Idle tuning 408 automatics??
10-28-2006, 04:43 PM
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Idle tuning 408 automatics?? I've been working with a couple of 408, automatic, big cam, big stall cars trying to get them to idle well after they were professionally (I won't name names but it's a well respected company) tuned but idled horribly. In fact one of the cars would stall just moving it around the shop.
Both cars are use the maf and both have 90/90 setups. They both search drastically up and down for idle and as I said the worse one will actually stall when moving it around.
Using HP tuners how should I attack this?
My thinking is to put them both into SDOL and tune between the adjustable throttle blades and Idle airflow tables to get them to idle decently. These are the first larger than stock displacement motors I've tried to tune so do I want to keep the IAC counts in the 30's and 40's like I do on my h/c ls1?
So far that's what I've been shooting for and it's helping but I can't keep the counts in the 30's and 40's consistenly.
What should I tweak to help limit the up and down surging or seaching the motor is doing at idle?
I've only spent a little while on each car before I ran out of time but I'd like to put some time in and get them to idle properly so the input will be appreciated. Thanks.
Brian
Both cars are use the maf and both have 90/90 setups. They both search drastically up and down for idle and as I said the worse one will actually stall when moving it around.
Using HP tuners how should I attack this?
My thinking is to put them both into SDOL and tune between the adjustable throttle blades and Idle airflow tables to get them to idle decently. These are the first larger than stock displacement motors I've tried to tune so do I want to keep the IAC counts in the 30's and 40's like I do on my h/c ls1?
So far that's what I've been shooting for and it's helping but I can't keep the counts in the 30's and 40's consistenly.
What should I tweak to help limit the up and down surging or seaching the motor is doing at idle?
I've only spent a little while on each car before I ran out of time but I'd like to put some time in and get them to idle properly so the input will be appreciated. Thanks.
Brian
10-28-2006, 07:45 PM
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Generally heavy surging at idle can traced to the 0-1200rpm range of the main VE being too rich. For starters, try reducing these values of -5% until you see 0 to +3% LTFT's at idle. This should help. I also sent you a PM with a little more detailed information to help you out.
11-07-2006, 08:36 AM
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Any luck? Ive been messing with mine for months now trying to get it o straighten out. My ltft's are 0-4 range depending on the day. The IAC steps are right in line, and my RAF has been dialed in. I think Im just going to give up and get over it. But its a real PITA to drive in public when it wants to do that.
11-12-2006, 12:22 AM
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Have you guys tried reducing the lower VE table to start with? Also, how is start up and do you smell raw gas? My 402 idles real nice, but it took a long time to get there.