knock/air fuel question....im stumped...
12-27-2003, 08:56 PM
#1
knock/air fuel question....im stumped... ok here is the deal. i heard detonation in only 3rd gear at high rpms after one WOT run. figured ok maybe the car isnt warm. tried again and in 2nd and 3rd got some KR about .5-1.5* but the o2's were reading about 915-940. i did a 4th gear run and at about 5000 rpm got 1.2* of knock and the o2s were goin down to about 915. now i have headers and its really weird, before with my other o2's i was getting real consistent readings. im thinkin about getting new o2's, should i and where should i get them? and about how much do they cost? i put my old rears in why would the numbers not wanna stay consistent? im thinkin about bumping up my PE about 1% so i dont get any detonation and then ill check it again after i get o2's. but here is the thing. one WOT run in 4th i got no knock? and the o2's were reading higher? could those old o2's just be damaged? this is all i cna think of really, im gonna get a wideband tune soon but i just wanna get this OK for now
12-27-2003, 09:11 PM
#2
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O2s read higher when cold, headers make colder
exhaust, so you may want to see a higher number
than a stock-manifold car on the O2s. The heat
variation between runs can easily make more
mV difference than any mixture change. With
iron log manifolds and close-in O2s there is more
consistency (and even there nobody has more
than a rough idea of mV against mixture.
These cars do have a built-in fuel pressure fade
and maybe you just want Predator to hit you again
with an injhctor table or PE vs RPM tweak to keep the
mixture more level as you run up. Without a better
idea of true mixture all you can do is cut 'n' try.
exhaust, so you may want to see a higher number
than a stock-manifold car on the O2s. The heat
variation between runs can easily make more
mV difference than any mixture change. With
iron log manifolds and close-in O2s there is more
consistency (and even there nobody has more
than a rough idea of mV against mixture.
These cars do have a built-in fuel pressure fade
and maybe you just want Predator to hit you again
with an injhctor table or PE vs RPM tweak to keep the
mixture more level as you run up. Without a better
idea of true mixture all you can do is cut 'n' try.
12-27-2003, 09:18 PM
#3
Originally Posted by jimmyblue
These cars do have a built-in fuel pressure fade
and maybe you just want Predator to hit you again
with an injhctor table or PE vs RPM tweak to keep the
mixture more level as you run up. Without a better
idea of true mixture all you can do is cut 'n' try.
and maybe you just want Predator to hit you again
with an injhctor table or PE vs RPM tweak to keep the
mixture more level as you run up. Without a better
idea of true mixture all you can do is cut 'n' try.
the plan im gonna shoot for is seeing where i get knock, which seems to be 915, im gonna make it go away and get up another 10 mv i think 935 should be a safe range. does this sound like a good idea? any other suggestions?
i wanna try and replace the o2's and dont know where i should get some good ones from...or are the bosch ones at advance good to get?
12-27-2003, 09:40 PM
#4
Originally Posted by jimmyblue
These cars do have a built-in fuel pressure fade
and maybe you just want Predator to hit you again
with an injhctor table or PE vs RPM tweak to keep the
mixture more level as you run up. Without a better
idea of true mixture all you can do is cut 'n' try.
and maybe you just want Predator to hit you again
with an injhctor table or PE vs RPM tweak to keep the
mixture more level as you run up. Without a better
idea of true mixture all you can do is cut 'n' try.
Jimmy -what do you mean they have built in fuel pressure fade???
joel
12-27-2003, 09:41 PM
#5
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Because the regulator is in the back with the
pump, all forward pressure drop from there is
unregulated (flow resistance, acceleration).
The fuel pressure often drops from maybe 58
at idle to low 50s at WOT. The only thing that
makes up for this is the injector flow tables.
I think you get heater codes when the PCM
needs to run the heater too much, or running
the heater still doesn't get the sensors hot
enough to work to the PCM's satisfaction.
As they age they need more heat to work as
well.
As you run more exhaust flow & power the
sensor should get hotter and its output voltage
decline. You can't separate the fuel fade from
the temperature effects without better
instrumentation. The dyno w/ wideband, if
you can also log in-car O2s, would maybe give
you a decent calibration point for further
tuning using the in-car O2s later. At least
you'd know what 915mV @ 5000RPM really
means, AFRwise, on your car.
Meanwhile just tweak it up like planned.
pump, all forward pressure drop from there is
unregulated (flow resistance, acceleration).
The fuel pressure often drops from maybe 58
at idle to low 50s at WOT. The only thing that
makes up for this is the injector flow tables.
I think you get heater codes when the PCM
needs to run the heater too much, or running
the heater still doesn't get the sensors hot
enough to work to the PCM's satisfaction.
As they age they need more heat to work as
well.
As you run more exhaust flow & power the
sensor should get hotter and its output voltage
decline. You can't separate the fuel fade from
the temperature effects without better
instrumentation. The dyno w/ wideband, if
you can also log in-car O2s, would maybe give
you a decent calibration point for further
tuning using the in-car O2s later. At least
you'd know what 915mV @ 5000RPM really
means, AFRwise, on your car.
Meanwhile just tweak it up like planned.
12-27-2003, 09:45 PM
#6
ok i hear what yoru sayin, thanks. so would you rec. gettin new o2's or puttin the others back in? or nothing at all? what shoudl i tell predator to do to the tune or what to check? and is this somethign they can do without having any info from me besides the tune?
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12-28-2003, 12:19 PM
#9
i just did a top end cleaning on my car and went out. on the way to do it i got knock in 2nd gear and the o2s were reading about 910-920, would false knock cause these numbers on the o2 to get leaner? i didnt get any knock in 3rd. when i went into 4th i got a little more knock. i went back and looked at my notes and adjusted the PE to 1.75% and before like that it was running 935-945 mV with no knock.
so i really wanna know if false knock could cause the o2s to read leaner cuase i couldnt hear detonation. and with the headers making the numbers reading higher on the o2's is it possible that 915 before headers coudl translate to about 935 or 945 after the headers? do they make that big of a difference? thanks
and will headers always cause you to run rich? cause at first i was at 965 and knocked it down to 945 and that seems to be the limit i figured it would run richer than that...please let me know!
so i really wanna know if false knock could cause the o2s to read leaner cuase i couldnt hear detonation. and with the headers making the numbers reading higher on the o2's is it possible that 915 before headers coudl translate to about 935 or 945 after the headers? do they make that big of a difference? thanks
and will headers always cause you to run rich? cause at first i was at 965 and knocked it down to 945 and that seems to be the limit i figured it would run richer than that...please let me know!
12-29-2003, 08:50 AM
#11
How much total timing are you running right now?
With long tubes and an offroad pipe using factory tuning my air/fuel was in the 11's at WOT. I leaned it out to around 12.8 to 13.0 and my factory o2's were reading in the .890 - .910 range. I wasn't seeing any knock at WOT with 27-28 degrees of timing.
Chad
With long tubes and an offroad pipe using factory tuning my air/fuel was in the 11's at WOT. I leaned it out to around 12.8 to 13.0 and my factory o2's were reading in the .890 - .910 range. I wasn't seeing any knock at WOT with 27-28 degrees of timing.
Chad
