car does not start sporadically - MR2 SW20 3S-GTE - G4X Plug-in

[ChrisUR]

Hi,

we struggle with a weird problem for some weeks now and cannot find the issue.

The car is a Toyota MR2 SW20 Turbo with 3S-GTE engine - it is running a G4X Plug-in and a RacerX Trigger Kit (36-1 crank and 1 cam, fully sequential)

Sporadically the car simply does not start - it turns the starter, the ECU is showing both triggers as active and there is a RPM. We tried to bridge the ignition and injection relay to exclude an electrical problem to the coils or injectors.

We ran several logs, it is showing all vital parameters as far as I can see, it builds up fuel pressure etc.

The weird thing is that sometimes the cars starts on the first try, sometimes it starts like 6 times in a row but then out of a sudden it does not start. When it is starting it is running perfectly well, does not die and does not have any trigger errors or other issues. But when it does not start it doesnt matter how long you turn the starter, it is not firing up at all.

I suspect it has something to do with the trigger but cannot find the mistake we are making here. The only thing I found is that on a similar car (running the same triggers but a G4+) the Trigger 1 is set to "sync mode cam trigger 1x" - if I dial that setting in for the G4X car it does not start at all - never.

So my idea is that the car can't sync between cam and crank so doesnt know in which stroke it is - sometimes it is in the right stroke and starts and sometimes it s in the wrong stroke. That said my understanding is obviously too limited to understand why this happens here. I played around with the edge of Trigger 2 (set it to rising, changed to falling - makes no difference) - I also played with the sync tooth (it was set to 1, changed it to 3 - makes no difference).

We made a trigger scope and a log when the car doesn't start and also when it does start. I looked at the Trigger scope but it looks quite similar in both cases - maybe I'm missing something here ?

This issues is driving us nuts, so I really hope you have an idea or see the issues out of the logs !

Thank you,
Christian

PC Datalog - no start.llgx PC Datalog - Log no start.llgx Trigger Scope - 2023-11-3 2;18;51 - start.llgx Trigger Scope - 2023-11-3 2;18;51 - no start.llgx Toyota-MR2-3S-GTE 430HP.pclx

[ChrisUR]

We have worked out the following so far:
- with Trigger 2 Falling it seems to start better/more reliably
- we then set Sync Cam Pulse 1x
- with Sync Tooth 1 it doesn't start at all
- with Sync Tooth 2-8 it doesn't start either, from Tooth 9 it starts, but not always
- We then set the Sync Tooth to 10,11 and 12, so it often starts, but not always

Summary for today:
- for the first time ever you can now (sometimes) start it with Cam Pulse Sync activated, which was never possible before
- When it starts, it runs as smoothly as butter
- you can also tell that it now takes a little more time to start because it does the sync (when it starts)
- unfortunately it still only starts cleanly a few times and then sometimes not at all

In the end, you can finally start it with Cam Sync switched on, but it hasn't changed the overall result, it still doesn't start 100% reliable.

[keizsr]

Hello, when it is difficult to start, there are times when you turn the ignition switch off and then on and it starts normally with cranking.When you look at the log, after you cannot start with cranking, the dwell time remains at 7.7.In this case, turn the ignition switch off and then turn it on. Then it seems to change to the set value. I have a similar experience, but I don't know the cause. It happens suddenly.
This is my experience and may not be correct.

[Adamw]

Sync mode needs to be set to Cam pulse 1X.  Sync tooth 1, falling edge for both trig 1 & 2.  Change the trigger offset by 360 if it doesnt start with those changes.  Base timing will need to be checked again after changing trig 1 edge.

Will need a fresh log if it still doesnt start reliably with those settings.  

 

  

[ChrisUR]

Adam,

you are such an expert - awesome reply ! Tried it today, first put all Triggers to Falling, did not work, then switched from -353 to 7 offset and it started right away. Tested it for like 7 attempts in a row and it started perfectly (sometimes sooner, sometimes later, but catched up always finally).

So I guess my problem is solved :-)

Just for my learning, how did you find that the trigger has to be set to falling and why did it work with -353 before and needed to be turned around 360degrees ?

Thank you so much !

Christian

Toyota-MR2-3S-GTE 430HP.pclx PC Datalog - both triggers falling - cam pulse 1x - offset 7 - started 7 times in a row.llgx PC Datalog - both triggers falling - cam pulse 1x - offset 5 - started 1st attempt.llgx Scope 3 - both triggers falling - cam pulse 1x - offset 7 - started.llgx Scope 2 - both triggers falling - cam pulse 1x - offset -353 - no start.llgx Scope - both triggers falling - cam pulse 1x - offset -353 - no start.llgx PC Datalog - both triggers falling - cam pulse 1x - offset -353 - 5 attempts no start.llgx

[Adamw]

The fact you said it wouldnt start when you turned on sync suggested it was syncing on the wrong stroke, so changing offset by 360 corrects that.  Shifting the sync tooth past the cam edge position would effectively acheive the same thing so your observation that sync tooth >9 worked confirms that.  

Sync tooth 1 is always preferable as that means it is performing its sync test as early as possible (slighty quicker start), so it is better to adjust the offset rather than sync tooth when you are 360 out.  

Either edge would work in theory, but the fall time is about 1/10 of the rise time on the ZF sensors so you will get slightly more accurate timing using falling edge.  

 

On 11/4/2023 at 11:04 AM, ChrisUR said:

We then set the Sync Tooth to 10,11 and 12, so it often starts, but not always

This comment suggests that the offset may not be your only problem, so you may still have another tune related issue, but time will tell.    

[ChrisUR]

thank you so much - lesson learned :-)