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1997 Lean Hot Start

 
Old 08-25-2018, 04:11 PM
  #1  
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Default 1997 Lean Hot Start

Freshly turbo'd 1997
Stock engine.
Stock turbo from a CA18, bar and plate intercooler
Q-Max reroute, 195* thermostat
GM open element IAT sensor in the throttle body elbow
FlowForce 640cc injector kit

So the car is running great at 12psi. We drove it around and tuned for about 30 minutes. Idled well before at around 900rpm. Parked the car in my driveway and loaded it up so that my friend could drive the car home. Cranks it up, after a few seconds it climbs from 13.5afr to 18 and dies. Crank it back up and it does the same thing. Injector settings are correct as given my FlowForce. I would hope they wouldnt heat soak so badly as to cause this issue, being they are supposed to be such a high quality injector.

Attached is a log of starting, afr climbing and dying. Attached is also the tune. Any help is greatly appreciated. Tell me why I'm dumb.
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File Type: msl
2018-08-25_14.17.55.msl (146.9 KB, 14 views)
File Type: msq
couragemiata97tune.msq (117.1 KB, 12 views)
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Old 08-25-2018, 11:56 PM
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warmup correction quickly goes from 122% @ 11.4afr to 100% @ 16afr. All of this happens from 4 seconds to 16 seconds, or 12 seconds total. At 16:1, you already have an issue, but, EGO does nothing to correct it, staying at 100% (no correction) during the entire log. This is due to it having a 30 second delay before activating. At that point, it's allowed to take 0.1% changes to fuel. Keeping in mind that your issue is going from ok at 127% fuel to not ok at 100% fuel, you would need 270 corrections before you might be back to a decent idle afr. At 16 ignition events per second, assuming a 850rpm idle, or 14 revolutions per second, that'll take another 30ish seconds to correct. EGO also never corrects below 1300rpm according to your tune, so this is only assuming you change that part of your tune.

Hopefully you're following my logic, and seeing the issue by now. What I'm really trying to say is that it's a tuning issue, not an injector issue.

You have two choices. Make EGO takes over aggressively as soon as ASE approaches 0% correction, or tune ASE to stay active longer. Generally you need 30+ seconds of idling for heat soak affects to subside, and at 170* (your coolant temp in the log), ASE is active for 180 engine cycles, or 12.8 seconds at 850rpm.

I generally like to make ASE last a little longer, but at a certain point, you'll be wasting a bunch of fuel if you ever restart when it hasn't sat for 5+ minutes. Then tune EGO to take over as soon as ASE is over.
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Old 08-26-2018, 05:18 PM
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This is all good accurate well thought out advice.

Dann
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Old 08-26-2018, 06:01 PM
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Yeah. that all makes sense now that its spelled out to me.

The wideband in the car has an obnoxiously long heat time so he will have to sit KoEo for a little before starting maybe but thats his fault. I have made all the appropriate changes in the tune. He didnt leave me a key to test it but when I can burn it to the car and test drive it I will report back for anyone else who needs it.
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Old 08-27-2018, 08:09 PM
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So its still doing it. I blame me. I believe that I made the corrections that you suggested Curly but I may not have implemented them correctly. Please tell me why I'm dumb. Attached are a few logs and the current state of the tune.

We also have a new problem of it stumbling and stalling coming off of a blip, seemingly due to how lean it is.
Attached Files
File Type: msq
97miatatune2.msq (117.1 KB, 10 views)
File Type: msl
2018-08-27_19.08.14.msl (326.6 KB, 8 views)
File Type: msl
2018-08-27_19.15.47.msl (142.4 KB, 11 views)
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Old 08-27-2018, 11:08 PM
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You decreased the EGO lower limit to 600, that's good. You gave it an extra 2% authority, not really necessary. If your EGO needs to correct much above 10% or even 5%, you really just need to do some tuning, so I'd return that back down to 15% for now. I'm opening your tune as a temporary file, and the "step size" is greyed out, not sure why. But that should be 1%, so every time it corrects, it's a full percentage point. Then then ignition events per step to 32, that's roughly twice a second. Oh I found it, change the algorithm back to simple for now.

You made the EGO corrections, but it doesn't look like you made any ASE changes. I'd up those first by a few revolutions/% points and go from there. Just log them and look for a smooth transition (steady afr) as ASE shuts off to when EGO takes over. When you're not heat soaked, you shouldn't need EGO, when you are, you will.
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Old 08-28-2018, 09:40 PM
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It lives! And works well! Huge thanks to you, Curly. You have been immeasurably helpful. Really.

Attached, for future reference, is attached a log of the problem, a log off the fixed tune, (I cleaned it up a touch more after this) and the tune file as it currently sits. This is so that anyone who is having the same problem can follow along with the process and see what the initial solution was here. There will be lots of fine tuning from here to smooth it out but this has solved the dangerous AFR flare on this particular vehicle.
Attached Files
File Type: msq
97miatatune3.msq (117.1 KB, 16 views)
File Type: msl
corrected log.msl (390.8 KB, 11 views)
File Type: msl
Problem log.msl (239.3 KB, 8 views)
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