LTFT at 25% part 2
LTFT at 25% part 2 Wow, that 3bar FF thread has my head spinning...
SO, I'm back with another 25% LTFT problem. Maybe it will help some of the newbs like myself.
LQ4 - L92 heads - LS3 intake -92 FAST TB - 85mm MAF
If you read my first thread, you know I had a coil harness issue.
Now that the engine starts and runs much better I'm tying up more loose ends. After several minutes of run time, I started to get a pretty severe stumble right off idle and noticed the definite change in the tone of the engine as soon as it went to CL. Sure enough LTFT at 25%. STFT 18-19% both banks!
Everything I read mostly said vacuum leak, especially if the STFT drop way down when the throttle is opened. I did see a drop but it didn't go to 0. Maybe low teens. Another cause could be bad MAF. I have no codes but MAF is only showing 10-20 g/s no matter where the throttle position.
Because this is a new startup, leak is a possibility. Did a smoke test. Nothing. Triple checked everything. Nothing loose or unplugged. Right before spraying the carb cleaner around, I decided to pull the MAF connector. Cleared trims and fired it up. Well guess what, you guys already know....trims stayed down and I could actually see O2's switching now.
If you're still with me, is another used 85mm the answer? No more GM new?
What will happen running with the MAF unplugged?
What about the IAT sensor? Should I put the connector back in without the yellow sensor wire for the MAF so the IAT will work?
Appreciate the help.
SO, I'm back with another 25% LTFT problem. Maybe it will help some of the newbs like myself.
LQ4 - L92 heads - LS3 intake -92 FAST TB - 85mm MAF
If you read my first thread, you know I had a coil harness issue.
Now that the engine starts and runs much better I'm tying up more loose ends. After several minutes of run time, I started to get a pretty severe stumble right off idle and noticed the definite change in the tone of the engine as soon as it went to CL. Sure enough LTFT at 25%. STFT 18-19% both banks!
Everything I read mostly said vacuum leak, especially if the STFT drop way down when the throttle is opened. I did see a drop but it didn't go to 0. Maybe low teens. Another cause could be bad MAF. I have no codes but MAF is only showing 10-20 g/s no matter where the throttle position.
Because this is a new startup, leak is a possibility. Did a smoke test. Nothing. Triple checked everything. Nothing loose or unplugged. Right before spraying the carb cleaner around, I decided to pull the MAF connector. Cleared trims and fired it up. Well guess what, you guys already know....trims stayed down and I could actually see O2's switching now.
If you're still with me, is another used 85mm the answer? No more GM new?
What will happen running with the MAF unplugged?
What about the IAT sensor? Should I put the connector back in without the yellow sensor wire for the MAF so the IAT will work?
Appreciate the help.
If you're still with me, is another used 85mm the answer? No more GM new?
What will happen running with the MAF unplugged?
What about the IAT sensor? Should I put the connector back in without the yellow sensor wire for the MAF so the IAT will work?
Appreciate the help.
Looks like I'm going to be ordering some of these.
http://terminalsupplyco.com/Store/Pr...px?pc=12020321
TECH Senior Member
Joined: Apr 2002
Posts: 6,080
Likes: 17
From: So.Cal.
Sounds like if you fix the wiring problem then maybe your MAF might work properly.
If you replace the MAF, it must match your MAF table (unless you know how to generate/correct it).
With MAF unplugged, if you see a MAF DTC (any of P0101, P0102, P0103) your PCM will be running exclusively from the VE table.
Yes, you need IAT.
If you replace the MAF, it must match your MAF table (unless you know how to generate/correct it).
With MAF unplugged, if you see a MAF DTC (any of P0101, P0102, P0103) your PCM will be running exclusively from the VE table.
Yes, you need IAT.
Yeah soon as I knew I had voltage back the MAF started reading, hopefully correct. O2's starting switching again too.
Where would I find info on this or different MAFs?
Thanks joecar for the info!
Where would I find info on this or different MAFs?
Thanks joecar for the info!
TECH Senior Member
Joined: Apr 2002
Posts: 6,080
Likes: 17
From: So.Cal.
MAF's have peculiar behavior that is affected by the before/after plumbing...
so even if you copy another vehicle's stock MAF's table, chances are that you will still need to correct your MAF table when running that vehicle's MAF in your vehicle;
and any aftermarket MAFs will definitely need your MAF table being corrected (usual method is using a wideband, making sure to exclude VE contribution, and with trims disabled).
so even if you copy another vehicle's stock MAF's table, chances are that you will still need to correct your MAF table when running that vehicle's MAF in your vehicle;
and any aftermarket MAFs will definitely need your MAF table being corrected (usual method is using a wideband, making sure to exclude VE contribution, and with trims disabled).
TECH Senior Member
Joined: Jun 2016
Posts: 22,291
Likes: 3,616
From: Central Cal.
So, even though one might have the requisite 6-8" of straight flow before the MAF sensor, other factors (total tract length, how many bends, etc.) can still enter into the final calibration due to differing flow velocities, added turbulence, etc.? Many variables... ALL arguments FOR tuning, no matter how small any changes are...
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Verdad Gallardo I see what you're saying about needing to tune for my or any particular situation, I was asking where to get the initial data to populate the MAF table, and I think you just answered that....copy it from a stock tune that uses the same MAF i have.
Thanks
Thanks
Staging Lane
Joined: Jan 2017
Posts: 63
Likes: 2
From: CT
Awesome thread. My MAF is hollowed and aftermarket says Delphi but no damn part number. My car stumbles when idle at full temps unless I put it in Neutral. Unplugged the MAF and car runs a million times better and has way more power. I heard just spraying the MAF isn't enough and you have to use a Q-tip which I will probably do. I have had it unplugged for about 2 months and maybe 1,000 miles on it and only showing on HP tuners MAF light code. I plugged it in maybe once a week for a few hrs and I can't stand driving the car with rough idle and surge at a long light. When the car is at a Low RPM under load going up a hill at a low speed the MAF just doesn't like it. Car had a tune from other owner and sadly it's for this MAF when I bought the car, looking for stock MAF with honey comb still intact. Running with the MAF unplugged shouldn't do any damage and I did some hard runs and the car seems to be happier.
Last edited by 1999ls1sscamaro; Sep 14, 2017 at 09:48 PM.
Still scratching my head here .. If I didn't state this already, this is a mail order tune.
My tuner states MAF flow numbers are correct in logs I'm sending him.
With +30ish % fuel being added and no other obvious problems with vacuum, my tuner lowered the injector data to LS1 values. Immediately the trims dropped to more normal range. Idle and driving.
But why?
the top end is a 2010-11ish complete stock LS3 pull off from SLP a few years ago.
Weren't/aren't all GM stock LS3 injectors 42lb?
Or am I missing something else
My tuner states MAF flow numbers are correct in logs I'm sending him.
With +30ish % fuel being added and no other obvious problems with vacuum, my tuner lowered the injector data to LS1 values. Immediately the trims dropped to more normal range. Idle and driving.
But why?
the top end is a 2010-11ish complete stock LS3 pull off from SLP a few years ago.
Weren't/aren't all GM stock LS3 injectors 42lb?
Or am I missing something else