The V8 Owners Forum -

hello all,

Currently i am using a GEMS efi 4.6 v8 camshaft sprocket...

But does anyone know how GEMS understands the pulses....

Ie does it use the missing material parts or the area of solid material to fire the injectors from....

I know theres 4 pulses per revolution....but need to know when the injectors are fired per revolution.

Here is a pic.

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cheers

scott

Not being an expert.....

I assume it is a Hall effect sensor, it will sense the peak of each tooth as the engine rotates, the 4 slots will be to reduce the weight of the gear.

Is there a "flat" tooth on this gear? or as magnet built into one tooth, to give a different signal for TDC, or is there another pick up at the rear of the engine? i.e. on the crank

My V8's aren't that advanced

according to the LR rave, it produces 2 pulses per 360deg of cam rotation.

The sensor is mounted directly on the centreline of the slots....

But i am trying to find out which slots produce the pulse to time the injectors.

scott

Seight-V8 wrote:according to the LR rave, it produces 2 pulses per 360deg of cam rotation.

Hi Scott,

Thanks for explaining it to me, I fail to see how 2 pulses are produced with 4 webs passing the sensor for m360 rotation:?:

3 dots 1 dash per 720degs - its a phase sensor, engine angle is taken from the crank sensor.

Gems & Bosch have slightly different arrangements BTW.

Given there is a 60-2 tooth crank trigger on the flywheel, the cam doesn't do much more than provide synchronisation pulses. (ie the timing of them is not critical, as long as they happen in the right "quadrant")

Seight-V8 wrote:according to the LR rave, it produces 2 pulses per 360deg of cam rotation.

The sensor is mounted directly on the centreline of the slots....

But i am trying to find out which slots produce the pulse to time the injectors.

scott

Surely its 2 pulses every 360deg of crank, not cam. I.E one turn of the crank is half a turn of the cam and you have 4 holes or spokes so 4 pulses per 360deg of cam.
The signal should spike on the metal and drop on the hole.

rave says....

it is a hall effect device which produces four pulses for every two revolutions of the engine.

So thats only 2 pulses per 1 crank rotation...as my triggerlog shows me....

What i was trying to work out....is how GEMS understands the triggering....so i could save time by replicating it in my VEMS setup...

I plan to make a new trigger wheel anyway...for VEMS with the trigger at TDC....and hopefully tune the rest in VEMS.

scott

In each 360 degs of crank rotation it will see either 2 short pulses or 1 short + 1 long from the cam sensor - hence the ecu deduces which stroke the crank is on based on either criteria.

Accuracy is pretty irrelevant it is always comparing the data vs the crank information, a single pulse passing a known point on cam or even off a rocker arm would achieve a similar result.

Simple what's the problem, are you trying to read too much into its operation?

Seight-V8 wrote:I plan to make a new trigger wheel anyway...for VEMS

I too am looking at doing this over the winter. My goal is to get a solution that allows me to keep the duplex timing chain in an "intermediate" timing cover (probably using the shorter Honeywell hall sensor from the VEMS shop). If we can save some money and effort by working together to produce a batch of trigger discs, I would be happy to do this.

hello dave,

Sure sounds good to me....

I've already drawn a cad model of the GEMS camshaft sprocket from a new one i measured at work.

I've also done a design of what i think the vems needs...for camsync....

Something like this....



Where the falling edge is bang on tdc.....

Although everything is still in the design phase....so any input welcomed...

Think the duplex chain would need the gear profiles altering to suit the roller chain, but if i can get one to measure i can alter it to suit.

scott