WRX9X Trigger Inquiry/Discussion

[Arktikpenguin]

Hey guys, I just wanted to pick your brain really quickly about an issue and otherwise confusing situation with my triggering on my engine.

 

For context, I own a 2002 Impreza WRX fitted with a built EJ257 utilizing the EJ20 sensors (V7-10 JDM). For around 3000 miles, I drove my car and had 2 minor issues. One was what I believe to be a slight misfire at cruise, and the other was sometimes long cranking/multiple cranks to start the car when it otherwise started just fine on the same map the previous day and would shoot gunshots out of the exhaust. I figured maybe it's my fueling at crank!

Recently I found that my tensioner seized, caused the crank to jump 5-6 teeth, and ultimately ended in some Piston to Valve contact. Before I did verify all this, I pulled a triggerscope of the car and noticed it didn't seem muddled, but thought maybe I have a trigger issue. I then stumbled upon a thread of a not so happy camper. 

Now, I was not thinking this was an issue with my ECU, but likely an issue with the Adjustable Cam Gears I had been provided by Tomioka Racing. After reading the thread below, I noticed that I had the exact same issue as this user. My crank reading was V7-10, my cam reading was V1-6. Wtf?

When Tomioka originally released their gears, they had 1998 and older gears, and a claimed 1999+ cam gear set. I jump to their website and find.... in 2023 they now added a separate 2001-2003 Cam Gear with 2 teeth for the trigger, and 1999+ are 7 teeth for the trigger. I have the wrong gears as I ordered my set in mid 2022. I never thought anything of checking the cam gear as 1999+ = 2 teeth (as I incorrectly thought).

After reading the thread below, I also see trigger 2 should be set to Reluctor. My car shouldn't even be running well or at all with Trigger 2 set to V7-10 and a Reluctor due to the incorrect cam gear, but it ran fine. I checked my Trigger 2 and found it is set to Optical/Hall and using a Rising Active Edge with a Pull-Up set to ON. I would normally see about 2 trigger errors in a 30 minute drive on Trigger 1, but I cannot log Trigger 2 error counters.

My question is, how the heck was my car running decently with the trigger setup for Trigger 2 being so incorrect? Was the ECU potentially ignoring the Cam sensor and just trusting the crank itself at this point (even with timing), or is there something I'm overlooking? The cam gears as far as I know don't even have close to identical spacing for engine timing.

FWIW, I have the correct cam gear now so it's not an issue to me.

 

[semih]

if you have my99 cam gears(7 teeth), you have to use my99 crank sprocket  

later engines have 2 teeth cam gears and different crank sprocket

[Adamw]

With a missing tooth crank wheel, all of the engine control is done from the crank wheel, the cam is only used to determine the correct phase during initial start up, once running it will only look at the cam to resync if there is an issue with the crank signal.  

With your trigger 2 set to optical/hall and the wrong tooth count cam wheel, it would mean the ecu would occasionally sync on the wrong phase during cranking so it just wouldnt start.  Basically you have a 50/50 chance of syncing correctly so it would probably start normally about 50% of attempts and other times it would just crank with no signs of life or possibly the odd backfire.  It shouldn't cause any issues when running.  

 

[remski2]

Out of curiosity.. why would you put EJ20 sensors on a EJ257 ?

[Arktikpenguin]

On 11/1/2023 at 7:35 AM, Adamw said:

With a missing tooth crank wheel, all of the engine control is done from the crank wheel, the cam is only used to determine the correct phase during initial start up, once running it will only look at the cam to resync if there is an issue with the crank signal.  

With your trigger 2 set to optical/hall and the wrong tooth count cam wheel, it would mean the ecu would occasionally sync on the wrong phase during cranking so it just wouldnt start.  Basically you have a 50/50 chance of syncing correctly so it would probably start normally about 50% of attempts and other times it would just crank with no signs of life or possibly the odd backfire.  It shouldn't cause any issues when running.  

 

This would make sense completely, and is exactly what I thought would happen. My car would start about 50% of attempts immediately, or would crank over with no signs of starting ever, and occasionally a large backfire out of the exhaust.

On 11/1/2023 at 3:38 PM, remski2 said:

Out of curiosity.. why would you put EJ20 sensors on a EJ257 ?

Sorry, forgot to mention I'm using S20 Ej205 heads chamber matched to an EJ257. My 02 wrx originally came with an EJ20, but I'm pretty sure EJ205/255/257 all use the same crank pulley up to a point. S20 heads being the USDM EJ205 heads, have no spot for rear mounted cam sensors in the heads. As far as I'm aware, if I wanted to easily use Ej257 sensors for the cams (with B25/V25 Heads) I'd have to modify my harness significantly. Even with B25/V25 heads, I'd have Ej205 cams and cam gears and use the 2.0 Cam sensor as that is what works best.