Partial Instrument Panel Failure?

#1

After having absolutely no problems with the electrical systems on the car, I’m experiencing a series of failures.[ol][li]Or or about Wednesday of last week: the Odometer and Trip Odometer stopped working – it’s possible that I pushed the T/O plunger and stripped the gears while the car was moving, after filling up on Wednesday[/li][li]Today: when I started the car, everything appeared to be working correctly, then, after a 3-point turn to move it from the position it was in after pulling it off the trailer last night:[/li] [ul]
[li]the gas gauge went from ½ to less than empty (and pressing (1000) & (1) on the OBC does not change the display from the standard function),[/li]
[li]the water temp gauge dropped to less than 0,[/li]
[li]the econometer swings wildly between 5 & 20 mpg when sitting still, and[/li]
[li]the stock tachometer stopped working between idle and ~3,000 rpm; above 3,000, it randomly spazzes out, momentarily drops to 0 when the brakes are tapped, the turn signals or the head/parking lights switched on. (My aftermarket tach, wired to the coil, works just fine.)[/li]
[/ul]
[/ol]
The speedometer is working fine (showing 3-4mph fast, according to my TraqMate’s GPS compass function).

I haven’t been near the wiring for the instruments since November of last year, when the rest of the cage was installed. I recently pulled the cruise module, but I did it carefully and cleanly, without cutting or yanking on any wires. The instruments were working perfectly when I pulled into the pits after yesterday’s race.

I’m going to pull the instrument panel later, once it cools off, but other than loose connectors or compromised wiring behind the dash, is there something/somewhere I should be looking for a common cause to these issues?

Thanks! :ermm: :pinch:

Post edited by: sharkd, at: 2006/07/31 11:47

#2

I thoroughly dislike hunting these kind of gremlins. My first guess would be that you have a bad ground somewhere. I would start with ground junction right below inst cluster (and a bit to the left of steering column IIRC) – it should be bunch of wires stacked on one bolt Since everything worked before pulling out CC, do you remember at which location you disconnected ground wire?

The difference between your instrument speedometer and what GPS tells you is normal – all speedometers are intentionally made to show3-4% (or there about) higher then actual speed.

Igor

#3

Igor wrote:

[quote]Since everything worked before pulling out CC, do you remember at which location you disconnected ground wire? [/quote] I simply disconnected the round connector and fed the wire back through the firewall – there was no ground. The stalk was disconnected via the molex connector stack on the steering shaft and the VDO module was just disconnected from the DME. I didn’t pull the entire wiring harness. :unsure:

#4

Dan,
I would suspect Grounding issues first as well, then the batteries on the Service Indicator board…what is the status of your SI lights? have you ever been able to reset them? The Tach symptom is the giveaway for this

The ODO is gear driven and over time the heat and time make the gears brittle and they will break if you hit the reset while they are turning(car not stopped)
they can be replaced if you desire but in a racecar…

#5

sharkd wrote:

I agree that it can be SI board related (good point).

As for ‘no ground wire’ – I just looked at the drawing that I made when I pulled the CC harness out ( I sold it, I think that it’s in Brazil someplace… :woohoo: ). My representational diagram shows brown (ground) wire that that goes to that ground junction point I referred earlier. The brown wire has an “one wire connector� on it – one end goes to the main harness and another onto that ground junction. At least on my harness (87 325is), the brown wire branched from the main harness between clutch switch connector and round (main) connector [the one that has 7 wire connections; 3 big and 4 small].

Now, with that "clear as mud" description, I still unclear if that is the source of your problem :blink:

Igor

#6

What I meant was that I didn’t pull the CC harness, just the lead from the servo unit that went through the firewall. I’ll pull the cluster tomorrow and look at the chassis ground (I know what you’re talking about, that’s where I grounded the aftermarket tach 9 months ago.) I’ll also look at the SI board – in the 14 months I’ve owned the car, the lights were reset once, when the head was replaced due to rocker failure in May of last year.

#7

sharkd wrote:

did the reset "take"…in other words do you still have a bunch of green lights or did it run down to red pretty quickly?

#8

It only got up to three green lights as of this weekend.

#9

good chance it is the batteries then

#10

there’s actually a good thread on bypassing the SI board here:

http://www.e30tech.com/forum/viewtopic.php?t=22120

that way you can take the batteries out of the equation and make sure the cluster gets good power. Other things to do while you have it out include checking the board for cracked traces and solder joints, looking for and cleaning up corrosion, and checking the grounding nuts on the back of the temp and fuel gauges. Take those two nuts off, pull the modlues off the board, clean up the contacts and put it back together making sure not to overtighten the nut and crack the wave washer. And if you’re still having ODO problems, take a look at the gears there, you’re probably missing a tooth or two. They are replaceable as well.

Do all that and the cluster is ready for another 20 years of service! :wink:

Post edited by: ecpreston, at: 2006/08/02 07:27

#11

ecpreston wrote:

[quote]there’s actually a good thread on bypassing the SI board here:

http://www.e30tech.com/forum/viewtopic.php?t=22120[/quote]Unfortunately, my instrument cluster isn’t the type that can be jumpered – it’s a different design.

That said, I found the problem.

I put in a known-good SI board yesterday with no changes, checked the G200 ground and found nothing wrong, but heard a pop when I turned the ignition key to ‘on’. So, I popped the hood – no fuses blown. (Bear in mind that in my infinite wisdom, I replaced the standard fuses with fancy "light-up" fuses that have a glow filament when they blow.) So, I leave the hood open and turn the key again, to find the ‘pop’ and Fuse #10 lights up like a Christmas tree. :pinch: Doh! :blush:

I spent all that time going through the Bentley’s instrument panel pin-outs, when I should have flipped another ten pages and checked the fuses for common circuits. (The reason everything was working momentarily after cranking, and the pop noise was that the glow filament was carrying enough current to energize the circuits briefly.)

While I’m glad it was nothing expensive, I am a bit red-faced – it kind of reminds me of a laptop failure I had in college (I replaced the motherboard, the video card, and the power controller, only to pay another $200 to have a shop tech find out it was a bad RAM module, the one thing I didn’t test.)

#12

Okay, now, I’ve really found the problem.

Turns out that my little bit of agricultural racing at VIR did have an impact on my car. In all the bumps and spins, the harness between the back-up light switch and the console made contact with the giubo.

Under acceleration, the Green/White wire, now partially stripped of insulation would occasionally ground on the transmission, shorting fuse 10 (a low-amp catch-all fuse).

So, a word of advice: If you go four wheels off, two wheels off roughly, or have contact with another car, put the car up on jackstands and check the reverse switch wire – it’s on the passenger side, running from about ½-way along the housing, back to the shifter.

#13

Good track down Dan. Thanks for the heads up (not that we hope to have an agricultural incident as spectacular as yours at VIR!). At Mid-Ohio this weekend, David Herrington had a similar, weird, wiring issue. Ended up to being in the wiring to the in-tank fuel pump. We never found where it was and ended up doing a quick fix with a direct wire to the pump, but he was unable to make the race - probably because the fuel system had vapor lock.

Ed