got a 91' 740, ran the codes, one of them is the speedometer sensor, well, since I got my car I've done changed every sensor on it... anyhow, the question is, where is the speedo sensor on this b230f? the speedometer works occassionally, sumtimes when I turn on the car it goes crazy and then theres times where it just lays dead... what could this be...?

 

Here's the sensor on the rear cover of the differential...

Check the connections first, they are exposed to the elements. The sensor itself seldom fails. The speedo can and does fail in the cluster. Loose connections on the back of the cluster will mimic speedo failure sometimes. Also, the ignition switch wearing out can cause some funky readings...wiggling it and watching to see the effect, if any, can sometimes narrow it down.

 

thanx for the info, u've been a great help since I got my 740's, I got sum codes from it the other day, said sumthin about the ect n knock sensor(missing signals), I switched them out from my other 740(89') n got the same codes back plus sum, dont know, I had posted them like a week ago but no one replied... thanx for ur help though.. I love my car.......thanx to this forum...

 

Your symptoms sound exactly like what happened on my '91 740. I'd certainly try what Swift suggested, checking connections and so forth, but in the end I think you're gonna end up replacing it. I was told that the '91 740 speedos were particularly bad about failing due to the crappy capacitors they used that year, which leak all over the circuit board. I replaced my speedo with another from the wreck yard a couple of times before finally sending it off to one of the few speedo shops that is willing and able to fix the problem. Cost $260, but it's been working great for about 6,000 mi. now. (Trip meter too!)

If you decide to pull the cluster be sure to disconnect the battery first. The circuit board is exposed, on the outside of the cluster, and it has a built-in fuse which is easy to blow while you're moving things around. 240's have the circuit board on the inside, where it's protected, so this is yet another case where changes are not always improvements...