Megasquirt Support Forum (MSEXTRA)

Same question as Jean (now we see what engine it is), where are the injectors?

If they are anywhere near the inlet ports you are going to have problems with batch (untimed) injection, esp. with only 2 squirts/cycle as per the msq.

Also, what are you seeing on your wideband while this is happening (there isn't enough to see in the short bit of log from earlier in the thread, plus that bit of log looks like a fairly stable idle, no signs of hunting).

thanks for your help guys.

I understood the charge robbing and other issues with the siamese head. I have 2 injectors spraying inline with the minisport manifold inlet via a small plenum. The plenum has a belmouth shape to it to introduce some turbulence as the air enters turns into the engine.

I have tried different numbers of injection events and 2 seems to be the smoothest.

I have included a photo

I have a late model mini air bypass valve. I think it may be the source of my problems. its vacuum operated which is fine for on and off driving. I think whats happening is the airbypass is closing at really small throttle openings and dumping 10psi in at really low rpms..

I thought i would be able to tune this out but it may not be possible.

i was also thinking maybe setting my fuel maps up 16x16 and making the bins around where boost comes in closer together so i can tune it a little finer.

I would redo the VE table, 4 rows for boost is plenty.

This will give you 12 rows for drive ability and a broader range for idle tuning.

David

With such a setup, I'd say you're likely wasting your time chasing any problem because you're almost certainly suffering from charge robbing. That will make cylinder 1 and 4 very lean causing misfire. You need to start with 4 squirts/alt and go from there. But with more squirts, it also means shorter pulses at low RPM/load so you need to get all the injector parameters correct, not just use some guesstimate. You'll need to actually measure the dead time.

Or better yet, go for port injection, ditch the EDIS module, add a cam sensor and go full sequential. But that a big step.

Jean

The photo still doesn't show enough to be certain but, from your description, it sounds like you have created something similar to the SC (Specialist Components) throttle body assembly, ie, the injectors next to each other and in a common bit well before the manifold splits into the two runners and their respective siamesed ports.

If so, others have made such a setup work with untimed injection including use of ECUs other than the SC one. How well they have made them work is a bit subjective as very few of us actually measure the inner and outer AFRs separately but that's another story....

It's often described as a "wet manifold" or "electronic carb" setup but can only work if the injectors are far enough away from the split in the manifold to allow adequate fuel/air mixing before the split and do not individually point in directions such that one injector could favour one set of cylinders to the other. If they are too close to the ports good results will be hard to achieve, and if they point in different directions, you will get different results every other time you start the engine because they don't know which half of the cycle they are operating on (which is just a 50:50 chance on startup without a cam sensor).

And with a minimum of 4 squirts per cycle, for the reason above, if you get better results with anything less, then another setting (ie, dead time, battery voltage, to name but a couple) are wrong.

If you only have one wideband, consider installing a second so you can monitor inner vs. outer cylinder AFRs. With a supercharged setup that should be relatively easy, it only gets complicated with a turbo because of the pressure dependency of the LSUs.

And, as others have said, EDIS is just so last millenium and all this dwell stuff where you think your issues started is most likely a red herring. Just install a couple of ignitor chips and drive the coilpack direct.

thank you guys much appreciated.

i did consider the charge robbing.

I figured it may be less of an issue under boosted conditions.

I did have enough foresight to modify and old dizzy body I had and put a VR sensor in it.I am also using 680cc injectors Because full sequential is on the cards.

the injectors are set up very much like the SC throttle body you mention. I have just got my furnace set up so I am going to cast something a little more elaborate.

I will have a play and get back to you

mini-dunger wrote: i did consider the charge robbing.
I figured it may be less of an issue under boosted conditions.

Experience has shown that is probably true, but most likely down to the "mild" cams used on forced induction engines, ie, the two inlet valves in the siamesed port aren't open at the same time for as long as they would be on a high performance normally aspirated engine.

But getting idle/low power right is harder - fuel injection is in discrete pulses rather than the continuous mixing of a carb so when those pulses are small, you either have to mix it all up well away from the inlet valves to try and replicate a carb, or inject as close as possible to the valves in perfectly timed pulses so it goes through the valve you want. The latter is what Jean wrote the siamese sequential part of the code for which a few of us use very successfully.

If you do go down that route, a cutdown, modified dizzy is what most of us use for the cam signal but with a hall or opto switch as the standard MS2 hardware only has one VR input.

Anyway, good luck with the project.

hi guys

its me michael again


I am not entirely sure how to interpret my tooth log.

could someone run their eye over it for me?

I am also at my wits end about the fact that it ran fairly well without any board mods...... and the board mods made no difference?

this log is rife with zeros....

surely this isnt correct?

ok guys disregard the tooth logs.

they are useless with edis.