chevy1500z71

is this an issue for anyone else?

recently i swapped in a new motor, its a 355 with forged lightweight pistons, just below or around 9:1 compression ratio, dart heads, and a lunati cam with 1.6 rockers making about 520 lift exhaust and 500 intake, cant remember the duration, on a 112 centerline(duration isn't enough to make this cam have alot of overlap) and of course the whipple supercharger. it all works well and runs good, but i think a 160 degree thermostat may be too cold, the thing is, no mater how much i tune the ve ables, i will get it to run good at around 160 degrees but if i drive the truck for a long time, it will hit 170 degrees or so and then all of the sudden its running lean, if i richen it up, it will run good at 170degrees, but then on the normal short trips it stays at 160 degrees and will run way to rich. is there some correction factor table for degrees that i need to be playing with? or is this just kind of a result of having a cold thermostat?

i think this did exist on my last motor(also had a 160 t-stat) but it was not a noticable issue becasue the water pump was old and such, it used to run at about 170, it couldn't hang around at 160 like it does now. with a new water pump, and running 25% coolant instead of 50% like the last motor was using(water cools beter then coolant),i think the cooling system is overall more efficient, amplifying the problem.

changing the thermostat requires pulling the blower off(it sucks, but i cant see how Whipple could have managed any other way) so i hope theres a way i can tune this out.
the ecm is just a 7427 in a 95 truck.

any help would be appreciated.

305sbc

iTrader: (3)

Assuming your spark is identical in both situations then there must be a table changing the AFR based on coolant. I would check first because spark advance can change your AFR.

If you are running open-loop then I'd check the open-loop AFR vs coolant.
I'd search through the hack for whatever code you're running. There might be a coolant table that affects the BPW calculation in there.

Ronny

iTrader: (1)

My engine flips to CL at around 160 or so. when datalogging on a cool morn I can see it flip CL from open then back to open after I drive for a while at higher steady speed only to go back closed after engine gets more heated. Then it stays CL for good. I run 180 stat. I think what you are seeing is coolant right at 160-170 and moving OL-CL-OL. I feel most of us believe a 160 therm is a bad idea for EFI. CL feedback from 02 sensor keeps you at stoich. OL is a set table for A/F with coolant reference. If I lock OL I will see 13.5/1 or so(commanded to 14.0/1.). when I run CL I see 15.0/1 slightly leaner than stoich.

chevy1500z71

ill have to look and see when i have closed loop enabled, i think its pretty low, like 80 degrees.

but to be honest, i havnt had much time to tie up all the loose ends from this motor swap, i basicaly put the new motor in, added 3 points to the ve table across the board and fixed up the idle a bit and called it good for break in and never got around to tuning it properly, it ran decent at the drag strip(around 12:1 wot) so i never had alot of motivation to mess with it i guess. i dont really remember, for all i know i could have closed loop disabled, i really dont even remember. iv got to go throgh it this weekend.

it was running like 13:1 all the time with fouled plugs and a questionable cap and rotor(i could hear the motor poping like it was down a cylinder with the cutouts open) so i replaced the cap and rotor, changed the plugs, and now it runs alot beter but all of the sudden its running richer. i mean, it will iddle at 11:1, when i crack the throttle it will dip to 9:1, stumble and then pickup to 10 or 11:1 and cruise down the road in ther 12s, slowely creeping towards the 13s as it warms up. then all of the sudden, as if its out of no where my idle changes from surging up and down runnign rich to a more uniform loping, and this is because all of the sudden its idling at 15.5:1!

also, i think my map sensor is bad, its never been changed for all i know. sometimes ill be sitting there idling and the engine light will come on, it will stumble and die, then ill fire it up, engine light gfone, no big deal. the codes come up map sensor high input ot low input, whichever one indicates low vacuum. i think this is becasue of a bad map sensor, it could be from the motor surging, maybe it shouldnt be seeing such low vacuum at idle when it surges into 5 on the vacuum guage, causing it to throw the code. or my guess would be the map sensor is going bad.