cam sensor question

[Hoople]

I guess the area that confuses me is why would the bike stall after loosing the cam sensor signal. Once the bike see's the cam signal and starts, it is in sync. with the crank signal. From that point on, as long as the crank signal exists, the computer knows where the cam position is by it's first signal.

Once an engine is in phase, yes in a perfect world it would remain in sync until you turned the engine off with the key. But what if a rider was going down the interstate at 60mph and he accidently flipped the run/kill switch to OFF and then back to ON. Without a cam sensor there would be no way to restore injector phasing. You must have a way to restore sync if by chance you happen to loose it. Also, any type of electrical glitch can let you loose phasing.
The early MM systems, have no way to restore phasing on the fly so by default the engine just dies in the absence of a cam position sensor. It's better to have that than trying to run an injected engine out of phase.

Now on late model Delphi "96" bikes, there are no cam sensors. They only have a crank sensor with a two missing tooth flag. Those Delphi systems will "phase up" during cranking by seeing the crank slow down during a compression stroke. It sees two close compression strokes and can determine "who is where". That's the reason the coil won't fire during a simple cranking spark test if the plugs are removed.
It's because it can't figure out which piston is at TDC of compression.

But the Delphi ECM has firmware in it, that will force a re-phase on the fly should the engine hick-up during a run cycle. You can actually flip the bars kill switch to the kill position and back to "run" and phasing will restore itself. This became all new when Delphi came on board with HD. Ion- spark retard is also a Delphi development that is embedded in the firmware.

I believe any MM bike will stall if the cam signal is lost. The MM ECM doesn't have the needed software. It has to die because you just can't run the risk of running out of phase. The firmware/hardware that was developed by Delphi changed all that.

 

[tech2]

Good info hoople. i do understand and agree with the cam phasing, I was only questioning why the bike would not stay running (lost cam signal) at least until the next start sequence. I know it's all in the programing of the ecm. Anyway, I just came back from a 150 mile run after replacing the cam sensor and all is well.
No stalling or driveability issues. Thanks again!

Just for interest sake I researched the VAS patent used on Harleys for a better understanding of it's operation. It shows a schematic of the hall effect and the VAS with a very detailed explanation. If the pdf attachment doesn't work try this
Patent US5613571 - Rotational speed/tip sensor - Google Patents.

View attachment US5613571 (1).pdf

 

[Jennmarr]

Hoople and Tech2, I think I have learned more about fuel injection systems from this thread than everything else I have read. It has been a pleasure to follow your discussions.

 

[tech2]

I'm glad that I was not the only one that benefited from this thread, Jennmar. It certainly has been a learning experience for me as well.
I put on another 175 miles today and all is well. I am still going to find out more about the ECM on this bike and the available software. If and when I do I will post the results.