bad maf??
bad maf?? ok just put a comp 236/244 .580 lift on a 112in my car, and we're still having trouble getting it tuned right. still has trouble on start getting it to idle, ignition problems, and low hp numbers. put down 365.
but the main problem is the air fuel ratio. its running really rich at idle. everytime the tuner sets the AFR to say 13:1 it keeps going back to 18:1. something some where is telling the pcm to dump a crapload of fuel into it.
ive tried everything. ive checked and i dont think i have a vacuum leak, my intake is sealed. i only have one vacuum line left on it and its the one that connects to the back of the intake manifold, i think it go to the lines for the vent/ac controls. i have removed pcv, air pump, air lines, evap canister, all that.
been through 2 sets of plugs, its fouling them. when i pull them out theyre covered in black soot.
the only conclusion i can come to now is i might have a bad maf. ive just replaced my ported ends with stock ends...didnt help. its possible i couldve touched the resistors on the inside of the sensor and messed them up.
whatever is going on its like its getting air the maf isnt seeing. any advice? like i said the tuner tunes it then i goes back to the same thing.
but the main problem is the air fuel ratio. its running really rich at idle. everytime the tuner sets the AFR to say 13:1 it keeps going back to 18:1. something some where is telling the pcm to dump a crapload of fuel into it.
ive tried everything. ive checked and i dont think i have a vacuum leak, my intake is sealed. i only have one vacuum line left on it and its the one that connects to the back of the intake manifold, i think it go to the lines for the vent/ac controls. i have removed pcv, air pump, air lines, evap canister, all that.
been through 2 sets of plugs, its fouling them. when i pull them out theyre covered in black soot.
the only conclusion i can come to now is i might have a bad maf. ive just replaced my ported ends with stock ends...didnt help. its possible i couldve touched the resistors on the inside of the sensor and messed them up.
whatever is going on its like its getting air the maf isnt seeing. any advice? like i said the tuner tunes it then i goes back to the same thing.
Originally Posted by FL Junkie
everytime the tuner sets the AFR to say 13:1 it keeps going back to 18:1. something some where is telling the pcm to dump a crapload of fuel into it.
Just curious, but did your tuner change anything in the MAF, open loop fueling, VE, or injector flow rate tables??? If not, he hasn't changed anything in terms of fueling and I would be on my way to find another tuner real fast! Aside from a mechanical problem, there's no reason why he shouldn't be able to get your AFR lined up.
TECH Fanatic
Joined: Aug 2005
Posts: 1,691
Likes: 1
From: Sunny London, UK
To tame a cam like that others would go open loop, speed density with no maf and depending on lope etc you might even be better off with tps fueling at low map and idle cells.
The maf isnt going to like the reversion and erratic flow.
Does it run ok over say 2000 rpm? Good fueling and spark there? If so then try speed density and/or alpha-n fueling (tps).
The maf isnt going to like the reversion and erratic flow.
Does it run ok over say 2000 rpm? Good fueling and spark there? If so then try speed density and/or alpha-n fueling (tps).
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The MAF is a minor player at idle / cruise and contributes
more to the final airflow number as RPM rises. Your idle
fueling errors come from a now-whacked VE table and
intake air shoot-through, both due to the big cam. The
air shot through will fool the wideband (and your NBO2s
as well). Cam big enough to let air shoot through before
closing, can also let exhaust pulses back into the intake
on opening and then the MAF souble-samples the air
(sort of). So the MAF -could- be getting fooled and
adding even more bogus data to the mix but at idle this
is not your number one problem.
First off I would try and get it straight, open loop. Set
the closed loop enable temp to 300 or something, let
it warm up, your EQ Ratio (OLFA) table should be at 1.000
and you can tune the airflow side up; no MAF would make
it really straightforward (only one contributor) but you
still need an AFR reference you can trust. That may not
be the wideband but it's a start, if wideband can get and
stay at 14.7:1 by VE table diddling, and the exhaust smells
good, you might believe it. Work from idle on up to 3000RPM
at least, free revving it, to get the low- to mid-MAP part of
the VE table sensible. That cam is going to whack things a
fair ways into the RPM band. Then you can start hooking
things back up - MAF, than closed loop enable, one thing
at a time and fix them as you find their faults.
more to the final airflow number as RPM rises. Your idle
fueling errors come from a now-whacked VE table and
intake air shoot-through, both due to the big cam. The
air shot through will fool the wideband (and your NBO2s
as well). Cam big enough to let air shoot through before
closing, can also let exhaust pulses back into the intake
on opening and then the MAF souble-samples the air
(sort of). So the MAF -could- be getting fooled and
adding even more bogus data to the mix but at idle this
is not your number one problem.
First off I would try and get it straight, open loop. Set
the closed loop enable temp to 300 or something, let
it warm up, your EQ Ratio (OLFA) table should be at 1.000
and you can tune the airflow side up; no MAF would make
it really straightforward (only one contributor) but you
still need an AFR reference you can trust. That may not
be the wideband but it's a start, if wideband can get and
stay at 14.7:1 by VE table diddling, and the exhaust smells
good, you might believe it. Work from idle on up to 3000RPM
at least, free revving it, to get the low- to mid-MAP part of
the VE table sensible. That cam is going to whack things a
fair ways into the RPM band. Then you can start hooking
things back up - MAF, than closed loop enable, one thing
at a time and fix them as you find their faults.