Just for spare parts

The results of the tach experiment are in. And the winner is.....the engine computer (not me).

Hooking up the pulse generator with 5V amplitude waves to the ECM did not drive the tach. I checked at a few frequencies simulating 1000, 2000, and 4000 RPM. No go. I also checked the RPM's with the OBD scanner. This confirmed the computer was on and also confirmed zero from the RPM input.

There may be another input to the ECM that is needed (may be from the camshaft sensor). Although it would have been nice to use the OEM tach at this point it is just easier to replace the tach and speedo with aftermarket replacements.

Oh well. No big deal. Into the spare parts closet for the pulse generator. Never know when I might need one again!

Just for the hell of it

I'm still waiting for the 2/0 wire to arrive. It should be here before Christmas. In the mean time I'm still fooling around with the tach.

As I mentioned before I'd like to keep the stock tach if possible. Worse case scenario I replace it. Not a big deal, but not as fun either.

Speaking of fun, in order to simulate the new motor spinning and the new RPM sensor I decided to build a pulse generator. This pulse generator creates square wave pulses of different frequencies. These square wave pulses basically duplicate the output of the RPM sensor. By feeding pulses of a known frequency I can see if the engine control module(ECM) will properly drive the tach.

Now I could have easily purchased a pulse generator, but what fun would that be. Any excuse to sit by the fireplace on a cold day, look productive, and use a soldering iron shouldn't be passed up.

This is a picture of the circuit while I was playing with it.


Here it is mounted on a board. I'm showing you the nice side of the board. My soldering is not pretty!


And here is a picture of the oscilloscope tracing showing the square waves produced by the pulse generator. As an aside Ebay is your friend(...oscilloscope...$4 ebay :-))


Next step is to attach the generator to the ECM. The ECM expects a voltage of 5V. This only puts out 1V so I'll need to hook it up to a small amplifier for testing. Maybe I'll build the amp too! Oh wait, I already built one a few years ago for my son's guitar ....just for the hell of it :-)

Just the ECM

That's the engine control module. Since there is no engine it would make sense that no ECM is needed. Not the case since the tachometer and speedometer inputs run through the ECM. So I guess I'll hook it back up.

The ECM is connected to the vehicle by two connectors each with over 60 individual wires. The top connector has the cable attached. The bottom does not.



Most of the 100+ wires that go to the ECM are for engine functions no longer needed. Out of all the wires I only need 8 (power, ground, ignition signal, CANH, CANL, vehicle speed sensor, crankshaft position sensor, and OBD communication).

With factory manual in hand I went through the bundle of wires and separated out the ones needed. The rest I bundled up, cut, and bagged. Eventually I'll cut off the wires not needed since they are bulky and get in the way.

Next I connected my OBD scanner and turned on the ignition. And as luck would have it the scanner started communicating with the ECM.

So now that I know the ECM works the next step is to hook up a new RPM sensor and see if the ECM accepts the input.

One last thing. Here is a picture of the instrument cluster partially installed. The signal lights are on top. The lower lights are dash illumination that get covers put on later. The lights seem to work fine although I need a couple more bulbs.

Just lots of acronyms

To everyone following this blog (all two of you, you know who you are) I apologize for not posting for a while. I'm sure you have been waiting with bated breath and were in the midst of going into withdrawal :-)

I haven't been posting, but that doesn't mean work has not been progressing. Currently I'm waiting for some wire to arrive. It is on back order.

In the mean time I've been working on the instrument cluster. Until I started taking the instrument cluster apart I didn't realize how few of the original cluster lights and gauges I could get rid of. Here is a picture of the original cluster.


The obvious gauge I wouldn't need was the fuel level. Some people actually do keep it and use it to track battery state of charge. I have another gauge for this so out it goes. Same with the engine temperature; no engine to temperature :-)

There are a bunch of lights indicating various engine conditions: too hot, change oil, service, battery, low coolant, etc. These would be sacrificed.

In the end there are only a few things I wanted to retain: tachometer, speedometer, odometer, turn signals, high beam indicator, and night time cluster illumination. In addition I will be adding a new gauge that lets me monitor battery voltage, battery amps, amps used, amps remaining, and a few other things.

This is the exploded view of the cluster.


In the old days each light and gauge in the instrument panel (I/P) would have dedicated wires. Vehicle speed sensor (VSS) to speedometer, crank position sensor (CKP) to tachometer, etc. Now a days cars have several computers collecting and dispensing information. Two of these are the engine control module (ECM) and body control module (BCM). They talk to each other and the sensors via a controlled area network bus (CAN Bus).

So the VSS sends its signal to the ECM. The ECM converts the analog VSS signal to a digital signal and broadcasts the information over the CAN. The BCM hears the VSS signal broadcast on the CAN and retransmits it to the I/P. The I/P then has a chipset that signals the speedometer needle to move.

They say that going from the analog way to the digital way saves 30meters of wire and decreases the car weight by dozens of pounds. It also makes "hacking" into the car electronics a hell of a lot harder. Oh for the pre-acronym days :-)

So here's the I/P circuit board. The four big white things are the four gauges. The bulbs are for the turn signals and I/P illumination. The little, rectangular white spots are LED's for all the warning lights.


Now I need room to fit the new gauge that keeps track of the batteries and motor. It has two parts, a display and a dial to select different display functions. Here is the display portion. The selector dial is a little smaller.



I decided that the best place to place the display was where the old temperature gauge was located. There were a few LED's there that I would not need. So after cutting out the unnecessary circuits and mounting the display I have this:



Next I had to do the same thing for the selector dial. The old fuel gauge on the far left was a good place. I also soldered a few wires to some LED"s to use as indicator/warning lights for the controller. This is the rear of the board after everything was mounted.



Here's what the front looks like.


On the left is the selector dial stem. On the right is the new display. I painted over the old markings where the thermometer was located. I need to paint over the old fuel gauge markings.

Next step is to get the I/P working again. I installed the I/P back into the dash and powered it up. The turn signals work (they are the only thing on the I/P that is directly wired and does not go through the CAN). The I/P illumination also works.

As expected most of the LEDS no longer work since I cut through the portion of the board that contained their circuitry. As for the speedometer and tach testing them will be a little tougher. I need to reconnect the ECM since the VSS provides data to the speedometer via the ECM.

The tach is a little tougher. Since I removed the engine I no longer have a crankshaft or a crankshaft sensor to provide data for the tach. I do have a sensor that will provide the new motor RPM's. I plan on connecting the new sensor to the ECM in place of the old sensor. Hopefully the new signal should satisfy the ECM. If not then I'll just pull the old tach and get an old fashioned analog one as a replacement.