Flaky Motec ADL?

[Wizco]

I've got a Motec ADL, that's gone flaky.

Power it up, everything appears OK. Start the car, everything appears to be OK.
Rev the engine, and water temp goes immediately to 380 degrees, the oil temp goes to 380 degrees, oil pressure is 15 psi engine running or not, and the wheel speed goes to 126 mph with the engine off.

Power the Motec down, back up, and everything looks normal till you rev it again.
Alternator is good, battery is good. I've grounded the Motec directly to the battery in an attempt to rule out a bad ground. Same results.

I'm guessing the Motec dash itself is toast, but before I start throwing money at it, I'm wondering if anyone here has any ideas?

Car is a standard Formula Mazda.

[Maciej]

I've got a Motec ADL, that's gone flaky.

Power it up, everything appears OK. Start the car, everything appears to be OK.
Rev the engine, and water temp goes immediately to 380 degrees, the oil temp goes to 380 degrees, oil pressure is 15 psi engine running or not, and the wheel speed goes to 126 mph with the engine off.

Power the Motec down, back up, and everything looks normal till you rev it again.
Alternator is good, battery is good. I've grounded the Motec directly to the battery in an attempt to rule out a bad ground. Same results.

I'm guessing the Motec dash itself is toast, but before I start throwing money at it, I'm wondering if anyone here has any ideas?

Car is a standard Formula Mazda.

Fried sensors?

[Pi_guy]

Are the sensors wired to the motec or does the data string come from the ECU?
Check to see if it is not in a simulate mode.
Can you see the configuration with the dash manager?
Try using the monitor function in Dash Manager when you run it see if numbers match as to what is shown on dash.

Multiple grounds can create grounding loops go back to original wire configuration.

[Darryl Wills]

monitor the input voltage to the ADL..Your voltage regulator may have just gone out in the alternator

[David Ferguson]

My guess is you have a wiring harness that is shorting an 8V or 5V supply when the engine is rev'ed. A NTC (Negative Temp Coefficient) temp sensor will read a high-value temperature (low resistance) when there is no power supplied to it.

To make sure it's not a bad sensor -- try removing half of them -- does the problem still happen to the ones connected? If so, re-connect those, and remove the other half. Does the problem still happen. If so then it's not any of the sensors.

You may be able to find this without even running the car. Just wiggle the wires in the harness. Start wiggle the wires at each sensor end (this is usually the most fragile), and also try anywhere the wiring goes around frame tubes, or could contact bodywork.

For the pressure sensor does it change if you disconnect the the sensor? It should, but if not, then I suspect either a configuration issue, or failed wiring.

[Wizco]

To answer some of the above:

No ECU, it's a webber'd standard Formula Mazda. Sensors are wired to the Motec.

Voltage from alternator is 14 volts.

Disconnecting the water temp changes the dash display from 380 to a negative number.
Oil Pressure reads 15 with the engine on or off, sensor connected or not.

Haven't tried disconnecting any other sensors yet.

I have tried wiggling wires. The Op sensor, water sensor, and oil temp sensor are all with 2-3 inches of each other, and the wiring is all in the same harness. My first thought was chafing of the harness heading from that area of the car to the Motec, and I spent a fair amount of time checking those runs.

The I realized the wheel speed sensor is on the front of the car, and it's coming from a completely different direction.

Ground loop is an interesting idea. The system worked fine last season. Flaky readings are new this season. Only changes to anything electrical over the winter was rewiring the rain light circuit. I have disconnected it completely after getting flaky readings to eliminate that variable.

I'm leaning towards the Motec dash itself has gone bad, but don't want to start throwing money at this till I know more.

[Pi_guy]

My comment on the ground loop was from you "grounded the motec directly to the battery".

My other reason is to try communicating with the device as to see if you have errors tossed during communication. Using monitoring program to see channel data.

Wiring insulation can deteriorate from temp changes and stresses and not have a outward physical mark using something like a Cirrus tester is one way to determine harness issues.

[mikey]

Water temp is a thermistor and if open circuit then usually results in negative (-40) degrees. So if hooked up its pegged high then I'd suspect a short in that circuit, external from the dash.

[David Ferguson]

I would look for the 5V & 8V supplies. Do you have power on the Oil Pressure sensor connector (I would expect 5V on the 3-pin packard connector)? What about the wheel speed (8V?), beacon receiver (could be 8V or 12V), and download port (8V)?

Since this only happens with the engine is rev'ed -- what happens if you disconnect the tach signal? (I assume coming from the MSD box to a digital input).

Perhaps your shift-light outputs are triggering this problem.

If you want to send me your dash to confirm that it is OK, I can test it on my bench, or even pop it in another car for testing.

ferg@veracitydata.com

[SpacemanSpiff]

As a preface, I've never worked with any of Motec's stuff. However, if all of your sensors are acting up, I would question if its a sensor or wiring harness issue. Unless you have an intermittent short on a power or ground path, I can imagine a flaky sensor, but not all of them.

What happens if you just slightly open the throttle? Does the same happen or do you need to really step on it? As far as I'm aware, there are only two ways a dash system should be RPM dependent. First, maybe the tach signal is doing something loopy that's throwing the dash off. Pretty slim chance, but I suppose anything's possible. Second is that your charging system presumably is tied in. I like the idea of a failing voltage regulator that Darryl put forward. A quick voltage spike could be resetting internal fusing on the dash or something similar, which would kind of explain the issues. Alternatively, you could be undercharging and not powering some circuits.

Pretty easy to check with a WalMart grade volt meter (don't measure amps, you'll destroy meters quickly). You can also check the sensors that way if you're concerned.

[Wizco]

Haven't had a chance to play with it, we were running the car last weekend.

It was suggested locally that the alternator may be the problem. I need to check that this week, and see if that's the problem.

I agree that several sensors are unlikely to go at once. I'm down to either a short in a harness, screwy voltage from the alternator, or the Motec itself.

A slight bump in revs doesn't do anything, (the gauges still read correctly) coming in to the pits, all gauges are pegged on the high side, kill the master switch and reboot the Motec, and all is well till you get on the revs again.

David, if the alternator theory doesn't pan out, I'll be in touch.

[SpacemanSpiff]

Also check your belts. It's a long shot, but it's cheap. I had charging problems on my Miata during college that went away around town (so the alternator was fine), and the battery was brand new. Unfortunately the belt was so shot that it was slipping on the alternator pulley at high RPM's, resulting in really weird effects driving down the highway.

[Prsginc]

The problem is the ground from the MSD ( black wire). Ground it directly to the engine.