L31MaxExpress
I'm Awesome
The inside diameter of the MAF.
at a loss. replaced MAF
- Thread starter Chevy Express
- Start date
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L31MaxExpress
I'm Awesome
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Someone had put a 3" on either my brothers Suburban or Tahoe before he bought it. I later caught it while tuning the truck.
454cid
Sooper Pooper
The new replacement for out trucks is a retrofit of a newer part.
Chevy Express
Newbie
na don't have that issue, fits perfect. ty though
stutaeng
I'm Awesome
Ok, so the formula for MAF sensor should report numerically the engine displacement in grams/second for every 500 RPM of engine speed, "roughly."
Example: a 5.7L engine should be seeing at 1,000 rpm: 5.7x2 = 11.4 grams/second reported by the MAF sensor. The "2" is because there are (two) 500s in 1,000.
I was messing around with my generic scanner and here are of the numbers I was getting. In my case, the scanner reads lb/min. The conversion factor is to multiply 7.60 to get to grams/second.
In my example, at 1,000 rpm I got 1.39 lb/min.
So: 1.39x7.60 = 10.6, close to rounding error. 2,000 and 3,000 rpm values are similar.
If your scanner reads gr/sec, then it's easy enough to hold your RPM at 1000 and double your displacement: it should say 7.4x2=14.8. Say 15 gr/sec.
It follows that there should be a linear increase in values with increase in RPM.
I hope this helps.
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Chevy Express
Newbie
appreciate this . will look at it as soon as i can
454cid
Sooper Pooper
GM says the MAF should read ~7.05g/s at hot idle, in closed loop, in park/neutral with accessories off.
Download one of the manuals here on the forum, as long as the year is close, it'll be fine.
Download one of the manuals here on the forum, as long as the year is close, it'll be fine.
Chevy Express
Newbie
So an update.
I'm still screwed. But there is an update.
So i replaced the delphi with a Ac delco reman. Numbers looked much better things started zeroing out for the most part.
The issue. When going over bumps with the MAF plugged in, it starts bucking. Short term fuel trim on Bank 2 starts going rich, I assume to compensate. once the bouncing is over, the bucking ends, and the fuel trim on bank 2 starts going negative to deal with the added fuel trim. Bank 1 through this is unaffected.
I did end up unplugging the MAF sensor 3/4 of the way home, unfortunately not during my highway test. it seems as though the bucking ended ( i thought maybe it was the fuel injector wiring on the bank 2 side) but unplugging the maf should have had the bucking continue.
I watched the voltages on o2 and they were moving all over the place, so I didn't see anything inconclusive.
As far as I am concerned this is some kind of electrical problem. when the MAF is unplugged it seems to go away, maybe i will go for another 50 dollar gas test drive tomorrow.
what i don't understand is disconnecting the MAF should affect both banks. this issue seems to only be bank 2, when the engine goes into speed density mode or whatever fallback it does, does it stop using the 02's for trims? the trims do appear to be trimming, so i figured they are still in use. but it seems like it can only be the 02's at this point, as they are the only independent things on the bank that could cause this.
I feel like this is going to get expensive at a mechanic's, if I can't figure this out. I still think the original MAF had issue's it seems all my power is back and trims are normal until the bucking starts
IF anyone has a remote clue I am all ears.
I'm still screwed. But there is an update.
So i replaced the delphi with a Ac delco reman. Numbers looked much better things started zeroing out for the most part.
The issue. When going over bumps with the MAF plugged in, it starts bucking. Short term fuel trim on Bank 2 starts going rich, I assume to compensate. once the bouncing is over, the bucking ends, and the fuel trim on bank 2 starts going negative to deal with the added fuel trim. Bank 1 through this is unaffected.
I did end up unplugging the MAF sensor 3/4 of the way home, unfortunately not during my highway test. it seems as though the bucking ended ( i thought maybe it was the fuel injector wiring on the bank 2 side) but unplugging the maf should have had the bucking continue.
I watched the voltages on o2 and they were moving all over the place, so I didn't see anything inconclusive.
As far as I am concerned this is some kind of electrical problem. when the MAF is unplugged it seems to go away, maybe i will go for another 50 dollar gas test drive tomorrow.
what i don't understand is disconnecting the MAF should affect both banks. this issue seems to only be bank 2, when the engine goes into speed density mode or whatever fallback it does, does it stop using the 02's for trims? the trims do appear to be trimming, so i figured they are still in use. but it seems like it can only be the 02's at this point, as they are the only independent things on the bank that could cause this.
I feel like this is going to get expensive at a mechanic's, if I can't figure this out. I still think the original MAF had issue's it seems all my power is back and trims are normal until the bucking starts
IF anyone has a remote clue I am all ears.
stutaeng
I'm Awesome
So issue is "only" happening going over bumps? Some wire is chaffed, a ground is losing contact or something in that realm, if I had to guess. But don't guess. At some point I was going to say that the MAF also has the IAT sensor, but you've since replaced it. Also, it would be helpful to look at the wiring diagram. I vaguely recall there is something else on the MAF circuit, maybe more than one thing.
Unfortunately, it sounds like this is going to require advanced diagnostics. I doubt anyone here can give any good advice beyond. We're mostly parts changers here anyways...
Oh, I just realized you are in PA...rust and corrosion do crazy things to wiring, terminals grounds and connections. Alternatively, do a continuity check of the relevant wiring, moving around wiring to see if you "catch it in the act." Depending on the condition, it may be better to remove the entire engine/transmission harness to inspect, repair as required and re-loom the harness. The loom and wiring that goes down the bell housing gets really brittle due to heat.
I used to watch South Main Auto in New York, and I now occasionally watch Pine Hollow Diagnostics (somewhere in Pennsylvania?) on YouTube. The guy on Pine Hollow even does mobile diagnostics. Both excellent for this kind of work.
Good luck.
Edit: since it's an RV and has sat for a long time, add mouse/rat/squirrel chewing thru wiring as a suspect too...
Unfortunately, it sounds like this is going to require advanced diagnostics. I doubt anyone here can give any good advice beyond. We're mostly parts changers here anyways...
Oh, I just realized you are in PA...rust and corrosion do crazy things to wiring, terminals grounds and connections. Alternatively, do a continuity check of the relevant wiring, moving around wiring to see if you "catch it in the act." Depending on the condition, it may be better to remove the entire engine/transmission harness to inspect, repair as required and re-loom the harness. The loom and wiring that goes down the bell housing gets really brittle due to heat.
I used to watch South Main Auto in New York, and I now occasionally watch Pine Hollow Diagnostics (somewhere in Pennsylvania?) on YouTube. The guy on Pine Hollow even does mobile diagnostics. Both excellent for this kind of work.
Good luck.
Edit: since it's an RV and has sat for a long time, add mouse/rat/squirrel chewing thru wiring as a suspect too...
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Chevy Express
Newbie
South Main auto is 2 and half hours from me. IDK if i am at that point yet.
I believe i had 2 issues. I believe my MAF was slowing failing (threw out of range and lean codes) and a bucking issue with bumps. after replacing the MAF, my power has significantly returned, but going over bumps still causes bucking and fuel enrichment on short term fuel bank 2. Unplugging the MAF seems to have cured the bucking problem, what I am trying to determine now is what sensors are removed from the equation when the maf is disconnected. I am hoping the 02 but IDK.
I believe i had 2 issues. I believe my MAF was slowing failing (threw out of range and lean codes) and a bucking issue with bumps. after replacing the MAF, my power has significantly returned, but going over bumps still causes bucking and fuel enrichment on short term fuel bank 2. Unplugging the MAF seems to have cured the bucking problem, what I am trying to determine now is what sensors are removed from the equation when the maf is disconnected. I am hoping the 02 but IDK.
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