Bad Tune, Vacuum Leak, Bad O2 Sensors? Log inside.
05-06-2016, 02:39 PM
#1
Teching In
Thread Starter
Join Date: May 2016
Location: Houston, TX
Posts: 4
Likes: 0
Received 0 Likes
on
0 Posts
Bad Tune, Vacuum Leak, Bad O2 Sensors? Log inside. I've been battling some interesting issues ever since I got this car (replacing another '04z that was lost to the Memorial Day floods in Houston last year).
The car is a 2004 Corvette Z06
The mods the car has are as follows:
Heads/Cam package (NO IDEA on the specs, though the heads are stamped 317, could be patriots or one of the other companies that were tweaking original GM castings)
FAST 90/90 manifold/TB
Callaway Honker intake
LG Long Tubes
Random Tech High Flow Cats and X Pipe
Callaway Double D Exhaust
Ever since I got the car I have noticed that my fuel mileage has been way down as compared to my old car, (19-20mpg @80% highway driving) and I've always noticed a hydrocarbon smell that I chalked up to the cam/HF cats. However, of late the car has started to have some issues that have made me think that something isn't right, so I purchased a ScanTool OBDLink MX scanner to log what the car's computer was picking up.
The symptoms that I was experiencing are as follows:
-Occasional rough idle, bouncing from the "normal" idle that is somewhere around 9-950 to 1200, then dropping to the 400s and back. When this happens (the low idle drop) the below listed P0522 will be triggered, which makes sense. The car has been hooked up to a mechanical gauge and tested with these symptoms present and oil pressure is not an issue at all. I have not seen any consistency to when this idle issue shows up as I've had it happen after the car has been sitting overnight as well as 15 minutes after I had just driven it for 30 minutes (and in some cases the first drive had no issues at all, and it only flared up on the second trip).
-When the idle issues are present, there is also an accompanying issue of what is a pretty violent "stumble" that occurs low in the RPM range, that feels as if the car was cutting all of its power and falling flat on its face. I've found that if I get the RPMs up above 2500 to about 3k this condition goes away, and the subsequent idle issues *typically* go away, though this isn't always the case. Sometimes, this "stumble" will cut off and then when the car picks back up the power comes on hard, taking off somewhat violently.
As to what the scanner was picking up, here are the results:
https://drive.google.com/open?id=0B9...2V4ZDY0Rk9lX0U
For reference, the error codes that I have seen are:
P0522
P1546
U1016
U1096
U1255
U1040
U1000
(also have no comms to the RFA, and I have tested the wiring back there and it's good, so I think that receiver might be bad. The remote locks have never worked since I got the car, and I've tried all the usual suspects to fix them)
I have replaced the following:
-New AIR tube gaskets
-2 New ignition switches
-New valvesprings ( .650 Patriot Gold springs)
-New spark plugs/wires with plug wire insulation boots installed.
I have inspected the wiring to the O2 sensors and everything appears fine, no melting from the headers.
I have inspected/cleaned the engine grounds from the battery to the chassis, block to chassis on both sides of engine, and checked/cleaned the connections at the starter.
I have checked the connection at the PCM and cleaned it up.
Fuses have been checked in both fuse boxes.
PCV line has been checked for leaks, as have the hoses connecting the MAF to the TB.
I have cleaned the MAF with MAF cleaner, and have also cleaned the TB butterfly.
Now, to the logs. Obviously the LTFTs are WAY high on both banks, so the engine thinks there's a lean condition. I don't currently think there's a vacuum leak, but I could be wrong. The next thing I'd do would be to replace the intake manifold gaskets, which I'm not super pumped about doing, if I don't have to. There's also the concern of a cracked FAST manifold, but I'd figure a vacuum leak would cause the symptoms that I'm experiencing to be much more consistently present.
Next, do the O2 sensors look like they're operating normally? It's my understanding that they should fluctuate in a wave-like pattern, which I don't see here as the numbers are pretty steady most of the time, and with spotty extreme changes. I'm hoping this is the issue as it would be the easiest thing for me to change out, but also don't want to just replace parts *****-nilly if not necessary. As the car does have 67k miles on it, I decided to order some new O2 sensors (got the rear sensors to put in the front locations, due to the better heating elements), and will be installing them once they get here.
Lastly, could this just be a bad tune?
It's weird to me that the O2 sensors are reading rich, yet the LTFTs are indicating a lean condition and adding fuel... Shouldn't the rich O2 reading make the PCM pull fuel instead of adding it?
The coolant temps as shown in the DIC appear normal, and gradually build from cold and remain constant once the engine is warm, so I don't think there's an issue with that sensor, which I know can cause some of these problems.
I'm only now trying to gain an education on these reading with what I've found from the internet, so any help that anyone can provide would be great!
Thanks!
Pat
Update: Here's a new log with the MAF recording in g/s, which keyed me in to the possibility that it's BAD, as the reading is at least 4x higher than it should be, which would explain the lean reading and rich reading O2 sensors:
https://drive.google.com/open?id=0B9...mRNMkxYejZFXzA
Here's a log with the MAF disconnected, which I know will only provide for so much in that the IAT is crucial for the PCM to figure out the fuel trims, and it's built into the MAF on my car since it's an '04.:
https://drive.google.com/open?id=0B9...2pkcmg1RG1ydm8
The car is a 2004 Corvette Z06
The mods the car has are as follows:
Heads/Cam package (NO IDEA on the specs, though the heads are stamped 317, could be patriots or one of the other companies that were tweaking original GM castings)
FAST 90/90 manifold/TB
Callaway Honker intake
LG Long Tubes
Random Tech High Flow Cats and X Pipe
Callaway Double D Exhaust
Ever since I got the car I have noticed that my fuel mileage has been way down as compared to my old car, (19-20mpg @80% highway driving) and I've always noticed a hydrocarbon smell that I chalked up to the cam/HF cats. However, of late the car has started to have some issues that have made me think that something isn't right, so I purchased a ScanTool OBDLink MX scanner to log what the car's computer was picking up.
The symptoms that I was experiencing are as follows:
-Occasional rough idle, bouncing from the "normal" idle that is somewhere around 9-950 to 1200, then dropping to the 400s and back. When this happens (the low idle drop) the below listed P0522 will be triggered, which makes sense. The car has been hooked up to a mechanical gauge and tested with these symptoms present and oil pressure is not an issue at all. I have not seen any consistency to when this idle issue shows up as I've had it happen after the car has been sitting overnight as well as 15 minutes after I had just driven it for 30 minutes (and in some cases the first drive had no issues at all, and it only flared up on the second trip).
-When the idle issues are present, there is also an accompanying issue of what is a pretty violent "stumble" that occurs low in the RPM range, that feels as if the car was cutting all of its power and falling flat on its face. I've found that if I get the RPMs up above 2500 to about 3k this condition goes away, and the subsequent idle issues *typically* go away, though this isn't always the case. Sometimes, this "stumble" will cut off and then when the car picks back up the power comes on hard, taking off somewhat violently.
As to what the scanner was picking up, here are the results:
https://drive.google.com/open?id=0B9...2V4ZDY0Rk9lX0U
For reference, the error codes that I have seen are:
P0522
P1546
U1016
U1096
U1255
U1040
U1000
(also have no comms to the RFA, and I have tested the wiring back there and it's good, so I think that receiver might be bad. The remote locks have never worked since I got the car, and I've tried all the usual suspects to fix them)
I have replaced the following:
-New AIR tube gaskets
-2 New ignition switches
-New valvesprings ( .650 Patriot Gold springs)
-New spark plugs/wires with plug wire insulation boots installed.
I have inspected the wiring to the O2 sensors and everything appears fine, no melting from the headers.
I have inspected/cleaned the engine grounds from the battery to the chassis, block to chassis on both sides of engine, and checked/cleaned the connections at the starter.
I have checked the connection at the PCM and cleaned it up.
Fuses have been checked in both fuse boxes.
PCV line has been checked for leaks, as have the hoses connecting the MAF to the TB.
I have cleaned the MAF with MAF cleaner, and have also cleaned the TB butterfly.
Now, to the logs. Obviously the LTFTs are WAY high on both banks, so the engine thinks there's a lean condition. I don't currently think there's a vacuum leak, but I could be wrong. The next thing I'd do would be to replace the intake manifold gaskets, which I'm not super pumped about doing, if I don't have to. There's also the concern of a cracked FAST manifold, but I'd figure a vacuum leak would cause the symptoms that I'm experiencing to be much more consistently present.
Next, do the O2 sensors look like they're operating normally? It's my understanding that they should fluctuate in a wave-like pattern, which I don't see here as the numbers are pretty steady most of the time, and with spotty extreme changes. I'm hoping this is the issue as it would be the easiest thing for me to change out, but also don't want to just replace parts *****-nilly if not necessary. As the car does have 67k miles on it, I decided to order some new O2 sensors (got the rear sensors to put in the front locations, due to the better heating elements), and will be installing them once they get here.
Lastly, could this just be a bad tune?
It's weird to me that the O2 sensors are reading rich, yet the LTFTs are indicating a lean condition and adding fuel... Shouldn't the rich O2 reading make the PCM pull fuel instead of adding it?
The coolant temps as shown in the DIC appear normal, and gradually build from cold and remain constant once the engine is warm, so I don't think there's an issue with that sensor, which I know can cause some of these problems.
I'm only now trying to gain an education on these reading with what I've found from the internet, so any help that anyone can provide would be great!
Thanks!
Pat
Update: Here's a new log with the MAF recording in g/s, which keyed me in to the possibility that it's BAD, as the reading is at least 4x higher than it should be, which would explain the lean reading and rich reading O2 sensors:
https://drive.google.com/open?id=0B9...mRNMkxYejZFXzA
Here's a log with the MAF disconnected, which I know will only provide for so much in that the IAT is crucial for the PCM to figure out the fuel trims, and it's built into the MAF on my car since it's an '04.:
https://drive.google.com/open?id=0B9...2pkcmg1RG1ydm8
Last edited by NotLawReview; 05-09-2016 at 01:31 PM. Reason: Updated Logs
05-09-2016, 08:16 AM
#3
Teching In
Thread Starter
Join Date: May 2016
Location: Houston, TX
Posts: 4
Likes: 0
Received 0 Likes
on
0 Posts
Front and rear sensors are in place and are wired correctly. I believe the rear sensors are either sims or tuned out. I bought new sensors for the front (rear sensors) that I will be installing once the front/rear adapters get here from Racetronix tomorrow.
The code I'm getting is P1546, not P1516, which is an A/C circuit low voltage error, which like the "low voltage oil pressure sensor" I believe to be a result of the RPMs dropping too low and as a result providing insufficient voltage to certain components.
The code I'm getting is P1546, not P1516, which is an A/C circuit low voltage error, which like the "low voltage oil pressure sensor" I believe to be a result of the RPMs dropping too low and as a result providing insufficient voltage to certain components.
05-09-2016, 01:32 PM
#4
Teching In
Thread Starter
Join Date: May 2016
Location: Houston, TX
Posts: 4
Likes: 0
Received 0 Likes
on
0 Posts
Update: Here's a new log with the MAF recording in g/s, which keyed me in to the possibility that it's BAD, as the reading is at least 4x higher than it should be, which would explain the lean reading and rich reading O2 sensors:
https://drive.google.com/open?id=0B9...mRNMkxYejZFXzA
Here's a log with the MAF disconnected, which I know will only provide for so much in that the IAT is crucial for the PCM to figure out the fuel trims, and it's built into the MAF on my car since it's an '04.:
https://drive.google.com/open?id=0B9...2pkcmg1RG1ydm8
Thoughts? Does it make sense/look like i'm on the right track in thinking the MAF is bad?
I know that most expect there to be codes when the MAF goes bad, but the data seems to make it look like that's not always the case...
https://drive.google.com/open?id=0B9...mRNMkxYejZFXzA
Here's a log with the MAF disconnected, which I know will only provide for so much in that the IAT is crucial for the PCM to figure out the fuel trims, and it's built into the MAF on my car since it's an '04.:
https://drive.google.com/open?id=0B9...2pkcmg1RG1ydm8
Thoughts? Does it make sense/look like i'm on the right track in thinking the MAF is bad?
I know that most expect there to be codes when the MAF goes bad, but the data seems to make it look like that's not always the case...
05-10-2016, 10:24 AM
#5
Teching In
Thread Starter
Join Date: May 2016
Location: Houston, TX
Posts: 4
Likes: 0
Received 0 Likes
on
0 Posts
SURPRISE! BAD MAF and NO CODES!
The adapter (to convert a rear sensor plug to a front sensor plug) will be delivered today and the new o2 sensors will be installed tonight.
However, over the last few days it has really been bugging me that both the LTFTs were high and the o2s were reading rich, as they should be the opposite of each other, so I decided to look closer at the MAF readings. I changed my logger to g/s instead of CFM as in the original logs and noticed that I was getting 20+g/s at idle!
Bought a new MAF sensor and installed it last night, idle was IMMEDIATELY rock solid, and here's what I have logged:
https://drive.google.com/open?id=0B9...XVpRXV5MElIYjQ
As you can see, the LTFTs are now NEGATIVE and everything appears to have been learned as it should.
However, my fuel economy hasn't quite improved like I expected it to, and I think that's a result of the o2s reading lazy and rich. Once I swap them tonight I hope to see a significant change.
Also, once concern that I have is that the car is not pulling up high like it did with the really rich LTFTs and the bad MAF, and that surprised me as I was expecting a big change in the seat of the pants feel as I would think that the car would be making more horsepower with the A/F being closer to where it should be. The car gets to 5k RPM and just feels like it stops pulling and the power curve goes flat. I will note that it looks like the MAF is still providing a slightly higher reading than I would expect it to (10 g/s at idle), so I'm not quite sure what the cause of that is.
Hopefully the o2s make a big change in things and the trims get back to where they should ideally be, and my power/MPG will return.
The adapter (to convert a rear sensor plug to a front sensor plug) will be delivered today and the new o2 sensors will be installed tonight.
However, over the last few days it has really been bugging me that both the LTFTs were high and the o2s were reading rich, as they should be the opposite of each other, so I decided to look closer at the MAF readings. I changed my logger to g/s instead of CFM as in the original logs and noticed that I was getting 20+g/s at idle!
Bought a new MAF sensor and installed it last night, idle was IMMEDIATELY rock solid, and here's what I have logged:
https://drive.google.com/open?id=0B9...XVpRXV5MElIYjQ
As you can see, the LTFTs are now NEGATIVE and everything appears to have been learned as it should.
However, my fuel economy hasn't quite improved like I expected it to, and I think that's a result of the o2s reading lazy and rich. Once I swap them tonight I hope to see a significant change.
Also, once concern that I have is that the car is not pulling up high like it did with the really rich LTFTs and the bad MAF, and that surprised me as I was expecting a big change in the seat of the pants feel as I would think that the car would be making more horsepower with the A/F being closer to where it should be. The car gets to 5k RPM and just feels like it stops pulling and the power curve goes flat. I will note that it looks like the MAF is still providing a slightly higher reading than I would expect it to (10 g/s at idle), so I'm not quite sure what the cause of that is.
Hopefully the o2s make a big change in things and the trims get back to where they should ideally be, and my power/MPG will return.