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095 Choosing a trigger method

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First off great, informative webinar! I have one question for you since you were discussing your dislike of the OEM Nissan CAS. do you have a similar opinion of the 2nd generation 13-b rotary CAS, or other combined crank/cam measuring sensors? I see kits out there to convert those systems to true, trigger wheel style and was rethinking their usefulness after watching the webinar.

Thanks in advance!


Great webinar. Thanks.

I have a question: I used the AEM EPM to run modified Chevy V8. The Engine has large cam with large lift and overlap. The EPM has multi-tooth 24 for trigger and one sync tooth. It replaces the engine distributor. I had timing drift issues when after driving the car for several miles, I find the timing drifted (advanced). The problem caused damage to piston rings. After viewing this webinar, I am thinking that maybe my problem was due to the resonance. The cam and timing chain wobble may have caused the sync tooth to pops over trigger tooth or the opposite.

After replacing the rings, I am thinking about using trigger from crank with 60-2 trigger wheel.

@Rotar-wee! in the rotary world it seems the 13B CAS system has been well proven to be effective and it only takes a look at what most of the high end drag engines are running to see that the CAS is the popular choice. My personal preference is still a crank trigger (eccentric shaft) system but I guess if it isn't broken, don't fix it :)

@SONofSON the trigger disc we made for the SR20 was essentially the same as the AEM unit and we found it worked well with a stock SR20 but with a modified engine it wasn't a 100% solution. Any time you're taking the engine position data from a distributor drive you're introducing some possible noise into the system. Inevitably there will be some backlash in the distributor drive as well free play in the cam chain itself. This can result in harmonics that may affect the accuracy of the timing. I can't say that's what happened to your engine but it also isn't impossible.

It's always interesting to see how solid the ignition timing stays if you watch the timing with a timing light while you smoothly increase the engine speed through the rev range (with the timing locked). In the perfect world the timing will be rock solid but with many trigger systems you'd be quite surprised to see exactly how much it moves.

In the webinar you mentioned a setup that uses a missing tooth crank wheel for Ref and a Sync level that effectively decodes which half of the 720 deg cycle the crank is in. I understand how that would work. My question is, which ECU platforms support this trigger method?

@64hardtop, it's not an uncommon trigger mode so I'd imagine most ECUs could decode it. In the Link ECU for example this is configured as a multitooth/missing for Trigger 1, with a cam level input for Trigger 2.

"It's always interesting to see how solid the ignition timing stays if you watch the timing with a timing light while you smoothly increase the engine speed through the rev range (with the timing locked). In the perfect world the timing will be rock solid but with many trigger systems you'd be quite surprised to see exactly how much it moves"

Thanks Andre,

When I locked timing and rev the engine, it is almost solid with +/- 2deg variations. It is when I drive the engine and put load, It advances to way too far than it is in the base map and never come back to where I set it idling at.

Hola. The Nissan CAS problems is something i have been aware of for some time and i have delt with it in a propper manner. I Just happen to have a couple logs showing this.

Here is my car. VG30DETT engine with the original CAS disk for triggering duties. Look at the RPM trace. That is what the ECU actually think is going on.

Here is the same car but with a propper crank fitted trigger. (24-1 and aem disk in the CAS for cam synk)

Also note the red line below RPM. This is RPM ROC (Rate Of Change) or Delta RPM if you will.

This is from a RB25DET engine with AEM`s disk in the CAS for bot crank AND cam signal (no crank fitted wheel).

The RPM is smoother but look at the red line below. That one shows that the main problem with this setup is still present.

Theese are all Link ECU logs.

Recently i came across another VG30DETT engine with the same valvetrain as i have. This one runs the stock CAS (360 slot wheel) so i know this engine also have timing scatter problems. However this car runs a Haltech Pro plugin ECU.

On this car there is NO rpm artifacts in the logs at all. Its actually smoot as a babys but. This tells me that Haltech is filtering the hell out of its trigger signal totaly masking the problem...

Thanks Andre, how is that trigger pattern decoded in Motec MX00 speak?

Thanks for the feedback Andre and everyone. It is much appreciated.


With AEM EPM 24+1. Would it be wise to trigger at different edges for Ref and Sync? like rising edge for Ref, and falling edge for Sync. I had it set to trigger on falling edges for both Ref and Sync. Just to see if it makes any difference for my case.

Attached Files

Hi 64 Hardtop,

A tooth/teeth missing on the Crankshaft (Ref) and a single Sync tooth on the Cam would use Mode 5 (One missing twice a cycle, i.e. 24-1) or 7 (Two missing twice a cycle, i.e. 36-2).

SoS, in your case, if that is the capture from your engine, then I would use either Falling for both, or Rising for both. This is to make sure that the edges that are read are spaced as far apart as possible, so that if there is any movement relative to the the to edges, the chance of them swapping is minimised.

If you where to use a Falling edge on the Crank, and a Rising edge on the sync, if there was a small bit of movement in the relation between the Crank and Cam (Toothed belt cam drives can do this) then it is possible that the Crank edge being read by the ECU will move to the previous tooth, this will result in the engines timing being advanced or retarded by the angle between Crank edges.

BlackRex, Thanks for your input. Yes that is the AEM EPM capture. It makes sense what you have mentioned. I had it falling edge for both ref and sync. and had issues with timing advances.

Now I am putting 60-2 crank trigger and will try that. I have coils wired for direct fire. But there is a good feature in Elite 2500 which allows me to keep the wiring for direct fire and trigger coils waste spark. This is to set the min. home rpm way more that I ever reach, say to 10000 and tick the quick start functions. The ECU will not look for home signal and trigger coils waste spark.

thanks for all the support. started engine with 60-2 crank trigger and and my trigger problem is resolved.

Attached Files

About the Nissan CAS problem. I just ordered a Taarks crank trigger kit (24 tooth wheel, Honeywell GT101 sensor) and Taarks hall sensor kit for sync. Anyone have any experience with that setup or similar from a different supplier for the SR20?

@Oluf while I haven't used these trigger kits from an aftermarket manufacturer, I've converted a few Nissan engines of various forms to crank trigger with 24/1 inputs with great success. The only thing to be careful of is the location of your sync input relative to the reference teeth on the crank. With the adjustability of the CAS, it's very easy to have the sync input occur close to one of the reference teeth and this can cause as many trigger issues as you'd see with the stock CAS. If you have a scope or your ECU has a trigger scope function, this can be used to ensure correct alignment.

Thank you for your reply Andre. I did not fully understand what you said about the location of sync, but i will do some research on that so i don't end up with an unstable setup. I will be using the Motec M150 ECU.

With this sort of trigger system the reference input is fixed in relation to the crank rotation simply depending on where you've located the trigger teeth and the sensor. Generally once this is installed, the inputs will occur in the same place with respect to crank rotation. On the other hand the RB CAS can be rotated to move the sync input relative to the reference input. This is where you can get into trouble if you locate the sync input so that it aligns with a reference tooth (or at least very close to one). The input capture function on the current MoTeC GPA/GPR package will help you make sure this is correct.

Thank you for clearing that up Andre.

Quick question, why are Hall sensors far more plentiful in the after market than the reluctor style?

i have had issues with my 30yr old distributor contained trigger system (3sgte) and am looking to go a crank trigger and cam trigger running 36-2 as this seems the most utilized. (however 60-2 would offer more resolution?)

but stock system is reluctor (as alot of toyotas are) and yet aftermarket is 90% hall and I'm curious why that is?

also any good cheap USB oscilloscopes purely for checking cas signals? wouldn't mind verifying mine now and after the new system?

A few reasons: The modern ECU is looking for a square wave and conditions a VR sensors' sinusoidal signal to a square wave anyway, why not just feed it one first? Also noise, when a hall sensor works it just works, a VR sensor can get funky depending on speed and proximity while still sort of working. There're a whole host of other reasons why a hall sensor is better, though 95% of the time a VR sensor works just as well as a hall sensor.

so with a 36-2 CAS the cam ref should occur when the missing tooth occurs?

i know the missing teeth is ideal at 60" BTDC, juat checking when the cam tooth ideally occurs

No, with a missing tooth you basically want the cam synchronisation input to occur anywhere except the missing teeth. There's a lot of confusion around the ideal location of a missing tooth gap and some ECUs are sensitive to the location so you're best to follow their guidance. With others however it's really not an issue and you simply correct for the location in the base timing. After all, once the ECU is synchronised it should always know the engine position unless you've got a triggering issue.

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