Questions from a newbie

[Drew Skinner]

Yeah, that's what got me thinking that I had a vacuum leak. My stock VE along with the cam netted some 4-5ms pulsewidths at idle, which had me changing fuel soaked plugs every week and not driving the car for fear of washing out rings and other nasty things. After reading Bruce's tuning tips and prog101, I tried the old take %error in BLM and multiply VE and that made everything much worse (~6-7ms PW) so I went the other way with VE. 

My stock programming at 40-50KPA and 750 or so rpm had the ECM looking at VEs in the mid-high 60%, so I cut that back little by little and the idle PWs have come down to 2.0-2.4ms. I'm kinda at a loss, because this is obviously the opposite of what the ECM seems to want, but the engine is much happier. People (tuners) I have talked to with bigger cams and such have mentioned that at low rpm (idle) larger cams with lots of overlap are less efficient and therefore require less fuel or VE in the table. Looking at Bruce's VE table for the crossfire stuff I'm thinking I'm on the right track, I tried building a table closer to his and the car wouldn't idle. So I think I've found the two extremes and just need more iterations to get it right. As it is I haven't touched the upper VE table so the car hesitates as it crosses the magical 1600rpm limit into the other VE table and PWs jump up about 1.5ms or so.

Does this logic sound completely screwy or does it seem like I'm doing alright here?

Drew (waiting for the king sized CSH)
'89 IROC

>>> RRauscher at nni.com 01/16 6:51 PM >>>

Drew,

You mentioned trying to lean the VE table down, maybe a typo, but high BLMs
would be adding fuel. A 40-45 Kpa idle sounds good, about 16" vac. With a
224 @ .050 & .465" lift, 108 LDA, runs about 50-55 Kpa in a 327.

BobR.



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