304 running on 808 in ski boat - idle surge

Holden/Delco Tuning. ALDL, OBD 1.5. Circa 1989 to 2004.
rhys_main
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Re: 304 running on 808 in ski boat - idle surge

Post by rhys_main »

Thanks VL400! Much appreciated!
rhys_main
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Re: 304 running on 808 in ski boat - idle surge

Post by rhys_main »

Is there a guideline for the AFR that the 304 idles best?
I’ve read conflicting figures.
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jenko
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Re: 304 running on 808 in ski boat - idle surge

Post by jenko »

try 14.6 - 14.7 really something you need to play around with ,its specific to each application
I like to keep my mixtures around 14.7 at idle so as to keep o2 sensor and plugs clean at idle but I am not running a huge cam
every one has there own opinion and way of doing it none of which are necessarily wrong
rhys_main
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Re: 304 running on 808 in ski boat - idle surge

Post by rhys_main »

Hi all,
I’ve spent quite a bit more time qweaking... the NVRAM makes it sooo much easier!
I’m aiming for an idle around 600rpm and have found that it’s is not happy any leaner than 12.5 and I’ve had to pull the idle spark back to about 22-24 deg to get it to settle!!
I’m not holding out much hope of getting anywhere near 14.6-14.7 afr at idle
Any thoughts on this would be much appreciated!!
heff0018
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Re: 304 running on 808 in ski boat - idle surge

Post by heff0018 »

600rpm sounds quite low. My 265 with a stock cam isn’t happy under 750. It sits at 13.5 at idle when warm.
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antus
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Re: 304 running on 808 in ski boat - idle surge

Post by antus »

Personally i would run that 14.7 at idle either but like jenko says it depends on the engine. Also at low pulse widths any small error in the opening times makes a bigger difference as a percentage of fuel delivery and you'd need a wideband to see it. (Havnt read the whole tread, not sure if you've covered this). If injectors are standard and fuel pressure is correct then this wont be an issue.
Have you read the FAQ? For lots of information and links to significant threads see here: http://pcmhacking.net/forums/viewtopic.php?f=7&t=1396
rhys_main
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Re: 304 running on 808 in ski boat - idle surge

Post by rhys_main »

Had a bit more of a tinker today with the boat out on the water.
I've found that the key to the low idle (600 RPM) seems to be bringing the timing right back.
Best results I've achieved are with idle spark adv at 16 deg.
With this, I've got the wideband reading 13.5 with some fluctuation.
This low spark advance seems to be the only thing that will settle the idle and stop it from hunting/surging while out of gear... it also seems to provide more resistance to stalling when dropped into gear (dog clutch)... I've given the closed loop idle spark a bit more leash (up to 8 deg) which helps this process.
Is there any negatives (or potential future problems) to running the idle spark advance so low?
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