Accel DFI tuning help - won't idle

[LiveandLetDrive]

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!

[GregWeld]

Originally Posted by LiveandLetDrive

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!

You do know that there is a learning "session" so to speak when you stab the dual sync distributor to make certain the cam sensors are where they should be. Did you do that when you re-installed the distributor? Do you remember this from the first install.... the red and blue LEDS inside the dual sync.

Have you checked for vacuum leaks?

Have you tried running in BATCH mode instead of Sequential?

[supremeefi]

Great starting points Greg.
There's obviously something that changed with the rebuild. As memtioned, check timing and set it to batch to see if it makes a difference, then go from there.

You can send me your cal if you like, I'll check it over.

Mark
[email protected]

[LiveandLetDrive]

Worth mentioning that I didn't build it the first time so while I'm intimate with the internals the EFI setup is new to me. I'm going to recheck the distributor sync setup as I did not go through the LED process. I did mark the distributor (rotor-to-body and body to intake) and realigned in upon reassembly but I should set it up the right way. Also, not sure if I mentioned in my original post that I tried to align one of the four magnets on the trigger wheel as close as possible to #1 firing TDC, might that not be right? It has 6 possible orientations in bolting to the crank and that's one thing I didn't mark or photograph well when disassembling. I will get back as soon as I've checked these out. Running in batch will be interesting as well. Thanks so far!

In the meantime, here's the beast:

[supremeefi]

Why not use the ignition trigger out of the dual sync to narrow it down? Has the rotor moved? It is adjustable.
Set the Force timing to whatever is easiest to see on your balancer. That way it won't jump around.

Keep us posted.

[Revved]

/\/\/\/\/\

ACCEL expert on the case!!

One of these days he might even remember to drop me that email about the next ACCEL training class so I can see if it is as good as he says it is!!

Nice Vette BTW!

[supremeefi]

Originally Posted by Revved

/\/\/\/\/\

ACCEL expert on the case!!

One of these days he might even remember to drop me that email about the next ACCEL training class so I can see if it is as good as he says it is!!

Nice Vette BTW!

It's the 19th and 20th in Boca Raton Florida. Let me know if you're headed that way.

[Revved]

Originally Posted by supremeefi

It's the 19th and 20th in Boca Raton Florida. Let me know if you're headed that way.

Hmmm.... don't think that will work.... Already taking a week off for Palm Beach BJ... Let me know next time there is one closer to TX!