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Performance, Brainstorming & Tuning Talk about modifications, or anything else associated with performance enhancements. Have a new idea for performance/reliability? Post it here. No idea is stupid! (please use Detailing and Appearance for cosmetic ideas)

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Old 09-15-2004, 12:57 AM   #11
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I took mine out before mounting my new tb to fwi coupler last week before I went to the track. No noticible improvment, and in fact I did not match my PB (although close) but I got a lot of slip off the line (with slicks) so I attribute my non PBs to that and not the removal of the MAF screen. Either way it doesnt seem to have done much for me.
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Old 09-15-2004, 01:20 AM   #12
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Quote:
Originally Posted by DrJay
Very interesting find, good job! I'm still reading it right now but as far as the scantool readings the ST and LT fuel trims are where to look for the 128 number. LT being long term fuel trim, and ST being short term. LT is the average, but ST you can watch change as you drive.
I found that BLM is the same as LT. Just different terminology. Anyway, when I had the MAF screen out, the idle settled down just fine, but was a little rough, but not uncomfortably. I also noticed at idle, the MAF g/* dropped to 3.25 from around 4.8 and I interpreted that as better efficiency, but then I noticed the BLM maxing out, so it appears the ECM was compensating for the increased airflow by pumping up the fuel. I think what'* happening is, the MAF is tuned to be accurate with screen on, but with it removed, it reads low with the increased flow (because of extra flow passing around it). The problem is, the BLM (or LT) is limited to 160, so it can't go higher, so it could potentially cause the engine to run too lean under certain conditions.

I found it also interesting that according to the article, the only thing the computer learns is BLM and BLM cell values, and it learns very quickly. When I put my screen back in, the BLM was back to the old values within 30 minutes and 10 miles of driving.
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Old 09-15-2004, 01:26 AM   #13
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I was noticing leaner than normal for me 02 numbers at the track, and a little higher KR. I think I'll put my MAF screen back in tomorrow and see if it clears up.
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Old 09-15-2004, 01:58 PM   #14
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Quote:
Originally Posted by Rogue
I was noticing leaner than normal for me 02 numbers at the track, and a little higher KR. I think I'll put my MAF screen back in tomorrow and see if it clears up.
It'* funny you mention KR. I checked my scan logs, and found that my knock count dramatically increased while the screen was removed, when under moderate acceleration and similar temperature and load conditions. This confirms that screen removal can cause a lean condition. I think this also might be why a smaller diameter (3" vs 3.5") intake helps, because it brings the flow back down, more closely matching the flow with a screen and stock intake. I was also thinking maybe running larger flow injectors in combo with the screen removal may work, since the ECM will still add fuel based on the assumed stock injectors. This may effectively center the BLM (or LT) back to the center value of 128.

This is just a theory, so don't take my word for it. Try it for yourself.
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Old 09-15-2004, 02:08 PM   #15
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Quote:
Originally Posted by GreenMachine
Quote:
Originally Posted by Rogue
I was noticing leaner than normal for me 02 numbers at the track, and a little higher KR. I think I'll put my MAF screen back in tomorrow and see if it clears up.
It'* funny you mention KR. I checked my scan logs, and found that my knock count dramatically increased while the screen was removed, when under moderate acceleration and similar temperature and load conditions. This confirms that screen removal can cause a lean condition. I think this also might be why a smaller diameter (3" vs 3.5") intake helps, because it brings the flow back down, more closely matching the flow with a screen and stock intake. I was also thinking maybe running larger flow injectors in combo with the screen removal may work, since the ECM will still add fuel based on the assumed stock injectors. This may effectively center the BLM (or LT) back to the center value of 128.

This is just a theory, so don't take my word for it. Try it for yourself.
I'm already running larger injectors but the PCM is programmed for them so no overfueling may be occuring.
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Old 09-15-2004, 02:25 PM   #16
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Quote:
Originally Posted by Rogue
Quote:
Originally Posted by GreenMachine
Quote:
Originally Posted by Rogue
I was noticing leaner than normal for me 02 numbers at the track, and a little higher KR. I think I'll put my MAF screen back in tomorrow and see if it clears up.
It'* funny you mention KR. I checked my scan logs, and found that my knock count dramatically increased while the screen was removed, when under moderate acceleration and similar temperature and load conditions. This confirms that screen removal can cause a lean condition. I think this also might be why a smaller diameter (3" vs 3.5") intake helps, because it brings the flow back down, more closely matching the flow with a screen and stock intake. I was also thinking maybe running larger flow injectors in combo with the screen removal may work, since the ECM will still add fuel based on the assumed stock injectors. This may effectively center the BLM (or LT) back to the center value of 128.

This is just a theory, so don't take my word for it. Try it for yourself.
I'm already running larger injectors but the PCM is programmed for them so no overfueling may be occuring.
Okay, just another thought. Your PCM is probably programmed to work with screen on, so maybe you need to increase injectors up another notch.
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Old 09-15-2004, 03:30 PM   #17
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My LT is 138 and my ST is 128 until i put it in gear, then it switches to 135. If my understanding is correct then an AF calibrator cannot correct this because it changes the AF ratio and not the preasure itself right? or would the ECM change the FP when it sees that my MAF readings are different. How bad is this for my car?
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Old 09-15-2004, 04:11 PM   #18
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Quote:
Originally Posted by jachin
My LT is 138 and my ST is 128 until i put it in gear, then it switches to 135. If my understanding is correct then an AF calibrator cannot correct this because it changes the AF ratio and not the preasure itself right? or would the ECM change the FP when it sees that my MAF readings are different. How bad is this for my car?
I'm just starting to understand this, but from what I read so far and confirmed on my car, the LT is made up of 16 different cells, each cell corresponds to a different MAF/speed combination. In my case, at idle, it jumps to cell 16. At around 30MPH part throttle it was in cell 5. Each cell has a value which ideally would be 128. So when you shift from neutral to drive, it may switch from one cell to another, which explains LT changing from 138 to 135. Depending on the car, the LT can vary. On some older cars it is limited to a range of 118 to 138. On my car, a 95 SSEi, it goes up to 159, I don't know the lower end. Since yours is a 93, it might be pegging at 138, just a guess. If it is pegged, you may be running lean, because it has no room to go higher. A higher number indicates it detected a lean condition and is compensating by making it richer. A reading of 128 would be considered ideal.

The scantool I'm using lets you see what cell you're in, and the LT does change over time, but at a slower pace then the ST. When I switched in/out the MAF screen, the LT ramped over a couple minute period. Anyway, the bottom line is, if it is always at a high number and never changes over time, it'* probably running lean. With my MAF screen in, my LT varies between 120 and 130.
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Old 09-15-2004, 09:12 PM   #19
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I was reading about this about a week ago and it seems its capable of 0-255 and even moving up a block. Linky time:

http://www.chevyhiperformance.com/techarticles/49738/

Scroll down to Understand GM EFI
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Old 09-16-2004, 02:17 AM   #20
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Quote:
Originally Posted by DrJay
I was reading about this about a week ago and it seems its capable of 0-255 and even moving up a block. Linky time:

http://www.chevyhiperformance.com/techarticles/49738/

Scroll down to Understand GM EFI
Look at section "Chevy computer in School" section of your link, it mentions the clamp
I mentioned, so normally it doesn't go from 0 to 255.



Quote:
GM programmers often clamp the block-learn to minimums and maximums closer to 128. When any block-learn cell hits the maximum allowable value, a data trouble code is set, the Service Engine Soon dash light illuminates, and the computer defaults to open-loop operation.
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