In an effort to solve some other MS/trigger related issues on my car(BP4W swapped into a 94 chassis, MS2), I installed a 36-2 trigger wheel. After changing the needed settings, firing the engine, checking base timing, and verifying all the crank/cam signals, I decided to unplug the cam sensor with the engine still running to verify my signal logs. To my suprise, the engine did not immediately die as I had expected, but ran and rev'ed without any hiccups.
Is the cam sensor no longer needed on a BP4W if a 36-2 wheel is installed? Is the cam sensor only used to find sync during startup? Would I run into issues running without the cam sensor under high load/RPM or some other condition?
I am running sequential injection and wasted spark.

I ask this because I have an adjustable cam wheel on the exhaust cam, but my cam sensor would never read the adjustable wheel on the intake side, so I was stuck with the stock cam wheel. Not needing the cam sensor would allow me to install my adjustable cam wheel on the intake side for that 2HP gain and +10 street cred.

 

You won't get sequential without a CAM trigger. The MS defaults to wasted spark/batch when it loses sync.

Edit: minor ninja

 

So when I remove the CAM signal, the ECU drops back into batch, then automatically reverts to sequential when the CAM signal returns?
I guess I'm just surprised MS could do that so quickly and seamlessly.

 

The CAM signal is only used to determine the engine cycle. The crank sensor is used to keep in sync with the engine and time all the injection and ignition events.
As soon as the ECU synchronizes on the engine cycle it does not need the CAM signal any more.

 

Like others have said before, the ECU only uses the cam signal during startup to switch to sequential. After it switches to sequential, the signal from the cam is no longer needed so unplugging the sensor makes no difference until you either shut it off or the engine loses sync from a bad crank signal. You won't get a sync loss from a bad cam signal once it is sequential.

 

slightly out of topic, what sensor are you running with this and how is it wired in? I have a 36-2 installed on my BP4W swapped 96 but I read that you’ll have to use a different sensor/wire it into the CAS

 

I used all BP4W OEM sensors, so an OEM crank sensor, and OEM cam sensor. My chassis was a '94 so I used the VVT swap thread for wiring information and wired both as needed into the OEM wiring.

 

Is your MS2 a DIY or a PNP2 unit made for your chassis?

 

At that point I think it was a DIY MS2 unit for a '94. The wiring remains the same weather it is a DIY or PNP unit.

 

Sorry for the hijack but I'm too sad and desperate to care.

So if my VVT swapped 95 is experiencing sync loss, id be better looking to the crank sensor than the cam sensor, as the ECU no longer references cam signal after startup?

 

VVT uses cam position at all times. You should be able to tell which sensor is losing sync with the high speed logger or I believe the status field.

 

I think it's time for a sticky thread that points to the connector issues on VVT engines at the cam sensor. It's real simple: heat/age at the connector will give a really noisy signal that MS decoders have real trouble with and even factory ecu can't deal with all the time. Get rid of the factory connector and solder wires directly to the cam sensor (it's one bolt to remove) or solder a pigtail with a connector directly to the sensor with whatever three wire connector you want. Like this https://www.etsy.com/listing/1123863...m-angle-sensor

The issue was figured out years ago by the Spec Miata boys and posted on this website by a forum member which I can't remember but am eternally grateful to. I wish I could find that thread but my search skills suck.

Anyhow, I think this issue definitely deserves a sticky. A one post thread with the snip from the thread that had the SM solution would be all that's needed.

edit, so you get a better mental picture: From the SCCA/NASA rules, here is the relevant regulation.
SCCA 9.1.7.1.o.9/NASA 12.17.1: An electrical pigtail ranging from 3” to 6” in length and terminated with any 3 pin electrical connector may be soldered and potted to the OEM cam sensor for the purpose of correcting a known issue with the factory connection. The factory harness connector may be removed and replaced with the appropriate mating connector.

2nd edit: from mazdaracers where the SM boys do their thing https://mazdaracers.com/topic/5310-c...or-issues-fix/

 

this is the wiring