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Discussion Starter · #1 ·
Heya all, Just wanted to let you know that I have removed the PCM from my truck by building some simple electronics to replace the big box. The crank position sensor feeds my tach a good clean signal now, the pre-heat is controlled by a 555 timer circuit that is mounted into my dash, and the alternator is controlled by a ford regulator (as seen here on the forums). I am more than willing to share the simple circuits that I built if anyone is interested. These are not terribly complex circuits to build, but knowing the basics (ie anode from cathode on a diode) is a must. :thumbsup:
 

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sounds like something you should shine up and sell...imagine those that mod trucks for these engines would be interested
 

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I would be interested in the schematic if it’s not to complicated I’m sure I have a few 555 chips around and a few diodes.
Thanks.
 

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Discussion Starter · #7 ·
Hey all, thanks for the interest! Its been fun to rethink the engineers work at Dodge. So I should clarify- my truck started off as a hack job- its a '83 D-350 4x4 with a '93 Cummins TD. The shop that did the work did it quick and dirty- they were told to 'just make it go'. Alot of the wiring was just cut, with the minimums connected to 'make it go'. Since it was all chopped anyway, I was able to figure out how things were wired and what is necessary and whats not. I don't have or want A/C, auto trans, or idiot lights. I wanted (and have) a full cockpit with all the guages- the tach being one of the most important. To feed the tach, the PCM has two linear regulators inside that supply the crank position sensor- 5, 8(or 9) volts, and ground. Replacing this portion of the circuitry is as easy as using a 7805 +5v regulator, and a 7808 (or 7809) for +8v (or +9v) from radio shack. My tach is an Auto-meter 0-4krpm marine standard unit for gas engines and is expecting a fast high voltage spike to meter from (most tachs operate this way). So a small amplifier circuit is needed to take the small pulses (2 per rev- like a 4 cyl) out of the sensor and create a nice clean spike for the tach- similar to the backlash pulse in the ignition coil of a gasser. A FET a couple resistors, and small transformer make this quick and easy. Yes I will get schematics up ASAP. This amplifier should also be able to provide a trigger for the cruise control since it wants the same type of input as a tach.
The timer for the pre-heat is more tricky, but is based on this ("]http:// ) 555 PWM circuit I found last year and have played with in many variations. The basic idea is a circuit that will turn the heater on for about six seconds, then off for about three- you start the engine when the heater turns off the first time- and continues to cycle on/off for about thirty seconds or so. The value of C2 and the rheostat R1(100k variable resistor) need to be altered so that the pulse width is in seconds instead of thousandths of a second as its shown. I'll get the exact values and revised schematic up soon- wrote them down... somewhere. Instead of the motor for the load, the FET (Q1) controls the relay that supplies ground to either the alternator or the heater relays. When activated, the alternator turns off and the heater turns on. More notes to follow as I hook up more and more stuff (water-in-fuel light is soon) and get cruise control on the beast as well. I'll have more info and exact specs posted inside the week... cheers all.
 
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Discussion Starter · #10 ·
A/C is an easy one- its either on with a switch to the compressor clutch, or its off -either by the driver or the over-pressure switch. The PCM just controls the relay for the A/C- all its using for input is the safety pressure/ temp switch. The PCM is only a gathering point for the wiring- it does nothing amazing in regard to the A/C compressor. A/C will turn on full until the pressure or temp rises to the point that the switch turns off the A/C clutch. Thats it- wire the relay in series with the pressure/temp switch, and it will cycle on/off as the compressor operates. This is how A/C systems have operated for many decades, and our trucks are no different.
 

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Discussion Starter · #12 ·
Tach circuitry

View attachment 21428 K, so here is the tachometer driver circuit that I built to take the small signal out of CPS and amplify it to operate almost any tach. Have fun. I'll try to get the pre-heat timer circuit up soon...
 

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Discussion Starter · #13 ·
Why the heck didn't the attachment come up? what the? it was there when I previewed, but now it disappeared... sheesh. I'll try again I guess...
 

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Discussion Starter · #15 ·
can anyone tell me why the attachment was there in preview mode, but disappeared when I posted? The 'Attachment 21428' is a .jpg of the schematic for the circuit... what the???
Sorry ya'll, I 'll have to try again... wierd.
 

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Discussion Starter · #16 ·
hello? is there an admin that can clarify any of this? How do I attach photos or graphics from my own machine? the attachment system seems pretty straightforward- whats wrong?
 

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Discussion Starter · #17 ·
 

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Discussion Starter · #18 ·
okay, sorry it took so long. The schematic for the tach driver/amp circuit is up in my truck pics area- check it out if it interests you... cheers all.
 

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Discussion Starter · #20 ·
Gyman98: How'd you get that image to post up? I tried a bunch of times to make that happen... anyway, glad that you could- thanks!!
Everyone else: I know its hard to see here, so download the image and blow it up a bit to get the details. PM me if you need any clarification... cheers all.
 
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