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SVTPerformance's Chain of Restaurants
Tuning À la carte
Dies on Return to Idle
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<blockquote data-quote="SecondhandSnake" data-source="post: 15738897" data-attributes="member: 116684"><p>Latest update:</p><p>Ran it with the Cobra ISC tables. Didn't die all the time, saved itself a few times, but still died on occasion.</p><p></p><p>Then I moved on to cold start and man what a mess that was. Still had lots of surge. When it cold starts it surges around 800-1200, very rich (~10AFR), which is to be expected with the load reading 0.8-1.6. Meanwhile desired idle I've jacked up to 1600 RPM, and it's just not getting there. It smooths out once you open the throttle, but idles like crap there. It seems like it's just not getting enough air to be able to idle up where it wants. ISC DC is around 80% there.</p><p></p><p>What didn't help:</p><p>Smoothing out the MAF curve in that region. It's ugly, but apparently it is dialed in. I wondered if this was the cause because there's a pretty steep drop off below cold start high idle.</p><p></p><p>Flattening out the cold fuel table. With the load reading >1, it wants to run reeeeeeally rich.</p><p></p><p>What helped a little:</p><p>Adjusting the throttle stop screw out around a full turn did increase the idle (though surging) at least a little closer to desired.</p><p></p><p>Old revisions were able to idle up and then slowly come down, very well controlled. What was the difference in those tunes? I wondered. That high idle region was waaaaaay leaner in the old revisions than this one. This meant potentially an extra 1.5-2lb/min of air compared to fuel. So we're back to the theory of not enough air.</p><p></p><p>I know this region is dialed in with the most recent revision because the old ones would buck like mad cruising there, and this one holds the AFR right in check in that region.</p><p></p><p>So what are the next steps?</p><p>More throttle stop adjustment.</p><p></p><p>Increasing values in the ISC neutral idle air table. Before I changed to the correct 03 tables I did find dumping in a bunch of ISC air helped.</p></blockquote><p></p>
[QUOTE="SecondhandSnake, post: 15738897, member: 116684"] Latest update: Ran it with the Cobra ISC tables. Didn't die all the time, saved itself a few times, but still died on occasion. Then I moved on to cold start and man what a mess that was. Still had lots of surge. When it cold starts it surges around 800-1200, very rich (~10AFR), which is to be expected with the load reading 0.8-1.6. Meanwhile desired idle I've jacked up to 1600 RPM, and it's just not getting there. It smooths out once you open the throttle, but idles like crap there. It seems like it's just not getting enough air to be able to idle up where it wants. ISC DC is around 80% there. What didn't help: Smoothing out the MAF curve in that region. It's ugly, but apparently it is dialed in. I wondered if this was the cause because there's a pretty steep drop off below cold start high idle. Flattening out the cold fuel table. With the load reading >1, it wants to run reeeeeeally rich. What helped a little: Adjusting the throttle stop screw out around a full turn did increase the idle (though surging) at least a little closer to desired. Old revisions were able to idle up and then slowly come down, very well controlled. What was the difference in those tunes? I wondered. That high idle region was waaaaaay leaner in the old revisions than this one. This meant potentially an extra 1.5-2lb/min of air compared to fuel. So we're back to the theory of not enough air. I know this region is dialed in with the most recent revision because the old ones would buck like mad cruising there, and this one holds the AFR right in check in that region. So what are the next steps? More throttle stop adjustment. Increasing values in the ISC neutral idle air table. Before I changed to the correct 03 tables I did find dumping in a bunch of ISC air helped. [/QUOTE]
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Dies on Return to Idle
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