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Took my intake manifold off (01 WS6) and cleaned out the valley cover area and intake ports. Replaced knock sensors while I was in there. I deep cleaned my intake manifold with simple green and a brush, and removed my fuel injectors and gaskets from the manifold before doing so. Rinsed it out, let it dry, put it all back together. Fired it up and no check engine light, however getting a P0430 (Catalyst system efficiency below threshold bank 2) and P0200 (Injector circuit/open). I checked all my injector wires, everything is snug and nothing looks damaged. No good deed goes unpunished, are there any red flags on what I could have unsettled to cause these codes?
Edit: On a second startup and code scan, it's now throwing quite a bit, which is unsettling. Getting P0307 for Cylinder 7 Misfire, P0327 and 0332 for both knock sensors, and P0300 for random/multiple misfires. I'm at a loss. I methodically replaced both knock sensors with AC Delco OEM sensors and replaced the harness with what I thought was a high quality Dorman harness. I took my time (spent all day) and while I got a lot of oil cleaned out of my intake and intake ports, I've seemed to take the car backwards and am cringing at what kind of rabbit hole I'm about to go down.
Last edited by cascadesys; Feb 24, 2024 at 09:36 PM.
P0430/P0420 are very common on the 2000+ cars. GM actually extended the warranty on the cats for those model years for this very reason, but that extension was only to the 10 year point - hence long expired in your case. Coatings tend to wear off the cat substrate and reduce the ability of the cat to effectively "scrub" the exhaust. No big deal, nothing to worry about unless you have to pass an emissions test. I don't really see how anything with the intake manifold work could have caused this. The code is tripped when the PCM sees comparative data (between front and rear O2 sensors on a given bank) that is outside the acceptable threshold. If there was a wiring issue with the O2 sensor harness, you would see more O2-related codes than just this one.
On the other hand, the injector code would seem to be entirely related to having disconnected the fuel rail and associated harness. Something didn't connect back together properly with the harness, or a connector was damaged, etc. Do you have a scanner that can look at individual cylinder misfire data? Does the engine seem to be running correctly with no loss of power or misfires, etc.? If fuel trims are way off due to improper operation of an injector(s), perhaps that has caused some O2 readings that might have tripped a P0430 that was on the verge of happening anyway (again, a common problem on the '00+ cars).
P0430/P0420 are very common on the 2000+ cars. GM actually extended the warranty on the cats for those model years for this very reason, but that extension was only to the 10 year point - hence long expired in your case. Coatings tend to wear off the cat substrate and reduce the ability of the cat to effectively "scrub" the exhaust. No big deal, nothing to worry about unless you have to pass an emissions test. I don't really see how anything with the intake manifold work could have caused this. The code is tripped when the PCM sees comparative data (between front and rear O2 sensors on a given bank) that is outside the acceptable threshold. If there was a wiring issue with the O2 sensor harness, you would see more O2-related codes than just this one.
On the other hand, the injector code would seem to be entirely related to having disconnected the fuel rail and associated harness. Something didn't connect back together properly with the harness, or a connector was damaged, etc. Do you have a scanner that can look at individual cylinder misfire data? Does the engine seem to be running correctly with no loss of power or misfires, etc.? If fuel trims are way off due to improper operation of an injector(s), perhaps that has caused some O2 readings that might have tripped a P0430 that was on the verge of happening anyway (again, a common problem on the '00+ cars).
I have the BlueDriver reader which links to my phone and is fairly comprehensive. It is idling at a constant RPM but feels rough, I can feel a little more vibration than usual sitting there. I did another code scan and it's saying Cylinder 7 misfire, which is of course the hardest one to get to. It's also showing P0300 random/multiple cylinder misfire. It's also now throwing pending trouble codes for Knock sensors 1 and 2, which is making me sick to my stomach since I just replaced them with brand new AC Delco OEM sensors and a new Dorman harness. I spent my entire day getting the manifold off and back on, so the idea of pulling this apart again is upsetting but I'll do whatever I need to do.
Looks like there was new information added with an Edit after my first reply. So things have changed (many more codes, and evidence of a misfire added).
At this point, it looks like some sort of wiring harness issue(s). Something (or several somethings) is (are) pinched, broken, not making full or proper contact, etc. That would be my first suspect if none of this was an issue prior to the intake removal. There might also be a vacuum leak (improper intake torque, or possibly a pinched, poorly seated, or dirty/damaged gasket) accounting for some of the problems (such as #7 misfires, rough running) - but that wouldn't explain the knock sensor codes.
Looks like there was new information added with an Edit after my first reply. So things have changed (many more codes, and evidence of a misfire added).
At this point, it looks like some sort of wiring harness issue(s). Something (or several somethings) is (are) pinched, broken, not making full or proper contact, etc. That would be my first suspect if none of this was an issue prior to the intake removal. There might also be a vacuum leak (improper intake torque, or possibly a pinched, poorly seated, or dirty/damaged gasket) accounting for some of the problems (such as #7 misfires, rough running) - but that wouldn't explain the knock sensor codes.
Thank you for the quick reply. I suspect it’s possible the knock sensor wiring harness is pinched, so that’s one avenue I’ll explore. I had none of these issues prior to intake manifold removal, but I was getting detonation at WOT and that led me to remove and clean all the oil that had built up before I added a catch can. It was very messy so I’m glad I cleaned it out, though creating this code storm for myself was an unintended outcome. As far as the injector harnesses each of the eight plugs physically look fine and fully seated, I can’t see any wires that look pinched. Im guessing I’d need to bust out a multimeter to get a better idea of where the issue is on the harness?
The P0307 is a good starting point, see if there is any issue with connectivity of the injector harness at the #7 injector. Maybe even just try some wiggling of the wires there, unplug and replug at the injector, see if anything changes with idle quality. Can you watch individual cylinder misfire data in real time with your scanning device? If so, look at that too and see what (if anything) changes with #7 totally disconnected.
Additionally, there could still be some sort of vacuum leak from a poorly seated/damaged/dirty intake gasket for one (or more) of the cylinders. But since you're getting the injector code, it's obviously best to start there. Regardless, if there is a harness issue with the new knock sensors then the intake has to come back off. Make sure to thoroughly inspect the gaskets at that time, consider replacing them if you didn't already do so during the sensor swap (even if they are new, there could be defects so just check closely if fixing the injector/wiring problem still leaves you with any amount of misfires/rough running - for this reason I would try to fix whatever is causing the injector code prior to removing the intake again, then you'll know whether or not that was the sole cause of the misfires/rough running).
The P0307 is a good starting point, see if there is any issue with connectivity of the injector harness at the #7 injector. Maybe even just try some wiggling of the wires there, unplug and replug at the injector, see if anything changes with idle quality. Can you watch individual cylinder misfire data in real time with your scanning device? If so, look at that too and see what (if anything) changes with #7 totally disconnected.
Additionally, there could still be some sort of vacuum leak from a poorly seated/damaged/dirty intake gasket for one (or more) of the cylinders. But since you're getting the injector code, it's obviously best to start there. Regardless, if there is a harness issue with the new knock sensors then the intake has to come back off. Make sure to thoroughly inspect the gaskets at that time, consider replacing them if you didn't already do so during the sensor swap (even if they are new, there could be defects so just check closely if fixing the injector/wiring problem still leaves you with any amount of misfires/rough running - for this reason I would try to fix whatever is causing the injector code prior to removing the intake again, then you'll know whether or not that was the sole cause of the misfires/rough running).
Thanks, I did do brand new gaskets on the intake manifold and checked to make sure they were flush and uniform. Here’s a photo
I really appreciate everyone’s suggestions, I might be in the clear on the misfire. After sleeping on things I took another look at number 7 this morning and realized that the retaining clip on the number seven injector was rotated 90° and preventing the plug from going in all the way. I reinserted that,
I’m still getting the codes for both knock sensors, so I’m guessing I will have to pull the intake manifold to check the wire and work on that.
Last edited by cascadesys; Feb 25, 2024 at 05:01 PM.
I really appreciate everyone’s suggestions, I might be in the clear. After sleeping on things I took another look at number 7 this morning and realized that the retaining clip on the number seven injector was rotated 90° and preventing the plug from going in all the way. I reinserted that,
I’m still getting the codes for both knock sensors, so I’m guessing I will have to pull the intake manifold to check the wire and work on that.
So the P0307 is gone, P0200 is gone, and the idle quality has returned to normal? If so, that's great news - and then you don't need to worry about an intake gasket vacuum leak having anything to do with the problem, so all that's left to deal with is whatever happened to the knock sensor harness.
If the P0430 is still present after all of this, but nothing else is amiss, I wouldn't worry about it being directly attributed to any of the work you've done. Again, a defective cat substrate is a very common problem on the 2000-02 cars.
So the P0307 is gone, P0200 is gone, and the idle quality has returned to normal? If so, that's great news - and then you don't need to worry about an intake gasket vacuum leak having anything to do with the problem, so all that's left to deal with is whatever happened to the knock sensor harness.
If the P0430 is still present after all of this, but nothing else is amiss, I wouldn't worry about it being directly attributed to any of the work you've done. Again, a defective cat substrate is a very common problem on the 2000-02 cars.
Everything is gone now except P0327 and P0332 (both knock sensors - circuit low). Idle quality is good and I did a few WOT pulls and the detonation that I sought to solve was also gone, probably from all the oil crud I cleaned out of the intake manifold and intake ports. I should have left the knock sensors alone since I am not sure they were the issue, but since I had it all apart I figured it was worth doing. I’m guessing it’s inevitable that I’m gonna have to pull the manifold again to fix those, as it’s either that I pinched the harness or didn’t torque them enough? I did set my 1/2” torque wrench all the way down to 11ft/lbs but they felt very tight and the wrench still wasn’t clicking to indicate torque set, so I didn’t want to snap them. Same thing happened with my oil pressure sensor, when I was torquing that to 15ft/lbs it felt very tight but I kept going waiting for the torque wrench to click, and I ended up snapping the assembly. Both knock sensors felt pretty tight but because I was reluctant to snap them I stopped when I started needing to pull pretty hard.
I pulled my intake manifold, here is what my knock sensor harness looks like. I don’t see anywhere that looks crushed or pinched. I tried torquing them further and the threads snapped off
Last edited by cascadesys; Feb 26, 2024 at 05:06 PM.
Damn man, that sucks. I've heard even AC Delco sensors can be crap, that only actual genuine GM ones work. I was lucky and had a pair of brand new ones available, the ones I'd purchased at the parts store were junk and I had to redo them after 50 miles. ICT billet makes relocation brackets so you no longer have to pull your intake to change them, but I'm unsure if they'd work on an F-body: https://www.ictbillet.com/ls-gen-iii...9-lq9-lm4.html
Were they GM sensors? If so, hard to imagine that both sensors failed immediately out of the box like that. That's why I still feel that something must be up with the connectors or harness somewhere along the line. If they were not GM, then that might be the problem.
Were they GM sensors? If so, hard to imagine that both sensors failed immediately out of the box like that. That's why I still feel that something must be up with the connectors or harness somewhere along the line. If they were not GM, then that might be the problem.
I just put two new ones in (Delphi) and got a 3/8 to 1/2 adapter to run my 22mm socket off my 3/8 torque wrench and torqued it to 132in/lb (11ft/lb) and got clicks this time on both. It’s possible I overtorqued them last time, my torque wrench shows all the way down to 11ft/lb but it’s possible that it doesn’t go that low. I cleared the codes and fired it up, so far so good. Will take it for a drive tomorrow and pray these don’t return.
Just took it for a test drive, P0430 has returned (Catalyst) as well as P0327 (Knock sensor 1 circuit low bank 1). So the good news is that one of the knock sensor codes is gone, but the second is still there, which means the intake manifold has to come off yet again. Very frustrating. The knock sensor wire harness looks fine, so I'm not sure if my next troubleshooting should be to replace Knock sensor 1 again or the harness. I've been considering a full exhaust which will solve P0430 but this knock sensor issue is driving me bonkers.
I would drive it a bit more first, make sure the code for the other knock sensor doesn't come back before assuming it's just the one. There could still be a wiring issue, something that is marginal and will, in short order, show the other code as well. It would suck to keep taking this apart and guessing at the cause. If the other sensor doesn't trip a code after quite some time, then it's probably not a larger issue with the harness that would go beyond the connector for the one sensor still showing a code (or just a bad sensor itself).
As for the P0430, again, this is no worry unless you have to pass an emissions test. It's not an indicator of a flow restriction, it just means that you have a cat that is inefficient at reducing tail pipe emissions.
I would drive it a bit more first, make sure the code for the other knock sensor doesn't come back before assuming it's just the one. There could still be a wiring issue, something that is marginal and will, in short order, show the other code as well. It would suck to keep taking this apart and guessing at the cause. If the other sensor doesn't trip a code after quite some time, then it's probably not a larger issue with the harness that would go beyond the connector for the one sensor still showing a code (or just a bad sensor itself).
As for the P0430, again, this is no worry unless you have to pass an emissions test. It's not an indicator of a flow restriction, it just means that you have a cat that is inefficient at reducing tail pipe emissions.
Thanks, worth noting is that I didn’t have any codes prior to taking my manifold off for cleaning initially. I decided to do the knock sensors and wires while I was in there (doh). The guide I used said 11ft/lbs and I see on the sticky that it should be 15ft/lbs so I wonder if that could be a factor. I have a nice multimeter, is there a method to test everything before I bolt the manifold back on again?
Thanks, worth noting is that I didn’t have any codes prior to taking my manifold off for cleaning initially. I decided to do the knock sensors and wires while I was in there (doh). The guide I used said 11ft/lbs and I see on the sticky that it should be 15ft/lbs so I wonder if that could be a factor. I have a nice multimeter, is there a method to test everything before I bolt the manifold back on again?
I just checked my factory GM service manual, it says 15lb-ft for knock sensors for an LS1. But I don't think being at 11lb-ft would be the cause of a P0327. I'm not sure what the normal ohm reading would be for this knock sensor, I've never checked. But you can certainly check for continuity at the connector(s), wiggle the harness around and see if you can cause some changes in readings. But if the problem is the connector itself, then the harness might check out fine until it's plugged into the sensor. I guess you could always try replacing the sensor again, see if you can exchange it under warranty.
I just checked my factory GM service manual, it says 15lb-ft for knock sensors for an LS1. But I don't think being at 11lb-ft would be the cause of a P0327. I'm not sure what the normal ohm reading would be for this knock sensor, I've never checked. But you can certainly check for continuity at the connector(s), wiggle the harness around and see if you can cause some changes in readings. But if the problem is the connector itself, then the harness might check out fine until it's plugged into the sensor. I guess you could always try replacing the sensor again, see if you can exchange it under warranty.
Your guidance has been very helpful on this journey, thank you. I think I had some debris in the threads of bank 1 and that was causing issues, because when I went to back it out the nut of the sensor spun inside of its housing. I had to remove the valley cover to twist it out with channel locks, and while I have the valley cover off I decided I may as well go ahead and do the LS6 valley cover and PCV mode while I'm this far. I exchanged my Delphi sensors for two brand new ones, tested them both with a Fluke multimeter and get a solid 100.8K ohms of resistance on both, so these should not be DOA. I also got a brand new harness to be sure. I'm going to install the LS6 valley cover tomorrow evening, install both of these and torque them to 20NM aka 180in/lbs aka 15ft/lbs, reinstall everything, and hope for the best. I looked at the plug for the knock sensors where it connects to the rest of the car harness and everything looks fine.
Your guidance has been very helpful on this journey, thank you. I think I had some debris in the threads of bank 1 and that was causing issues, because when I went to back it out the nut of the sensor spun inside of its housing. I had to remove the valley cover to twist it out with channel locks, and while I have the valley cover off I decided I may as well go ahead and do the LS6 valley cover and PCV mode while I'm this far. I exchanged my Delphi sensors for two brand new ones, tested them both with a Fluke multimeter and get a solid 100.8K ohms of resistance on both, so these should not be DOA. I also got a brand new harness to be sure. I'm going to install the LS6 valley cover tomorrow evening, install both of these and torque them to 20NM aka 180in/lbs aka 15ft/lbs, reinstall everything, and hope for the best. I looked at the plug for the knock sensors where it connects to the rest of the car harness and everything looks fine.
Glad to have been helpful, I'm just sorry that you have to keep pulling that intake back off! Talk about a hassle.
Sounds like you have two good sensors now, or at least as much as you can possibly know that they are good, and with the new harness that also eliminates another possibility. Maybe that #1 sensor was damaged during installation due to the debris? It's a good sign that the one with the code was also the one that came apart during removal - something wasn't right there.
Seriously, I wish you the best of luck. I think you've got it now, but still - good luck on what is hopefully your final assembly!
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Codes after intake manifold cleaning 
