4A-GE Excessive Blowby 3000km after Rebuild

[ballpencil]

oh those are stock high comp pistons. i haven't yet put in the gze ones. i was running very moderate map before this one (max advance was only 22 deg) and got the first blowby problem with it on high rpm. The first blowby was not as bad though.

[andrew_mx83]

while i havent drawn up my own ignition maps (yet -moving to EDIS/megajolt myself shortly) i wouldnt say those are crazy piston-melting numbers, as long as its not running lean...

my dads old engine ran upto 50deg max advance, went like the clappers and took quite a while before it melted the pistons. moved to forged slugs and had no issues. my daily is currently running on lpg with stock ecu running spark. theres no AFM so no load compensation on timing, from what ive seen with the timing light it just increases linear with RPM, im guessing its running around 60deg at full noise. not ideal but with the high octane fuel i get away with it.

[ballpencil]

while i havent drawn up my own ignition maps (yet -moving to EDIS/megajolt myself shortly) i wouldnt say those are crazy piston-melting numbers, as long as its not running lean...

i thought so too. i read even the stock one went up to 45 degrees! a simple google with "4age stock spark maps" yields this. AFRs are great as it's 12.5-13.0 around the high RPM. i kept my eyes on the wideband numbers (installed one on dash) during the high RPM run. cruise speed until 3000rpm is set a tad lean at 15.00 with closed loop and high authority on O2 correction. reasonable, no? so what happened to my slugs then? whatever it is, i'm gonna put brand new oil pump now!

my daily is currently running on lpg with stock ecu running spark. theres no AFM so no load compensation on timing

so.. stock ECU with alpha-N system? is this possible? sorry for the off-topic, n00b at this.

[andrew_mx83]

not sure what alpha-n is, but its stock mx83 cressida ecu and electrics etc. all ive done is unplug the injectors, remove the fuel pump and also delete the air flow meter.
AFAIK the stock computer uses the AFM to sense load and reduce timing accordingly.
surprisingly it still runs spark without it, although im assuming its in a limp home type map. not sure if timing is corrected on TPS value or not, but i doubt it.
as i said on the timing light advance increases with revs, ive seen about 50deg at what sounded like 4500-5000rpm, so im assuming this will continue upto the 60degree + range at 7000rpm. base timing is somewhere around 15-20deg (cant remember). its basically just tuned by ear and bum dyno, with the timing light purely for reference.
i have no issues with detonation but it must be hard on the big end bearings.

sounds like you know what you are doing, are you sure you didnt hear it pinging? if not check other items for signs of oil starvation such as bearings, cam journals and lifters.

[ballpencil]

sounds like you know what you are doing, are you sure you didnt hear it pinging? if not check other items for signs of oil starvation such as bearings, cam journals and lifters.

to be honest, with all the rattles, squeaks and noises my car is making, i might miss some pinging but i doubt that. there should be serious pinging sound to cause that damage and i must have heard it? off to DIY some knocking warning lamp then. good thing i kept my knock sensor.

will do on oil starvation signs check.

not sure what alpha-n is

spark and fuel maps based on RPM vs TPS. not on RPM vs MAP.