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Got a scangauge2....now what do I learn?

 
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LoudImpala
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PostPosted: Mon Jul 09, 2012 7:43 pm    Post subject:  Got a scangauge2....now what do I learn? Reply with quote

So I got my scangauge 2 installed this weekend. Been playing around with it a bit, seeing that it gives some pretty neat information. I wish I had it a long time ago.

I added the commands or whatever to scan for KR and LTFTs. Seems I am getting a bit of KR, sometimes around 25% throttle up to about 4 degrees, and at WOT it has topped out at 5.3. My car is stock except for the K&N CAI and the PRJ wires with Autolite 605s. I plan on getting the ZZP 3" DP and possibly the front PLOG next pay, then the catback with res delete, and finally a tune from Overkill. (still haven't heard from him in over a month now - making me a little hesitant).

Anyways, so now that I got this scangauge, what exactly can I learn from it? I get KR, but the LTFT is a little confusing to me. When I give it throttle, it stays around 0-3, and I've even seen -4 at times, but as soon as I let off the throttle, it bounces up to sometimes 15, and idle seems to like 10-11. What exactly is going on here, and how can I diagnose any problems with the scangauge besides the obvious code scanning?

Here's a WOT pull I did on my way home today.

http://s40.photobucket.com/alb.....185238.mp4

Loud
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outonthetiles
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PostPosted: Mon Jul 09, 2012 7:58 pm    Post subject:   Reply with quote

LFTF's should be as close to 0 as possible.

Your car uses a set fueling table to reach a commanded air/fuel ratio. In closed loop fueling, your upstream oxygen sensor detects the actual air/fuel ratio, and then the fueling is corrected using fuel trims. LTFT's are the percentage the computer is adjusting your injector pulse width from the preset fueling table. You shouldn't see more than 10% in either direction.

At WOT, you are in open loop fueling meaning that the O2 sensor is not being used to calculate fueling. Instead, it uses the last known LTFT before it goes into open loop. Open loop is used at WOT, and also when the car is cold before the O2 sensor is properly heated up.

If your LTFT's are way off, it could mean a few different things. I'd start by cleaning your MAF sensor and checking for any vacuum leaks. If your O2 sensor is old (over 80k), you may consider buying a new AC Delco unit.

A few degrees of KR is normal on a stock tune for a 3800. You're on the right track by wanting to open up the exhaust.

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LoudImpala
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PostPosted: Mon Jul 09, 2012 8:04 pm    Post subject:   Reply with quote

outonthetiles wrote:
LFTF's should be as close to 0 as possible.

Your car uses a set fueling table to reach a commanded air/fuel ratio. In closed loop fueling, your upstream oxygen sensor detects the actual air/fuel ratio, and then the fueling is corrected using fuel trims. LTFT's are the percentage the computer is adjusting your injector pulse width from the preset fueling table. You shouldn't see more than 10% in either direction.

At WOT, you are in open loop fueling meaning that the O2 sensor is not being used to calculate fueling. Instead, it uses the last known LTFT before it goes into open loop. Open loop is used at WOT, and also when the car is cold before the O2 sensor is properly heated up.

If your LTFT's are way off, it could mean a few different things. I'd start by cleaning your MAF sensor and checking for any vacuum leaks. If your O2 sensor is old (over 80k), you may consider buying a new AC Delco unit.

A few degrees of KR is normal on a stock tune for a 3800. You're on the right track by wanting to open up the exhaust.


I've been plagued by vacuum leaks and it's possible I still have one. My RPMS bounce around by about +/- 40 RPM at idle too. Little variances I wasn't noticing on the needle but the scangauge tells me so. I'm still also feeling a bit of a shudder at times during idle, but not throwing any misfire codes or anything. I'm wondering if it's the stock motor mounts and trans mounts.

The MAF was freshly cleaned about a month or so ago, and the O2 sensor is a brand new AC delco sensor just installed about 2 weeks ago. I got rid of the bosch sensor I had put in there temporarily.

Loud
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outonthetiles
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PostPosted: Mon Jul 09, 2012 8:11 pm    Post subject:   Reply with quote

The rough idle and LTFT's being off would lead me to believe there's a small vacuum leak somewhere.

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LoudImpala
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PostPosted: Mon Jul 09, 2012 8:17 pm    Post subject:   Reply with quote

outonthetiles wrote:
The rough idle and LTFT's being off would lead me to believe there's a small vacuum leak somewhere.


What's the safest way to check for vacuum leaks? Starter fluid, Carb cleaner, TB cleaner, or propane? I've read about all of them being used. I'm not trying to blow my face off or my motor up.

I've visually checked over most of the tubing, and everything seems to look ok. Hopefully it's not the EGR tube. That looks like a PITA to change.

Loud
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outonthetiles
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PostPosted: Mon Jul 09, 2012 8:27 pm    Post subject:   Reply with quote

I've used ether and carb cleaner..

A bad LIM gasket could also cause a vac leak..

You might want to consider a smoke test if you can't find it, but I'd wait for a second opinion that you actually have a vac leak before dropping the coin on that.

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PostPosted: Tue Jul 10, 2012 10:11 am    Post subject:   Reply with quote

FWIW, I got worked up over the fuel trims on my Aeroforce shortly after I got it. I posted a few questions on a couple of forums and the general consensus was the values the Aeroforce reported for the STFTs and LTFTs aren't anything to write home about. I'd assume that the Scangauge is the same way. That being said, I don't think I'd worry about it unless its reporting you are running super lean or super rich.

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outonthetiles
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PostPosted: Tue Jul 10, 2012 1:34 pm    Post subject:   Reply with quote

Up to 10% in either direction is nothing to worry about. If you're consistently seeing more than that, and not just spikes, that's something to look into. I was seeing a constant -13.5% in my 02 LSS before cleaning the MAF sensor, now I have more normal fuel trims.

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slowsol
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PostPosted: Tue Jul 10, 2012 9:31 pm    Post subject:   Reply with quote

Wow I have to thank you. After watching your video I realized my scanguage KR didn't have the decimal point. I double checked the settings and sure enough I messed up a few numbers. Changed it and works great now. Plus it took care of all my 'KR' on the interstate and part throttle it was telling me I had. THANKS

On a side note. I use mine to monitor KR, LTFT, A/F, and IGN.

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