tachometer/fuel economy gauge

coolbear1 · 10-10-2005, 10:34 PM

I have an 88 325i convertible with an instrument cluster problem.
I cannot get the tach and fuel economy gauge to work.

I understand that the main culpret when this happens is the batteries in the service indicator board going bad.

I have removed the instrument cluster and service indicator board and even gone so far as to remove and re-solder new lithium batteries into the board. But to no avail. I even replaced the board whith a known good one and no tach.

I have checked voltage and ground at the three plugs on the back of the instumrnt cluster per the bently manual and it checks out. Also I am getting fuel economy signal to the on board computer because it is calculating average mpg and range.

I have also replaced the tach and fuel economy gauge with a known good one and it doesn't work.

Any one with any clues?

I've invested too much to give up at this point.

I might have to install another car on the gauge!

panzerbmw · 10-11-2005, 05:29 AM

I put a new motherboard in. I had a strange similar problem, with the tach not working. After changing many of the components in the cluster (tach, fuel, speedo, SI board, and motherboard, I somehow came up with a combination that worked.

coolbear1 · 10-12-2005, 04:39 PM

Did your fuel economy gauge work before and afterwards?
I assume by motherboard you are refering to the motherboard the tach and speedo plug into. Unfortunatly I did. sort of.

I put an instrument cluster out of my 85 325e that works in it, but not in my 88. I assumed it was because the 88 is motronic.1 , and the 85 is the older version Motronic DME, even though they look identical.

But you my be onto something that could work for me also.

I think I will try swapping components and boards around to see what happens. I already have the steering wheel and the trim off.

Thanks, Panzer.

I'll let you know.

panzerbmw · 11:49 AM

I think the FEG went out too, perhaps the whole right side of the cluster as I believe I was chasing a faulty water temp gauge. I know the 'e' cluster won't work correctly because the tachs are different. I 've done this to hilarious effect. The 'i' motor will rev way past the redline with the 'e' tach. My parents own an auto parts store so I was able to frankenstein a few different clusters and see what works. You may be on to something with the DME vs. 1 thing. Just be EXTREMELY careful with those plastic tabs on the top. BTW, I probably changed the SI board in the process.

flatlander · 11-05-2005, 09:04 PM

My 88 iX had this same problem and I did all of the things that you have mentioned while trying to fix it. My speedo had also stopped working so it was a slight adrenaline rush while in the proximity of police. Anyway I got the speedo working but the tach and feg still didn't work. shortly after all the work I went out to a dead battery...I had left my Sirius receiver turned on for a few days. I couldn't get to the battery since my key won't open the trunk so I had to charge from the starter connection. Don't ask me why but since that day the tach has worked fine. The feg even worked for about a week and then died again. Two months later and the tach and speedo are still working. My assumption is that there is a connection at or near the starter that was loose that I bumped while jumping the car.

coolbear1 · 11-06-2005, 08:29 PM

I fixed it. It was the SI board. The one out of my 85 won't work in the 88.

Go figure.

I purchased one on e-bay for 35 bucks + shipping. All is good in 88 e30 cabroland.

I am putting it for sale in the mullet wrappers (Auto trader and the like, for those of you who don't speak Florida Cracker).