Suzuki Forums banner

1 - 15 of 15 Posts

·
Registered
Joined
·
19 Posts
Discussion Starter #1
I have a 2008 Suzuki XL8 AWD model with the GM LY7 engine in it, that is experiencing some strange issues.

I was having problems with misfires on bank two and after checking the timing and the ODB scans I found that the cat. was plugged and the upstream o2 sensor was shot on bank 2. Cleared the cat. and replaced the upstream sensor, everything seemed to be running fine afterwards. Right now I'm running with the cat on bank 2 deleted. The house is in place, but all the catalyst media has been removed because it was destroyed. I expect it to throw code for cat inefficiency, but it shouldn't affect performance.

Recently I was trying to pass someone so was revving kind of high it started to do the same thing again. Low power, rough idle, CEL indicating misfire. After checking the codes I noticed that there were a lot codes that don't seem to make sense. I don't remember what the exact codes numbers are off the top of my head, but I remember what they were for.
  • randoms missfire
  • missfire 2, 4, 6
  • cold start idle air
  • various codes for ignition coil primary/secondary malfunction
  • camshaft sensor
  • crank shaft sensor
What doesn't make sense to me is that I know the camshaft sensors are good because they were recently tested/replaced. I also know that both the cam and crank shaft sensors are good because I back probed the ECU and all the signals were correct and in time. I'm fairly certain that the coils are good because I'll shuffle them around, and the problem doesn't move with the coil. Once the car gets into this state it seems to stay this way. However sometimes if I mess with the o2 sensor (disconnect/reconnect/run with no o2 sense data) under some random condition the car will suddenly preform fine idle clean and rev smoothly so long as the rev count is kept low to keep it from entering the strange state. This sort of leads me to believe that is something going on with the fuel trims.

I'm sort of at a loss, it seems like the misfire could be cause by vacuum, but I did the propane enrichment test and was unable to find anything, but it is a possibility that I missed something. Further when it idles it idles extremely rough. Unless there was a vacuum leak the size of a shop vac, I've never seen vacuum impact idle so aggressively. I'm also thinking it could be an electrical issue either with the harness or the ECU since it's throwing codes for sensors that I know are good.

Anyone has any idea about how to approach this?

Thanks,
Alan
 

·
Registered
Joined
·
5,919 Posts
first off, replace the missing CAT, that will certainly be screwing things up and I bet the poor things trying to get the fuel trims right between the 2 banks and its leaning out that much its misfiring and the misfire on that bank with be sending wild power pulses thru the system and causing a timing mismatch between cam and crank on that bank.
 

·
Registered
Joined
·
19 Posts
Discussion Starter #3 (Edited)
first off, replace the missing CAT, that will certainly be screwing things up and I bet the poor things trying to get the fuel trims right between the 2 banks and its leaning out that much its misfiring and the misfire on that bank with be sending wild power pulses thru the system and causing a timing mismatch between cam and crank on that bank.
While I agree that running with no cat. on bank 2 is not beneficial it really shouldn't affect the fuel trims. That value is pretty much exclusively reliant an the upstream o2 sensor which is not affected by the catalytic converter. I was waiting to replace the cat. after diagnosing the misfires because the misfires are what caused the death of the previous cat. Dumping that raw fuel into the converter causes it to heat up and destroy all the catalyst media.

Regarding the timing, I really see the misfires being the cause of electrical issue more the opposite, the misfires are a symptom of electrical issues. I misfire I don't think has any pathway back to the ECU to create random signals that trip the ECM. The timing is mechanically set, not something that will change by misfire.

I did some testing on the upstream o2 sensor, seems like its not providing the correct output. Output is holding around 0.01 sometimes jumping up to 0.1, but it's not oscillating between 0.1 and 0.9 as it should. Looking at bank 1, that is the pattern that is seen. I know the o2 sensor is good because it was replaced. At this point I'm assuming exhaust gasket leak, or cracked manifold so its constantly reading fresh air. Because of this the short term fuel trims are around 25% which is way higher than it should be.
 

·
Registered
Joined
·
8,983 Posts
Your diagnostic approach is that of a novice and is tantamount to guessing...

You need to gather your wits and formulate a diagnostic path.. then follow it... not jumping around and chasing down rabbit holes..
 

·
Registered
Joined
·
19 Posts
Discussion Starter #5
Your diagnostic approach is that of a novice and is tantamount to guessing...

You need to gather your wits and formulate a diagnostic path.. then follow it... not jumping around and chasing down rabbit holes..
Okay so what do you suggest? I don't think the path I'm following is that unreasonable. Misfire caused by lean/rich condition, fueling condition directly linked to upstream o2 sensor, test upstream o2 sensor reading find that it is not providing optimal values why? Sensor is know good, must be some other factor causing the sensor to report incorrectly.

Frankly I'm not trying to be an asshole, but your post doesn't really contribute very much to the discussion. I assume your intention isn't to antagonize the poster, but it sort of comes off as such.
 

·
Registered
Joined
·
5,919 Posts
I did some testing on the upstream o2 sensor, seems like its not providing the correct output. Output is holding around 0.01 sometimes jumping up to 0.1, but it's not oscillating between 0.1 and 0.9 as it should. Looking at bank 1, that is the pattern that is seen. I know the o2 sensor is good because it was replaced. At this point I'm assuming exhaust gasket leak, or cracked manifold so its constantly reading fresh air. Because of this the short term fuel trims are around 25% which is way higher than it should be.
OK, you answered your own question. The upstream sensors rely on the Cat to provide backpressure and the mixture is controlled mainly by the upstream O2 sensor, but if the downstream isn't getting the correct info then there will be issues. There is a significant mixture difference before and after the cat, which is fed back into the ECU to alter mix and to a certain extent advance as well. If the upstream sensor is not tracking as it should, and you really want to prove the sensor, swap it with the other bank, I bet its fine.
If you have a cracked manifold etc then you will see or hear it. Wet a rag and hold it over the exhaust and see if you can hear a leak.

Regarding the timing, I really see the misfires being the cause of electrical issue more the opposite, the misfires are a symptom of electrical issues. I misfire I don't think has any pathway back to the ECU to create random signals that trip the ECM. The timing is mechanically set, not something that will change by misfire.
I disagree. Basic Timing is determined by crank sensor. The cam sensors and the correlation between crank and cam sensors determine advance or retard depending on load and VVT (if fitted) settings. My engine goes from 15 deg ATDC to about 28 BTDC depending on load and temperature. Misfire can certainly cause false triggering of the ECU, and can get into cam and crank signals as these wires all run together in the same loom. When you get significant misfires, the V6 engines have a nasty habit of getting "whip" in the timing chains causing a cam timing mismatch between the banks, bringing up codes and screwing with the overall timing.

You may be correct that your misfire is a lean/rich issue, but you need to get fuel trims where they should be to prove it. Check all grounds and power supplies first. Especially the grounds for the coils on the bank with issues as it all seems to be one side that affected, and the only thing common to all 3 coils is the power supply.
 

·
Registered
Joined
·
8,983 Posts
2013GV Thanks for jumping in. had to go for a 7hr drive to airport, pick up youngest daughter (Hmmm! 39)
 

·
Registered
Joined
·
5,919 Posts

·
Registered
Joined
·
19 Posts
Discussion Starter #9
OK, you answered your own question. The upstream sensors rely on the Cat to provide backpressure and the mixture is controlled mainly by the upstream O2 sensor, but if the downstream isn't getting the correct info then there will be issues. There is a significant mixture difference before and after the cat, which is fed back into the ECU to alter mix and to a certain extent advance as well. If the upstream sensor is not tracking as it should, and you really want to prove the sensor, swap it with the other bank, I bet its fine.
If you have a cracked manifold etc then you will see or hear it. Wet a rag and hold it over the exhaust and see if you can hear a leak.


I disagree. Basic Timing is determined by crank sensor. The cam sensors and the correlation between crank and cam sensors determine advance or retard depending on load and VVT (if fitted) settings. My engine goes from 15 deg ATDC to about 28 BTDC depending on load and temperature. Misfire can certainly cause false triggering of the ECU, and can get into cam and crank signals as these wires all run together in the same loom. When you get significant misfires, the V6 engines have a nasty habit of getting "whip" in the timing chains causing a cam timing mismatch between the banks, bringing up codes and screwing with the overall timing.

You may be correct that your misfire is a lean/rich issue, but you need to get fuel trims where they should be to prove it. Check all grounds and power supplies first. Especially the grounds for the coils on the bank with issues as it all seems to be one side that affected, and the only thing common to all 3 coils is the power supply.
I'll concede your point regarding the cat. and back pressure. I've ordered a replacement and will install it when it arrives to see if its able to provide the correct readings for the o2 sensor. The o2 sensor is known good, I don't have a doubt that it is working as it should and is just reading the conditions that it's provided. I'll check out the exhaust manifold thing.
 

·
Registered
Joined
·
5,919 Posts
While you're waiting for the CAT to arrive, check coil power supplies and grounds on the dodgy bank. If all 3 are misbehaving as you suggest, theres got to be a common cause on that bank, Having a mismatch with only 1 cat won't be helping but its worth checking all the supply and ground lines and check the loom for chafed wires where it clamps onto the engine coming in from the body
 

·
Registered
Joined
·
19 Posts
Discussion Starter #12
While you're waiting for the CAT to arrive, check coil power supplies and grounds on the dodgy bank. If all 3 are misbehaving as you suggest, theres got to be a common cause on that bank, Having a mismatch with only 1 cat won't be helping but its worth checking all the supply and ground lines and check the loom for chafed wires where it clamps onto the engine coming in from the body
Yeah I'll pull the loom apart and do a visual inspection as well as testing resistance back to their source. I'll report back with my findings.
 

·
Registered
Joined
·
5,919 Posts
the coil triggers go direct to the ECM, power from IG coil 20A fuse, gnds go to (I think) the ground point rear of engine on firewall but i'ts been a while since I worked on a V6
 

·
Registered
Joined
·
19 Posts
Discussion Starter #14
the coil triggers go direct to the ECM, power from IG coil 20A fuse, gnds go to (I think) the ground point rear of engine on firewall but i'ts been a while since I worked on a V6
I think measure direct to battery ground should be fine shouldn't it? After all its ultimately where the current has to flow. If it shows particularity high then you'll have to figure out where in the path its getting loaded.
 

·
Registered
Joined
·
5,919 Posts
yep, that will check all ground connections in that circuit
 
1 - 15 of 15 Posts
Top