2G Fuel trim, Timing, Logging, and P0170 CEL

[matthewdesigns]

OK, I've searched and read a number of posts, but can't seem to put together all of what I'm looking for.

Mods are current in my profile.

What I'm trying to get to is an understanding of what I'm seeing in my logger as it relates to the P0170 (fuel trim malfunction) CEL I keep throwing. (I'd post a log, but I'm not getting any cooperation from OBDGraph and Excel...and I've read the "How to post logs" tech article..it's just not cooperating).

Here's the situation: Every few days I throw the P0170 fuel trim CEL and reset it. I've logged under both WOT and at cruising speeds. When cruising, my short term trim is 117% consistently, long term is 112%. So I'm running lean, right? When I go WOT, my short term trim reads flat...0% added. Is this because the car is in open loop at WOT?

Am I correct in thinking that the CEL is being thrown because I'm chronically lean?

As for timing, at WOT it drops to 8-9* at tip-in, and rises slowly to 14-15* at 6500rpm. I can't see knock on my 2g ECU, so I'm guessing that I'm knocking a little and having timing pulled as a result. Or is this fairly normal (I've read that 15* at max boost/rpms is about right)?

I'm running 16psi of boost. I have 1 pinhole boost leak that I can't squeeze tight enough to overcome (pressure tested to 20lbs).

Based on my logs, I feel like I'm right on the edge of running too lean. I've logged a few runs with my MBC turned way down (to see what lower boost will yield), but it looks like I'm creeping to the 16lbs I'm running, because turning it down has not decreased peak boost... I have not disconnected the MBC yet to see if that's right for sure.

I know I have questions scattered through the message. I'm just trying to make sure I've got a decent understanding of what's going on here.

Thanks in advance,
Matthew

 

[spyderturbo007]

Here's the situation: Every few days I throw the P0170 fuel trim CEL and reset it. I've logged under both WOT and at cruising speeds. When cruising, my short term trim is 117% consistently, long term is 112%. So I'm running lean, right?

Yes, at cruise and idle. But, are we talking about the car in your profile? If so, there is something wrong here. The 2g ECU outputs the FT's based around zero, so you shouldn't see something in the 100's. You only get that on 1g's.

When I go WOT, my short term trim reads flat...0% added. Is this because the car is in open loop at WOT?

You can disregard FT's at WOT since the ECU doesn't care about this value.

Am I correct in thinking that the CEL is being thrown because I'm chronically lean?

Yep, well, kindof.

The FT's are designed to allow the ECU a compensation range for changing conditions. When you exceed this compensation range, the ECU is unable to correct any further and you get popped with the p0170 Fuel Trim Malfunction (Bank 1) CEL.

As for timing, at WOT it drops to 8-9* at tip-in, and rises slowly to 14-15* at 6500rpm. I can't see knock on my 2g ECU, so I'm guessing that I'm knocking a little and having timing pulled as a result. Or is this fairly normal (I've read that 15* at max boost/rpms is about right)?

Actually it sounds normal, but without seeing the entire log and airflow value, I can't say for sure. As your turbo spools, the ECU retards timing in anticipation of knock. After that point the timing should increase steadily to around 16 - 17 degrees when running stock injectors with no tuning device.

I'm running 16psi of boost. I have 1 pinhole boost leak that I can't squeeze tight enough to overcome (pressure tested to 20lbs).

Make sure you keep an eye on airflow and don't max out your fuel system. You can easily run out of fuel running the 16g on the stock fuel system. Oh, and fix that leak.

Based on my logs, I feel like I'm right on the edge of running too lean. I've logged a few runs with my MBC turned way down (to see what lower boost will yield), but it looks like I'm creeping to the 16lbs I'm running, because turning it down has not decreased peak boost... I have not disconnected the MBC yet to see if that's right for sure.

Most likely your front O2 sensor is dead or dying. Does it cycle at idle / cruise? You should see it bouncing back and forth between 0.20 and 0.80volts, or so. What value do you get on the logger when at WOT?

 

[matthewdesigns]

Yes, at cruise and idle. But, are we talking about the car in your profile? If so, there is something wrong here. The 2g ECU outputs the FT's based around zero, so you shouldn't see something in the 100's. You only get that on 1g's.

Yep, the car in the profile...and my bad, it does read in a zero-based system. I guess I transposed the 100 in my mind, and then the keyboard. I do occasionally see a negative number, typically at low rpm cruising.

Actually it sounds normal, but without seeing the entire log and airflow value, I can't say for sure. As your turbo spools, the ECU retards timing in anticipation of knock. After that point the timing should increase steadily to around 16 - 17 degrees when running stock injectors with no tuning device.

I'll try to save a logged chart as a jpeg and post it that way.

Make sure you keep an eye on airflow and don't max out your fuel system. You can easily run out of fuel running the 16g on the stock fuel system. Oh, and fix that leak.

My software apparently does not read intake airflow rate. I set it up to scan this parameter in a log last night, and the value read 0 for the entire log.

Most likely your front O2 sensor is dead or dying. Does it cycle at idle / cruise? You should see it bouncing back and forth between 0.20 and 0.80volts, or so. What value do you get on the logger when at WOT?

Again, I don't think the logger is reading/reporting this correctly. My o2 values, as reported on my logger, read from 0 to 580. And I never see the cycling you suggest (and I've previously read about). The sensor is only 6 months old...could it be bad already? And it reads 0 at WOT...but I don't trust what it's telling me.

I'm using OBD Gauge as my logger. I also have TunerStein, but there's a glitch in the player, so I can't get the logs into my computer from my palm. And the files won't transfer via the infrared port like the OBD Gauge files will. Should I be looking for a new logging program? I can't afford DSMLink at this point. Other suggestions? Pocketlogger?

I'll get my hands on a t-bolt clamp for that pesky leak.

Thanks for your input so far!

 

[spyderturbo007]

I have only ever used the pocketlogger program, so I can't really help you with the software problems. I must say, that I rarely see people with problems with the pocketlogger software. I'll let that decision up to you.

It's going to be really hard to diagnose your problem without a reliable logger.