lean surging...TBI
08-04-2008, 01:30 AM
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lean surging...TBI
Been a while since I have posted here (I think some of y'all might remember me tho, heheh )
Ok so I have an '84 Vette with the (yes dreaded) Crossfire, running the 8746 ECM. I just did some cam/head work to the engine, and I'm having a "lean surging" issue in closed loop...maybe some of you with more tuning experience will chime in.
Basically (and this thing has ALWAYS done this)...when the A/F bounces back and forth between rich and lean, it dips WAY into the lean side, but the rich side seems very normal. I just don't have to funding for a WB02, but what I am using is a meter that I designed myself, that ONLY measures the areas outside of stoich (with 10 LEDs for each side, and takes into account the logarithmic response of the NB sensor). Granted it isn't a WB, but it's WAY better than the generic 10-segment A/F meters, and based on what I feel in the car and have seen in WinALDL, I believe the reading. Like I say it has ALWAYS done this...but until I went to a pretty aggressive cam recently, well it really wasn't an issue.
The engine is your basic 355 (no stroker), 2" TBs, siamesed X-fire intake (I have been running this for a few years now with great success), long tube headers...previously a Crane 2050 cam (fairly mild flat cam) and stock heads. The recent change to the engine was to an Edelbrock 2204 hydraulic roller cam (12 deg overlap @.050), Performer 70cc heads, and Crane full roller rockers (1.5). With this MUCH more aggressive cam this "surging" is a LOT more noticeable, and quite unacceptable.
Idle surprisingly is not bad at all (ohhh boy is it ever lopey!), it isn't perfect but tolerable for now, but this happens any time the ECM is in closed loop, be it at idle or at 3000RPM (the O2 sensor does cool off to the point of going OL at idle).
None of the O2 parameters are making ANY difference (R/L thresholds, proportional gains...etc). I am using Tunerpro/WinALDL with Ben73s $61 XDF downloaded from Craig's site.
This "lean surging" is of course making it just impossible to do any tuning, and I can't figure out WTH is causing it! (maybe the past few months of fume inhalation has something to do with that)
Any ideas out there?
TIA
EDIT: Oh yea forgot...90# injectors @ 20psi...came to 116# or so as I recall. BPW adjusted accordingly.
Ok so I have an '84 Vette with the (yes dreaded) Crossfire, running the 8746 ECM. I just did some cam/head work to the engine, and I'm having a "lean surging" issue in closed loop...maybe some of you with more tuning experience will chime in.
Basically (and this thing has ALWAYS done this)...when the A/F bounces back and forth between rich and lean, it dips WAY into the lean side, but the rich side seems very normal. I just don't have to funding for a WB02, but what I am using is a meter that I designed myself, that ONLY measures the areas outside of stoich (with 10 LEDs for each side, and takes into account the logarithmic response of the NB sensor). Granted it isn't a WB, but it's WAY better than the generic 10-segment A/F meters, and based on what I feel in the car and have seen in WinALDL, I believe the reading. Like I say it has ALWAYS done this...but until I went to a pretty aggressive cam recently, well it really wasn't an issue.
The engine is your basic 355 (no stroker), 2" TBs, siamesed X-fire intake (I have been running this for a few years now with great success), long tube headers...previously a Crane 2050 cam (fairly mild flat cam) and stock heads. The recent change to the engine was to an Edelbrock 2204 hydraulic roller cam (12 deg overlap @.050), Performer 70cc heads, and Crane full roller rockers (1.5). With this MUCH more aggressive cam this "surging" is a LOT more noticeable, and quite unacceptable.
Idle surprisingly is not bad at all (ohhh boy is it ever lopey!), it isn't perfect but tolerable for now, but this happens any time the ECM is in closed loop, be it at idle or at 3000RPM (the O2 sensor does cool off to the point of going OL at idle).
None of the O2 parameters are making ANY difference (R/L thresholds, proportional gains...etc). I am using Tunerpro/WinALDL with Ben73s $61 XDF downloaded from Craig's site.
This "lean surging" is of course making it just impossible to do any tuning, and I can't figure out WTH is causing it! (maybe the past few months of fume inhalation has something to do with that)
Any ideas out there?
TIA
EDIT: Oh yea forgot...90# injectors @ 20psi...came to 116# or so as I recall. BPW adjusted accordingly.
Last edited by MrBill; 08-04-2008 at 01:35 AM.
08-04-2008, 02:40 PM
#2
Re: lean surging...TBI
try pulling some timing 3000 rpms and < ? I idle at 20A.
I am currently commanding stoich at 14.00/1 and raised my R/M/L thresholds 10% attempting to enrichen .
I believe it is possible to run open loop(only) 3000 rpms and under as well, although I am OL only idle and under 5 mph. I did for a while run OL exclusively as an experiment and found it helped surging BUT gas mileage was terrible(aka sucked). I recall on WB I was about a full point richer.
I am currently commanding stoich at 14.00/1 and raised my R/M/L thresholds 10% attempting to enrichen .
I believe it is possible to run open loop(only) 3000 rpms and under as well, although I am OL only idle and under 5 mph. I did for a while run OL exclusively as an experiment and found it helped surging BUT gas mileage was terrible(aka sucked). I recall on WB I was about a full point richer.
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