86 328e cluster issues

[GK E30]

I recently purchased an 86 325e for my son to drive (first car) and have been working through some issues to make it reliable for him. I knew there were issues with the cluster when I bought it, no worries, anything can be fixed. It's a lot better than it was but still not as good as I'd like.

The main issue and my biggest concern was the fuel and more importantly the temp gauges. I've managed to get the temp gauge rock solid and the fuel working and correct about 90% of the time. The fix for these was a combination of cleaning and adding some solder to the grounding points on the board and making sure they were tight when I put everything back together.

The one that's driving me nuts is the tach. Sometimes it works sometimes it doesn't. Yesterday in my latest attempt to fix them all, I reflowed all of the pins for the blue, yellow and white multipin connectors as well as about 80% of the other solder connections on the board. I did not reflow the connectors where the SI board, tach and spedo connect. I put everything back together and all gauges worked but I only had one working cluster illumination light. I thought maybe I knocked a bulb loose or perhaps it just went bad. A few hours later I went out for a test drive and both of the illumination lights worked but no tach. The econometer has always still worked even when the tack doesn't. This morning I drove the car to work and still no tach. No tach at lunch. This evening leaving for work I was back to all gauges working and only half of the dash lit. On the way home the cluster became fully lit and I still had a tach.

I believe the SI board is ok. It was replaced at some point as it's the newer style with lithium batteries and orange sealant all over it. Also I have reset the SIL and all lights have remained out as one would expect.

I have searched and read and then searched and read some more to get to this point and am running out of ideas.

I did not use flux when I reflowed the board yesterday. Could this be an issue? Maybe I should flux and try one more reflow?
Is there a crack in the board?

I have also cleaned ground connection G200.
I have removed and reseated fuses 9 and 10
I've checked the 3 pin connector C104 for tightness but not signal.

I've also removed an aftermarket stereo installation where a PO had hacked into the heat dial for illumination and the OBC for 12v constant memory.

Anyone have any ideas or thoughts?


Also thanks to all who post here. There is an amazing amount of knowledge shared here that I feel lucky to have access to.

[Gregs///M]

I would start by replacing fuses 10, 12, and 21 with 7.5A.

Then, If you have never replaced your SI board batteries, assume they are dead. If the batteries are covered in the orange coating, they are almost 25 years old and surely dead. Just because the SI board looks clean and the batteries look clean, does not mean it is good.

Also, check the inside corners of the SI board. See my thread on the topic, it might cause your tach to not work.
http://www.r3vlimited.com/board/showthread.php?t=274422

Since you were reflowing solder, why didnt you reflow the section between the speedo, tach, and SI board. That is one of the most important parts to reflow.

I would start with those suggestions. Other possibilities are cracked electrical traces on the cluster main board, burnt up SI board, or burnt out motor for the tach.

[GK E30]

Gregs, thanks for answering. After following several of your posts you seem to be the go to guy for all things cluster related.
I will give the fuses a shot. It's easy enough to try them.

I went out with my son tonight for some practice driving and when we first left I was back to only one illumination light and no tach. I cranked the heater up and set to defrost to try and get as much heat in and around the dash as possible and in about 10 minutes I had all lights and gauges working and remained solid until we got home about an hour later.

The SI board batteries read 2.9v at room temp. I thought about putting the board in the freezer for a little while to see if that changed but have not tried that.

The only reason I really have for not reflowing the SI, tach and speedo connectors is that I was trying to work the connectors in groups to see what fixed the problem. I know there were loose contacts on the blue and white connectors. I could wiggle the wires and drop all of the gauges before repairing them.

The is a small amount of damage from incorrect screws on the SI board. On one side it is without a doubt board only damage. The other side, nearest to the coding plug, it looks like the trace has been hit but not broken. I looked at it under magnification but didn't check with a meter. I'm embarassed to say that I may have caused that damage myself by not paying attention to the screws that went in there. Since the tach is acting the same as before I ever took the cluster apart I'm kind of discounting that trace as part of my problem. I do plan to at least seal the damage where the trace is exposed.

Don't know if this is a clue to anything but when the tach isn't working it rises up and stays at about 1900 rpms. If I rev the engine hard it will deflect down to 0 and then back up to 1900. When turning the engine off it doesn't go back to 0 but stops about a quarter of an inch from 0. Turning the headlights off and on about three times will cause it to creep back down a little with each cycle of the lights.

[Gregs///M]

The SI board batteries are 3.25V when new. 3.0V or lower is considered dead. Although its not considered definitively dead, cause current load must also be checked, in your case I would go ahead and confirm your batteries are indeed dead.

I bet you replace the SI board or batteries and your tach will perform everytime.

[E30NJ]

The temp and gas gauges have bad grounds and they need to be cleaned every 2 to 3 years. The Si board batteries are not horrible to replace but you need good soldering skills.