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[Z06] left over bolt, maybe missing ground after head swap, wiring diagram needed
C6 Corvette ZR1 & Z06General info about GM’s Corvette Supercar, LS9 Corvette Technical Info, Performance Upgrades, Suspension Setup for Street or Track
left over bolt, maybe missing ground after head swap, wiring diagram needed
I had a bolt left over, I know, no jokes.
Looks like a trim or bracket bolt, so didn't worry too much about it.
It came from the passenger side of the car, was taken off from the top, if that helps?
My tuner, Pat G, says I have a big imbalance between the two banks, and thinks I have a bad plug, plug wire, or maybe a missing ground "on the back of the head".
I have an 08 Z.
Does anyone recognize this bolt?
IS there a ground back there that I missed? - I looked hard tonight and didn't see anything.
Anyone have a diagram of the wiring and maybe the ground points from the engine harness they could share?
Looks like a bolt out of the fan bracket. There are 2 bolts like that, lower drivers side.. top passenger side. Bolts are not shown in the picture below.
Last edited by amdoverclocker; 05-05-2015 at 09:25 PM.
I have my heads off now. I just went through all of my bolts and don't see any with that big of a washer. The closest bolt that looks like that is one of the ABS mounting bolts.
Mine is a 08 Z also. Sorry not much help.
Just recently pulled the heads on my car. The only bolt on the back of the heads was the passenger side. It was a larger bolt (15mm head) that attached a wiring harness to the head. No other bolts on the heads to my recollection.
Just recently pulled the heads on my car. The only bolt on the back of the heads was the passenger side. It was a larger bolt (15mm head) that attached a wiring harness to the head. No other bolts on the heads to my recollection.
that's the only bolt on the head, which I did get back on when I reassembled the car.
I'm really after the possible loss of ground, still looking for a wiring diagram.
that's the only bolt on the head, which I did get back on when I reassembled the car.
I'm really after the possible loss of ground, still looking for a wiring diagram.
thanks!
Got your PM. I am attaching a PDF of some schematics and diagrams. If there is a ground missing from Bank 2 it could be an issue with the splice packs that connect the grounds from the individual coils together and then connect the left and right side banks grounds together and to G107 on the engine block. If the ground path for bank 2 is connected properly then your problem is elsewhere.
Got your PM. I am attaching a PDF of some schematics and diagrams. If there is a ground missing from Bank 2 it could be an issue with the splice packs that connect the grounds from the individual coils together and then connect the left and right side banks grounds together and to G107 on the engine block. If the ground path for bank 2 is connected properly then your problem is elsewhere.
Bill
Thanks Bill.
I'll take a good hard look at the diagrams and see what I can see.
mk
I'm pretty sure the primary reason for grounding the coil packs to each head is so that the spark doesn't try and go through the bearings to find its ground. Without the ground you may get arcing on bearings because it had to travel through the block, engine mounts, etc to try and find a ground.
Originally Posted by zulatr
If I was missing one of the three main engine grounds, would the associated system work at all?
Example;
if I missed G107, that grounds the coils, would the coils fire at all?
Or if I missed G106, that grounds the ECM, would the car even run?
I'll check them all tonight, not sure how I'm going to even get to some of them, and make sure they're all tight, but I'm thinking this isn't it.
I'll try the cylinder balance function in HPTuners to see if that tells me anything, maybe focus me in on one area at least
If I was missing one of the three main engine grounds, would the associated system work at all?
Example;
if I missed G107, that grounds the coils, would the coils fire at all?
Or if I missed G106, that grounds the ECM, would the car even run?
I'll check them all tonight, not sure how I'm going to even get to some of them, and make sure they're all tight, but I'm thinking this isn't it.
I'll try the cylinder balance function in HPTuners to see if that tells me anything, maybe focus me in on one area at least
If there isn't another indirect ground path you are correct. The problem may not be at the ground point but at the splice pack that feeds the ground point. If the ground wire from cylinder 6 isn't connected properly in the splice pack that might cause the issue. Another potential problem is a damaged conductor due to something that happened when somebody was working close to it. It doesn't take much to damage a wire if something heavy hits it, lays on it or it gets pinched in something.
If you have a large disparity between LTFT's at idle, and the difference is reduced at higher RPM, that is indicative of an exhaust leak.
If the imbalance is always present, that could be an injector not firing, spark plug not firing, damaged O2 (but if it's cycling properly with the correct high and low voltages, it's probably fine), vacuum leak on one side of the manifold, etc.
The easiest way to tell if you have a gross issue with a particular cylinder is to use a thermal gun (you know, the ones with the display on the back to measure temps - get one the can tead up to 1000 degrees), and shoot each exhaust manifold port and see if they are all running around the same temp.
No matter the issue, do NOT let this go unaddressed!
Last edited by Dan_the_C5_Man; 05-07-2015 at 05:42 PM.
If you have a large disparity between LTFT's at idle, and the difference is reduced at higher RPM, that is indicative of an exhaust leak.
If the imbalance is always present, that could be an injector not firing, spark plug not firing, damaged O2 (but if it's cycling properly with the correct high and low voltages, it's probably fine), vacuum leak on one side of the manifold, etc.
The easiest way to tell if you have a gross issue with a particular cylinder is to use a thermal gun (you know, the ones with the display on the back to measure temps - get one the can tead up to 1000 degrees), and shoot each exhaust manifold port and see if they are all running around the same temp.
No matter the issue, do NOT let this go unaddressed!
Pat disabled the LTFT to help him with his remote trimming, so I can't offer much there.
I noticed the diff in the STFT in the lower rpm and loads, in a full throttle pulls the short term curves are right on top of each other.
I have gone over all the things I can, am going to replace the plugs tomorrow, and then take more data. I do have an infrared gun, not sure of the top range - take shots at idle? I'll also run the cylinder balance test in HPT and see if that tells me anything.
Do you by chance do HPT, and want to take a look at my logs after the plugs are changed?
Pat disabled the LTFT to help him with his remote trimming, so I can't offer much there.
I noticed the diff in the STFT in the lower rpm and loads, in a full throttle pulls the short term curves are right on top of each other.
I have gone over all the things I can, am going to replace the plugs tomorrow, and then take more data. I do have an infrared gun, not sure of the top range - take shots at idle? I'll also run the cylinder balance test in HPT and see if that tells me anything.
Do you by chance do HPT, and want to take a look at my logs after the plugs are changed?
I do, and I can (but Pat G. knows his stuff, not sure if I will add much additional value, other than a second set of eyes). Just for everyone else's benefit - when LTFT's are enabled (as they normally would be), the STFT's will always look "ok", because the LTFT's will add or subtract fuel to bring the STFT's back to zero.
Any hint of "it's wacky at idle and good at higher rpms / load" condition, the very first thing you should validate is no exhaust leaks, anywhere, typical with headers.
Last edited by Dan_the_C5_Man; 05-11-2015 at 08:18 AM.
Looks like a bolt out of the fan bracket. There are 2 bolts like that, lower drivers side.. top passenger side. Bolts are not shown in the picture below.
Bingo, the upper right is where this bolt goes - thanks for the insight!
I do, and I can (but Pat G. knows his stuff, not sure if I will add much additional value, other than a second set of eyes). Just for everyone else's benefit - when LTFT's are enabled (as they normally would be), the STFT's will always look "ok", because the LTFT's will add or subtract fuel to bring the STFT's back to zero.
Any hint of "it's wacky at idle and good at higher rpms / load" condition, the very first thing you should validate is no exhaust leaks, anywhere, typical with headers.
I did a cylinder balance test, and it came out basically perfect, 99% and 100% across the board - this was after changing plugs.
I re-torqued the exh manifold bolts (stock manifolds), nothing was loose.
I confirmed all of the grounds per Bill's helpful diagrams, all present and accounted for.
Got another log last night, haven't looked at it, will send it to Pat G this am and see what he thinks.
I did a cylinder balance test, and it came out basically perfect, 99% and 100% across the board - this was after changing plugs.
I re-torqued the exh manifold bolts (stock manifolds), nothing was loose.
I confirmed all of the grounds per Bill's helpful diagrams, all present and accounted for.
Got another log last night, haven't looked at it, will send it to Pat G this am and see what he thinks.
The fact that it is a stock manifold, assuming you didn't separate the manifold from the cat (the 4 bolts / gaskets), and you've checked to validate no leaks between the head and manifold (usually you can hear therm / see them - black soot around the gasket), I'd say it's safe to check that possibility off the list.
All you are left with is intake manifold or injector air leaks. You can validate those with propane gas or carb cleaner, while logging / looking at O2's (just be careful / flammable).
Last edited by Dan_the_C5_Man; 05-12-2015 at 08:31 AM.
The fact that it is a stock manifold, assuming you didn't separate the manifold from the cat (the 4 bolts / gaskets), and you've checked to validate no leaks between the head and manifold (usually you can hear therm / see them - black soot around the gasket), I'd say it's safe to check that possibility off the list.
All you are left with is intake manifold or injector air leaks. You can validate those with propane gas or carb cleaner, while logging / looking at O2's (just be careful / flammable).
wouldn't intake show up in the cyl balance test?
logs still show the same mis-match B1 to B2.
I did separate the pipes from the manifolds, listened hard for a leak, couldn't find one (though I do have an oil leak now - DAMN!).
I was thinking of swapping the o2 sensors left to right, though that's a pain.
Was also thinking of swapping injectors left to right since that's easy, but I got off everything upto the exhaust ports because of the cyl balance results.
05-05-2015, 09:15 PM
left over bolt, maybe missing ground after head swap, wiring diagram needed
