Noisy tach signal coming from 4AGE VAST ignition setup

[aw1234dude]

I've been searching alot on this forum and have seen people with similar problems as me but no real explanation or final solution. I am currently running MS1 V3.0 with megasquirt n spark on my 4AGE with the stock VAST ignition system. I have followed all the wiring and modifications found on this web page (http://www.diyautotune.com/tech_article ... ta_mr2.htm).

I am getting alot of noise in my RPM signal and I'm getting spikes in my RPM every couple seconds while driving. I can have the throttle very steady so I will only be using on or two bins in the VE table and the car will surge and lean out randomly then go back to normal as if nothing happened. I have grounded all grounds to a single chassis ground. I am thinking about running shielded wiring directly from the ignitor to the harness adapter I made to try to shield it from any interference.

I have attached a log and the .msq
If anyone that has had similar problems and any ideas please help!

[aw1234dude]

So I ran shielded wire from the ignitor signal to my megasquirt and I am still having bad idle and hesitation throughout. I also plugged the stock computer back in to see if it had the same stumbling problem and it didnt. It ran as though it was stock eventhough the car still had the larger injectors in place.

[thechuckster]

you want to make sure you've earthed the shield at one end only?

and the ground at the dizzi is grounded at the adaptor (as you've not got the factory ECU to do that for you?

[dcg9381]

I'm dealing with something simliar on a 22RE - I get spikes in the factory tach.. Megasquirt RPM seems to be fine, although I keep having turbo issues that keep me from really chasing it.

What's odd:
I did the same vehicle twice. Two different motors.
Same megasquirt. *slightly* different harnesses (one uses a wideband and GM IAT).

The second implementation has tach noise. What I mean by that is that I get a "floating" tach ocassionally - usually when the truck has been warmed up for a while. It will float up to 2-3k and then the additional RPM seems to be added to that base.

Megasquirt is grounded the same way on both implementations.. I've tried unplugging darn near everything and still have this issue. The tach is signaled from the ignitor itself.. There must be noise in that signal or perhaps a bit of a floating ground, I think it takes a decent amount of voltage to get the tach to register...

Will work on it more once I get a new turbo on...

[dcg9381]

Well, I thought I had this licked, but it's happening again.
One data point is that at 2700 RPM (megasquirt), I'm indicating 4000 rpm on the tach. That's a factor of 1.48, darn close to 1.5... which is hmmm..

It seems that I'm actually triggering the coil MS rpm x 1.5, which isn't good.. I verified this via a coil triggered tach.

I tried replacing the inductive pickup on the distributor, same result and actually reproduced it with another distributor on the end of a drill.
Grounding the distributor directly to the battery - no difference.

Noise isn't always there, but it does seem to be "on" or "off" - can't find anything that corresonds to the difference.

I guess I'm back to scoping signals as soon as my oscilliscope probes arrive...

[dcg9381]

More info - still haven't licked this problem yet:


I've got an old school analog diagnostic tool that does RPM and dwell. You know, some of that pre-EFI stuff that sits around in the garage.
It's setup for an 8 cylinder. There's an indication that we should take the 8 cylinder reading and double it, which I'm ignoring .

I have a 4cylinder engine. I'm assuming that my distributor turns 360 degrees per every 2 engine rotations.

So, the timing of ignition pulses should be:

1000 crank RPM = 500 distributor RPM = 4 pulses per distributor revolution = 2000 pulses per minute = .030 pulses/sec = 30 ms between pulses

2000 crank RPM = 15 ms between spark pulses

3000 crank RPM = 10 ms between spark pulses


Again,
Megasquirt indicates 1000 rpm.
The engine is at 1000 rpm.
OEM tach indicates 1500 rpm
Diagnostic tool indicates 1500 rpm (8 cyl reading)
Scope, as I read it, indicates 30 ms between charge / discharge (spark?) - which should be 1000 rpm by my math.

What am I missing? Is there something I don't understand about reading the coil on the oscilliscope?

Megasquirt RPM:
http://lakebox.dnsalias.com/photos/1988 ... /msrpm.jpg

OEM Tach:
http://lakebox.dnsalias.com/photos/1988 ... 500rpm.jpg

Diagnostic tool:
http://lakebox.dnsalias.com/photos/1988 ... C06129.JPG

Oscilliscope, looks like 30ms between pulses:
http://lakebox.dnsalias.com/photos/1988 ... esat1k.jpg



More confusion - so maybe someone can straighten me out here.




Again,
Megasquirt indicates 1000 rpm.
The engine is at 1000 rpm.
OEM tach indicates 1500 rpm
Diagnostic tool indicates 1500 rpm (8 cyl reading)
Scope, as I read it, indicates 30 ms between charge / discharge (spark?) - which should be 1000 rpm by my math.

What am I missing?

Megasquirt shows 1000 rpm:


OEM Tach shows 1500 rpm:


Diagnostic tool shows 1500 rpm:


Oscilloscope, looks like 30ms between pulses at the coil - but reading the coil is a bit funky. maybe someone can help here?
http://lakebox.dnsalias.com/photos/1988 ... esat1k.jpg

VAST system diagram for reference:




Oscilloscope of VAST NE, it should be noted that this is actually a 5v to 2v.
Ignition on, we're at 5v, triggering to 2v. Not a 12v like the VAST diagram above indicates.. Maybe this is goofy on the 4runner or otherwise impacted by being connected to megasquirt? Again, 30ms pulses on the dot - indicating 1000 rpm.

http://lakebox.dnsalias.com/photos/1988 ... signal.jpg


Oscilloscope of VAST IGt. I expected this to be a bit dirty, but it looks pretty square to me. If I should up the resolution on this to look at the wave itself, let me know. It ends up being a 3v square wave when it should be 4v (per testing the OEM) - I think we need to adjust that pull up resistor in the VAST docs again.. Note, I also checked to see if dwell was working, worked great. Again, solid 30ms between pulses.

http://lakebox.dnsalias.com/photos/1988 ... signal.jpg


So, why does my diagnostic pickup on the tach AND my oem TACH think I'm getting 1500 rpm? There has to be a simple answer here somewhere....


Additional info:
scoped the tach input.
It appears to be a 30v square wave. The wave isn't terribly clean, I'll let you guys have a look, but frequency as I read it at the scope is the same as megasquirt ignition in/out, meaning at 1000rpm, I see a waveform ever 30ms.

This is 5ms/div, 10v/div:
http://lakebox.dnsalias.com/photos/1988 ... sig5ms.jpg

Closer look, 1ms/div 10v/div:
http://lakebox.dnsalias.com/photos/1988 ... ign1ms.jpg

[stealthiskey]

Has anyone ever figured this out? Currently have the same problem on corolla with 4age. OEM tach seems to read almost 2x what the engine is actually running after connecting the MS2 ECU. Used to work fine on the OEM ECU.

[Matt Cramer]

Has anyone ever figured this out? Currently have the same problem on corolla with 4age. OEM tach seems to read almost 2x what the engine is actually running after connecting the MS2 ECU. Used to work fine on the OEM ECU.

What are you using for an ignition on this car, and how is your tach wired up?

[stealthiskey]

The way I set it up, basically following the JamesL article and the diyautotune link "option C", MSII PCB3.0.

http://www.diyautotune.com/tech_article ... rt_122.htm
http://www.diyautotune.com/tech_article ... ta_mr2.htm

In short using the VAST ignition system and feeding the NE signal to the MS2 opto input. Had to fine tune a pull up resistor there, I think I might have settled with 2k ohm.

MS2 ECU plugs in to the stock harness connectors. Made a short jumper adapter to plug in to the stock conenctors with a DB37 on the MS2 side. Never did anything with the stock tach connection. Assume it is spliced into the NE signal just before the OEM connectors.

[Matt Cramer]

In that case, the tach should be triggered from the VAST module.