Z28 LT1 $EE Tuning issues

[lionelhutz]

Sure, but the actual IAC counts don't matter, just that the idle air is going through the IAC and idle passages instead of the throttle blades. So, you're doing everything right to try and balance the BLM values.

Does the idle get better if you run/drive it and get the exhaust temperatures up?

[Terminal_Crazy]

Sure, but the actual IAC counts don't matter, just that the idle air is going through the IAC and idle passages instead of the throttle blades. So, you're doing everything right to try and balance the BLM values.Does the idle get better if you run/drive it and get the exhaust temperatures up?

I've pretty much gone through everything I can find & checked several times.No. The nice idle changed by about 50 RPM. Even hot it's changing by 75-100 RPM. I'll have a play with some of the feedback delay timings and try reducing them & see if that improves anything.I now know it can idle nicer than it does.I'm currently digging the drive up so might not be able to get out for a week or two.Thanks for the feedback.Mitch

[steveo]

first try overriding closed loop and resetting blms when it gets hot and acts up (use eehack). that will confirm 100% that its a problem with closed loop config. if it doesn't completely solve the problem by going open loop, look elsewhere for the problem

if you need closed loop to make your car run properly, you blew your tune. It should run almost exactly the same in or out of cl.

[Terminal_Crazy]

OK guys. I sat one night and played with Steveo's EEHack and played withe the idle settings.

Basically playing with Timing & Idle speeds to find the sweetest idle.

I started at 1000 rpm and dropped 50 rpm each time then swept idle timing between 25 & 40 degrees.

I've written (cobbled) some software to filter the logs similar to a recent post by John Ballard ('95 383 LT1 Corvette). There was also one linked on LT1PCMtuning.com by Christian Millard.
I averaged MAP for each advance for each of the requested idle rpm's.
I averaged Injector Bpw again L&R against each advance for each rpm.
I also wanted to compare the variation of the idle speed vs the commanded idle speed so have calculated an RMS value for the difference.

Anyway...
Obviously the higher the idle speed the better the overall idle quality.
Interestingly the lowest idle speed i was able to manage was around 450 as the IAC was hitting zero. It was struggling to get lower but didn't stall. I guess enough air is leaking past the throttle body.

The car seems to want 39 degrees timing. Average MAP is lowest. Injector bpw seem to match much more closely.

I was under the impression that 383's would need less timing and 39 sounds a lot. Every other 383 seems to be about 34. Would the bigger ports & valves cause it to need more due to slow and laggy airflow ?
I also only had knock showing up on the low 20's advance. Upto 41-42 degrees never lit the dial.

I still need to get underneath & double check the exhaust isn't catching but the weather here is a bit grim at the moment.

Just thought i'd update with some findings.

I now have more thoughts & questions on filtering log data and analysing it. Anyone interested in a seperate discussion on analyzing log data in general ?

Thanks
Mitch

[steveo]

idle and timing in general is also a 'by feel' thing. it's not just getting the most vacuum or most efficient burn, although those things are nice. at a certain point when advancing timing, MAP will increase or decrease by only a tiny bit for a while. this is a plateau during which extra timing doesn't matter. you want to tune it to the very beginning of that plateau to avoid excess combustion temperature and higher emissions.

~40deg advance at idle seems kinda nutbar to me

[steveo]

I now have more thoughts & questions on filtering log data and analysing it. Anyone interested in a seperate discussion on analyzing log data in general ?

oh definitely as long as i can steal any good ideas for eehack ;)