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Discussion Starter · #1 ·
I am looking for data- specifically what the crank and cam sensors put out on the 1st gen Dakota/Durango with V8. Specifically, I need to learn this signal (waveform) so I can replicate it for an engine swap to get the tach to work. According to the shop manual, the tach is driven from the crank sensor via the PCM and CCD bus. My testing so far shows this alone will not trigger the tach- a cam input was also needed.

The crank looks to be an 8 pulse per revolution sensor, while the cam looks to be a 1 PPR sensor. Both are 3-wire sensors, with power, signal, and ground. Both operate on 5 VDC.

This site shows blurry data via low-res pics from a 2000 Dakota, and shows how to connect a scope to the PCM wiring:
Rectangle Font Line Screenshot Parallel


I no longer have a running Dodge engine to gather from, so if anyone here has or can get it, I'd appreciate it.
 

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C'mon Dodge - NEW DAKOTA
2003 Dakota Club Cab Sport 4.7L
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I can't specifically help you with this, but I question the 8 ppr and 1 ppr numbers. Those numbers wouldn't be high enough resolution for any kind of timing needs for the ignition system.

Count the flywheel teeth and that's the number of pulses you should expect per revolution, same for the cam sensor. And pretty certain that one or both will have a missing tooth for an index pulse.

Where did you get those numbers?
 

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Discussion Starter · #3 ·
I can't specifically help you with this, but I question the 8 ppr and 1 ppr numbers. Those numbers wouldn't be high enough resolution for any kind of timing needs for the ignition system.

Count the flywheel teeth and that's the number of pulses you should expect per revolution, same for the cam sensor. And pretty certain that one or both will have a missing tooth for an index pulse.

Where did you get those numbers?
The data came from the factory service manual. On page 8D-3, the relevant text says this for the crank sensor (emphasis added), and I've inserted a screencap of the layout from the manual:
On 5.2/5.9L V-8 engines, the flywheel/drive plate has 8 single notches, spaced every 45 degrees, at its outer edge (Fig. 4).
The notches cause a pulse to be generated when they pass under the sensor. The pulses are the input to the PCM. For each engine revolution, there are 8 pulses generated on V-8 engines.

Font Parallel Circle Diagram Auto part

The data for the cam sensor is on pages 8D-3 and 4:
The camshaft position sensor is located in the distributor on all engines.
The sensor contains a hall effect device called a sync signal generator to generate a fuel sync signal. This sync signal generator detects a rotating pulse ring (shutter) on the distributor shaft. The pulse ring rotates 180 degrees through the sync signal generator. Its signal is used in conjunction with the crankshaft position sensor to differentiate between fuel injection and spark events. It is also used to synchronize the fuel injectors with their respective cylinders.

When the leading edge of the pulse ring (shutter) enters the sync signal generator, the following occurs:
The interruption of magnetic field causes the voltage to switch high resulting in a sync signal of approximately 5 volts. When the trailing edge of the pulse ring (shutter) leaves the sync signal generator, the following occurs: The change of the magnetic field causes the sync signal voltage to switch low to 0 volts.


The cam 1x pulse was a guess on my part as that is what many modern EFI engines use. Using the data given, the pulse ring rotates 180 degrees, in effect making it a 1-tooth (1x) sensor. The service manual shows both sensors are 3-wire sensors.
 

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C'mon Dodge - NEW DAKOTA
2003 Dakota Club Cab Sport 4.7L
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Well that surprises me, I learn something new each day. I work for a major American motorcycle manufacturer (no not THAT one) and I need to look at ignition systems from time to time. The crank sensor on our bikes pulses dozens (or hundreds?) of times per revolution. I can't remember the number.

The CAM makes sense, it's distributor - derived in this case and effectively fixed ratio geared to the crank. The CAM pulse effectively serves as the index pulse for the crank.

I still don't understand why the PCM would need the CAM input for the tach, but you've established that it does. Maybe it uses it for another purpose. Does this engine use a mechanical advance?

So you know the number of pulses, you know the voltage excursions, what piece of information exactly are you missing?
 

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Discussion Starter · #5 ·
I worked on converting an older UJM Suzuki to Microsquirt EFI a few years back and that's where I first learned about trigger wheels & pulses. I think that project used a 24-2 wheel due to limited space under the side engine cover. As I recall, there was some concern about a higher number of teeth being able to be read by the sensor.

I know the Gen 3 LS engines use a 24x wheel (my swap), while the newer Gen 4 motors use a 58x wheel. The Dodge is very low compared to these.

I was able to get a higher quality image from the site that posted the 2000 Dakaota scope screenshot and will insert it below. I'm still learning about square waves, frequency, and duty cycle. I'm trying to decode the data there to see if I can discover what is needed, then compare what I have now. I have ordered a function generator/signal reader with dispaly that will help me in that area.

What I'm trying to discover is the frequency and duty cycle of the Dodge sensors. My rough calcs based on the below picture are about 8 Hz frequency & a 69% duty cycle. Presuming this was taken at an idle under 1K RPM, those numbers are close.
Rectangle Product Slope Font Personal computer
 

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C'mon Dodge - NEW DAKOTA
2003 Dakota Club Cab Sport 4.7L
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Don't read too much into those waveforms, there is nothing to "decode". I suspect the scope is missing some pulses or aliasing because of a too-slow sample rate. The waveforms in a correctly running engine, correctly sampled by an oscilloscope set up right -- would not look anything like that blue waveform. The spikes falling in the middle of the pulses are a dead giveaway.

Aliasing is a phenomenon that happens with a digital scope when sampling at a rate that isn't at least 2x and preferably 10x the rate of the waveform signal. It can fool even an experienced technician, I've been doing this 40 years and I still get bit.

The waveforms should look uniform. The cam waveform should show pulses in this case of 1/8th the crankshaft signal. And they wouldn't necessarily be of the same pulse width or duty cycle.

More teeth on the encoder wheel means smaller teeth, so a smaller change in reluctance, your sensor needs to be closer to the teeth and more sensitive.

You are going to need a circuit to divide the 24 tooth sensor output by 3 to get 8 pulses per rev. That's easy to do. Not sure about your camshaft signal. Check out Dakota Digital for some boxes made to do just this kind of thing.
 

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Discussion Starter · #7 ·
Thanks for the info. I have two tach ratio/voltage adapter boxes from a place called Widget Man as well as a sine to square wave converter for low voltage input. He's helping me with this as well. The boxes have both 12V and 5V outputs. I used the 5V outputs.

Using just the tach ratio/voltage boxes (3:1 crank and 1:1 cam), I got no tach movement. When I added the wave converter to the crank output, the needle worked, but it was reading too fast regardless of the ratio I input, and it was bouncing 200-500 RPM. I think the likely solution is to add a second wave converter to the cam box.

I also tried using the tach wire output of the GM computer, it is supposed to be 4 pulses per revolution with a low voltage square wave. I got no tach movement using any of the above combinations or by putting the wave converter in front of the boxes.

I'm not going to do anything else until I get the readings from the function generator so I can see what the GM sensors and the ratio boxes are outputting.
 

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C'mon Dodge - NEW DAKOTA
2003 Dakota Club Cab Sport 4.7L
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Well here's a couple more bits of info, do with this as you see fit. Powered sensors should put out digital waveforms, not sine waves. Secondly, your function generator can't show you anything -- only a representation of it's own output. It's not a o'scope. Not gonna show you the sensor waveforms. So my humble suggestion is to get yourself an oscilloscope, stand-alone or PC based. I've used a couple of the Chinese function generators, they have a cute LCD display but that's a facsimile of the output signal. There is no substitute for a good scope and knowing how to use it. Best of luck with your project! Keep us posted.
 

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Discussion Starter · #9 ·
Yes, all of these 3-wire Hall sensors will output a digital square wave signal.

I misnamed a couple of the devices here:
The low voltage wave converter will convert either a sine or square wave to a square wave. Using one of these made the tach come alive.

What I called a function generator is actually called a signal generator/reader. The specs show it can read frequencies from 1Hz~100MHz. It has dual LCD screens for data since it is a dual channel device. If this does not do what I need it to, I have a 30-day return window. Any suggestions for an affordable (say under $200) scope hardware/program I can use with a Windows 10 laptop?
 

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C'mon Dodge - NEW DAKOTA
2003 Dakota Club Cab Sport 4.7L
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Picoscope makes a series of affordable units, some include waveform generators. I haven't used them myself but the specs look impressive for the price.

The waveforms you posted earlier were taken with a Picoscope... likely the user did not know how to set it up correctly for the waveform he was recording. I'm not familiar with the user interface so it's difficult to understand the setup shown on the screen. It claims 500 ms per division but then down below the divisions look like 62.5 ms. Nothing adds up.
 
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