zammobhoy
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| posted on 26/8/15 at 12:26 PM |
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Megasquirt wandering AFR
Hi,
Struggling to get stable AFR for IVA emissions. Got a new-built Westfield with standard 1.8 blacktop zetec and MS2 V3 installed. Engine idles great at
12:1 AFR but gets lumpy when I start to lean the mixture off towards 14.7:1. I took a datalog yesterday for the first time and it looks incredibly
spikey. Appreciate anybody with any ideas as to what could be causing this noise? Screengrab below
Cheers,
Paul.
 
Wandering AFR
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MikeRJ
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| posted on 26/8/15 at 01:14 PM |
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The MAP signal looks ridiculously noisy. Are you trying to run a speed-density algorithm on individual throttle bodies?
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coyoteboy
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| posted on 26/8/15 at 04:07 PM |
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Most of your sensor signals are looking unusually spikey to be honest, thought it's hard to tell for sure at that size of image.
It doesn't drift to lean and misfire as the MAT temps go up does it?
Many lower compression engines won't run idle at 14.7:1 unless you get the timing bang on, but with that much noise on the lines you're
fighting an uphill battle anyway. Which grounding scheme have you followed? Can you draw a diagram of each and every contact point for each sensor and
ECU? I also found the LC-1 heater drive causes massive noise if grounded to the same as ANYTHING else lol - it's a big switchmode supply
generating spikes galore.
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SPYDER
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| posted on 27/8/15 at 09:00 AM |
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Hi Paul. The V3 mainboard should have a dedicated sensor earth return pin to which ALL your sensors must be grounded. Mine is a green/yellow wire
IIRC.
My wideband has a main (chassis) earth for the heater circuit and a separate sensor earth to the ECU.
The ECU grounds (black wires) should be earthed at the same spot on the engine block or head.
Lots of info on the net ( and in the manual ) about this critical and often troublesome issue.
I had problems with ECU resets caused by electrical noise which turned out partly to be from failing alternator diodes which I replaced. I also
fitted new braided earth straps to both engine and battery negative terminal. I fitted noise suppressors to alternator and fuel pump as well as
fitting those little clip-on ferrite suppressors to the injector and coil wires. Sorted.
I never had spiky plots like yours though. Even your battV is jumping about.
Get your grounding scheme looked at first. Check engine earth strap. Remove it, clean and replace.
Check battery terminals. I'd try a quick log with the alternator disconnected too. Disconnect it BEFORE starting car, NOT whilst running.
Noise can be picked up from adjacent wires too. Look for ECU supply wire or sensor wires being near to coil or injector wiring.
The screening on the VR sensor wire should only be grounded at one end too.
The list seems endless.
Do a log (ha-ha) each time you change anything.
Edited to add: Some wiring diagrams on the net for the V3 board show a separate sensor earth connection, pin 7.
Some do not.
[Edited on 27/8/15 by SPYDER]
[Edited on 27/8/15 by SPYDER]
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coyoteboy
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| posted on 27/8/15 at 11:42 AM |
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quote:
Originally posted by SPYDER
Do a log (ha-ha) each time you change anything.
This is genuinely about the first time this year I've actually laughed out loud at something online.
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britishtrident
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| posted on 27/8/15 at 12:15 PM |
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quote:
Originally posted by SPYDER
Hi Paul. The V3 mainboard should have a dedicated sensor earth return pin to which ALL your sensors must be grounded. Mine is a green/yellow wire
IIRC.
My wideband has a main (chassis) earth for the heater circuit and a separate sensor earth to the ECU.
The ECU grounds (black wires) should be earthed at the same spot on the engine block or head.
Lots of info on the net ( and in the manual ) about this critical and often troublesome issue.
I had problems with ECU resets caused by electrical noise which turned out partly to be from failing alternator diodes which I replaced. I also
fitted new braided earth straps to both engine and battery negative terminal. I fitted noise suppressors to alternator and fuel pump as well as
fitting those little clip-on ferrite suppressors to the injector and coil wires. Sorted.
I never had spiky plots like yours though. Even your battV is jumping about.
Get your grounding scheme looked at first. Check engine earth strap. Remove it, clean and replace.
Check battery terminals. I'd try a quick log with the alternator disconnected too. Disconnect it BEFORE starting car, NOT whilst running.
Noise can be picked up from adjacent wires too. Look for ECU supply wire or sensor wires being near to coil or injector wiring.
The screening on the VR sensor wire should only be grounded at one end too.
The list seems endless.
Do a log (ha-ha) each time you change anything.
Edited to add: Some wiring diagrams on the net for the V3 board show a separate sensor earth connection, pin 7.
Some do not.
[Edited on 27/8/15 by SPYDER]
[Edited on 27/8/15 by SPYDER]
After watching Youtube videos I used an oscilloscope + DC current clamp to look for noise on alternator output I was surprised how good it was
for spotting alternators on the way out.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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zammobhoy
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| posted on 27/8/15 at 03:08 PM |
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Thanks for all your replies guys, much appreciated.
In a way it's good to know that the logs look bad in comparison to what you guys have seen before, makes me think that when I get the noise
sorted, the car will run well - it honestly does not run badly considering the mess that is the datalog 
I've got a list of things to go through now.
Separate earth for LC1
Separate return wires for input sensors
Scope alternator output for noise
MS already has numerous grounds to cylinder block
Fix ECU power take-off, currently same as injectors (oops)
After that I might look at suppressors and in-line chokes
I'll keep y'all posted
Paul
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