Cam position sensor (jumpy ignition timing)

[Mr. Y]

Hello guys.

Just wanted to share some experience...
I always had problems with jumping ign timing on my 7M. I mean when I set ignition to 15* e.g. timing mark (looking with timing gun) was jumping in 18*-12* range (approx). Such thing was with stock ECU, Haltech E8 and AEM, so it's definately not ECU problem.

I thought that it's poor construction trouble, CPS is mounted on shaft that is rotated by exhaust cam, that is driven via timing belt, so there is a lot of free play there.

Of course there is always custom crank trigger option, but it requires a lot of fabrication (machining trigger wheel and mouning it to crank pulley).

Ok, that's what I did... Took one of VR-sensors from stock CPS, took piece of alluminium from trash can and mounted VR sensor just near intake cam gear. So cam gear becomes trigger wheel - very simple.

Cam gear has 48 teeth, original gear in CPS has 24, so standalone must be configured accordinally.

Here's how to do it in AEM:
1) Set Tooth control table to: 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 3 0
2) Set Coil#2 mux table to: 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
3) Set Coil#3 mux table to: 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0

After that mod I got much smoother engine operation, actual ign. timing is exactly where I want it.

w.b.r.
Denis

 

[figgie]

Cam gear has 48 teeth, original gear in CPS has 24, so standalone must be configured accordinally.

On both case remember that is 24 tooth/48 tooth per RPM or 48/96 tooth per engine cycle. How are you reading the CAM Gears as they are not Iron or any ferrous material?

 

[Mr. Y]

Stock 7M cam gears are ferrous =) At least magnet sticks to them.

BTW, put about 70miles today with new sensor setup. Car runs fine at all RPM ranges (till 6500). Previously I had some intermediate ignition breakup problems at high RPMs.

 

[figgie]

AEM does not need a Sync signal?

 

[Mr. Y]

It does. I'm using stock sync tooth and pickup inside oem CPS.

 

[MK-111]

the stock cps is a bit hit and miss in that respect.
I tried 3 before I found a good one for the megasquirt, the first 2 suffered badly from sync loss and random dropouts. the 3rd one is rock solid.
checked all the air gaps between the vr sensors and teeth, wiring and connectors, and the vr sensor casings for cracks, and found nothing that was out of spec or damaged.

 

[suprajunky]

hey Denis,i hope you can help me with my problem.I own a 90 mkiii turbo,i recently replaced the gasket to the thermostat housing.I had to remove the (cps).i put it back together and the car will not start.Do i need to make adjustments to the cps ?????

 

[ForcedTorque]

Ok, that's what I did... Took one of VR-sensors from stock CPS, took piece of alluminium from trash can and mounted VR sensor just near intake cam gear. So cam gear becomes trigger wheel - very simple.



w.b.r.
Denis

Question 1: Will this work with stock ECU?

Question 2: Can you please post pictures of what you did?

hey Denis,i hope you can help me with my problem.I own a 90 mkiii turbo,i recently replaced the gasket to the thermostat housing.I had to remove the (cps).i put it back together and the car will not start.Do i need to make adjustments to the cps ?????

Sounds like you just might. Please explain how you went about removing and replacing the CPS. Did you follow the TSRM?

 

[adampecush]

In response to the original post, I don't see how this is much different from getting the signal off the CPS assuming minmial play in the helical gear connecting the cam and CPS. The cam gear is still belt driven, so there will be those natural flucutations either way. Perhaps the pickup used in the CPS was on its way out...

 

[grifter679]

now the only thing to worry about is the slack in the timing belt as it drives the cam gears, with the cps, you have to take in account the backlash between the cps gear and the exhaust cam gear

 

[TurboStreetCar]

Pics Please.

Id love a direct crank/cam trigger