NotLawReview

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 mods the car has are as follows:
Heads/Cam package (NO IDEA on the specs)
FAST 90/90 manifold/TB
Callaway Honker intake
LG Long Tubes
Random Tech High Flow Cats and X Pipe
Callaway Double D Exhaust
Callaway Sway Bars

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. Here are the results:

https://drive.google.com/open?id=0B9...UxES3d4dV9oNDA


The symptoms that I was experiencing that prompted me to get this were:
Random rough idle that would bounce down to 500 or so RPMs and then up to 1200 RPMs, and would occasionally die. The idle would remain rough until I made it to the stop sign down the street where I would also make sure to get to about 2500-3k RPMs, and then everything would be fine. Also, sometimes paired with this would be an issue that was like the throttle was cutting out on me, as if the car was cutting spark or something. Very strange.

When this would happen, the error codes that I would get were:

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
-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.



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.

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.

Lastly, could this just be a bad tune?

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

enoniam

The P0522 code is for low oil pressure. May want to check oil level and monitor what the pressure is doing.

O2 sensor readings should be bouncing between around 0.15 and 0.75 or so. You won't seem too many readings around the middle they are generally either high or low.

NotLawReview

Yeah, that code was showing up when the idle would drop really low before dying; I've (as well as my mechanic) tested the pressure and everything is fine. The voltage going to the oil pressure sensor was dropping due to the car trying to die/dying.

The more I've read about the O2 values, the more it appears that they aren't oscillating like they should. I'm going to swap them out and hope that corrects the fuel trims.

enoniam

Yeah, you've got some mid-range readings that repeat 3 or 4 times which doesn't seem copacetic.

NotLawReview

Appreciate the help, really hope new sensors take care of the problem.

MRc5z

Did the new o2 sensors take care of the issue??

NotLawReview

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.

schpenxel

How do you know the WOT AFR is where it should be? Do you have a wideband that isn't included in this log?

NotLawReview

Sorry, that's all based on my assumption that the adjustments that the PCM are making are correct and are targeting 14.7. I do not have a wideband, just the bluetooth OBDII scanner and the Torque software on my phone. I have no idea if this is actually the case as I have no idea as to whether the car is on its tune that was at one point present, or if it's based on the car's default tune due to someone reflashing the ECU at some point.

I have quickly learned that this car has never run properly in the time that I've owned it (10 mos or so) so I really have no idea what it's supposed to feel like, but I do have a previous '04 c5z to compare it to (which was MUCH torquier on the low end but didn't scream up top like this one, at least before the MAF change).

I just noticed that the car isn't pulling up high as well as it did before changing the MAF, when the LTFTs were indicating a very lean condition.

schpenxel

You really need a wideband, otherwise it's about 95% guessing as soon as you start putting in aftermarket parts/tunes.

Factory O2 sensors do nothing at WOT, so there aren't any fueling corrections @ WOT

Once WOT the computer is just going to use the airflow # it's calculating from the MAF reading, divide by the commanded AFR, and use that to figure out how much fuel to inject. The MAF airflow # could be totally wrong though and the AFR could be 15:1 @ WOT and the computer would still never know and never do anything about it. Without a wideband you'll never really know

You can look at narrowband O2 voltages to get a really really rough idea of what's going on (basically just whether it's richer or leaner than 14.7:1), but that's pretty much it

NotLawReview

I gotcha.

So would this be the reason why my car feels "flat" in the upper RPM range now that I've replaced the MAF? The bad MAF was recording really high values, which could be closer to the actual airflow of what the FAST intake could handle, so the extra air/fuel allowed the engine to scream up top, and now that there is a MAF that is working in place it could be based on the default tune, and thus not providing enough fuel for the airflow that may actually be there?

It just seems weird to me that I'd change the MAF, have the trims level out, and now the car effectively stops pulling at 4500-5k and is just making more noise up to redline.

schpenxel

It could be too rich or too lean up top which could cause the behavior you're seeing--no way to know without a wideband though

NotLawReview

So, for this reason it seems like I'd be best served not pushing the car until I got it properly tuned?

I'm going to swap out the o2s and check out the plugs to see if they need to be changed as well (changed them in December), so things should be as close to ideal as possible for the tuner when I get it in.

schpenxel

Yeah I wouldn't go too hard on it until it's looked over. It may be perfectly fine but tuner can say for sure.

enoniam

Network ***** here at work won't let me open your latest data log but I will say that I would expect around 10 g/s of airflow at idle for a non-radically cammed LS engine.

RonSSNova

Agree

NotLawReview

That's right at what I'm getting with the new MAF installed; the old one was pulling twice that so it was definitely bad...

I finally got the correct O2 sensors as I found out the hard way that the '04s had different plugs than all of the other model years in that the connectors are female instead of male.

Once the new 02s go in, the car is scheduled to get tuned this friday/saturday, so hopefully after that happens all will be running properly again!

Thanks everyone for their help, I'll let everyone know what I learn once I get it back from the tuner Sat afternoon.

-Pat