i engine in seta, tach doesnt work

[Kershaw]

ok, so here's a rundown

1. bought the car with an early model i engine swap and a seta cluster or at least the seta tach (5.5k redline.)
2. all the gauges worked. but the engine barely ran.
3. swapped the early model i engine for a late model i engine
4. all gauges except the tach work
5. the cps worked on the new engine when pulled, but i put the old cps in there that worked before the swap just to check. no dice.
6. swapped clusters for a late model i cluster which worked when pulled. while out, i checked the SI board batteries. both clusters were good.
7. gas gauge now only half works, i read up on that and the early model gas gauge will go in to replace that.
8. replacement late model tach still does not work.

im at a loss. any advice?

[Wh33lhop]

Is the coding plug good? SI batteries good? Tach fuse good? (does the econogauge work?)

[jlevie]

When you swapped engine did you also swap the engine harness? If so did the harness you removed have a white 3-pin connector pigtailed off the harness near the DME connector?

The late M20B25 harness only has a black 3-pin connector near the DME connector. An early M20B25 harness has an additional 3-pin connector. On cars that use the later harness (from 9/87) the tach signal reaches the cluster via C101. But on an early harness the tach signal is via the white connector. If the harness doesn't match the car you won't get a tach (or econometer) signal to the cluster.

[StereoInstaller1]

When you swapped engine did you also swap the engine harness? If so did the harness you removed have a white 3-pin connector pigtailed off the harness near the DME connector?

The late M20B25 harness only has a black 3-pin connector near the DME connector. An early M20B25 harness has an additional 3-pin connector. On cars that use the later harness (from 9/87) the tach signal reaches the cluster via C101. But on an early harness the tach signal is via the white connector. If the harness doesn't match the car you won't get a tach (or econometer) signal to the cluster.

jim, you are such a stud!

[Kershaw]

When you swapped engine did you also swap the engine harness? If so did the harness you removed have a white 3-pin connector pigtailed off the harness near the DME connector?

The late M20B25 harness only has a black 3-pin connector near the DME connector. An early M20B25 harness has an additional 3-pin connector. On cars that use the later harness (from 9/87) the tach signal reaches the cluster via C101. But on an early harness the tach signal is via the white connector. If the harness doesn't match the car you won't get a tach (or econometer) signal to the cluster.

i guess thats it.

fml.

i do not want to swap engine harnesses. any other solutions? and if that is the only one, will an early model engine harness work on a late model engine?

[jlevie]

There's no difference in M20B25 engines, regardless of when it was produced, with the exception that the engine from an IX is different from one from an I/IS. The differences in the two engine harnesses reflect changes in the body wiring of the car. So unless you want to modify the wiring you need to use the harness that matches the car. I sort of think that a SuperETA would want the late harness, but I'm not sure which it used. A comparison of part numbers on realoem.com should tell.

[TrentW]

Not trying to threadjack, but I've got a Seta and and am looking into swapping in a late model "i" engine i have also. Then I would use the lower end to build a stroker for my 89 325is. I've been unable to find a detailed thread that covers this. I know I'd need a new ECU and 4:10 diff--it's my wife's automatic. Can you guys help?