Megasquirt / Wideband issue - duff output.

[bertelli_1]

Just fitted a bigger turbo to my car & plugged in the laptop to retune it (not used the laptop for weeks). My afr flicked between 10:1 and 20:1 at idle, same when revved and driven around. The readings are the same when using both megasquirt & innovate sortware (they also use a different serial cable).
So I canged the sensor - same result.
So I changed the wiring loom - sane result.
So I plugged a handheld gauge into my sensor with its own power supply. This worked up to around 3.5k rpm under boost, then the afr goes off the scale lean although I think the sensor may be getting too hot (it takes a few seconds for the reading to get back to normal after coming off the throttle.

So I'm thinking I have a software issue but can it affect both megasquirt and innovate?? Any ideas welcome........

[GreenV8S]

Could it be an earthing issue? This would cause most trouble when using the analogue output (where the output voltage is offset from earth so any earth resistance result in duff results) but I suppose it could also throw the internal ACD out, maybe? I think the Megasquirt forum would be the ideal place to ask.

[Steve_D]

I spent ages chasing the same problem. Whilst mine turned out to be a defective LC-1 the main response I got from all manner of forums came back to the need for all earth's to be to the same point like a chassis rail but (and I still can't get my logic engine to handle this one) they must not all be on a single earth stud. I'm told something like a row of tapped holes with one wire to each is the way to go.

I used one of these with a big fat wire coming of and onto the chassis.

Seems to work fine.


Steve

[GreenV8S]

Steve_D said:

I spent ages chasing the same problem. Whilst mine turned out to be a defective LC-1 the main response I got from all manner of forums came back to the need for all earth's to be to the same point like a chassis rail but (and I still can't get my logic engine to handle this one) they must not all be on a single earth stud. I'm told something like a row of tapped holes with one wire to each is the way to go.

I used one of these with a big fat wire coming of and onto the chassis.

Seems to work fine.


Steve

I can only guess that having a stack of connectors onto a common stud causes the load to pass through several 'layers' of connectors before reaching the ground point, so the voltage difference would be cumulative as you work your way up the 'stack' of connectors. My loom earths the wideband controller to the ECU and then the ECU earth carries on to vehicle ground, so even if the ground is imperfect at least the lambda controller and ECU will agree about it.

[bertelli_1]

My ecu and lambda earths are in the same place, all on 1 stud. If it is an earth fault its odd that I've never had a problem before - the wiring has not changed.

Edit: when I fitted the new loom I earthed it straight to the battery, not the common earth point & the problem persisted.

Edited by bertelli_1 on Monday 30th June 20:03

[GreenV8S]

Two stray thoughts - both could be rubbish:

If it's overheating, fit a heat sink. (It's a known problem, I believe.)

I have an idea that the sensors might be sensitive to back pressure. Don't recall anyone ever saying they are, but they do include a gas pump and it's the sort of thing that seems possible to me. Could it be picking up pressure pulses, or turbo back pressure, or something?

Edited by GreenV8S on Monday 30th June 20:12

[bertelli_1]

GreenV8S said:

Two stray thoughts - both could be rubbish:

If it's overheating, fit a heat sink. (It's a known problem, I believe.)

I have an idea that the sensors might be sensitive to back pressure. Don't recall anyone ever saying they are, but they do include a gas pump and it's the sort of thing that seems possible to me. Could it be picking up pressure pulses, or turbo back pressure, or something?

Edited by GreenV8S on Monday 30th June 20:12

There may be an overheating issue but don't see how it would cause a problem at idle on a cold engine.

The same applies for back pressure - off boost the exhaust will cope with a slightly bigger turbo.

I'm not discounting these ideas but the random earth fault seems more likely.

[Mr2Mike]

GreenV8S said:

I have an idea that the sensors might be sensitive to back pressure. Don't recall anyone ever saying they are, but they do include a gas pump and it's the sort of thing that seems possible to me. Could it be picking up pressure pulses, or turbo back pressure, or something?

They are somewhat sensitive to back pressure as you say, but the symptoms are increasing inaccuracy as you move away from stoichiometric. At ~14.7:1 they are much less sensitive.