Toymods Car Club Inc: Tech & Conversions => 7mge tuning, pinging, AFR's and other crap... LONG

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ed_ma61
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May 2002

7mge tuning, pinging, AFR's and other crap... LONG	Sun, 18 January 2004 14:13

my engine got pulled off the dyno today at 4000rpm due to it pinging (not badly, but pinging none the less). it was happily making a wad of power up to 3500rpm, when the power suddenly leveled off significantly, and she started pinging... then she hit 4000rpm exactly, she came back to life, made more wads of power (and i think stopped pingning)... but then the dyno run ended as the driver was too nervous to continue. im quite familar with this 'hit' of power at 4k rpm, but have never experienced any pinging in the 3.5-4k hole preceeding it. the engine has had pinging issues in the past when running hot, or with hot intake temps, or if trying to drive at WOT @ 20kmh in 4th gear... im trying my best to sort this issue out generally, but there seems to be something specifc going on around 3.5-4k. i initially put this 3.5-4k issue down to the stock ecu not being tuned to the new engine characteristics, and simply experiencing a switch from closed loop to open loop at 4k rpm, and the power coming with the extra fuel open loop provides. but todays run done at WOT should all be in open loop, and the afr's are reflective of this... despite odd occurences in the power output and pinging, the afr curve is smooth, and calmly goes from 14.4 at 2000rpm, to about 12.3 at 4000rpm when the run was stopped. nothing odd occuring in between. problems ive considered: TPS is not calibrated to the size of the new throttle body setup (compared to stock) and i have noticed with my AFR gauge that it seems to stay in closed loop too long when driving normally (ie not WOT)... eg, new throttle body can be only slightly open, but the engine is under quite a bit of load, but she stays around 14.5:1 ... until 4000rpm where it shifts into open loop, mixtures suddenly go rich, and power kicks in considerably. ive noticed it can get quite lean just before this 4k rpm transition, and ive tried not to 'gun it' too hard on the pedal in this area for fear of pinging. however - today, the run was all done at WOT, and she STILL had this weird drop in output at 3.5-4k rpm .... plus she started pinging. HOWEVER, the afrs are clearly NOT closed loop during the run, and were steadily going from 14.4 (at 2000rpm) to about 12.3:1 (by 4000rpm). Nothing terribly interesting occurs to the afr plot when she was supposedly pinging (afr of about 12.8:1 at this point), and then BAM... 4k rpm kicks in, power goes right back up... nothing reflected in the afr plot... im stumped maybe cam timing maybe some ecu open loop tansition maybe the whole thing is up the fuck and needs a new ECU i just dont have the cash for anything serious managemnt wise, and im trying to dodge it all together to make it work adequetley. im considering water/methanol injection (i have all the stuff here to hook it up, just need to make an RPM trigger to make it work)... but this has its downside as i understand things should be leaned out to optimise the benefit. ive also played with the flap spring in the AFM (as she was originally running REALLY rich in open loop mode - almost 10:1). i leaned it out a bit, then reset the ecu to let it 'learn' closed loop settings with the new spring preload. this hasnt changed closed loop mixtures at all, and has leaned out the top end nicely as seen on the afr curve today (12.5:1 or so - though i didnt get to see what it continued to do as the power increased). however, it made zero difference to whats going on in the 3.5-4k rpm black hole i installed a new radiator and thermo fans to keep engine temps down (she does ping a lot more if i let it get up in the temp range... so i try and keep it on the cooler side of normal operating temps). im not sure if this cooler temp changes the fuelling via some kind of correction factor (richer mixture), or whether it is the cooler cyl temps in themselves which are to blame for losing the pinging. i did notice today that she was NOT running hot at all on the rollers. bugger it... i dunno. i know it needs a proper ecu, but plain and simple - it isnt going to happen $$ ... just this damn 3-4k rpm thing... what is going on! ayway, if youve got any ideas! please fire away. in the meantim, im resetting the cam timing back to stock, bringing ign timing back to about 18deg total adv, and ill start again from there... ps - many many gtech runs have been done, and she consistantly gets 14.9 @ 98.5mph on the 1/4 (1400kg car inc driver). also happily does 0-60mph in about 6.3secs. i calculate rwhp to be around 185 using these results. mods: 10.8:1 c/r - head decked - block decked - piston tops decked piston tops shaped, chamfered and polished comb chambers shaped and polished valves ground and swirl polished ported in and ex ports port matched manifold custome plenum and upper manifold twin 57mm throttle butterflies with custom 3" mandrel intake pipe - (single 60mm stock) stock cams (254 dur - shitty skinny cams!) -in adv about 7-8 crank degrees -ex retarded about 2-4 crank degrees -(have full timing data if you want it) rods ground, polished and peened arp b/e fasteners everything balanced headers 6-2-1, 1.5" primaries, 2" secondaries, 2.5" common + cat + muffler about 25deg total ign advance metal head gasket also: intake pipe origin and filter is located outside the engine bay (behine front apron) and all intake piping within the bay is wrapped in fibreglass heat wrap, then covered in aluminium heat tape. 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