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Spend your time finding the cylinder that is misfiring during a live run. Get the misfire counts off each cylinder. This will help you find your problems more than fuel trims.Your trims are showing that your fuel is within specs and you may have an internal problem if your ignition is OK.
Spend your time finding the cylinder that is misfiring during a live run. Get the misfire counts off each cylinder. This will help you find your problems more than fuel trims.Your trims are showing that your fuel is within specs and you may have an internal problem if your ignition is OK.
Will have to get the more advanced snap on scanner to check individual cylinders tomorrow. Ignition should be fine at this point since I’ve replaced wires, plugs, and cyl 2 coil since that’s the one that had higher misfire counts.
If it had an internal problem, wouldn’t it sputter all the time? When warm, the trims are in the -2, -3 range and the car has power all around. Confused at this point.
I read a thread on here that a guys intake manifold gaskets were crushed/worn and would only misfire when cold until the engine warmed up, expanded, and sealed everything back up. Does this make sense?
Got the check engine light to come on this morning for P0300.
I noticed I could make the idle dip to ~500 if I just barely blipped the throttle.
Here’s the LTFT and the freeze frame data for when the code was set. I know I still need to figure out which cylinder is misfiring. Hope to do that tomorrow
Depending on the load with almost 15% positive long term fuel trims it’s either a vacuum leak or an injector misfire being that high…I’ve explained a few times here how to diagnose for a vacuum leak…good luck !!
Depending on the load with almost 15% positive long term fuel trims it’s either a vacuum leak or an injector misfire being that high…I’ve explained a few times here how to diagnose for a vacuum leak…good luck !!
got cylinder two still missing quite a bit. Also found the large diameter PCV hose that goes over the PCV valve very cracked so I’m going to take a look at that tomorrow. Gets dark so early now.
I know you just replaced the plugs, but I might suggest checking compression, you could have something like a valve or spring issue that only presents cold.
Someone mentioned smoke testing which is definitely in order here just to rule out Expansion related intake leaks.
I know you just replaced the plugs, but I might suggest checking compression, you could have something like a valve or spring issue that only presents cold.
Someone mentioned smoke testing which is definitely in order here just to rule out Expansion related intake leaks.
Will definitely be smoke testing it tonight and will report back.
I do not have compression testing tools but wondering if I can use a endoscope camera to go down the oil filler tube and take a look at the valves/springs that way?
Compression testing gauge shouldn’t cost you too much and would be good to have around. Try the smoke test first especially with it cold. Is cylinder 2 sharply the problem or are there multiple cylinders showing misfiring?
Compression testing gauge shouldn’t cost you too much and would be good to have around. Try the smoke test first especially with it cold. Is cylinder 2 sharply the problem or are there multiple cylinders showing misfiring?
Smoked it tonight. Smoke coming from the intake manifold where it meets the head at cyl 2 mostly, slightly at cyl 7, and the air bridge.
Going to re seal the intake manifold and maybe get a new intake as the air bridge is also leaking at the sealing joints.
May take me some time in order to get the time to do the job as it will be my first time but will report back when done.
Awesome find!!! I just did my LS6 intake manifold again to replace the Oil pressure sensor and it really wasn’t bad… however my car is clean and I just finished building it, AND my car doesn’t have EGR (not sure if yours does). All in all it’s not a bad job. Send pictures of the faulty gaskets!
Oh and be sure to torque the manifold per the instructions, there are two stages and I feel like it’s super important on get that right. Also don’t drop anything down your intake runners. 👍🏻👍🏻
Awesome find!!! I just did my LS6 intake manifold again to replace the Oil pressure sensor and it really wasn’t bad… however my car is clean and I just finished building it, AND my car doesn’t have EGR (not sure if yours does). All in all it’s not a bad job. Send pictures of the faulty gaskets!
Oh and be sure to torque the manifold per the instructions, there are two stages and I feel like it’s super important on get that right. Also don’t drop anything down your intake runners. 👍🏻👍🏻
My car is also pretty clean and the few things I’ve done on it have gone very smoothly :crosses fingers : Didn’t think corvettes had EGR? I know they have the AIR system.
I did read about the torquing sequence. Also read somewhere that blue locktite should be used on the threads of the intake bolts? Is that true? Only saw on one post. Correct part number is Felpro 92438 correct?
Wish I got pictures of the smoke but was too caught up doing it.
Last edited by MAGREDC5BASE; Dec 1, 2021 at 09:08 PM.
Awesome find!!! I just did my LS6 intake manifold again to replace the Oil pressure sensor and it really wasn’t bad… however my car is clean and I just finished building it, AND my car doesn’t have EGR (not sure if yours does). All in all it’s not a bad job. Send pictures of the faulty gaskets!
Oh and be sure to torque the manifold per the instructions, there are two stages and I feel like it’s super important on get that right. Also don’t drop anything down your intake runners. 👍🏻👍🏻
Did the manifold gaskets with new Felpro gaskets, and a new PCV system.
Air bridge is still leaking but the car started up really nicely. However, coolant temp was 84 degrees by the time I completed the job. The real test will be once I get a new air bridge and start the car cold.
Has anyone had experience with the Vararam intake tube? I want to keep the stock air box as I drive the car in the rain sometimes.
Here are some pictures:
Yes I cleaned and vacuumed the mess in between the intake ports.
Cool man! So the full cold start will be the real test. Say, I couldn’t figure out where my knock sensor connector was supposed to be situated, do you have any pictures of that?
Cool man! So the full cold start will be the real test. Say, I couldn’t figure out where my knock sensor connector was supposed to be situated, do you have any pictures of that?
I don’t have any pictures of that but it went near the oil pressure sending unit if I’m not mistaken.
Will report once I get a new air bridge and do a cold start. Thank the lord for smoke machines
I've started the car up 3-4 times now cold and will idle perfect cold. Still has a tiny tiny bit of misfiring due to the air bridge still leaking. The Vararam tube will be here today and will update once again when I have it installed.
The car now idles 98% better than it did cold before changing the manifold gaskets so I'm confident that was the main issue.
Not without issue though, of course the oil pressure sending unit is now pinned at 80 four days later.... My mistake for not changing it while the manifold was off. Why Chevy didn't make the cowl removable like on BMWs so that you could easily get to the back of the motor is beyond me.
Thanks to everyone that chimed in on this thread. Also, if anyone knows of a clean way to dremel the cowl and make it easily removable and weathertight, that would be amazing.
Perhaps you might consider buying/making a relocation kit for the oil pressure sender?? That's what I'm going to do when I swap out my LS1 intake. That way it will be unobstructed and easy to change when it fails again
Perhaps you might consider buying/making a relocation kit for the oil pressure sender?? That's what I'm going to do when I swap out my LS1 intake. That way it will be unobstructed and easy to change when it fails again
Yes definitely a bit late for that now. Definitely don't feel like pulling the manifold again especially so soon lol. Kicking myself for it now. Kind of wish I could cut out part of the cowl and make it re-installable with some weather stripping or something.
Watched a couple videos of people doing them with the manifold still on, but don't think I can do it. Maybe difference between LS1 and LS6 manifold? Mine is an '02 which I think means I have an LS6 manifold?
Final update: Installed a Vararam intake tube and now the car idles perfectly at all temperatures. Figured I'd chime in in case someone down the road has a similar issue. Thanks everyone for the help.
Hi all, I have noticed now that the temperature is starting to drop (New England), my C5 (2002 MN6) will run very rough until the engine coolant temp gets to around 100 degrees F.
It will register no codes in the PCM nor a check engine light. I purchased the car in June and have put about 2,500 miles on it and this has not happened until now. Was thinking of changing the plugs and wires as it is close to 100k miles but I feel like it is something else.
Has anyone had this issue and had it resolved?
So, just in case anyone cares, I was having a very similar issue with mine recently. It was intermittent, but becoming frequent. On cold starts, it would run super rough, with idle bouncing around and either dying or nearly dying unless I gassed it. It would then heat up to 220 (which is high for this car since I have a low temp thermostat) before calming down and acting normally. It seemed a bit unresponsive overall as well. No codes, but I did keep getting a pending air injection code, yet nothing permanent.
I flat-bedded it to Andy at A&A and it turned out to be an air injection check valve that was stuck. This was causing air to be blown into one exhaust bank, but not the other, creating an imbalance and making the car go nuts. Once the temp got to where the air injection shut off, it would even out, but there was apparently still an issue with the one valve creating a lean condition.
Either way, they cleaned the check valve and it apparently fixed the issue.
Thought this would be helpful in case anyone else has this issue
