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Thread: At wits' end ( short trip )

  1. #1
    Carb and Points!
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    At wits' end ( short trip )

    Working on an LS swap ( junk yard 6.0L LQ4 with 317 heads ) with 4L80e ( unknown history ) with 0411 computer (OS 12212156). It starts well but goes lean (15.5-16.5 AFR ) as it warms up and stays that way when driving ( afraid to drive it too far ). We are running a MAF. I must be adjusting in the wrong table or something because adjustments to the "open loop VE" table don't seem to help? What am I doing wrong?
    Any help is greatly appreciated.

    Attached what I am working with if someone that knows what they are looking at could look it over...

    Thank you in advance,
    Some Fool

  2. #2
    Fuel Injected! ralmo94's Avatar
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    If you are running a maf, VE won't make much difference until it goes to blended mode, example acceleration. Steady state operation is controlled mainly by the MAF. To tune the ve, you need to fail the MAF tune the VE, then turn the MAF back on and tune the MAF
    No need to re-invent the wheel. But we can make it better

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    Quote Originally Posted by ralmo94 View Post
    If you are running a maf, VE won't make much difference until it goes to blended mode, example acceleration. Steady state operation is controlled mainly by the MAF. To tune the ve, you need to fail the MAF tune the VE, then turn the MAF back on and tune the MAF
    YES, ^^^^^^this.
    The most common mistakes are the pcv lines, pay CLOSE attention to how GM did it and adjust accordingly. Do NOT try to tune around it, especially in the MAF tables. Leave them alone and fix what is causing them to be wrong. Also, it is very common to have a bad MAF sensor reading low. In neutral it should favor around ~6 grams at 600 rpm and ~25 qms 2500 rpm on stock 6l engine. Most stock 6l engines will pull ~230 gms at ~6000 rpm. If you are a lot lower suspect the MAF sensor. Don't buy anything but a real Delphi sensor. I don't even trust AcDelco anymore since most crap is from China.

    A recent example was I diagnosed a failing MAF sensor so the guy went down the street to NAPA and bought a 'refurb" MAF and it was worse than the one he had. Sent him back for a Delphi and problem solved except for the needed tune, and btw, stay out of the MAF table unless you think you are smarter that GM that spent who knows how many thousands of man hours making that table correct. If you have a tube screwing with your MAF table, throw it away ;)
    Last edited by In-Tech; 3 Days Ago at 10:47 AM.
    -Carl

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    Quote Originally Posted by In-Tech View Post
    YES, ^^^^^^this.
    The most common mistakes are the pcv lines, pay CLOSE attention to how GM did it and adjust accordingly. Do NOT try to tune around it, especially in the MAF tables. Leave them alone and fix what is causing them to be wrong. Also, it is very common to have a bad MAF sensor reading low. In neutral it should favor around ~6 grams at 600 rpm and ~25 qms 2500 rpm on stock 6l engine. Most stock 6l engines will pull ~230 gms at ~6000 rpm. If you are a lot lower suspect the MAF sensor. Don't buy anything but a real Delphi sensor. I don't even trust AcDelco anymore since most crap is from China.

    A recent example was I diagnosed a failing MAF sensor so the guy went down the street to NAPA and bought a 'refurb" MAF and it was worse than the one he had. Sent him back for a Delphi and problem solved except for the needed tune, and btw, stay out of the MAF table unless you think you are smarter that GM that spent who knows how many thousands of man hours making that table correct. If you have a tube screwing with your MAF table, throw it away ;)
    Unless the MAF is in a stock intake system on a bone stock engine with nearly no overlap it can be 20%+ off in calibration.

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    Sorry Fast, wrong!!!! If it's a cartridge MAF in a weird tube, correct. The truck MAF (Delphi AF10043) doesn't care unless it is too close to the throttle body(common mistake too).
    Attached Images Attached Images
    -Carl

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    It was always my understanding that MAF calibration was done on a test bench without the stock intake tube connected, or air filter. With tight radiuses and bends and what not, these could play with the speed of the air moving across different parts of the MAF.
    It was also my understanding that some elements of the tune were left close enough and not dialed in to save time and money as the O2 sensors were required for fine tuning fuel trims anyway. If the MAF is always correct, why do we get fuel trims on bone stock vehicles with no mods, and no defective issues. If a swap was done and the stock intake tube was not able to be utilized I could see the MAF curve being off a little bit. Also it was my understanding that MAF's don't like big cams from the reversion due to overlap,as this causes a pressure wave.
    I don't know. But I would definitely make sure everything is connected correctly before attempting to tune MAF curve, but I would also compare closed loop fuel trims to wide band and see if they agree.
    No need to re-invent the wheel. But we can make it better

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    Obviously GM doesn't tune EVERY vehicle, everything within "tolerance". example, We took a bone stock Camaro off the showroom floor to CARB so we could baseline our testing. Guess what? ...it failed bone stock. Got another one from the dealer, it passed...then we could do our aftermarket stuff and re-test for certification.
    You are correct on big cams and reversion double hitting the MAF, this is why distance can be massive criteria, tube size matters for transport delay when tube is larger than the MAF, tuning the MAF table doesn't FIX this but it seems some people get in there and think they are fixing something, you might fix something in one instance and totally fubar it in another instance. Air temp is critical as well as barometer. Also why GM has an air temp sensor in the MAF and even have some MAP sensors with built in air temp.

    Just food for thought :)
    -Carl

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    First off, thank all of you all so much.

    Ralmo94 I appreciate the clarification as I was unaware of how it works... Obvious new-b question..How do I "fail the MAF"? It is a swap and has the stock cam to the best of my knowledge.

    In-Tech I am attaching a few pictures of how I ran the pcv lines and would appreciate guidance if anything looks like it was not routed correctly. The log indicates that the MAF is at 7.23g/s for 620 rpm ( close enough?) but didn't check any other speeds ( I am at about 5K ft above sea level if that matters) but both LTFT is 7.81?

    Fast355 I am also including a picture of how I ran the intake tube to get a better idea of what I am working with.
    Attached Images Attached Images

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    Fuel Injected! ralmo94's Avatar
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    Quote Originally Posted by Some Fool View Post
    First off, thank all of you all so much.

    Ralmo94 I appreciate the clarification as I was unaware of how it works... Obvious new-b question..How do I "fail the MAF"?
    You edit the dtc code for MAF sensor range. There are two codes either one will work. Basically there is a high and a low frequency. When too high or too low the MAF is determined faulty and it will revert to speed density and use the ve table. You need to change the code for 1st fault sets the ses light, and change the frequency to number that will automatically fail the MAF for example set the high range at like 2hrz. As soon as it reads over 2hrz it should trip the code and go to speed density, you can now tune your VE table

    Obviously if you need to fix something with your pcv or something you want to do that first, as ve table is sensitive to any air flow changes.
    Last edited by ralmo94; 2 Days Ago at 07:07 AM.
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    Quote Originally Posted by In-Tech View Post
    Sorry Fast, wrong!!!! If it's a cartridge MAF in a weird tube, correct. The truck MAF (Delphi AF10043) doesn't care unless it is too close to the throttle body(common mistake too).
    I am NOT wrong! I have personally witnessed that style MAF as well as the earlier LT1/Vortec/LS1 MAFs do the same thing. The one in particular, I swapped the stock intake tube and box back on to and proved the MAFs (tried 2 different ones) were just fine. I then stuck an 04 LS1 Vette MAF curve in it and it worked with only slight adjustments needed. 5.3L with a 10" long straight 3.75" coupler off the throttle body into a cone filter on a vehicle with very limited engine compartment space. GM uses that same MAF with numerous different airflow tables.

    If what you said is correct, this would not happen. The only thing wrong here even was a missing air cleaner element. Fuel trims went +20% the moment the stock air box was mistakingly installed without a filter. Fuel trims were a little off with the open sensor end as well(probably from the mechanical fan blowing air across the sensor) Filter in place and they were sitting near perfect.
    https://youtu.be/m-qJ58scPJE

    My 4" cartidge MAF has a slightly modified GM Performance Crate 525 HP LS3 MAF curve but I need to add a flow straightner to it.
    Last edited by Fast355; 2 Days Ago at 10:29 PM.

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