MoTeC Global Forum

Have an early Subaru that's just been rebuild and has aftermarket cam pulleys.

Engine does sync up and start, but after that below 1500rpm getting "no sync" errors and engine isnt happy ( usually stalls )

Scoping the cam signal, generally it is a very good clean signal. But on the 3 tooth portion ( 3,1,2,1 ), the 1st and 3rd tooth give a good steady signal of similar voltage level. But the middle one is much lower, approx half the voltage.

Ive never scoped an OEM signal to compare voltages or patterns seen

Even at approx 3000rpm, the voltage level is only 2v. Sensor cannot be moved any closer to the teeth or it will hit. And further away loses signal altogether at the ecu.

Could this low voltage be enough for the ecu to lose the sync ? Would applying a sync mag level table with low mV levels be sufficient to fix it ? Other than replacing the cam wheel.
Even revving to 3-4k there appears to be no background noise levels and signal is totally clean.

The early ref/sync modes have to be exactly like the standard setup any minor miss alignment or angle change between the ref & sync cam will cause a problem.

I hope the indexing of the cam location and cam tooth pattern are exactly the same as the standard gear.

Ive heard of head gasket thickness changes causing problems even with standard cam gears.

The only fix was to use a hall sensor on the cam gear. This way the edges of the cam pattern don't cross over the crank pattern.

It syncs on crank, and is in sync above 1500rpm.

I only figured out how to use the scope logging after I left the car. But basically the trigger patterns look ok.

Except for the 3 tooth portion on the camwheel. The voltage of the middle tooth is very low compared to all other teeth.
So I dont think it is an alignment or indexing issue, otherwise it would be happening at more rpm's

Although even at 2000rpm or so the high peaks are only +- 4v The middle tooth is only half that.

Comparing to a M800 scope from a 2002 car, both cam and crank voltages are almost being clipped at that rpm. So generally voltages are low.
I didnt try the crank sensor to see what voltages it was sending.

Will try and get a crank and cam scope in a few days to compare voltages. And try setting the threshold below 2000rpm much lower in the hope the ecu will see the middle tooth better. Both cam and crank were just set at the "2" setting within the ecu.
I did briefly try a custom table but that was before I had a better picture of the actual voltages seen, but we were giving up at that stage anyway. Wasnt intending getting tied up with cars over xmas

Or as you say, a Hall sensor may be the way to go. Certainly easier than swapping camwheels.

we have similar problem with ej20 twin turbo since rebuild,but it will only fire 1 bank,can anyone suggest what type of hall sensor?

hornet75 wrote:we have similar problem with ej20 twin turbo since rebuild,but it will only fire 1 bank,can anyone suggest what type of hall sensor?

Oops...that reminds me. I was to check if the GT101 would fit. They look like similar dimensions. Will check now.

The cause of this problem is the aftermarket vernier pulleys. If I cant find an easy solution, the pulley will have to be changed which is a PITA after setting cam timing etc.

Well physically it should fit. Main body is 18mm diameter and 32mm long.

I think when I measured the Subaru it was about the same diameter albeit only 27mm long.

As to whether it is electrically suitable I dont know. But I think it should be.

Wiring on the M48 will need altered though to give the sensor a power supply and it needs to return to a different pin on the ecu for hall according to the wiring diagrams.