LiveandLetDrive
03-11-2013, 01:27 PM
Hello folks, running a pre-LS engine here but my usual forum haunts lack the EFI tuning knowledge necessary for the problem at hand. If anyone can suggest other forums where I might have more luck, please let me know!
What I've got:
Gen I, 383ci stroker, ~11:1CR, 286XR solid roller, ~550HP
Accel DFI v7.0, multiport sequential, four barrel throttle body
Crank trigger (four magnets on a wheel) and dual-sync distributor
The history:
The block of the original build of this engine cracked and after sitting partially diassembled for about a year in my garage I recently rebuilt it exactly to its original specs, largely to avoid any tuning issues. Prior to the rebuild it ran great, started fine (maybe taking 2-3 tries when dead cold), great street manners considering its max power.
The problem:
Since rebuilding it has not wanted to start and will not idle below ~1500RPM. Watching CalMap on the laptop, the AFR drops off the lean end like a cliff below 1500RPM. The closed-loop correction seems to try to compensate to no avail. Above 1500-1700 it has all of the insane power I remember from before the rebuild. The idle and poor starting are just killing any ability to drive more than around the block. Pre-rebuild the "target idle" was 930RPM. During starting it feels like it is kicking back and there is occasional backfiring. It was never like that before.
Fixes tried:
Most recently we tried moving the hall-effect sensor closer to the magnet wheel, down to ~.030 from ~.060. I believe the prescribed range is .050-.080. This seemed to maybe buy a hundred or two lower RPM but not an obvious difference.
Searched for vac leaks by spraying starter fluid around likely leak spots, vac ports, etc. Also capped off all non-essential vac hoses. No effect.
Changing the tuning shouldn't be necessary as no part of the engine changed, down to the same exact head gasket. I have been messing with the idle control setup only, and I have the pre-rebuild baseline and return to it from time to time as a sanity check. No dice.
Checked timing with light and monitored it on the laptop. Both seem to be in agreement. Hard to see with the light when it's constantly changing since idle wouldn't stabilize at 900, should recheck now that I've stabilized it at 1500.
Suspicions:
Sticky fuel injectors from sitting exposed in the garage and getting saw dust on them? Looking into rigging up a home cleaning setup.
Crank trigger not perfectly aligned with TDC?
Distributor rotation shouldn't matter (within some tolerance) for timing but maybe try rotating to see if spark timing is falling off the edge of the contact at low RPM?
Any other sensors could have gone bad from sitting? O2? Has to be something that would only matter at idle as higher RPM tuning feels excellent.
First battery was bad from sitting but bought a new one which didn't seem to help. Maybe alternator has gone bad, starving the whole system for electrons? New Optima yellow-top coming tomorrow but don't want to put it in until I know I won't kill it. $$$
Really feels like overly advanced timing to me the way it kicks back but don't know what could be wrong as the numbers seem fine and the crank trigger was moved block to block but never adjusted so I don't know how it could be out more than a couple degrees. Don't know how that would explain it dropping off the lean end at low RPM either.
EFI is new to me, suddenly carbs are feeling easy! But hoping to learn and figure this out without paying for tuning time! I do have a tuning-competent friend assisting me but he is stumped also. Any help will be greatly appreciated!
What I've got:
Gen I, 383ci stroker, ~11:1CR, 286XR solid roller, ~550HP
Accel DFI v7.0, multiport sequential, four barrel throttle body
Crank trigger (four magnets on a wheel) and dual-sync distributor
The history:
The block of the original build of this engine cracked and after sitting partially diassembled for about a year in my garage I recently rebuilt it exactly to its original specs, largely to avoid any tuning issues. Prior to the rebuild it ran great, started fine (maybe taking 2-3 tries when dead cold), great street manners considering its max power.
The problem:
Since rebuilding it has not wanted to start and will not idle below ~1500RPM. Watching CalMap on the laptop, the AFR drops off the lean end like a cliff below 1500RPM. The closed-loop correction seems to try to compensate to no avail. Above 1500-1700 it has all of the insane power I remember from before the rebuild. The idle and poor starting are just killing any ability to drive more than around the block. Pre-rebuild the "target idle" was 930RPM. During starting it feels like it is kicking back and there is occasional backfiring. It was never like that before.
Fixes tried:
Most recently we tried moving the hall-effect sensor closer to the magnet wheel, down to ~.030 from ~.060. I believe the prescribed range is .050-.080. This seemed to maybe buy a hundred or two lower RPM but not an obvious difference.
Searched for vac leaks by spraying starter fluid around likely leak spots, vac ports, etc. Also capped off all non-essential vac hoses. No effect.
Changing the tuning shouldn't be necessary as no part of the engine changed, down to the same exact head gasket. I have been messing with the idle control setup only, and I have the pre-rebuild baseline and return to it from time to time as a sanity check. No dice.
Checked timing with light and monitored it on the laptop. Both seem to be in agreement. Hard to see with the light when it's constantly changing since idle wouldn't stabilize at 900, should recheck now that I've stabilized it at 1500.
Suspicions:
Sticky fuel injectors from sitting exposed in the garage and getting saw dust on them? Looking into rigging up a home cleaning setup.
Crank trigger not perfectly aligned with TDC?
Distributor rotation shouldn't matter (within some tolerance) for timing but maybe try rotating to see if spark timing is falling off the edge of the contact at low RPM?
Any other sensors could have gone bad from sitting? O2? Has to be something that would only matter at idle as higher RPM tuning feels excellent.
First battery was bad from sitting but bought a new one which didn't seem to help. Maybe alternator has gone bad, starving the whole system for electrons? New Optima yellow-top coming tomorrow but don't want to put it in until I know I won't kill it. $$$
Really feels like overly advanced timing to me the way it kicks back but don't know what could be wrong as the numbers seem fine and the crank trigger was moved block to block but never adjusted so I don't know how it could be out more than a couple degrees. Don't know how that would explain it dropping off the lean end at low RPM either.
EFI is new to me, suddenly carbs are feeling easy! But hoping to learn and figure this out without paying for tuning time! I do have a tuning-competent friend assisting me but he is stumped also. Any help will be greatly appreciated!