Marine Digital Ignition system which utilizes MAP sensor?

[Uraijit]

I have a strange question for you guys, but here it is.

As some of you already know, I'm an importer of CNG conversion kits (to convert cars to run on natural gas). I've been wanting to experiment with a natural gas conversion on my boat.

First of all, I know it's not "marine approved", but I'm hoping to develop a system, and GET IT APPROVED. Gotta start somewhere, so please no lectures.

The system will be properly ventiliated, and there will be no electronic components in the engine compartment...

Anyway, with all the disclaimers out of the way, I'm looking for a marine ignition system that utilizes a MAP sensor to calculate timing advance.

The reason is that in order for the boat to run optimally on CNG, the timing must be significantly advanced, over a regular gasoline setup. This is because CNG has an octane rating of around 130.

Now, obviously, I don't want to have to get out my timing gun and turn my distributor every time I switch between fuels.

There is a module for CNG systems, which will modify a MAP/MAF sensor, signal so that the ignition will believe that the engine is at higher RPM, and advance the timing automatically. So when you flip the switch to go to CNG, the voltage level on the MAP automatically changes, and the ignition advances timing. Make sense?

Alternately, it can install a module which uses a crankshaft position sensor, but my engine doesn't have one of those either, and it wouldn't make sense to go to the trouble of trying to add one, since a map sensor would do as well, and be MUCH easier to install..

So I'm looking for a marine ignition system that will utilize a MAP sensor, so that I can install the CNG module to automatically modify timing advance, at the flip of a switch.

I really don't know anything about aftermarket ignition systems, and since virtually every modern car uses a MAF/MAP, this is the first time I've had to try and figure out how to add one.

Naurally, my points ignition on my carbed 1981 engine setup isn't going to have what I need on it. For now, I can time it manually, but since I'm trying to develop something that the Average Joe can easily use, I need to make the switching between fuels as seamless of a transition as possible (literally the flip of a switch).

 

[Uraijit]

Re: Marine Digital Ignition system which utilizes MAP sensor?

Maybe I'm over-complicating this. Perhaps the magnetic triggered distributor could be used with the module I mentioned before, which is intended for crank sensors? Same concept, right?

Anybody got any ideas?

 

[JustJason]

Re: Marine Digital Ignition system which utilizes MAP sensor?

any merc/volvo with a MEFI-5 setup uses a map sensor. They also have a CKP, TPS, IAC. IAT and pretty much everything from an automotive FI system.
Boats don't and probably will never use a MAF, as they are to sensitive for marine use.

So when you flip the switch to go to CNG, the voltage level on the MAP automatically changes, and the ignition advances timing. Make sense?

Nope, doesn't make any sense to me. for 2 reasons.
1. the map has nothing to do with timing. the timing is calculated by ecu by the ckp and the tps. The map is for setting the baseline fuel injecter pulse times (turn on time) and air/fuel ratio.
2. the map locks in once you start the boat. what i mean by that is say you boat all day at a 5000ft elevation. and you left the boat running and towed it down to sea level. the engine is going to remain running with the air fuel ratio it needs to be at 5000ft. It will not readust itself until you cycle the engine off then back on.

mefi modules are not updatable or rewritable. you cannot "chip" them like you can some automotive ecu's.

While anything is possible if you throw enough time and money at it. your going to have to play ernie the engineer and do what you need to do to see if you can get a custom ecu made to your spec's..... which is gonna be BIIIIIIGGGGGG bucks $$$$$$$$$$$$

Best of luck!!
CJ

 

[Uraijit]

Re: Marine Digital Ignition system which utilizes MAP sensor?

I'll try to explain. With a fuel injected vehicle, when it's switched to CNG, the fuel injectors are switched off, and are no longer part of the equation. The engine uses the MAF (not applicable to boats) or the MAP to calculate a lot of things, like Injector pulse width, and timing. Obviously, there are other sensors involved, such as o2 (again, not applicable on a boat). The modules modify the signals from what they actually are (based on the properties of CNG being different from gasoline), to what the computer SHOULD think they are (since it still thinks it's burning gasoline) in order to make it do what it should for optimal CNG burning.

Hard to explain, but it's like a color-blind person telling a person behind the paint counter that the paint chip his wife pointed out to him is "green" when it's really "blue". If you grab "green" paint, you've grabbed the wrong color, even though that's what he asked for. A third person, who knows that the color-blind guy doesn't really mean "green" when he says "green", he means "blue" so he tells the paint counter guy "blue".

The colorblind gets what he sees to be "green", and takes what is really "blue" paint home to his wife who picked it out.

The module acts as the "third person" to translate the signals for the computer.

Basically, what I would be doing would be "borrowing" the module from an EFI system, and using to to achieve the same result. Just with fewer sensors, because it's a more basic setup...

I know... None of it probably makes sense.

 

[JustJason]

Re: Marine Digital Ignition system which utilizes MAP sensor?

Nope... makes perfect sense. I know what your trying to do. Switch fuels on the fly. And i'm saying, a MEFI module is not the same as an automotive. They employ 2 different fuel stratagies. A MAF sends a variable signal to the ecu, but a MAP is a fixed signal.
When the ecu is designed using a MAP, all it cares about is the first intitial voltage reading and then if it goes above or below threshold.

 

[newport dave]

Re: Marine Digital Ignition system which utilizes MAP sensor?

Uraijit,
I think the easiest way to accomplish this would be to ditch the points and convert to an electronic ignition system modified to switch between two advance modules. MSD has programmable modules that you could use.


CaptJason,
Dude, come on.

any merc/volvo with a MEFI-5 setup uses a map sensor.

Neither Merc nor Volvo have used the MEFI5 controller. Merc never even used the MEFI4 controller.

the map has nothing to do with timing. the timing is calculated by ecu by the ckp and the tps. The map is for setting the baseline fuel injecter pulse times (turn on time) and air/fuel ratio.
2. the map locks in once you start the boat.

In a speed/density EFI system, the MAP is critical to determining engine load, and an increase in MAP will cause the module to advance the timing. The MAP is not "locked in" at start-up, the BARO is set, the MAP is constantly changing.

mefi modules are not updatable or rewritable.

Of course they are, anyone with $600 can buy the software to reflash a MEFI 1,2,3, or 4 ECM.

 

[Uraijit]

Re: Marine Digital Ignition system which utilizes MAP sensor?

Uraijit,
I think the easiest way to accomplish this would be to ditch the points and convert to an electronic ignition system modified to switch between two advance modules. MSD has programmable modules that you could use.


CaptJason,
Dude, come on.



Neither Merc nor Volvo have used the MEFI5 controller. Merc never even used the MEFI4 controller.



In a speed/density EFI system, the MAP is critical to determining engine load, and an increase in MAP will cause the module to advance the timing. The MAP is not "locked in" at start-up, the BARO is set, the MAP is constantly changing.



Of course they are, anyone with $600 can buy the software to reflash a MEFI 1,2,3, or 4 ECM.

Excellent thought, Dave. This idea would probably work perfectly! Albeit an expensive one, it's certainly a possible solution.

If my idea of using the crank advancer doesn't work the way I want it to, I'll probably go that route.

Does anybody remember if a crankshaft sensor puts out a pulse, or a voltage? It's been too long since I messed with one. I can't remember.

I'm watching some digital ignition systems on Ebay right now. I'll update with what I figure out.

Thanks!

Anybody else got any ideas?