2007 H2 Hesitation - NEED HELP
#11
07-21-2021, 07:16 AM
Sounds like there are many issues. Do you know if the fuel is good or what octane? Have you checked fuel pressure? What about the air cleaner? Have you replaced plugs and plug wires? If the compression and leak down test showed it was OK, why did he think you burned a valve?
If you've done the very basics above, look toward the knock sensors. If they are bad and or even shut off, its going to pull timing and pull power.
Tim
If you've done the very basics above, look toward the knock sensors. If they are bad and or even shut off, its going to pull timing and pull power.
Tim
#12
07-21-2021, 07:16 AM
I'm adding these to my list to ask him today. These are pretty specific things that I haven't asked. THANK YOU!!
#13
07-21-2021, 07:17 AM
I would find a local tuner and have them look into the ECM programming, looking specifically if any of the SES triggers have been turned off.
Unplug the MAF sensor and force it into Speed Density mode, see if it drives any better.
Screw a pressure gauge into the downstream O2 sensor bungs and see what the exhaust pressure is, should be below 1 psi.
It sounds as if the truck is in REP mode and if certain triggers are turned off it will not set any indicators
Has he tried a Crank Relearn Procedure on it?
Neal
Unplug the MAF sensor and force it into Speed Density mode, see if it drives any better.
Screw a pressure gauge into the downstream O2 sensor bungs and see what the exhaust pressure is, should be below 1 psi.
It sounds as if the truck is in REP mode and if certain triggers are turned off it will not set any indicators
Has he tried a Crank Relearn Procedure on it?
Neal
#14
07-21-2021, 07:22 AM
Grab your H2 and take it to a good GM dealer, the mileage you have on your H2 should not be having these kind of problems unless it was totally abused. Misfires, no power, codes, bad cats, this all make no sense. Short of having a couple of bad coils or deteriorated wires misfiresare uncommon with the mileage you have.
The LS/LQ9 is nearly a bullet proof engine. Bad 02 sensors will have more then 2 cylinders showing misfires as well as throttle body issues. It is true bad fuel injectors can cause burnt valves but a flow test can on those injectors will support that finding. 4L60 trans problems usually have shift flare issues or loss of ranges. I hate to sound judgemental but based on what you have said I think your mechanic is a parts changer and doesn't have a clue.
You need a pro to help you sort this out. A /GM dealer with a Tech 2/MDI 2 can give you a great deal of additional information your mechanic may be missing and give you a road to recovery that won't cost you a fortune.
The LS/LQ9 is nearly a bullet proof engine. Bad 02 sensors will have more then 2 cylinders showing misfires as well as throttle body issues. It is true bad fuel injectors can cause burnt valves but a flow test can on those injectors will support that finding. 4L60 trans problems usually have shift flare issues or loss of ranges. I hate to sound judgemental but based on what you have said I think your mechanic is a parts changer and doesn't have a clue.
You need a pro to help you sort this out. A /GM dealer with a Tech 2/MDI 2 can give you a great deal of additional information your mechanic may be missing and give you a road to recovery that won't cost you a fortune.
#15
07-21-2021, 07:25 AM
Unlikely. Likely the (bet it was not a GM) dealer lied and no cats were replaced.
The 2007 plug up cats fast. Mine is an 07 also. Then throws random cylinder codes.
Check the pressure at the 02 sensor before and after each of the 2 cats. That differential in pressure will tell you if the cat is OK or plugged.
Make sure the 2nd guy actually replaced the 2 cats and y-pipe assembly (all one unit), that he billed you for.
2 dealers told me my valves were toast. There was NOTHING wrong with the heads. But their stupid junky OBDII sensors or Tech2 suggested it was a valve problem. It was. The valves could not breathe. But that was due to plugged cat. Only on one side, but both banks were throwing codes. Plugged side throwing more codes.
I bet there was nothing wrong with your valve train, but the half of the block with the 1/3 cylinder bank is plugged, or otherwise affected.
As for your mechanic who has no clue as to what is wrong after 6 weeks, dump him. He is lost.
What bank are you getting the random codes on? If he can not answer that, you have a bigger issue.....
You can screw around, or take it to an GM dealer who used to sell Hummers.
The 2007 plug up cats fast. Mine is an 07 also. Then throws random cylinder codes.
Check the pressure at the 02 sensor before and after each of the 2 cats. That differential in pressure will tell you if the cat is OK or plugged.
Make sure the 2nd guy actually replaced the 2 cats and y-pipe assembly (all one unit), that he billed you for.
2 dealers told me my valves were toast. There was NOTHING wrong with the heads. But their stupid junky OBDII sensors or Tech2 suggested it was a valve problem. It was. The valves could not breathe. But that was due to plugged cat. Only on one side, but both banks were throwing codes. Plugged side throwing more codes.
I bet there was nothing wrong with your valve train, but the half of the block with the 1/3 cylinder bank is plugged, or otherwise affected.
As for your mechanic who has no clue as to what is wrong after 6 weeks, dump him. He is lost.
What bank are you getting the random codes on? If he can not answer that, you have a bigger issue.....
You can screw around, or take it to an GM dealer who used to sell Hummers.
#17
07-21-2021, 07:27 AM
Sounds like there are many issues. Do you know if the fuel is good or what octane? Have you checked fuel pressure? What about the air cleaner? Have you replaced plugs and plug wires? If the compression and leak down test showed it was OK, why did he think you burned a valve?
If you've done the very basics above, look toward the knock sensors. If they are bad and or even shut off, its going to pull timing and pull power.
Tim
If you've done the very basics above, look toward the knock sensors. If they are bad and or even shut off, its going to pull timing and pull power.
Tim
#18
07-21-2021, 05:19 PM
If your mechanic has the reputation you say he has and you trust him there is no reason to blame him, it sounds like he is troubleshooting everything he can to find the issue, these types of issues can be hard to find.
Neal
Neal
#19
07-21-2021, 08:02 PM
I'm curious about the SES light, was it flashing once you reached around 55 to 60 mph?
The P0300 code is a random misfire code and if accompanied by a flashing SES light often times indicates a need to perform a Crank Relearn procedure. The flashing SES light means there is a high probability of CAT damage from a very rich condition from the misfires. If any part of the rotating assembly was changed it can cause the ECM to loose the location of TDC causing the the acceleration and deceleration of the piston to be off from the previous learned location causing the P0300 code. The incorrect timing events can cause a rich condition in the exhaust if allowed to go for a long period of time and will damage the CAT over time depending on how rich it may not take very long to do damage and as someone mentioned above the fuel trims would show this condition if you haven't already corrected it.
A shop class diagnostic tool can perform the Crank Learn Procedure, it takes just a few minutes to do. It may not be the issue but it is an easy task to perform and has fixed the issue your having many times and if TDC is off it can cause a rather large loss of power. Not saying this is the issue but is one of the first things I would check.
Neal
The P0300 code is a random misfire code and if accompanied by a flashing SES light often times indicates a need to perform a Crank Relearn procedure. The flashing SES light means there is a high probability of CAT damage from a very rich condition from the misfires. If any part of the rotating assembly was changed it can cause the ECM to loose the location of TDC causing the the acceleration and deceleration of the piston to be off from the previous learned location causing the P0300 code. The incorrect timing events can cause a rich condition in the exhaust if allowed to go for a long period of time and will damage the CAT over time depending on how rich it may not take very long to do damage and as someone mentioned above the fuel trims would show this condition if you haven't already corrected it.
A shop class diagnostic tool can perform the Crank Learn Procedure, it takes just a few minutes to do. It may not be the issue but it is an easy task to perform and has fixed the issue your having many times and if TDC is off it can cause a rather large loss of power. Not saying this is the issue but is one of the first things I would check.
Neal
#20
07-22-2021, 07:19 AM
I'm curious about the SES light, was it flashing once you reached around 55 to 60 mph?
The P0300 code is a random misfire code and if accompanied by a flashing SES light often times indicates a need to perform a Crank Relearn procedure. The flashing SES light means there is a high probability of CAT damage from a very rich condition from the misfires. If any part of the rotating assembly was changed it can cause the ECM to loose the location of TDC causing the the acceleration and deceleration of the piston to be off from the previous learned location causing the P0300 code. The incorrect timing events can cause a rich condition in the exhaust if allowed to go for a long period of time and will damage the CAT over time depending on how rich it may not take very long to do damage and as someone mentioned above the fuel trims would show this condition if you haven't already corrected it.
A shop class diagnostic tool can perform the Crank Learn Procedure, it takes just a few minutes to do. It may not be the issue but it is an easy task to perform and has fixed the issue your having many times and if TDC is off it can cause a rather large loss of power. Not saying this is the issue but is one of the first things I would check.
Neal
The P0300 code is a random misfire code and if accompanied by a flashing SES light often times indicates a need to perform a Crank Relearn procedure. The flashing SES light means there is a high probability of CAT damage from a very rich condition from the misfires. If any part of the rotating assembly was changed it can cause the ECM to loose the location of TDC causing the the acceleration and deceleration of the piston to be off from the previous learned location causing the P0300 code. The incorrect timing events can cause a rich condition in the exhaust if allowed to go for a long period of time and will damage the CAT over time depending on how rich it may not take very long to do damage and as someone mentioned above the fuel trims would show this condition if you haven't already corrected it.
A shop class diagnostic tool can perform the Crank Learn Procedure, it takes just a few minutes to do. It may not be the issue but it is an easy task to perform and has fixed the issue your having many times and if TDC is off it can cause a rather large loss of power. Not saying this is the issue but is one of the first things I would check.
Neal
Now that the exhaust valves have been repaired the truck doesn't have any power, but the misfire readings on the computer are gone. It's like one problem was fixed, then another one started. Last night the mechanic had a buddy of his who was going to come to the shop so the two of them could go through the hummer together to test all of the sensors, electrical systems, grounds, etc... If no positive update today I've already put in a call to our local GM Dealership's service department and will have to have it towed there. But, When I call over today I'll ask about these issues as well.