OL Hunting idle diag

[Bayer-Z28]

2000 Camaro LS1 T56, SD, PatG Tq cam, 243 heads, LT's, FAST 102/NW 102, 42#, Racetronix 255 w hotwire fix.

I've had an open loop hunting idle issue I've been trying to track down.. I figure it's the chicken or the egg on this one. Anyone care to take a look at my work and see what it could be?

And FWIW, I'm STILL getting a darn Check light for "MAF HIGH FAIL".... I've tried every combination and I still get it. I have NOT touched the VE or PE parameters yet, so if they look off, it's still left over from the hack tune I got raped for. Got to fix my fuel pressure issues before I can mess with those.

[Bayer-Z28]

I have to log a new idle. Apparently I only saved that one as a config file...

Anyway, I matched the idle sections of my High/Low octane tables to my drive and park tables. Maybe it was grabbing a timing cell from somewhere. It only does it in open loop. Smoothes right out once the O2's warm up.

New log uploaded. It goes to about 20* timing, then bogs and it pulls timing down to about 10*.
I also uploaded the tune I where I changed some of the spark parameters.

[Bayer-Z28]

Anyone?

This PCM has been tuned by three shops in the 9 years I've owned the car. I'm about to just start from a fresh stock tune. The last hack to tune this, I've also found that the throttle cracker was extensively modified, which may also be to blame for the high rolling idle.

[PAT WS6]

i think ur maf fail is giving you this problem if its SD.

[Frost]

Anyone?

This PCM has been tuned by three shops in the 9 years I've owned the car. I'm about to just start from a fresh stock tune. The last hack to tune this, I've also found that the throttle cracker was extensively modified, which may also be to blame for the high rolling idle.

The TC is not active if you are sitting still...

There is not much in the log to use for diagnosing the swing. What are the IAC counts when this is going on as well as the STIT and LTIT's?

[Bayer-Z28]

^ I know the TC isn't used when sitting still, that's why i was thinking it could explain my high rolling idle. -Another issue.



IAC counts, no idea. STFT is around -3 to -.8 LTFT is -1.6.

I'm starting a stock tune now, but I'll keep this one as a backup.

[Bayer-Z28]

i think ur maf fail is giving you this problem if its SD.

Can you elaborate on that a bit more?

[jimmyblue]

When you say open loop idle - do you mean open loop
fueling, or open loop RPM control (airflow only)?

[Bayer-Z28]

O2 open loop. Before the O2's are warmed up and in use.. That's the only OL I know of, other than forced for VE tuning. Could it be something to do with my SD/MAF settings?

[jimmyblue]

SD seems so pick up a surging on my car where MAF is
more stable. I think this has to do with filtering of the
MAP / SD airflow value, the MAF does a lot of intrinsic
smoothing by its thermal nature. When MAP is real "busy"
it bumps fueling (and worse, if your EQ vs ECT vs MAP
is getting indexed to where enrichment is thrown in).
But MAP ^ -> air mass -> fuel, more fuel sags efficiency /
elevates MAP, etc. - a positive feedback.

There is some filtering of SD air mass as it moves, but
people like to pare this back for "throttle response" and
maybe idle wants more instead of less. I dunno if you can
be that "surgical" though. I've thought about mechanical
(manifold - long hose - MAP sensor) and electrical (RC)
filtering the MAP signal. But your problem is at idle where
the frequency of intake pulsations is unfortunately low
for electrical filtering. I have a suspicion that the real
MAP behavior is worse than shown (real vs sampled).

[Bayer-Z28]

It's just odd that it does it in open loop. I haven't forced OL yet to see if it comes back.

I was thinking about going back to MAF anyway, but I'm probably going to get the Pro interface soon anyway. Some of the EGR/WB tables can just make things more complicated than they need to be. Just gotta get my hands on a good MAF first. I'm wondering too if the MAP sees something, it could compare to what the MAF sees and the surging wouldn't occur, or it could stay the same.

I have the EQ set to run at Stoich when the car is warmed up, and I have the idle tables set rather lean, but not too too lean. (~Stoich) This whole tune needs to be re-done to avoid something that the last hack messed with, but seeing as it's cold out, I can only do so much right now. Can't really drive it much because it'd be like driving on ice.

I think I just have to look at the idle reagons of the spark and fuel tables and see which one makes a difference.

I did find this in the base spark (Park/Drive) tables. It jumped from 20* to 24* around the area where I'm having the issue. I can flash this tomorrow and do a trial and error to see what fixes it. changed the square area to 20 and interpolated vertically.