2005 SRX 3.6L V6. Purchased used w/ 60k miles in 2008. Almost immediately after purchasing, noticed a random hesitation at idle, felt like a misfire but never saw any check engine lights or misfire codes. As we have driven the car over the last 3 years, the misfire has gotten more frequent and severe.
Car now has 102,000 miles on it and this past month the misfire has gotten excessive. It is now setting off the engine light. I am getting random misfire codes on all cylinders. There is no ryhme or reason to which cylinder or bank it misfires on. I clear the codes, and then the next time it will be totally different cylinder(s) misfiring. Now the misfire is not just at idle, but mostly under high load partial throttle conditions while cruising. I can make it misfire just by going partial throttle, about 50-80% TPS, just enough that the tranny doesn't kick down and shift gears, thus creating a high-load situation on the motor. Almost immediately, the motor starts misfiring, and then the check engine light starts blinking indicating an active misfire, and you can really feel the car bucking too.
About a year ago at 80k miles I tried changing all the plugs. The old plugs looked fine, but I put new ones in anyways. I have swapped coils between banks and between cylinders, with no change in the pattern of misfires.
I know about the timing chain issue with the LY7 motor, and would actually be eager to identify that as the cause here, for sake of getting an actual diagnosis. It's just that I have NEVER gotten a single DTC for a camshaft or crankshaft position sensor. Only misfire codes. So, I'm wondering if maybe the chain is stretched enough to cause misfiring but not jump teeth and trip a cam/crank code? I'm not sure about this theory...
I took the car to the dealership (MotorWerks, Barrington, IL). They said it could be carbon build-up and wanted to sell me a top-end cleaning and injector cleaning. I plan on doing both these myself, but haven't done it yet. I got some GM Top End Cleaner and will follow the TSB procedure for soaking the piston rings 3 hrs and then changing oil. Will also do a fuel injector / top end cleaning using a mixture of 10%GM TEC and 90% gasoline in a pressurized canister hooked up to my fuel rail, so this should clean out the injectors and decarbonize the piston tops. I plan on doing this, but am very skeptical about it fixing the misfire issue.
As a side note - both cats on the car were replaced last fall under the EPA 5yr/80k mi warranty when I got codes about poor cat efficiency. Initially I hoped that maybe plugged cats were the culprit of the misfire, but no such luck. New cats, same 'ol misfires.
I should also add that one 2 occassions, the car has exhibited a no-start condition. Plenty of battery juice and gas, but when I cranked it would not fire. It happened once last spring, and then again this past week. It took about 4 or 5 periods of 30-seconds continuous cranking and blipping the throttle go get it to start. Once started and revved, it ran just fine, and then could be shut off and restarted normally. I am not sure what to think of this. Not bad gas, because it ran fine once started. Could this be a timing chain issue? Like where it had skipped a tooth and had intake/exhaust cams off synch, and after cranking for a LONG time, continued to skip teeth until it finally found the right combo and fired up again? Then again, if this were an intereference motor that would mean my motor should be toast too, and it's not, so that begs another question... is this an intereference motor or not? I am finding conflicting information on the internet about this.
I have read many of the posts on here about timing chain issues, and the one long thread by Brigga where he posts a video of his CTS with low-compression sounds exactly like my car did those 2 times it wouldn't start. But, then again, now that it is started, it runs "fine" except for the misfiring.
I plan on doing a compression check and leak-down test this weekend, to see if those tell me anything.
The car HAS been run low on oil a few times since I've owned it. It EATS oil alive, like 1qt per 1,000 miles. I do my best to keep it topped off, but too frequently find myself needing to add 2 or 2.5 qts to get it back full.
So my main question to you gurus out there is, does this sound like a timing chain issue or something else?
If so, I will replace the chain/gears myself using the Autozone kit. I would prefer to just tear apart the front of the motor and not take off the heads. But, then I fear:
1. Leaving loads of carbon buildup on the pistons and valves from all the "consumed" oil. And if this were the cause of the misfire, I would still have it after the TC replacement.
2. Not addressing the oil consumption issue. In Briggy's post, he mentions that the machine shop found severely worn valve guides which were the likely source of oil consumption. Obviously I would need to have the heads pulled and worked over to address this.
But... I don't want to pull the heads if I don't have to. I fear pulling head bolts on 100k+ aluminum blocks. I start getting nightmares about the TimeSert job I had to do on my 1996 Northstar... Do these LY7 alum blocks have similar issues with the threads failing?
Lots of questions I know... thanks for any/all responses.
-Jacob
Car now has 102,000 miles on it and this past month the misfire has gotten excessive. It is now setting off the engine light. I am getting random misfire codes on all cylinders. There is no ryhme or reason to which cylinder or bank it misfires on. I clear the codes, and then the next time it will be totally different cylinder(s) misfiring. Now the misfire is not just at idle, but mostly under high load partial throttle conditions while cruising. I can make it misfire just by going partial throttle, about 50-80% TPS, just enough that the tranny doesn't kick down and shift gears, thus creating a high-load situation on the motor. Almost immediately, the motor starts misfiring, and then the check engine light starts blinking indicating an active misfire, and you can really feel the car bucking too.
About a year ago at 80k miles I tried changing all the plugs. The old plugs looked fine, but I put new ones in anyways. I have swapped coils between banks and between cylinders, with no change in the pattern of misfires.
I know about the timing chain issue with the LY7 motor, and would actually be eager to identify that as the cause here, for sake of getting an actual diagnosis. It's just that I have NEVER gotten a single DTC for a camshaft or crankshaft position sensor. Only misfire codes. So, I'm wondering if maybe the chain is stretched enough to cause misfiring but not jump teeth and trip a cam/crank code? I'm not sure about this theory...
I took the car to the dealership (MotorWerks, Barrington, IL). They said it could be carbon build-up and wanted to sell me a top-end cleaning and injector cleaning. I plan on doing both these myself, but haven't done it yet. I got some GM Top End Cleaner and will follow the TSB procedure for soaking the piston rings 3 hrs and then changing oil. Will also do a fuel injector / top end cleaning using a mixture of 10%GM TEC and 90% gasoline in a pressurized canister hooked up to my fuel rail, so this should clean out the injectors and decarbonize the piston tops. I plan on doing this, but am very skeptical about it fixing the misfire issue.
As a side note - both cats on the car were replaced last fall under the EPA 5yr/80k mi warranty when I got codes about poor cat efficiency. Initially I hoped that maybe plugged cats were the culprit of the misfire, but no such luck. New cats, same 'ol misfires.
I should also add that one 2 occassions, the car has exhibited a no-start condition. Plenty of battery juice and gas, but when I cranked it would not fire. It happened once last spring, and then again this past week. It took about 4 or 5 periods of 30-seconds continuous cranking and blipping the throttle go get it to start. Once started and revved, it ran just fine, and then could be shut off and restarted normally. I am not sure what to think of this. Not bad gas, because it ran fine once started. Could this be a timing chain issue? Like where it had skipped a tooth and had intake/exhaust cams off synch, and after cranking for a LONG time, continued to skip teeth until it finally found the right combo and fired up again? Then again, if this were an intereference motor that would mean my motor should be toast too, and it's not, so that begs another question... is this an intereference motor or not? I am finding conflicting information on the internet about this.
I have read many of the posts on here about timing chain issues, and the one long thread by Brigga where he posts a video of his CTS with low-compression sounds exactly like my car did those 2 times it wouldn't start. But, then again, now that it is started, it runs "fine" except for the misfiring.
I plan on doing a compression check and leak-down test this weekend, to see if those tell me anything.
The car HAS been run low on oil a few times since I've owned it. It EATS oil alive, like 1qt per 1,000 miles. I do my best to keep it topped off, but too frequently find myself needing to add 2 or 2.5 qts to get it back full.
So my main question to you gurus out there is, does this sound like a timing chain issue or something else?
If so, I will replace the chain/gears myself using the Autozone kit. I would prefer to just tear apart the front of the motor and not take off the heads. But, then I fear:
1. Leaving loads of carbon buildup on the pistons and valves from all the "consumed" oil. And if this were the cause of the misfire, I would still have it after the TC replacement.
2. Not addressing the oil consumption issue. In Briggy's post, he mentions that the machine shop found severely worn valve guides which were the likely source of oil consumption. Obviously I would need to have the heads pulled and worked over to address this.
But... I don't want to pull the heads if I don't have to. I fear pulling head bolts on 100k+ aluminum blocks. I start getting nightmares about the TimeSert job I had to do on my 1996 Northstar... Do these LY7 alum blocks have similar issues with the threads failing?
Lots of questions I know... thanks for any/all responses.
-Jacob
