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Maxing out 85mm truck MAF on a "cam only" 5.7 - WTH?
I have read online anywhere from 450rwhp to 600rwhp is the HP level you exceed the maf frequency. Well this is my cam only sbe 5.7 ls1 today after I made some more changes to my custom air filter setup for more airflow. I still have a nice straight path before and after the maf as I always had. All I did was add even more filter area. This is a screen shot of one of my logs at WOT in 1st gear, seeing 11638hz from 6700rpm to 6800rpm and just before it hits a brick wall and I get a crazy lean condition and it can't rpm any higher. I guess i can't hit pause in the log the split second before hitting 12k hz.
Or at 11638hz it is maxed and the MAF just isn't perfectly tuned to the number in the PCM. In 2nd gear i can hold WOT all the way to 7600rpm and 11200hz is the highest I see, and no stumbles, revs totally clean. I'm guessing the engine is seeing just a bit less airflow in 2nd gear for some reason, less load on the engine?
Anyway I thought these MAFs could support a lot more HP than this. I guess it's time to scale (trick) the entire pcm at 75% if I want to keep the MAF, or go SD tune.
Does anyone have any ideas as to how this is happening on what would lucky to be a 430rwhp setup? When I'm WOT in 1st, I found if I back off the throttle a little right before i know it's going to have a spasm, and hold the throttle roughly 85% it just pulls straight past 7000 and I shift at 7600rpm and continues to pull WOT all the way to 7600 rpm in 2nd gear and the car does not miss a beat. So I can't see it being a fuel system issue or any faulty sensor issue. I have no codes thrown (and the important codes are turned on to show a fault). I have a fp gauge in the car and a solid 58psi the whole way through. Plus I know I have more than enough fuel system for well over 500rwhp.
I tried richen the PE table to target a whole 1.0 less in afr from 6400rpm onwards. But the car is acting up exactly the same. It hits 11,6xx hz in 1st gear and goes lean. Why only in 1st gear and not 2nd gear. That 400hz difference in 1st gear must be maxing it is all I can think of right now. Because it's not showing me 11,999hz it kind of throwing me off that it might possibly be something else. It is nothing mechanical. I've shifted it at 7600rpm WOT in 2nd gear more than 10x over now trying to diagnose this latest issue. And it is letting me carry the rpm to 7600rpm every single time in 1st gear when I just back off the throttle just before 6800rpm to around 85% throttle, where in the logs I will see the maf frequency drop to mid 10,000hz's and MAP value into the 80's. So it can rev clean at WOT, anywhere under 11,638hz. At 11,638hz in 1st gear (which is the highest hz i can manage to see in the log play backs) it begins to lean out badly on my wideband and starts breaking up.
Has anyone managed to log and see 11,999hz from a MAF car running a 12000hz limit PCM? Or are the MAF's just not that perfectly scaled/tuned to the 12,000hz number in the PCM and we will never see a perfect 11,999hz. I'm thinking my MAF must be done at 11,638hz because it is stuck at that number from 6700rpm to about 6780rpm. Even when adding multiple decimal points to the hz in the log, it doesn't even move .0001 higher or lower than 11,638hz right before the rpm brick wall and crazy lean condition. We're talking I saw 20:1 on my wideband gauge when this happens.
11,250 is the highest Maf frequency cell of the transfer function depending on the pcm. And it doesn't "pull fuel" when you max it. It just doesn't add any more. It just adds whatever fuel is commanded based on the predicted airflow of the highest cell in the mag transfer function. A cam only 5.7 isn't maxing an 85mm maf so either you've got something else going on, whether it be temperature or a bottle neck in the intake, or the maf is failing.
11,250 is the highest Maf frequency cell of the transfer function depending on the pcm. And it doesn't "pull fuel" when you max it. It just doesn't add any more. It just adds whatever fuel is commanded based on the predicted airflow of the highest cell in the mag transfer function. A cam only 5.7 isn't maxing an 85mm maf so either you've got something else going on, whether it be temperature or a bottle neck in the intake, or the maf is failing.
This is a 12,000hz 2002 PCM and I think that was obvious from my first post. If something else is going on then how am I already at 11,638hz / 420g/s at only 6700rpm ? It is so damn close to 12,000hz I don't think the log can catch it right before the spasm it is having. In my searches I've seen you mention the 85mm MAF supporting 600rwhp but I've noted others have maxed the 85mm at only 450rwhp. So you've been wrong before. The MAF seems to be working 100%.. The hz and g/s appear to function perfectly normal throughout the rpm and climb normally as rpm increases. At WOT 5,500rpm I'm around 10,500hz.
Top of 2nd gear WOT I'm at 11,200hz max and the car revs totally clean to whatever I want. In 1st gear if I just back off the throttle slightly before 6800 rpm where I'm already at 11,638hz and hold the throttle at around 85% it carries the rpm all the way past 7k clean. So how can it be anything else besides the MAF not letting it rpm clean at WOT in 1st gear? I'm also in manual mode (th400) so nothing in the PCM knows I'm in 1st gear other than the speed sensor knowing the speed. If it was ignition related or fuel related somehow else or mechanical it wouldn't be pulling to 7600rpm clean in 2nd gear, or in 1st gear when I just back off the throttle to around 85% and carry it.
I'm seeing 98 kpa MAP. It has a stock unported TB and ls6 intake. Temperature the intake temps were only 89F, I don't pull any hot air from anywhere.
I will sort it out. Time to ditch the MAF then I will know for sure it's not something else. The LS platform itself is great but this EFI sh*t sometimes is really not as good as people have been brainwashed to think it is. Every time i've had an issue recently I get no fault codes and i'm left to go over every single thing it "could" be in the system, including even stripping back wiring to resistance check it. Like last time with what ended up being faulty coils, did GM give us a way to simply bench test them to know if they're good or not? Nope.
FWIW scaling the tune will not help this issue. It does not reduce the frequency on the sensor to scale it. Just changes how much air it calculates at said frequency. You either need a 100mm maf or as you posted above, go SD
You can build a an ls7 100mm maf for cheap. Buy the couplings, the maf and a screen and good to go. 100 bucks if that. Since you tune yourself maybe just go with SD. You have the personal ability to monitor and make changes as you go anyways and really fine tune the car
This is a 12,000hz 2002 PCM and I think that was obvious from my first post. If something else is going on then how am I already at 11,638hz / 420g/s at only 6700rpm ? It is so damn close to 12,000hz I don't think the log can catch it right before the spasm it is having. In my searches I've seen you mention the 85mm MAF supporting 600rwhp but I've noted others have maxed the 85mm at only 450rwhp. So you've been wrong before. The MAF seems to be working 100%.. The hz and g/s appear to function perfectly normal throughout the rpm and climb normally as rpm increases. At WOT 5,500rpm I'm around 10,500hz.
Top of 2nd gear WOT I'm at 11,200hz max and the car revs totally clean to whatever I want. In 1st gear if I just back off the throttle slightly before 6800 rpm where I'm already at 11,638hz and hold the throttle at around 85% it carries the rpm all the way past 7k clean. So how can it be anything else besides the MAF not letting it rpm clean at WOT in 1st gear? I'm also in manual mode (th400) so nothing in the PCM knows I'm in 1st gear other than the speed sensor knowing the speed. If it was ignition related or fuel related somehow else or mechanical it wouldn't be pulling to 7600rpm clean in 2nd gear, or in 1st gear when I just back off the throttle to around 85% and carry it.
I'm seeing 98 kpa MAP. It has a stock unported TB and ls6 intake. Temperature the intake temps were only 89F, I don't pull any hot air from anywhere.
I will sort it out. Time to ditch the MAF then I will know for sure it's not something else. The LS platform itself is great but this EFI sh*t sometimes is really not as good as people have been brainwashed to think it is. Every time i've had an issue recently I get no fault codes and i'm left to go over every single thing it "could" be in the system, including even stripping back wiring to resistance check it. Like last time with what ended up being faulty coils, did GM give us a way to simply bench test them to know if they're good or not? Nope.
There was an 85mm MAF on my 2000 C5 when I bought it.
After tuning, it was nearly pegged. It was an alum housing that could be taken apart. And someone clearly had.
I replaced it with a 2002 Z06 unscreened MAF I bought off the Vette forum. The reported freq dropped significantly.
Had the car on the dyno 2 months ago, 9400hz at 7000 and it makes quite a bit more than 430hp.
So that's why I'd try another MAF at some point.
Good idea on the SD tune.
I read the thread on a phone and you didn't say what year in your post now did you? And if you knew how the MAF worked you would understand why you're hitting the max frequency. I maxed my MAF on my turbo setup, swapped to the LS7 MAF and STILL maxed the MAF. Made ONE change and it fixed my issue. Next time don't be an arrogant ***** in your response and understand I was only trying to help. You get more bees with honey. Good luck "fixing" your issue.
I appreciate your help and I wasn't being arrogant. I thought you were being a smart *** mentioning the 11,250z when it was obvious I have a 12,000hz pcm. Anyway I'm still learning and I will do more research on how the maf works. I don't need luck, I will learn and sort it out like I do everything else.
I appreciate your help and I wasn't being arrogant. I thought you were being a smart *** mentioning the 11,250z when it was obvious I have a 12,000hz pcm. Anyway I'm still learning and I will do more research on how the maf works. I don't need luck, I will learn and sort it out like I do everything else.
sounds like we both just misread each other's posts. I wasn't being a smartass either. I edited my last post. I've had the exact same thing happen as Ron said above so trying another maf is a good idea. Also, you said you're using a stock TB and intake. Are you using the LS1 style lid setup or an LT? Assuming you don't have a bad maf your issue is likely the size of the intake tract and the distance between the 85mm MAF and the TB or the tube prior to the maf. Essentially the airflow can't spread out enough across the larger opening so it's still seeing the higher frequency still. In my LS7 example if you step from a small opening to a large opening right at the maf, or the larger maf to a choke point, the airflow can't spread out across the entire tube so the maf element still reads more of the airflow than it should. When I swapped the pipe before the ls7 maf to a 4 inch prior to the maf itself, my frequency dropped significantly. A relatively easy way to test this is put a right angle coupler off the TB over to the driver side and run the maf in between 2 tubes of 4 inch each. You should see a significant drop in frequency.
There was an 85mm MAF on my 2000 C5 when I bought it.
After tuning, it was nearly pegged. It was an alum housing that could be taken apart. And someone clearly had.
I replaced it with a 2002 Z06 unscreened MAF I bought off the Vette forum. The reported freq dropped significantly.
Had the car on the dyno 2 months ago, 9400hz at 7000 and it makes quite a bit more than 430hp.
So that's why I'd try another MAF at some point.
Good idea on the SD tune.
Or, just order up a 632......
Ron
This is a factory plastic 85mm maf used on the VZ ls1 Holdens , part # 25168491 which from memory is the same as the 85mm vette maf's. It was removed from a perfectly running stock car. I'm sure the MAF isn't faulty. If there's something in the tune making it read higher than it can read I will do more research on it but there's really no point as I have another engine to go in the car which is going to make more HP than this maf will support. I was just surprised I would max this thing out on a cam only 5.7. I'm going over the steps to start an SD tune right now. My innovate wideband connected to the PCM will help me with the tuning to properly log AFR's with the vcm scanner.
sounds like we both just misread each other's posts. I wasn't being a smartass either. I edited my last post. I've had the exact same thing happen as Ron said above so trying another maf is a good idea. Also, you said you're using a stock TB and intake. Are you using the LS1 style lid setup or an LT? Assuming you don't have a bad maf your issue is likely the size of the intake tract and the distance between the 85mm MAF and the TB or the tube prior to the maf. Essentially the airflow can't spread out enough across the larger opening so it's still seeing the higher frequency still. In my LS7 example if you step from a small opening to a large opening right at the maf, or the larger maf to a choke point, the airflow can't spread out across the entire tube so the maf element still reads more of the airflow than it should. When I swapped the pipe before the ls7 maf to a 4 inch prior to the maf itself, my frequency dropped significantly. A relatively easy way to test this is put a right angle coupler off the TB over to the driver side and run the maf in between 2 tubes of 4 inch each. You should see a significant drop in frequency.
Here's my setup. I have my radiator tilted further back than the 98-02 cars and a custom over the radiator plastic intake and it is larger where it tapers into the MAF than the factory 98-02 LS1 style setup. It's hard to tell in the pic below but the height of the intake where it enters the MAF is actually taller than the actual MAF housing, and wider. The round MAF housing can fit in the intake. The MAF itself sits just about the same place as factory 98-02 cars and it's a bit straighter in line with the TB, not angled upwards.
If my MAF is too close to the TB do you think that would that cause a higher reading? The small K&N air filter you see below which is pulling air direct from the front of the hood gap is not the only air filter, the intake continues down under the radiator support and has another huge filter in front of the radiator and it pulls cold air from the spot light holes in the bumper also. It is a really free flowing setup. I don't have a pic on me right now of the rest of the intake behind the bumper
Running a ls style inlet lends more weight to the theory since the maf is right on the TB practically. If this was an LT style inlet I would suspect it less. If you have random parts laying around the test I put in the last post would be easy to test. Get that maf a foot from the TB and don't neck down the inlet. You mentioned earlier that other people max their mafs at 450hp and they have the same issue. The element in the larger housing is simply reading too much of the airflow still.
Running a ls style inlet lends more weight to the theory since the maf is right on the TB practically. If this was an LT style inlet I would suspect it less. If you have random parts laying around the test I put in the last post would be easy to test. Get that maf a foot from the TB and don't neck down the inlet. You mentioned earlier that other people max their mafs at 450hp and they have the same issue. The element in the larger housing is simply reading too much of the airflow still.
Thanks man for your help I will try it and see what happens. So i need more straight 4" pipe between the MAF and TB, but also do you think the MAF also needs more straight 4" pipe entering it to read less HZ instead of a huge opening tapering into it? Maybe without straight pipe before it, some weird turbulence is happening
Thanks man for your help I will try it and see what happens. So i need more straight 4" pipe between the MAF and TB, but also do you think the MAF also needs more straight 4" pipe entering it to read less HZ instead of a huge opening tapering into it? Maybe without straight pipe before it, some weird turbulence is happening
NP. It would be nice to have tubing before the maf to straighten everything prior to the maf but start with whatever you got and go from there. Hopefully a 90 degree coupler and some 4 inch pipe and you can prove that's what's going on. That fixed 2 ls7 maf setups I've done.
Thanks again. I just looked at the car and it does have a few inches of straight 4" just before entering the MAF and then it tapers out wide into the intake. If it ends up being the MAF position, I will get an ls7 maf card in 4" housing and persist with that instead so I know I can support more HP. I want to know there are no gremlins or problems tuning it before fitting my new engine.
Cool. If you do the LS7 make sure you get a Saxon honeycomb. They do an awesome job at straightening the airflow and stabilizing the maf frequency. Makes a world of difference when tuning.
Cool. If you do the LS7 make sure you get a Saxon honeycomb. They do an awesome job at straightening the airflow and stabilizing the maf frequency. Makes a world of difference when tuning.
Yeah i will. I've read about the tuning issues using the ls7 maf card without a honeycomb.
Just thought I'd update. It was the maf maxing out in 1st. New log below in 1st gear with SD tune. I also connected my LM1 wideband to the hp tuner to be able to log AFR's.
I think i'll keep fine tuning the SD as the maf caused me a lot of headaches. I don't think I want to look at it again. I already removed it before attempting the SD tune and replaced it with a nice free flowing 4" straight pipe. While i was there I removed the TB and modified the stop so the blade opens all the way and I also ported it. It won't be on the car for very long but I got excited.
As you can see afr's are pig rich on it's first outing as I just wanted to rpm the thing to know the maf was the culprit. After repeating what you see below 3x over in 1st gear and also 2nd gear, I can very confidently say problem solved. Maybe i'll go back to an ls7 maf card, but at this stage how well the car already runs I am only a day of tuning away from having the afr's perfect. Once you get the hang of tuning SD (with the help of some youtubers and the LM1 wideband) it's not too difficult at all.
01-12-2020, 05:26 AM
Maxing out 85mm truck MAF on a "cam only" 5.7 - WTH? 
