Yes and no. Depends on the engine. As RW said, some have carb heating and some don't. Technically for max power you want as cold of a mix as you can get as that carries the most oxygen into the engine, which is why you see all sorts of things done at the strip to cool the fuel and the inlet air. But, few of us need or use max power on a frequent basis, so what we need is a consistent AFR and that requires a consistent inlet air temp. REQUIRES. That's because almost all carbs are dumb and can't make AFR changes based on temp.

So the real question is what inlet air temp can be sustained both summer and winter. Ford gave us several Air Cleaner Temp Controllers with set-points from 70 degrees to about 105 degrees. I'd say getting summer air at 110 degrees outside and into the air cleaner without picking up a few degrees isn't going to happen, so I'd pick the 105 unit as that's about the closest I think we could get to constant temp. And that gives us the best chance of having constant AFR.

 

Today's update, with not much to report. (But the grass is cut and several other errands got run.) Called AEM and talked to Ping, the tech I spoke to yesterday. He asked me to tell him if his suggestion of using one of the filters they put on USB and other cords and slipping it over the tach wire worked. Didn't work at all.

Also, I asked him why the vacuum reading on the gauge itself is very close to what my vacuum gauges read, but the data the gauge records shows up at a bit less than half reality. He gave me several suggestions on changes to make on their AEM Data software, which has a very steep learning curve by the way, but none of them helped at all. Finally he asked that I send him a couple of my data log files. So I recorded a new one and took a video of the gauge readings while logging the data. Then captured the screen image of that data on my version of AEM Data, showing roughly half the right vacuum readings. And I emailed all of that to him.

Then I worked on the tach reading. He had suggested a pull-up resistor, which by itself would be fighting the DS-II box - to no avail. So I tried several different RC circuits, and made some progress but wasn't satisfied. I then pulled out the scope to find out what I'm working with and captured this from the DS-II tach wire. Kinda shows why the AEM gauge might be getting a few extra R's from time to time. Gonna have to think through the filtering plan. Ideas?

 

ask on the megasquirt forums for help on this one about cleaning up tach signal

probably best would be some sort of diode or a dedicated filter integrated chip from mouser.. put a Schottky diode to absorb the low spikes ?

i really really like the oscilloscope, i've never had one but they must be so fun to own.

 

Ok i did research on diyefi and they said basically the ideal gas law explains this

in kelvins the air density and therefore the fuel amount changes
273 kelvin is 0 Celsius 32 Fahrenheit
303 kelvin = 30 degrees Celsius 85.73 fahrenheit
313 kelvin is 40 degree celsius 103.73 fahrenheit

so 273 ( freezing) / 313 (extreme hot summer) = 0.87220447284 = 87 percent of fuel that needed in the winter.

or inverse

313 / 273 = 1.14652014652 percent of fuel that needed in the winter compared to summer.

I am not sure but about 14.6 percent more fuel is needed in the winter if everything is equal, what that means to AFR summer vs winter, better leave + 15 percent richer in summer. (richer in summer because the opposite aka going leaner in winter means extremely tough starts)

 

What you are seeing in the waveform is "coil ringing". Ohh that brings back ole days of "ringing" TV flyback transformers.... too find a bad one.

Some data logging equipment are not immune to it. So its counting the rings as RPM.

What you need to do is "clamp" the voltage down(get rid of the ringing). A 16volt(looking at your voltage levels) zener diode and resistor will help out. This will keep anything over 16 volts from reaching the data logger.

On the bottom of this page shows a voltage clamping circuit.
http://www.electronics-tutorials.ws/diode/diode_7.html

 

Patrick - While you are on the right track with the calculations, I can't help but believe something is missing as I doubt there is that much difference. However, it is a moot point because I will use a temp-controlled air cleaner to ensure the inlet air temp remains close to constant. As I said before though, those that done use the original temp-controlled air cleaners will suffer from changes in the AFR as the air temp changes.

Eddie - I agree that is certainly ringing. And the AEM is counting many of the negative edges as cylinders firing, hence the high and varying RPM. Unfortunately I can't open the site you linked to so can't say I agree with the schematic, but I'm sure it is what I'm thinking of as well. Basically it is a decoupling capacitor, a clamping diode, and a pull-up resistor. But, can you post a pic of the schematic?

 

I did a search for "zener diode voltage clamp" and that was the 1st web page I clicked on.



The top schematic is what you need. Don't worry about the "AC" source in the schematics, that circuit will work with DC voltages too.

There are many more circuits with more components, but this simple circuit does work as I used it before for fuel injector pulse monitoring

 

Thanks! I actually got that site to open on this phone, but for some reason not on the PC. But having the schematic in front of me helps. Now to see if I have any zeners in my parts drawers......

 

Wow., I haven't used a zener since days of Lucas electrics.
Newark, DigiKey, MKM or maybe even Amazon industrial will have what you need.
Radioshack is pretty hopeless these days.
I can only imagine what that scope trace would look like if you were running an AL6 box!

 

I used to be a component level repair tech, now days its just boards. A 22.1V zener diode was a common part in most power supplies. Was used to "bar" the circuit for over voltage protection causing the switch mode power supply to stop. But most times it burnt up the SMPS drivers!!

Yea, Rat Shack.... was good place till it became a "phone" only store. But now they are bringing back some electronics parts! I got my 5.1V zener diodes for my PSOM(92 to 96 speedometers) EEPROM programmer there. I recall I seen they had more voltages too.

Hmmm, AL6 multiple spark ignition.... That will be instresting to see on the scope. How many times could it fire at 4000 RPM...... and do any good?

 

Ok, I'll take a break in my hunt for the "right" zener to comment. So far I've found 33v, 12v, and 9.1v ones in my kit.

As for Radio Shack, they are my go-to place to sell old iPhones as they give top dollar. And they used to be good for components, but have gotten awful so I use my account at DigiKey. In fact, some of my zeners are still in their packages. But, they are days away on deliver and I'm in a "today" mood.

As for MSD, I'll see if I can get a good pick of the tach signal on David's truck as he's running an MSD.

 

And batteries. Lol. Every time I go there they ask if I need any batteries

Sent from my Telegraph using IB AutoGroup

 

Progress. I used the top filter in Eddie's post with a 100K input resistor and a 9.1v zener and got this:




That's a big improvement but at least two of the negative-going waves from the ringing still showed up to trigger the gauge, meaning that the RPM was showing roughly 3x what it should have been. But, since those "rings" aren't consistent you can't just divide by three and get good results. However, since there isn't much energy in the "rings" they can be filtered out. Here's what I got when I added a .068 mfd cap across the zener:




That's better and the gauge appeared to like it on the readout on my laptop, which shows instantaneous RPM if connected via USB. However, the true datalogging is getting lots of drop-outs:




You can see that the engine is idling at ~700 RPM, but there are points where it swings +/- 350 RPM, seemingly indicating that more or different filtering is needed. Still thinking about that. Ideas?

 

I think I may be at a usable point. BUT, there may be too much filtering. I used a 100k input resistor, a 5 v zener, and two cap's - one a .1 mfd ceramic and the other a .068 mfd mylar. Here's what the waveform looked like:




And here's the last few seconds of the log file. But, notice that both the AFR and the vacuum show glitches at 18:10 and 18:11 - that's because I blipped the throttle twice. Now note that the blips were filtered out on the tach.




I'm now wondering what filtering or active circuits the Ford tachs have. And, since I have one that works sometimes.......

 

Ok, I give up. Time to buy a good tach filter. Anyone know of a good one?

I did some searching and found this filter on the Arduino site and built it:





And here's the results I got on the AEM:





Note that the RPM is not only twice what it should be, which I could change in the pulse/rev setup, but it spikes badly. So, as said, I'm ready to buy something that is said to work. Will call AEM on Monday, but in the interim I'm asking for suggestions. In the interim I think I'll do something else.