My gauges don't work

[KIRIEIW]

Well just got the e30 insured today after swapping the motor out for a m20b25 (had a m20b27 before) but the gauges don't work, specifically the gas indication and rpms. When the gas gets low the light will go on but it always reads the gas as half tank unless you put more then half in (I think anyway, never put a full tank in yet ;)) anyways I assume it's the si battery's, what voltage do the replacements need to be, and is there a DIY that shows how to Solder the new ones in. Thanks again

[phenobarb1]

You might need to change the chip in the instrument cluster, when you go from an e to an i. It pops right in, no muss no fuss, either as a clip in the front of the cluster, or I think, on the back for older models. Can't remember, but I'm sure someone else can chime in on that. Either way, I don't think it's the SI board batteries.

[phenobarb1]

I should mention that I've never done an e to i swap, but I just feel like I recall this being an issue that people have mentioned. So, I could be completely wrong. If it was the SI batteries, I think the issue would have shown up before the swap, though maybe I misunderstood what you said.

[jlevie]

In my experience, a bad SI board doesn't affect the gas gauge but does affect the tachometer, econometer, and temperature gauge. Since the battery would have been disconnected for quite a while during the engine swap, the SI board batteries could have run down and that might be the tachometer problem. The fuel gauge problem is likely to be something else.

If you didn't use an 87 M20B25 engine harness wiring modifications are necessary for the tach to work. Did you do one of those?

[KIRIEIW]

In my experience, a bad SI board doesn't affect the gas gauge but does affect the tachometer, econometer, and temperature gauge. Since the battery would have been disconnected for quite a while during the engine swap, the SI board batteries could have run down and that might be the tachometer problem. The fuel gauge problem is likely to be something else.

If you didn't use an 87 M20B25 engine harness wiring modifications are necessary for the tach to work. Did you do one of those?

Nope. I think I just used the 88' harness, and if not that the old m20b27 harness would be in there. Also, I forgot to mention that a yellow light stays on (where the green-red battery power thing is on the cluster)

[dnguyen1963]

The yellow light is just a reminder that a service I (oil change) interval is due. I bet that your SI board/batteries are not good.

[jlevie]

Nope. I think I just used the 88' harness, and if not that the old m20b27 harness would be in there. Also, I forgot to mention that a yellow light stays on (where the green-red battery power thing is on the cluster)

In that case, the tachometer and econometer signals aren't reaching the cluster. Until 8/87 those signals were furnished to the car by C104, which a three pin connector pigtailed off the engine harness near the DME connector. From 9/87 on those signals are routed through C101. Production of cars with the M20B27 engine ended in 8/87, so modification of the harness or the car's wiring is necessary when using an 88 or later engine harness. The M20B27 harness won't work with an M20B25 engine.

[KIRIEIW]

In that case, the tachometer and econometer signals aren't reaching the cluster. Until 8/87 those signals were furnished to the car by C104, which a three pin connector pigtailed off the engine harness near the DME connector. From 9/87 on those signals are routed through C101. Production of cars with the M20B27 engine ended in 8/87, so modification of the harness or the car's wiring is necessary when using an 88 or later engine harness. The M20B27 harness won't work with an M20B25 engine.

I'll have to ask my dad, I don't think I was home when he was working on the car that day, he must have done some splicing and switched the plugs I assume. I'm hoping though replacing the si battery's will fix it though cause it was saying on pelican that if your rpms and or other clusters fail randomly that it's most likely the si battery's.