Megasquirt and lambda question

sowen · Post by **sowen** » Thu Oct 30, 2014 5:34 pm

I've got myself a MS2 kit from ExtraEFI for my SD1

I also have an AEM wideband lambda sensor fitted to one of my other cars which I think is suitable to work with the Megasquirt.

Question is, how well does a single lambda work on a V8 with two downpipes? I have the standard front section of exhaust on my SD1 V8, which is 4-2 cast manifolds, then 2-1 downpipes either side before the collector. I know the Land Rover's had a pair of narrowband Lambda's a bit further back after the last collector on the downpipes so that would be the obvious place to put my one. Is it a good idea to fit a bungs into each side to swap the probe over just to check both sides are running the same?

I've read on someone who's done a number of Megasquirt conversions in the past who's fitted the ecu but only run the ignition side of it using the Megasquirt to datalog the existing fuel system with a wideband lambda before going full MS. Once the tuning is done, is the wideband lambda necessary or adviseable to keep, is it worth swapping in a pair of narrowband sensors or is that a stupid idea which simply won't work or offers no benefits?

Any other advice for a newbie to full engine management? I've had Megajolt in he past so have a basic grasp of how to make things difficult for myself! I've started reading the manuals supplied with the kit and it kinda makes sense without actually having the stuff powered up infront of me, just wondering on some of the specific aspects of fitting MS to a RV8 using a hotwire manifold

DaveEFI · Post by **DaveEFI** » Thu Oct 30, 2014 5:48 pm

A narrow band O2 sensor is only of much use if you intend running at stoichiometric.

JSF55 · Post by **JSF55** » Thu Oct 30, 2014 5:52 pm

Knock Tec ? is that for knock detection ? if so how much and from where ?

sowen · Post by **sowen** » Thu Oct 30, 2014 5:55 pm

In theory if the wideband can help define the fuel map, then running on the fuel map should in theory match the lambda readings, in theory. If that theory is reasonable, then there would be no need to go narrowband, and I could remove the lambda kit altogether. Not having any practical experience on this I really don't know...

sowen · Post by **sowen** » Thu Oct 30, 2014 5:59 pm

JSF55 wrote:Knock Tec ? is that for knock detection ? if so how much and from where ?

It came from here via ExtraEFI

http://www.ms2tuning.com/products.html

The P38 block I have has a pair of knock sensors fitted, after my previous attempt with forced induction on a 4 pot, I want to have some proper knock detection rather than listening with my ears![/url]

JSF55 · Post by **JSF55** » Thu Oct 30, 2014 6:42 pm

Thanks for that, been looking at more expensive kits, but hopefully I can tie that into my megajolt

JSF55 · Post by **JSF55** » Thu Oct 30, 2014 11:20 pm

Found my earlier attempt at fitting an O2 sensor, if I had read the instructions first I would have rotated it further up and saved killing sensors. This is for my Inovate MTX I run for tuning I found it worked fine

Picture 001 by jsf55 pics, on Flickr

sowen · Post by **sowen** » Fri Oct 31, 2014 8:51 am

I'm sure on reading the instructions they are meant to be sat a certain distance from the engine, but if fitting at the y-piece under the exhaust works then that could work well for ease of installation. The downpipes need to come off to sort out a blow so may have a chance tomorrow if all goes well

DaveEFI · Post by **DaveEFI** » Fri Oct 31, 2014 9:32 am

MS allows you to compensate for the distance the sensor is from the engine. Obviously in an ideal world, the distance from each exhaust valve to the sensor would be constant. But few things are ideal.

By doing a log, you can work out how long the sensor takes to show a change in the mixture. Although measuring the distance gives a good starting point.

sowen · Post by **sowen** » Fri Oct 31, 2014 10:51 am

I think the SD1 standard exhaust should be fairly equal, so if that's the case then I'll try and weld a bung into the y-piece and make a start datalogging the existing setup. That would leave re-mounting the coilpacks and routing the wiring for the EDIS to them, and routing the EDIS back to the dashboard where I'll mount the MS ecu.

For the purposes of getting some baseline readings, I guess I only need to start by connecting a manifold pressure source and lambda to the MS ecu, which with the crankshaft trigger will be enough to run the EDIS and give a fairly definitive view of what's going on in the normal driving environment

DaveEFI · Post by **DaveEFI** » Fri Oct 31, 2014 11:16 am

My wideband sensor is mounted after the pipes join, and the cable routed upwards through the transmission tunnel under the ashtray - then routed along inside the tunnel consul to its ECU. I made a plate to replace the original Lucas ECU and there's room there for the MS, O2 ECU and knock sensor ECU.

Do be careful positioning the sensor as the seat mountings can foul it - if you're as unlucky as me.

sowen · Post by **sowen** » Fri Oct 31, 2014 11:58 am

I've been there before, welded stuff in place only to find fitting/removal is impossible without drastic disassembly!

So simply fitting a single sensor at the y-piece shouldn't cause any issues and is a sensible option

DaveEFI · Post by **DaveEFI** » Fri Oct 31, 2014 12:54 pm

With injection, there's no real reason why one bank should be different to the other. But ideally, you'd have one sensor per cylinder.

sowen · Post by **sowen** » Fri Oct 31, 2014 1:01 pm

I used to work on Cessna 182 light aircraft, the latest ones had CHT and EGT for each of the six cylinders, great for making people paranoid of the different readings each one was giving!

Baracus · Post by **Baracus** » Fri Oct 31, 2014 2:06 pm

I left my wideband in situ on the TVR because;

A) you can have the megasquirt run in closed loop mode under cruising conditions, always trimming to your target value which is good for economy.

B) i'm never done tuning the god damn thing due to cam swaps, big valve heads etc, the hunt for more power never ends!

I welded a bung into both down pipes but only tune on one, then do a quick swap of the sensor to the other bank for a quick check to see if AFRs are in the same ballpark.