 thing is that it threw a P0306 one time... but hasn't done it again since.

Rich

I completely understand what you're saying. I've had people that work on cars (and Northstar engines) all day long miss things with my car when it was serviced under warranty (because I typically don't let anyone touch my car otherwise). I can only point you toward the diagnostic steps outlined in the FSM (of which this is the first step - in big red letters). Just because it ran fine for a couple of weeks also doesn't mean this can't be the problem and can't be related to the crankshaft position sensor or associated wiring. Basically, without a scan tool everybody is simply guessing. If you want to tackle it yourself, this is a must.

_________________


Bose Luxury Sound System w/Touch Screen Navigation, Addition of Factory XM, 2005 MY Antenna, OnStar Upgrade (3G),
RainSense Wipers, Backup Camera, '00 Style Door Panel Courtesy Lights, Heated Washer Solvent, 2X Remote Trunk Release,
Turn Signal Mirrors, Center Console Courtesy Lamp, Rear Outboard Heated Seats, PVD Chrome 18" Factory Rims, Upgraded
Carbon Fibre Appearance Interior Trim, Highly Modified Main Body Harness, Instrument Panel, Door, Door Panel & Headliner
Wiring Harnesses, Custom Fuse Box & Tire and Loading Information Decals, Additional Acoustic Insulation

As stated in an email, do your best to pinpoint the cylinder w/o a scan tool by unplugging one injector at a time and go from there. PCMs can fail, so can crank sensors and cam sensors. If it is cyl #6 is in the front so easy to do a quick compression test on it. Nothing should be wrong mechanically after such a short time since the build, should have many miles to go on that engine now. With that said, if you have a cylinder that's getting fuel but no spark, I'd be concerned about cylinder wash down especially with fresh rings.

If I was close I'd diagnose this for you but the best I can do is help via interwebs right now.

You could remove the front coil and pull the plugs, have a quick look at them. Plugs will tell you a lot by their color. Email or post a pic.

If there's a fault with the build I'll take care of it, but I don't believe in jumping to conclusions so let's start with the basics.

How fancy is your scan tool? If it is more than a simple code reader, it should be able to read misfires. There is usually a "misfire data" menu. You can go in there and monitor in live time, current misfires by individual cylinder, as well as look up history misfires by individual cylinder.

You put in all new plugs, were they OEM temp range? Meaning, were they 41-987 or equivalent cross-reference.

_________________


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 have a Tech2. I am not near the OP's car right now, he's 4-5 hours away in Michigan. A Tech2 (and many other scanners) will show the misfire counts as you said across individual cylinders and it's very handy for diagnosis such as this. The plugs were either 41-987s or a Denso equivalent. I've never had issues with Denso plugs but any plug can fail and I'm hoping that's all that may be the issue here. Will wait to hear back from the OP via email.

I would quickly pull # 6 plug and be sure its proper: doesnt that setup use a spring for the plug?

_________________
poverty forces one to do unorthodox things

2000 SSEi
past rides:
1996 SSEi
1992 GTP
1987 Grand Am

The coil does, which is what we've been saying. Swap the coils.

_________________


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 meant that for the OP. Not sure what he's using.

On a T2's, it's usually under engine data, then a misfire data sub-menu.

_________________


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