Nissan RB25 CAS, how can I help?

Testing and development of Megasquirt 3

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Nissan RB25 CAS, how can I help?

Postby fr0st » Mon May 23, 2011 2:22 am

My MS3 just arrived in preparation for my new engine, a dry sumped RB25/30 :yeah!:

My current RB20DET is on it's last legs but is still running so it should make a good test case. If I kill the engine in testing there won't be any tears, better this than the expensive forged one. I used to run a MS2 doing fuel only based on the one input from the CAS which worked perfectly.

The manual currently says
Cylinder phasing unknown and likely incorrect (easy fix).
Awaiting testing on an engine


What is involved in determining the phasing?
Is it just a case of determining if the firing order is correct and that the advance shown in MS is correct at the engine?

Happy to help in any way I can. I'd really like to see MS make a name for itself in the Skyline/Nissan community, I was planning on writing up my full install so other's can repeat the process.

Thanks
-Matt
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Re: Nissan RB25 CAS, how can I help?

Postby jsmcortina » Mon May 23, 2011 2:24 am

fr0st wrote:What is involved in determining the phasing?
Is it just a case of determining if the firing order is correct and that the advance shown in MS is correct at the engine?

Pretty much, yes.

So if you are able to try it out that would be great.

James
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Re: Nissan RB25 CAS, how can I help?

Postby Scabd » Thu Jun 02, 2011 11:14 pm

You will have to definitely have to keep this topic up to date. I've got a RB25 that I just got mounted into my car. I was going to go with a MS2 and run a crank trigger. If I was able to run a MS3 using the factory CAS, that would be awesome. I've been searching and waiting for someone to figure it out before I order a MS2 or MS3.
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Re: Nissan RB25 CAS, how can I help?

Postby jsmcortina » Sat Jun 04, 2011 10:14 am

Chicken and egg.

If everyone waits for somebody to try it, then nobody will ever have it!

James
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Re: Nissan RB25 CAS, how can I help?

Postby fr0st » Sun Jun 05, 2011 2:49 am

A bit of progress but not much unfortunately, I've been a bit low on free time to spend on the car

I've got the MS wired along side the standard ECU but I can't get any RPM reading when using the RB25 ignition setting. Initial problem was the VR circuit wouldn't trigger, I ended up shorting R47 to boost the gain of the VR transistor and turn it into a switch. After that the RPM is working correctly when in basic trigger mode. I did the same mod to the MS3X Cam VR circuit by shorting R37 and the composite log seems to be showing the CAS triggering fine but when in RB25 mode the RPM just sits at zero.

Any idea's?
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Re: Nissan RB25 CAS, how can I help?

Postby fr0st » Sun Jun 05, 2011 2:50 am

Attached Log
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Re: Nissan RB25 CAS, how can I help?

Postby jsmcortina » Sun Jun 05, 2011 3:52 am

That isn't the pattern I was expecting at all and there's no cam signal... confused.

The VR circuit ought to work ok - you did install the pullup resistor to 5V ?

James
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Re: Nissan RB25 CAS, how can I help?

Postby fr0st » Sun Jun 05, 2011 7:35 am

Hmm... must be something wrong with my wiring. I'll go over the cam input tomorrow and I should be able to get it sorted. Really wishing I didn't lose my oscilloscope when I moved house!

The pullup resistors aren't installed since the standard ECU has its own pullup. I'll have to put them in once that's removed but for now it should be ok without them installed.

Does the crank signal look fine?
The RPM with basic trigger seemed to be stable and I figured the pulse train was accurate since triggering on the rising edge gave a stable rpm and the trailing edge didn't (as expected since the slots change size depending on the position).
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Re: Nissan RB25 CAS, how can I help?

Postby jsmcortina » Sun Jun 05, 2011 7:49 am

The crank trigger isn't what I'm expecting. It is four pulses, gap, four pulses, repeat

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Re: Nissan RB25 CAS, how can I help?

Postby fr0st » Mon Jun 06, 2011 12:58 am

I had another crack at it today and I think I have some of my VR circuit issues sorted.

I measured the input to U7A at 0.8v when the opto input is 0v and ~5v when opto is 5v. I wound the hysteresis fully counter clockwise then set the offset at ~2.5v on pin 3 of U7A. Once I did that on the crank and cam I got the attached datalog.

I switched it over to the RB25 ignition mode and I got an RPM but when I revved above ~1300 rpm it would lose sync. There must still be a problem with my VR mod which is going to be a pain to troubleshoot without a scope, I'll fire up Orcad and do a sim to see if I can find the problem. I may be better off using something like a CMOS buffer IC instead of an opamp but I'll wait to see what the sim says.

I've attached the log since I wasn't able to tell if the crank or cam signal was the problem. My guess is the cam since its the high frequency signal, the RPM using basic trigger on the crank signal was stable up to 5k RPM last time I checked it.
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Re: Nissan RB25 CAS, how can I help?

Postby jsmcortina » Mon Jun 06, 2011 6:32 am

Please post some composite logs taken with "log crank and cam" ignition mode set. (Engine won't run.)
Due to the way the CAS360 decoders are written, the composite logger will not work normally otherwise.

James
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Re: Nissan RB25 CAS, how can I help?

Postby fr0st » Sun Jul 10, 2011 12:08 am

Massive apologies for the delay on getting you the logs, been working my ass off to get holiday and finish the car.

Attached are logs of the car running off the standard ECU and the MS3 logging only. First log is starting the car and letting it idle, second log is starting the car and revving to 2.5k rpm to show the signal when sync is lost.
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Re: Nissan RB25 CAS, how can I help?

Postby jsmcortina » Sun Jul 10, 2011 2:38 am

Looking at those logs I can see that the hi-resolution signal is dropping out - can you see that too? (big gaps in the green trace)

If you are able to work on that, it would be interesting - perhaps try turning R11 a little more clockwise ? If you have access to an oscilloscope that would be ideal to measure the signal from the hi-res sensor and the signal that is reaching the processor. (ask me)

James
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Re: Nissan RB25 CAS, how can I help?

Postby XR Pilot » Tue Jul 12, 2011 6:42 pm

Very keen to see how this pans out, as I have an engine I can use this on but not until towards the end of the year. Not sure if it is known or has been mentioned but once this code is solid it will be able to be used on any twin cam Nissan RB engine (RB20 red top, RB20 silver top DE/DET, R32 RB25DE, R33 RB25DE/DET, R34 RB25DE/DET, R34 RB20DE, RB26DETT from R32 through R34 era) not just RB25s. In addition, the quad cam VG V6 engines (VG30DE, VG30DETT) use the same CAS. I can confirm 100% that these CAS sensors all use the same trigger pattern as I have swapped CAS' and OEM ECU's amongst all the engines mentioned. Hope this helps.
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Re: Nissan RB25 CAS, how can I help?

Postby fr0st » Wed Jul 13, 2011 6:53 am

I haven't been able to stop the cam signal dropping out by adjusting the resistors on the ms3x. I haven't been able to check but I suspect the op amp or input transistor may be running out of bandwidth. My multimeter reports the cam signal is around 3kHz near idle so its possible.

I've visited my local electronics shop this afternoon and bought a Schmitt buffer IC to replaced the op amp buffer on the CAM input. IIRC when I put an oscilloscope on the 360 degree output a couple of years ago it was a near clean trace with no noticeable noise. The schmitt buffer should work perfectly and provide more than enough noise rejection if there is any. I'll fire it up tomorrow and let you know if it's fixed the dropping out issue, hopefully this will get it sorted!
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Re: Nissan RB25 CAS, how can I help?

Postby fr0st » Thu Jul 14, 2011 12:54 am

Schmitt trigger is in with some improvement. It now followed the revs right up to 4k rpm (didn't want to annoy the neighbours too much) but I'm seeing a lot of unsync problems that cause the RPM to glitch. The glitching is most noticable when blipping the throttle. The schmitt is powered from the VCC and GND test points on the ms3x. It inverts the CAM and CRANK signals and send them direct to the processor.

It seems to be worse at idle and cranking than 2k rpm so it might have something to do with my weak battery + alternator or grounding?
I get a bit of engine noise through my stereo but not a lot, the MS is grounded to the same point as the standard ECU. I'm not 100% sure if that's the issue so I thought I'd mention it anyway.

I've attached a crank/cam log using the schmitt circuit. The pulses seemed perfect when logging and didn't seem to change when blipping the throttle. Any ideas on where I go from here?
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Re: Nissan RB25 CAS, how can I help?

Postby jsmcortina » Mon Aug 01, 2011 4:01 pm

I've made some code changes for Optispark today that might help (or might break it!)
I also changed the hi-res input to use PT4 as I found the same as you did that that MS3X cam input is not designed for that fast a signal.

James
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Re: Nissan RB25 CAS, how can I help?

Postby fr0st » Thu Aug 04, 2011 2:50 am

Sounds good, thank you!
I'll give it a go as soon as the updated Alpha is out
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Re: Nissan RB25 CAS, how can I help?

Postby winstonusmc » Sun Aug 14, 2011 3:12 pm

I just assembled my MS3 and almost finished the patch harness for my RB25/26. Is it safe to say hook the 360 degree output to the PT4 instead of the Cam in? I also need to know if you all will let me help you test this on my engine? Its a daily driven RB26. I would like to help test if I could.
Nissan Skyline R34 RB26DETT ran MS3/MS3X w/ factory Hitachi CAS (sold)
Nissan Silvia S14 RB25DE ITB/NA ran MS3/MS3X w/ factory Mitsubishi CAS (disassembled)
Datsun 240z L28ET running MS3/MS3X full sequencial and COP w/ DIY trigger wheel
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Re: Nissan RB25 CAS, how can I help?

Postby jsmcortina » Sun Aug 14, 2011 3:17 pm

Testers welcome, but be prepared to tear a few hairs out in the process.

James
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