Building an ignition system

Thanks, debe,

I have to crash now, long day tomorrow. I'll look into that.

Cheers

Bit of data on the Bosch sensor with var freq/man vac.

This one is a variable voltage output.

This might be of some help, its part of a Ford course i did some years ago for F150 series. Also have more detailed info on the 6cyl ford motor that uses a very simmilar computer.

An excellent point, Diver300,

I think John was refering to the presence of residual exhaust gasses in the cylinder. I don't think we can actually call those gasses 'air'. But they would serve to dilute the A/F mixture somewhat, not necessarily change the A/F ratio. After all, they've already been burned and don't have much left to give us. But it would affect the density, as you say.

If I remember right, the way most cams operate their valves ensures that there will always be a bit of the exhaust left in the cylinder. The intake valve actually begins to open while the exhaust valve is still open a tad. The outgoing gasses are supposed to help draw the incoming charge in a bit faster. But unless you want some of your incoming charge to be exhausted along with the burned gasses, you'll be wanting to close that exhaust valve before any of the fresh charge can reach the exhaust port. That pretty much guarentees there will always be a trace of exhaust gas left in there.

I don't know about Chevy or any other make, but on top of that Ford also gives us what is called an Exhaust Gas Recirculation valve. A particularly nasty little piece of emissions equiptment designed to let spent gasses back into the induction system to mix with the fresh air and be burned again. If that's possible. And, oddly, the valve is only connected to the passenger side exhaust manifold. There is none on the drivers side. Thats gotta affect the exhaust gas flow on that side of the motor.

I've had people claim that this helps make torque but I can't see how diluting the fresh charge with already burned gas can possibly be of any benefit in making power. Unless there is some kind of supercharging effect going on there. And when I took this motor apart to rebuild it, the induction system from the butterflies on back was absolutely filthy. I mean a sixteenth or more of gunk coating everything in there. Especially the back sides of the butterflies and the venturi of the throttle bodies behind them.

Needless to say, that little item is no longer present on my motor. However, its removal causes problems with the computer because it looks at that valves condition, open or closed, and uses that state in its fuel metering calculations. One has to trick the computer into thinking that the valve is closed so that it meters fuel properly. A major source of my unhappiness with the factory ECU.

That's some good info, debe,

It's very helpful to know what kind of signals those sensors give out. I'm going to try to stick to the ones that output voltage levels instead of frequencies. They are easier for me to understand and deal with. That Bosch MAP sensor that outputs voltage levels looks very usable. I need to find out what vehicles those were used on so I can get one at the parts store. Trying to obtain one using a part number usually nets you a blank stare around here. The one now on my truck is, of course, the frequency type.

A rough outline I worked up.


1 min = 60s = 60,000ms = 60,000,000us

To calculate cam rpm:

If cam rpm = 300
EventTime would be .025s = 25ms = 25,000us

8 x 25,000us = 200,000us

60,000,000us / 200,000us = 300 cam rpm

or:

60,000,000 / 8 = 7,500,000

7,500,000 / 25,000us = 300


If cam rpm = 1500
EventTime would be .005s = 5ms = 5,000us

7,500,000 / 5,000us = 1,500


If cam rpm = 3000
EventTime would be .0025s = 2.5ms = 2,500us

7,500,000 / 2,500us = 3,000


So:

Ignition is turned on.

Coils are turned on.

Box is turned on.

Program starts.

Loads the needed constants into the appropriate registers.

Waits for a #1 cylinder pulse: (Needed to ensure we get started at beginning of firing order)



Starter cranks:



Pulse #1 recieved by box

Start firing countdown

Stop Event Timer

Move Event Timer value to register

Start Event Timer (in microsecs)

Look at EventTime Register (should be zero at startup?)

Perform RPM Calc (7,500,000 / EventTime)


Look at Initial Advance Time Reg (Should be 5* Cam value)

Calculate Increased (mechanical) Advance Time


Get TPS value from ADC

Get vacuum advance value from ADC (register needed?)

Calculate Total Advance Time

Subtract Total Advance Time from Event Time

Put value in Firing Countdown Register

(Increment coil line select register, value = 1 to 8)

Pulse #2 recieved by box

Goto pulse #1

Nothing much to do with electronics, but EGR is about reducing the oxygen in the inlet gas, to cool the ignition and to reduce the NOx. The exhaust gas is a convenient source of gas with little oxygen in it. It is only taken from one manifold because not much is needed, and the majority that isn't needed goes straight out the exhaust. I doubt that the manifold back pressure is measurably different on the two sides.

Some time ago, I think it was Volvo who made a V6 with a turbocharger, where the turbine was only driven from the exhaust gasses from one bank, and it had different valve timing on the two banks. That was obviously really unbalancing the two banks, but I guess it worked.

https://en.wikipedia.org/wiki/Egr is quite informative about EGR.

The gunk & crap in the inlet manifold comes from the crankcase ventilation system. If you cant find the MAP sensor, Igethem for free from the wreckers here & probably could post one.

EGR info.

Ah,
I'd forgotten about the PCV valve.

I suppose it is the proximity of the EGR to the TB that made me think it was the culprit. Perhaps it's not as evil as I'd thought. At least in the dirt aspect.

"but EGR is about reducing the oxygen in the inlet gas,"?! That seems counterproductive to making power.

But anyway:

Ford Falcon XF Map Sensor
Part Details
Part : Ford Falcon XF Map Sensor
Part Number(s) : 9220066019
86DA9F479AA

Type : S/H
Engine Size : 4100
Body Style : WGN4
Priced From: $65.00
In Stock : 1 @ Te Puke
Outlet : Te Puke PartsWorld
Phone : 0800 100 494

Te Puke?

Googling the part number from your pic showed only a few references, all in Aus or NZ.

This was the most informative one. No year listed for the Falcon but the part number seems to indicate the mid 80's. I don't know much about Aussie Fords or their part numbering system but the DA part of the number does indicate an 80's model here. I'll look into that further. Hopefully they were not used only there.

Your offer is very generous, debe. I may have to take you up on it if I'm unable to find one domestically. I may try to contact Bosch and see if they still make the things or their equivelant. Grab a couple just in case if you can get them for free and it's not too much trouble.

Pics of the MAP sensors & have plenty of them as they were on GMH vehicles aswell. Also pics of carboned Inlet valves. EPA is not about fuel economy or power. Alot of EPA regs cause increase fuel consumption.

Yeah,

I was just looking at the Bosch site motorsport page. It looks as tho almost all their new map sensors put out a voltage and not a frequency. At least it appeared that way to me based on the graphs and data they showed. The simplest appearing one, 0-261-230-004, that had a vacuum hose input was 90+ euros and only used on European and Asian vehicles. Available from a UK supplier. Plus 19% tax and shipping. Ouch!

I also tried to look up a datasheet for a replacement MAP sensor for my truck that I have but not yet installed - BWD EC1609P - but they weren't giving any info like that out. Couldn't find an output decription anywhere on the net. My manual (Haynes Full sized Pickups & Broncos '80-'96) states that 'early' models had a voltage output while later ones had freq., so I'm sure the one I have will be that.
Don't know exactly where that line is drawn but maybe if I go to the parts store and ask for a '80 replacement, or as old as they have listed, I might end up with a usable new one. Hopefully for less than a hundred plus bucks. I need to figure a way to test the output. Almost any freq. would just appear as a voltage level to my multimeter.

Should have posted this earlier, shows vac to voltage output on the unit in the prev pics.

The easiest ignition system I worked on was the Ford Duraspark II system, from the late 1970s cars. I have several Ford ignition modules to test off the vehicle, and one that came loose from its case that allowed me to get a schematic from the PCB. I loathe the wax inside these repairable modules, but Ford made them for one-time use only and the output transistor isn't available separately. The wax, beryllium oxide, is a thermal insulation that supposedly succeeds where a suitable heatsink cannot be included in the aluminum case.

Sorry I haven't been around for a few days. Massive dental work. Plus I was distracted by my induction system project. About got that straightened out. Just waiting on a few parts and tools. I have to get some clearance over the valve covers so I can mount the coils. And I hate the flopped over upper intake manifold anyway. It is so unbalanced that it needs a prop rod to hold it up so it doesn't tear the bolts out of the soft aluminum lower. And the only place to attach the lower part of a rod is to the header bolts. I used the header bolt like the original factory and after a while it developed an exhaust leak. Header bolts are short and only need about 10 ft.lbs. to secure them when using aluminum exhaust gaskets. I suppose I could have used a stud on a valve cover bolt and made a new rod but that would still suck. Went back to the junkyard and got an old Mustang upper and TB. Found a 1" aluminum adapter plate online to mate with the truck lower, and a 1" resin spacer for in between. So that should give me adequate clearance for the coils, maybe 2.5 or so. The Mustang upper is much more balanced and I won't need the prop rod at all. But anyway, I'm digressing about the induction system.

shokjok, I had Duraspark II on a mid 80's Ranger I had built. It was very simple to install but not that reliable. I had a couple of fried modules during the time I had the truck. Never did figure out what caused them but they did run hot. I had wired them properly and used the ballast resistor. Made sure they had air circulation. Blue tab modules, if I remember right. I had stuck a '78 302/C4 in there. It was fun to drive around town. I surprised a few Camaros and Mustangs. But no overdrive and only got about 12/13 mpg. Not good on the highway with the 3.45 rear end. It was a cheap ignition system, tho. You could buy the whole lot, dist., cap, rotor, and box, for a bit over $100 new at the parts store.

Back to the ignition system on this truck.
I did test the new freq. output MAP sensor I have for my truck by alligatoring its power pins to a 5v power supply and hooking up my multimeter to its output pin. Got a steady reading whether at atmo pressure or with putting a vacuum on it with a little pistol vac that I have for bleeding brake lines and such. Just like I thought it would.
However, just about all the GM ones of the early 2000's are voltage output. Through 2006 according to a Haynes Chevy truck manual that I looked at. Don't know what happens after that. I should take my little test rig down to the parts store and test some GM ones. Find one that looks pretty and is easy to mount. Don't know if I can get my parts guy to go for that or not. Though I'm sure he'll be impressed.

Also.
Been looking at the Atmel chips. They don't look too expensive if you limit yourself to the simpler ones. Say 40 - 48 pins. I'll have to look again but I think there is one 48 pin that is 32 bit. The programming software is free for the basic versions, I think. I only took a quick look at them to get a general idea of what was out there.
Though it looks like the chips that allow for LCD screens have a lot of pins and are very expensive. I was hoping to be able to do a little realtime monitoring without having to drag along a laptop all the time. And maybe some on the fly adjustment of the high and low rpm settings, or the advance amounts at either end of the rpm range, using some pots wired to ADC lines.

I also need to look at the developer boards to find a general use one that I can use for later projects with other chip families. Not necessarily automotive in nature.

Forging onward