Tripminder Calculations

[Lutrova]

Taking a second look at the shop manual, there is a brief statement on how the digital fuel gauge has anti-slosh mechanics built into the module, which probably means a failure there wouldn't be serviceable.

Pivoting slightly, another issue I've encountered with the Message Center is its display flickering off completely, or the text changing to some nonsense or a single, super bright character. The incorrect text seems to me like a bad connection in one of the wires between the logic module and display, but the display turning off entirely could be a power supply issue. Or it could still be one of the logic-display wires, but the power supply is interesting because of an oddity in the wiring diagram.

The other two digital gauges are supplied by power only in Accessory or Run, but the Message Center components have constant power. What's strange is that the same circuit that supplies Message Center power also appears to run to the engine compartment light. I'm currently running a junkyard-find light, which has to be hit just right to turn on or off, which doesn't seem like intended behavior. The shop manual appears to be silent on its operation. Does anyone know what's supposed to trigger that light on or off? Is it opening the hood? And if so, how is the light aware that it happened?

[kishy]

Just straightening some uncertainties from above:

The boxy box (to 89, non-digital) anti-slosh module is a dedicated little box somewhere in the vicinity of the glovebox. It is often but not always orange.

The 90 analog cluster (which despite its aesthetic differences is fundamentally the same thing across Ford-Mercury-Lincoln) introduced the board which plugs into the cluster itself.

I was not sure how the digidash Lincolns did it; never had occasion to figure it out.

Hood lights use a mercury switch (or some comparable assembly); as the light assembly tips backwards the switch closes and the light turns on. You should find that the wire going to it is always hot.

[gadget73]

I'd be very unsurprised if the message center module doesn't just need an overhaul. Old electronics that live in a bad environment just don't hold together forever. I've had a lot of issues with buggy BS that turned out to be capacitors leaking goo on the board.

[Lutrova]

I can definitely see that being the case. As I look more into it, there just aren't that many wires connecting everything, and so far the amount of corrosion on the contacts has been minimal.

Have you found bad/leaking capacitors to be the most common form of failure on old car electronics? I don't think I can pull apart the display boards and have them survive, but the logic module is in a metal case, so it might be possible to disassemble and clean up. And the size of the circuits on these '80s boards look like they can't be too tricky to solder.

[sly]

Most of the old stuff is through hole... so yeah... usually easy.

[gadget73]

Have a digital dash and a message center unit from an abandoned idea. They are chunky through-hole parts, no fuss to deal with. Just clean the boards of any leakage that may have occurred.

leaky caps are just a general pestilence with old electronics. In the Mark VII, the EATC, overhead console, radio, tripminder, anti-slosh module, and the speedometer itself have all had failed caps. Caps in the Towncar's ECM barfed and leaked goo on the board.

[Lutrova]

I pulled the logic module earlier tonight, and it all came apart surprisingly easily. Unfortunately, nothing really jumps out as wrong to me.



To my untrained eye, the capacitors all appear to be in good shape.





It's a little hard to tell from the angle, but there's a tiny little chip with three wires running to it that was screwed to the bottom of the case with some thermal paste and a small wafer between it and the aluminum. There looks to be an identical chip mounted to the larger board, and judging by the second screw hole on the case it might have originally been mounted separately as well.



I assume all the marshmallow-like stuff is some sort of factory-applied insulation, and not some catastrophic failure.

This module did pass the quick test perfectly, except for some discrepancy between itself and the fuel gauge, which is known to be screwy. I do see some marks on the contact points with the wire connector, but I don't know if it's significant enough to cause any trouble.

Now that I've got this thing cracked open, is there anything I should be doing while I'm in here?

[DerekTheGreat]

Wow, it looks brand new and quality on top of that, although I was only 16 days old when it was built.

[slack]

I believe the 3 prong chip with the thermal paste is a voltage regulator.

[gadget73]

yeah, voltage regulator.

The white rubbery crap is basically like RTV gasket maker, just a slightly different compound that doesn't have acid to rot electronics. This one looks a lot different inside than the unit I have hanging around, but I think that one came out of an 82. That one was chock full of parts, this one is much more sealed, probably more reliable honestly.

Any evidence of leakage around the 3 caps on the board? The tubular things with wires sticking out of each end. usually when they get real bad it will start to ooze out of the rubber sealed end. More typically its the small ones that go bad too.

[Lutrova]

I was not quite seven years away from being born when this thing was made.

There are a lot of Ford part numbers on this thing, and it appears they were making a lot of changes over the years. Maybe half of the little doodads attached to the boards have E0 numbers, a couple have E1s, and the rest are E6s. The pictures I posted may not be quite large enough, but there are little Motorola logos on some of the black rectangular bits.

The case is certainly robust, but there are two large openings on the bottom. When I was removing the connectors with it still mounted under the dash, I could see right in between the boards to some of the capacitors. So the whole works have been exposed to air and whatever moisture was in it, but I guess dust wasn't able to settle inside.

Capacitors all look solid. I can't see any deformations on the three big ones, or any of the smaller caps or diodes. All the circuitry looks to be intact, too, although the board with the most junk on it is bowed slightly.

I think I'll just clean up the case, apply new thermal paste to the voltage regulator, and put it all back together. I'm sure I could analyze it more with a multimeter, but I don't know what I'm doing so I doubt I'd find anything useful.

[Lutrova]

Message center logic module is back in the car, and after running the self test it appears to be as functional as it was before. The display still cuts in and out occasionally, or shows only a fully bright single character, but this now seems more like a display module problem. I wouldn't be surprised if that part had bad capacitors, but as I've mentioned before, disassembling it non-destructively seems to be impossible.

Back at the fuel gauge, I've started running down the diagnostic test for erratic readings. The ground in the trunk is good. 0.3 Ohms between it and sheet metal at the sender connector. But after bypassing the sender with two wires, one 10 ohms and the other 72, both had the gauge reading empty. I tried connecting a spare level sender before plugging the one in the tank back in. Both were also reading empty at the gauge. So now my erratic fuel level has turned into an always empty, which at least is still the same diagnostic test. The only thing I changed was swapping out the two ground screws under the instrument panel, one of which is probably for the digital instrument panels. Not sure how that would impact my fuel reading, though.

So now that I've apparently ruled out the sender and the trunk ground, the next step is to pull the instrument panel and check the wire coming up from the fuel tank. I'd been banking on this being the problem, but after seeing the state of the message center module and other connectors under the dash, I'm not expecting to find any trouble. If that wire checks out, then the final step is to check voltage on the back of the fuel gauge. If it's at least 10 volts, then the gauge is bad. If it's not, then the shop manual wants me to correct the power circuit, however that might be accomplished.

[friskyfrankie]

Message center logic module is back in the car, and after running the self test it appears to be as functional as it was before. The display still cuts in and out occasionally, or shows only a fully bright single character, but this now seems more like a display module problem. I wouldn't be surprised if that part had bad capacitors, but as I've mentioned before, disassembling it non-destructively seems to be impossible.

Back at the fuel gauge, I've started running down the diagnostic test for erratic readings. The ground in the trunk is good. 0.3 Ohms between it and sheet metal at the sender connector. But after bypassing the sender with two wires, one 10 ohms and the other 72, both had the gauge reading empty. I tried connecting a spare level sender before plugging the one in the tank back in. Both were also reading empty at the gauge. So now my erratic fuel level has turned into an always empty, which at least is still the same diagnostic test. The only thing I changed was swapping out the two ground screws under the instrument panel, one of which is probably for the digital instrument panels. Not sure how that would impact my fuel reading, though.

So now that I've apparently ruled out the sender and the trunk ground, the next step is to pull the instrument panel and check the wire coming up from the fuel tank. I'd been banking on this being the problem, but after seeing the state of the message center module and other connectors under the dash, I'm not expecting to find any trouble. If that wire checks out, then the final step is to check voltage on the back of the fuel gauge. If it's at least 10 volts, then the gauge is bad. If it's not, then the shop manual wants me to correct the power circuit, however that might be accomplished.

Sounds crazy but is your battery really strong? I have seen many electrical issues caused by a weak battery. My friend's '96 CV, with digital dash, was showing "CO" and other erratic readings until we recently swapped out the old battery for a brand new one. So far (over a month) the erratic reading disappeared and all is good. Like I said, crazy but one never knows - does one?

[Lutrova]

I just replaced the battery a month or two ago, so it's brand new. And with the new battery I was still getting the erratic fuel level. The only things I think I changed before getting this always empty reading was pulling and reinstalling the message center module, and swapping out the two ground screws under the center of the dash.

I suppose if the gauge is the issue then giving it a once over for capacitors and such wouldn't be too bad, but the shop manual expects you to just throw out the old one, so I'd be going in blind.

[Lutrova]

It's been awhile, but I've continued to plug away at the fuel gauge in my spare time. I have a spare digital fuel gauge, the original from my car, which I decided to take apart to see if any obvious failure jumped out at me.





The assembly consists of two boards held in place in a plastic housing, secured by four screws and a bit of glue. The top board has the VFD mounted to it, while the lower board has most of the capacitors and other electronic doodads. The lower board has a part number E4VF-14A608-DA, which is the same part number Ford gave to anti-slosh modules for analog gauges.





There are five terminals on the back of the gauge. All but the ground are connected through the printed circuit that also serves the speedometer and turn signal/high beam lights. Fuel signal is obviously the signal from the level sender in the tank. Message Center must pass this information on to the message center logic module for its distance to empty calculation. Illumination, I believe, goes to the headlamp switch to control dimming of the VFD. I don't quite understand what the Ignition terminal is for, unless it's the power supply.

None of this information really gets me any closer to solving my erratic fuel level reading, but I figured the pictures might interest some. The circuit boards appear to be easily serviceable if you know what you're doing. That said, nothing looked like it had blown up or was covered in gunk. This fuel gauge had the same problem that I'm still facing after swapping it out for another, so either both gauges failed in the same way or my fault lies somewhere else in the system.