for the efi specialists - maf question

[mk e]

The "spec" for TTL compatibility is here.

http://digital.ni.com/public.nsf/allkb/ ... FB0067A4BD

Ignition circuits don't comply because an active low is a max of 16mA which is OK .......but the active high of 400 micro amps won't drive anything apart from another TTL input.

(bold added)

Exactly...which is what an LS coil trigger input is All the power to charge the coils and run the igniter comes though a different pin so the trigger pin just needs to have the correct High/Low potential, not flow any significant current.

I think the point you were originally making though was in the coils mucking up the 5V line and I supposed it could be. The better ECUs (I don't know if this includes MS) have at least 2 5V supplies to separate the stuff that adds noise from the stuff that doesn't. It seems pretty unlikely that's the issue here though because only the MAF is showing a noisy signal. The more probably answer is this is just a bad application for an MAF to begin with.

[peejay]

The "ignition reference low" leads, that'll be how the PCM detects a misfire and picks up a failed coil.
Different manufacturers have different ways of doing things, the japs usually use that lead to drive the tach too, as well as detect a coil failure.

No manufacturer that I am aware of directly detects coil failure. They just whine that there is a misfire and it is up to you to figure out why.

Only one manufacturer that I am aware of (SAAB) ever used the ignition coils to detect misfire (and I may be wrong on that, it may have just been to detect knock), everyone else does it by monitoring crank speed variation. Which was one of the reasons why certain cars lost manual transmissions when misfire detection was required, incidentally, so crank speed variation is not a "new" way but the original way.

In addition, I don't think anybody has used an ignition coil for tach reference since the 80s. It's all driven by the engine controller, either via direct signal or CAN communication with the instrument cluster, depending on if the cluster is networked or "dumb".

[peejay]

It seems pretty unlikely that's the issue here though because only the MAF is showing a noisy signal. The more probably answer is this is just a bad application for an MAF to begin with.

Agreed, the plenums would appear to be too small to damp out the "noisy" intake pulses you'd get from a cross-plane V8 that is divided bank to bank.
You will always end up with two intake pulses right next to each other and two that are an extra 90 degrees further apart.

I respect the space constraints involved here so the plenums cannot be larger and neither can the MAF-plenum distance. However I do wonder if a crossover pipe could be added to damp out the strange resonances. Yes, just like an exhaust crossover.

IIRC the BXR intake manifold for the 5.0 Mustang had a central plenum for exactly this reason.



There's an idea that was unfortunate in timing. There was no easy way back then to convert an engine to coil pack ignition, required since the distributor had to go.

[Belgian1979]

The boxes are 6 liter in capacity each

[upinthehills]

If you're trying to build a filter to produce a steadier air flow thru the MAF, maybe you need a smaller diameter connection from your large airboxes to the MAF units? If that connection is too large you just have huge airboxes going to your MAF. Does that tube need to be much bigger than the individual intakes? The cylinders are not all breathing at the same time...

Maybe you can put a division in the large airboxes to put stages of filtering in? Not sure I described that well, but they seem big enough to divide length wise.

[Belgian1979]

An LS1 maf is 3.5" outside diameter. That's the tube I'm using. Length is about 59" so quite long. Tube diameter and length are both important in the amount of restriction.

I just made the box as large as could be fit between the hood and the engine to function as an airsupply.

Aside the maf issue (which is a unfortunate thing, but it can be overcome) it points to pulsation in the inlet that will inhibit the production of power.

[Runit]

Belgian: The description of your MAF tubes reminded me of a story a friend told me. He was a data quality assurance engineer for GE. He oversaw some jet engine test cells. There were multiple cells that had been used for years. When a new more powerful engine began testing a problem with data repeatability developed. When one of the cell exhaust ducts catastrophically failed it was realized that the ducts had been going into resonance. The duct was reconstructed slightly larger in diameter. 2" I think he said. The data problems were fixed.

[SchmidtMotorWorks]

An LS1 maf is 3.5" outside diameter. That's the tube I'm using. Length is about 59" so quite long. Tube diameter and length are both important in the amount of restriction.

I just made the box as large as could be fit between the hood and the engine to function as an airsupply.

Aside the maf issue (which is a unfortunate thing, but it can be overcome) it points to pulsation in the inlet that will inhibit the production of power.

That tube length and diameter is out of proportion to the plenum.

[Belgian1979]

Belgian: The description of your MAF tubes reminded me of a story a friend told me. He was a data quality assurance engineer for GE. He oversaw some jet engine test cells. There were multiple cells that had been used for years. When a new more powerful engine began testing a problem with data repeatability developed. When one of the cell exhaust ducts catastrophically failed it was realized that the ducts had been going into resonance. The duct was reconstructed slightly larger in diameter. 2" I think he said. The data problems were fixed.

That's really interesting.

Do you think that the tube is moving/oscillating or the air inside is oscillating ?

A description of how this came along : originally this car is equiped with an engine driven fan and shroud. Due to the Corvettes radiator support & low hood lines there was no way I could get cold air to the engine in that way. At the time I had the filters on a short piece of tube (iron wire with some cloth over it) inside the engine bay, but of course the air temp was really high.

I went to dual electric fans and went with the tubes over the water tubes down to under the car. The tubes run in between the front cross member and stabilizer bar towards the filters that are mounted underneath the radiator. This make for a good supply of cold air.

However, the left tube (one that has the maf connected to the ecu) has the tube hanging in front of the fans. The right tube is attached to the crossmember and runs from there to the middle and under the car. Both will catch the wind/air coming from the fans and radiator.

I strapped everything as good as I could but the maf will still have a chance to bounce some since basically it's hanging on the tube.

Hm, food for thought.

[EthylCat]

[quote="peejay"][quote="joe 90"]
The "ignition reference low" leads, that'll be how the PCM detects a misfire and picks up a failed coil.
Different manufacturers have different ways of doing things, the japs usually use that lead to drive the tach too, as well as detect a coil failure.[/quote]

No manufacturer that I am aware of directly detects coil failure. They just whine that there is a misfire and it is up to you to figure out why.

Only one manufacturer that I am aware of (SAAB) ever used the ignition coils to detect misfire (and I may be wrong on that, it may have just been to detect knock), everyone else does it by monitoring crank speed variation. Which was one of the reasons why certain cars lost manual transmissions when misfire detection was required, incidentally, so crank speed variation is not a "new" way but the original way.

In addition, I don't think anybody has used an ignition coil for tach reference since the 80s. It's all driven by the engine controller, either via direct signal or CAN communication with the instrument cluster, depending on if the cluster is networked or "dumb".[/quote]

Here is a combustion sensing ignition system:

Pretty cool stuff

[Belgian1979]

An LS1 maf is 3.5" outside diameter. That's the tube I'm using. Length is about 59" so quite long. Tube diameter and length are both important in the amount of restriction.

I just made the box as large as could be fit between the hood and the engine to function as an airsupply.

Aside the maf issue (which is a unfortunate thing, but it can be overcome) it points to pulsation in the inlet that will inhibit the production of power.

That tube length and diameter is out of proportion to the plenum.

Too small and long ?

[Belgian1979]

I read that some guys from the msextra team tried something with ionsensing but it has been abandonned apparently.

[SchmidtMotorWorks]

An LS1 maf is 3.5" outside diameter. That's the tube I'm using. Length is about 59" so quite long. Tube diameter and length are both important in the amount of restriction.

I just made the box as large as could be fit between the hood and the engine to function as an airsupply.

Aside the maf issue (which is a unfortunate thing, but it can be overcome) it points to pulsation in the inlet that will inhibit the production of power.

That tube length and diameter is out of proportion to the plenum.

Too small and long ?

Probably but it isn't that simple, the shapes matter.

Just what I told you from the beginning, there is no formula that will provide the right answer, it is a problem that requires simulation to get clues. The dynamics are multiple orders high and beyond what any 1D simulation that I know of can represent, it is a 3 D volume problem with transient flow.

The chances of just making something like that with long ducts and having it work well are low.

[user-23911]

The "ignition reference low" leads, that'll be how the PCM detects a misfire and picks up a failed coil.
Different manufacturers have different ways of doing things, the japs usually use that lead to drive the tach too, as well as detect a coil failure.

No manufacturer that I am aware of directly detects coil failure. They just whine that there is a misfire and it is up to you to figure out why.

Only one manufacturer that I am aware of (SAAB) ever used the ignition coils to detect misfire (and I may be wrong on that, it may have just been to detect knock), everyone else does it by monitoring crank speed variation. Which was one of the reasons why certain cars lost manual transmissions when misfire detection was required, incidentally, so crank speed variation is not a "new" way but the original way.

In addition, I don't think anybody has used an ignition coil for tach reference since the 80s. It's all driven by the engine controller, either via direct signal or CAN communication with the instrument cluster, depending on if the cluster is networked or "dumb".

http://www.obd-codes.com/p0352

Standard OBD2 protocol.

Yes if you wire them up wrong, if the computer has bad design, you can end up putting noise into the 5V supply which is bad.


Anyway.......when ever a project car rolls into the workshop.......that's wrong...that's wrong too, that's wrong and that's wrong. It's a wonder that some of them even run?

[In-Tech]

The "ignition reference low" leads, that'll be how the PCM detects a misfire and picks up a failed coil.
Different manufacturers have different ways of doing things, the japs usually use that lead to drive the tach too, as well as detect a coil failure.

No manufacturer that I am aware of directly detects coil failure. They just whine that there is a misfire and it is up to you to figure out why.

Only one manufacturer that I am aware of (SAAB) ever used the ignition coils to detect misfire (and I may be wrong on that, it may have just been to detect knock), everyone else does it by monitoring crank speed variation. Which was one of the reasons why certain cars lost manual transmissions when misfire detection was required, incidentally, so crank speed variation is not a "new" way but the original way.

In addition, I don't think anybody has used an ignition coil for tach reference since the 80s. It's all driven by the engine controller, either via direct signal or CAN communication with the instrument cluster, depending on if the cluster is networked or "dumb".

Here is a combustion sensing ignition system:

Pretty cool stuff

Really cool stuff, Do you know what vehicles are using these? I'd like to dump the code and disassemble