The V8 Owners Forum -

Ah -sorry. My impression was it's a new installation.

Thanks for the explanation Stevie - So we are ignoring the units on the table and the values just represent are the 0-100% inputs from the MAF which has been plugged into the MAP input on the Omex.

So change KPa for the air mass input and we are all good assuming that the the output from the MAF has the same characteristic curve as the MAP or that parameters have been/can be made to make the input curves comparable. Sensor Setup - Conditions Corrections

What confuses me is the OP's mention that reconnecting dizzy improves the performance ! - If the dizzy is mechanically locked which it would need to be with the Omex - what is happening to give better performance with a fixed timing.

MAF signal also shared with the CUX14? I am assuming again - which always concerns me as to where the refernce voltage is being fed from.

Darkspeed wrote:Thanks for the explanation Stevie - So we are ignoring the units on the table and the values just represent are the 0-100% inputs from the MAF which has been plugged into the MAP input on the Omex.

So change KPa for the air mass input and we are all good assuming that the the output from the MAF has the same characteristic curve as the MAP or that parameters have been/can be made to make the input curves comparable. Sensor Setup - Conditions Corrections

What confuses me is the OP's mention that reconnecting dizzy improves the performance ! - If the dizzy is mechanically locked which it would need to be with the Omex - what is happening to give better performance with a fixed timing.

MAF signal also shared with the CUX14? I am assuming again - which always concerns me as to where the refernce voltage is being fed from.

Obviously we dont want to ignore the units, and we want them to all be correct...but it doesnt mean they have to be, and sometimes installers can do strange things either deliberately ( say because of system limitations ), or though lack of knowledge....sadly the latter is more common lol.

As for the dizzy....again, we dont really know how any of this system is installed, so we can only speculate as to how it should work...if installed correctly.

Is it using a crank trigger for timing, or is it using the dizzy as the trigger ? It could be either, and if the latter yes it "should" be locked...but it may not be.

Again, lots of unknowns.

And isnt this the same car someone was asking a few weeks or months ago, where they believed the engine had detonation or something ?

Apologies for the late reply and many thanks for the responses so far.
The Omex uses a trigger wheel from the crank. The distributor is not locked and is only used as a pointing devise to send the spark to the correct piston.
The reason for not locking it is to help align the rotar arm to the correct piston pin and helps stop cross Pin firing. ( as the Omex advances the timing the Vacuum or mechanical advance in the dizzy moves the advances the rotor tip closer to the correct piston Pin )
Yes I am still getting detonation but I am getting close to resolving this now.
The MAF set up is not working correctly probably down to set up. Due to the lack of advance especially at cruise speeds I am seeing high engine temperatures.
I have ordered a MAP sensor now for the Omex and will be having this set up on a RR soon so hopefully I can finally get this sorted and maybe even find out what sort of power I am getting.
Cheers

gilps wrote:The distributor is not locked and is only used as a pointing devise to send the spark to the correct piston.
The reason for not locking it is to help align the rotar arm to the correct piston pin and helps stop cross Pin firing

Are you sure that leaving the all the mechanical advance mechanism in and working actually achieves that? - Every car that uses an ECU for timing and a distributor that I have come across uses a fixed arm. Pretty sure that fixed datum is important. Just trying to get my head around what would happen if the dizzy is moving in relation to the crank trigger point whilst the ECU is advancing the spark.

As you need a good spark with a boosted engine having the rotor and pin aligned as well as possible seems essential and I dont think you get that with a rotor arm advancing and the ECU advancing.

Darkspeed wrote:

gilps wrote:The distributor is not locked and is only used as a pointing devise to send the spark to the correct piston.
The reason for not locking it is to help align the rotar arm to the correct piston pin and helps stop cross Pin firing

Are you sure that leaving the all the mechanical advance mechanism in and working actually achieves that? - Every car that uses an ECU for timing and a distributor that I have come across uses a fixed arm. Pretty sure that fixed datum is important. Just trying to get my head around what would happen if the dizzy is moving in relation to the crank trigger point whilst the ECU is advancing the spark.

As you need a good spark with a boosted engine having the rotor and pin aligned as well as possible seems essential and I dont think you get that with a rotor arm advancing and the ECU advancing.

True, align the rotor to cap posts as best as possible and lock it there. There is no need for the advance mech at all.

I'm a little confused now what is best, I asked the question about locking the distributor when I was fitting the Omex and was told not to, he explained the reason why which seemed to make sense. This is roughly what he said.
Firstly you need the original set up to work to set the Omex up so the original set up is never taken off and if there is ever a fault with any part of the Omex you have a back up ignition source by simply swapping two wires on the coil.

Secondly if you lock the distributor at a given point let's say rotar pointing to its pin on the dizzy cap at 15deg BTDC it will always be the same. So criusing with an advance of 38deg the rotor will be 23 deg away from its pin.

I am no expert so if this is wrong I would be very interested in what is best.

Thanks Guys
Chris

gilps wrote:I'm a little confused now what is best, I asked the question about locking the distributor when I was fitting the Omex and was told not to, he explained the reason why which seemed to make sense. This is roughly what he said.
Firstly you need the original set up to work to set the Omex up so the original set up is never taken off and if there is ever a fault with any part of the Omex you have a back up ignition source by simply swapping two wires on the coil.

Secondly if you lock the distributor at a given point let's say rotar pointing to its pin on the dizzy cap at 15deg BTDC it will always be the same. So criusing with an advance of 38deg the rotor will be 23 deg away from its pin.

I am no expert so if this is wrong I would be very interested in what is best.

Thanks Guys
Chris

As a backup, yes that would make sense.

As for the locking for rotor phasing...I guess it can depend on the width of the rotor arm and cap design. On a 4cyl there is scope for much wider gaps between outputs and also a much wider rotor arm so it will pretty much always be in good alignment.

On a V8 this would be narrower, so you would be correct. In order for phasing to be better aligned through the range of advance used, you may still want some degree of advance within the mechanism too to help keep the alignment as spark advance does change.

But if you are not currently having any spark related issues in this sense, just leave it as is. It's clearly been working fine.

Leaving the advance mechanism working (providing you're not taking the trigger for the dizzy) makes a great deal of sense. As getting the rotor position on a locked dizzy can be quite time consuming.

I'd be surprised if the electronics/mapping on a basic ignition only unit are designed to work from a MAF sensor - it's something you'd need to ask the maker about. And if using the existing one on a hotwire etc, there is going to be the problem of the two ECUs interacting in some way - if only a ground loop or whatever.

So a MAP sensor makes more sense - I'm surprised the Omex didn't come with one already fitted.

BTW, don't use the original dizzy vacuum feed unless Omex specifically say to do so. Most are designed to use pure vacuum. Easy way is to add a second take-off beside the fuel regulator one. You can buy screw in nipples to take the hose. Just drill and tap.

It's quite apparent from the load scaling units, MAF was not on the agenda. It isnt to say it cannot be made to work though.

But I just cant see why anyone would bother when MAP is so easy and pretty much the standard.

Thanks again guys for your help. Just one more question if that's ok might seem a silly one to you guys but worth asking by a learner. Does it matter about the length of the tube from the inlet manifold to the Map sensor. The under bonnet area is always very hot so I would like to install it in the cabin but this would mean having to use a vacuum pipe of about 3/4 of a meter long. Would this slow down the response of the Map sensor or make no difference.
Cheers Chris

Install it wherever is handy. Most modern cars they are mounted on the intake manifold, so heat etc isnt really a concern.

Whatever way you do it, mount with the pipe facing downwards, and ideally with the sensor high instead of low in case liquids managed to get in the line ( eg fuel or whatever ) as most sensors will not like this.

But hose length, unless it was huge, wont really matter but best practise would keep it short as possible.

Many thanks indeed.

My MegaSquirt is mounted in the cabin of my SD1 under the front passenger's feet - where the Lucas one was. No problem with hose length.

With MegaSquirt, the MAP sensor is built in. Same with MegaJolt.

My MS is well below the vacuum take-off on the engine, but has run just fine for many years,

I think in the early days of Megasquirt Bruce plumbed several meters of vacuum tube into a working system to prove that it made no difference.