Combined Trigger Systems

Hi, is there a way of getting both engine speed and position from 1 pulley on a camshaft. The reason I ask is that I have a 4 cylinder engine that does not have a crankshaft pulley. All the ancillaries are run from a pulley on the end of the crankshaft. Currently I am running a distributor set up and I would like to do away with the distributor. The engine is a Renault Alpine engine and is running an Emtron SL4 ECU.

Thanks for any help

Peter Rasmussen

It's hard to get really fine resolution with a small diameter trigger. How big of a trigger wheel diameter can youy easily fit to the camshaft accessory drive pulley? Can you put two triggers on it? One for engine speed / TDC (say 72-2 which could look like a crankshaft 36-1 wheel), and a second trigger to identify which engine phase it's in.

Alternately, have you considered a crank trigger on the flywheel? It often possible to machine a 60-2 pattern into the flywheel.

Hi David, your point about a small trigger wheel is exactly why I am trying to get away from the distributor set up. It is a ducilier distributor body which is very small in diameter. The cam pulley is 150mm in diameter and I have machined a 24-1 trigger pattern into it using a gt101 sensor so this should be good for engine speed but I am struggling to work out how to get a position trigger.

With most modern ECU's the single missing tooth wheel and single sensor on the cam is all you need for full 720 deg Sync. I expect the Emtron should do this fine with 24-1.

Your photo however shows 24 "teeth", not 24-1 that you stated? So you would be better to start again with that pulley and leave one of those holes out.

Also, if your sensor really is a GT101 (they have been obsolete for several years now so unlikely) then you should change it to a ZF GS1012 or Littelfuse 55505 as the GT101 does not work with missing teeth.

Thank you Adam for your input. Sorry the picture of the pulley was in production phase. It is now definitely missing one tooth.

I am concerned about your comment about the the sensor (Honeywell GT 101) only a few months ago and was led to believe it was the right one for my purpose. Have I been misled.

Can you explain a little more about 720 deg sync. I understand that there is 2 full rotations for every engine cycle but in all my research I haven't heard of 720 deg sync for an ECU.

I believe you will need to have two missing teeth on your 24-tooth wheel, 180 degrees apart, since you are trying to simulate a crank trigger. This will make your crank pattern 12-1, since it will see 11 (+1 missing) per engine revolution. I think this may be too few teeth for accurate engine timing, but it depends on the Emtron ECU implementation.

What you keep referring to as "position", more commonly known as "phase" or "sync" identifies to the ECU where in the 720 degree cycle current engine position is (the missing tooth will be the same relative angle to the top-center of cylinder #1)

The way to fit the sync sensor on the same pulley is to have a different hole/trigger at a different radius.

David, just a single missing tooth is all it needs - we are not trying to duplicate a 12-1 crank, all you need for 720 sync is one unique event once per cam rev (the missing tooth in this case). Most ecu’s can do this, I think the M1 that you are probably most used to doesn’t though which I guess is why you’re not familiar with it (Edit: actually I just checked and M1 does have this capability, ref mode "camshaft 1 missing four stroke").

Peter, the GT101 was originally designed as an industrial gear tooth sensor, it has logic built into it to correct for small changes in timing due to tooth runout and tooth spacing to give a smooth speed output. So when used with a missing tooth wheel the same logic tries to correct for the missing tooth by stretching out the tooth before it. The ecu will then have trouble detecting the gap. The other 2 sensors I mentioned don’t have this logic built in and are known to work fine with missing tooth wheels, they both are also dimensionally identical to the GT101 so usually drop straight in to the same bracket.

Thanks Adam, I understand the theory behind it now, however I can't see any way in the ECU configuring to select a 720 degree sync method. Perhaps Andre may be able to help me with this. It is a Emtron SL4

You would be best to ask Emtron or your dealer for proper help since their documentation is lacking, but since it is very similar to Link, my assumption would be as follows: Go to multitooth set-up, set tooth count to 24, missing tooth count to 1, Crank index position to camshaft, sync sensor position to OFF.

Your single sensor is wired to the crank input and uses the crank sensor settings, and you will have nothing wired to the sync sensor input and those sensor settings are irrelevant.