Automatic Compression Release
Are you sure youre not hearing the injectors deliver the prime pulse that is delivered at power up?
Stellar HDF Member
Joined: Mar 2012
Posts: 2,019
Likes: 599
From: Columbus, OH
Yes, doesn't make the noise with ACR's unplugged
Stellar HDF Member
Joined: Mar 2012
Posts: 2,019
Likes: 599
From: Columbus, OH
Friend of mine sent me this when I was trying to diagnose mine
I ended up replacing my battery
OP is getting a code so ECM is detecting a fault somewhere, my advice to them is to get the correct service manual for their bike and follow the diagnostic for that particular code
I ended up replacing my battery
OP is getting a code so ECM is detecting a fault somewhere, my advice to them is to get the correct service manual for their bike and follow the diagnostic for that particular code
Road Master
Joined: Jan 2017
Posts: 866
Likes: 248
From: N.Y.C
Its a very audible click,mine came after Harley issued a software update on the S models with the 110 motor. The bikes wouldn't start on the first cranks and kick back but fired on the next,was beating up the battery pretty good especially when cold.
Grand HDF Member
Joined: Nov 2009
Posts: 4,315
Likes: 1,663
From: Tampa
What youre doing here is assuming the engineers at Harley are savvy enough to design something like this. Considering they cant even isolate whats causing the sumping and fluid transfer in the M8, I stand by my original skepticism.
Deceleration of what, the piston? So you’re implying the code in the ECM is seeing a decrease in flywheel tooth speed across the CPS and incorporating that data into a certain MAP signal (even though the opposite cylinder is sharing that same MAP sensor) and engaging the ACR accordingly???
What you’re doing here is assuming the engineers at Harley are savvy enough to design something like this. Considering they can’t even isolate what’s causing the sumping and fluid transfer in the M8, I stand by my original skepticism.
What you’re doing here is assuming the engineers at Harley are savvy enough to design something like this. Considering they can’t even isolate what’s causing the sumping and fluid transfer in the M8, I stand by my original skepticism.
The missing tooth on the flywheel indicates that x many teeth later is a TDC event on a certain cylinder. Since there isn't a cam sensor and it is a single fire coil, the ECM has to determine if it is TDC Compression or TDC Exhaust (as well as which cylinder) in order to find engine phase and throw spark in proper time. The ECM sees flywheel deceleration on a compression event and because it has seen the missing tooth, it knows its a TDC event on a particular cylinder - it then finds engine phase. It can then verify by comparing to the MAP signal deltas read at specific moments in time. This is why some stock compression engines with S&S easy starts or compression releases had a hard time starting and why the spark plugs need to be installed when checking for spark.
While you may not believe this because you can't conceive it possible, I assure you it's true. It's basic Delphi EFI strategy and it's used in H-D EFI.
Regarding the ACR activation - when Auto ACRs were released, we were specifically told by engineering that they were activated on the compression stroke. If a software update sometime later has changed that, I do not know. But yes - the technology is certainly there to activate them on only the compression stroke - it's the same as throwing spark at the correct time.
Last edited by Ed Ramberger; Mar 28, 2019 at 07:42 PM.
Grand HDF Member
Joined: Nov 2009
Posts: 4,315
Likes: 1,663
From: Tampa
You're very skeptical, but this is one time you're pretty far off base. I'm not assuming anything, I'm sharing facts.
The missing tooth on the flywheel indicates that x many teeth later is a TDC event on a certain cylinder. Since there isn't a cam sensor and it is a single fire coil, the ECM has to determine if it is TDC Compression or TDC Exhaust (as well as which cylinder) in order to find engine phase and throw spark in proper time. The ECM sees flywheel deceleration on a compression event and because it has seen the missing tooth, it knows its a TDC event on a particular cylinder - it then finds engine phase. It can then verify by comparing to the MAP signal deltas read at specific moments in time. This is why some stock compression engines with S&S easy starts or compression releases had a hard time starting and why the spark plugs need to be installed when checking for spark.
While you may not believe this because you can't conceive it possible, I assure you it's true. It's basic Delphi EFI strategy and it's used in H-D EFI.
Regarding the ACR activation - when Auto ACRs were released, we were specifically told by engineering that they were activated on the compression stroke. If a software update sometime later has changed that, I do not know. But yes - the technology is certainly there to activate them on only the compression stroke - it's the same as throwing spark at the correct time.
The missing tooth on the flywheel indicates that x many teeth later is a TDC event on a certain cylinder. Since there isn't a cam sensor and it is a single fire coil, the ECM has to determine if it is TDC Compression or TDC Exhaust (as well as which cylinder) in order to find engine phase and throw spark in proper time. The ECM sees flywheel deceleration on a compression event and because it has seen the missing tooth, it knows its a TDC event on a particular cylinder - it then finds engine phase. It can then verify by comparing to the MAP signal deltas read at specific moments in time. This is why some stock compression engines with S&S easy starts or compression releases had a hard time starting and why the spark plugs need to be installed when checking for spark.
While you may not believe this because you can't conceive it possible, I assure you it's true. It's basic Delphi EFI strategy and it's used in H-D EFI.
Regarding the ACR activation - when Auto ACRs were released, we were specifically told by engineering that they were activated on the compression stroke. If a software update sometime later has changed that, I do not know. But yes - the technology is certainly there to activate them on only the compression stroke - it's the same as throwing spark at the correct time.
HD Forum Stories
The Best of Harley-Davidson for Lifelong Riders
7 Surprising Harley-Davidson Products that Are Not Motorcycles
Verdad Gallardo
8 Best Harley-Davidson Motorcycles Ever
Pouria Savadkouei
10 Worst Harley-Davidson Motorcycles Ever
Pouria Savadkouei
Killer Custom's Jail Break Is The Breakout That Refused to Blend In
Verdad Gallardo
Crazy Bunderbike Build Looks Amazing, But Is It Impossible to Ride?
Verdad Gallardo
Harley-Davidson Reveals Super Cool Cafe Racer Concept
Verdad Gallardo
Engraved Rebellion: Inside Bundnerbike's Glam Rock II
Verdad Gallardo
10 Motorcycles You Should Never Buy
Joe Kucinski
10 Things Harley-Davidson Needs to Fix in 2026
Verdad Gallardo
What I have described is factual. I dont need to prove anything. Im just sharing factual info.
Last edited by Ed Ramberger; Mar 29, 2019 at 07:16 AM.
Stage IV
Joined: Aug 2024
Posts: 4
Likes: 0
From: canada
how did you fix this? Mine is doing the exact same thing. My ACRs used to make the click noise when keying the ignition and would start perfect. Now Im getting ACR codes and it no longer makes the clicking ACR noise when keying the ignition and it wont start on first crank. It kicks back and then starts rough on the second start attempt. Once started the bike runs great now.