88 Cluster in 84 M50 swap, no start...unplug, starts...ideas?

[strang3majik]

Exactly as the extremely detailed title suggests.

I have an 84 318i I swap an OBD1 m52 into.

The original cluster I have to hit it for the tach to work, and the temp gauge circuitry is faulty even if I switch it with another gauge. I have a 6 cylinder coding plug in it. Starts right up, as I said, tach is intermittent.

So I picked up a cluster from a 1988 325is today, plug it in, temp gauge works, all the lights work, but the car will not start. Soon as I unplug the blue plug, it starts.

Anyone have any idea whats going on? This is like the last thing keeping me from driving it, and a working temp gauge is important...lol

[Gregs///M]

The starter command wire is black/green and goes into the blue plug (pin 1) However, it simply runs through the cluster and back out to the yellow connection (to OBC)(black/yellow, pin 22)

Something in the OBC or cluster is inhibiting that wire from reaching 12 volts. I bet if you put a meter on the black/green wire at the starter and try to start with the newer cluster, you will not see the voltage rise to 12v. However, you will see it with the original cluster.

try disconnecting the yellow plug only to see if you can narrow down the problem to the OBC or the cluster.

[strang3majik]

The starter command wire is black/green and goes into the blue plug (pin 1) However, it simply runs through the cluster and back out to the yellow connection (to OBC)(black/yellow, pin 22)

Something in the OBC or cluster is inhibiting that wire from reaching 12 volts. I bet if you put a meter on the black/green wire at the starter and try to start with the newer cluster, you will not see the voltage rise to 12v. However, you will see it with the original cluster.

try disconnecting the yellow plug only to see if you can narrow down the problem to the OBC or the cluster.

I don't know if it would be an issue, but I do not have an OBC. I have no yellow plug, it stays empty on my cluster.

And I have three clusters, it will start with only the original. I tried swapping gauges, everything. Seems only the original SI board will work or none at all.

So in other words...Only the original SI Board on any cluster OR everything unplugged, will it start.

And with any other combination it just turns over but will not start.

But it does turn over.



Also, only on the newer cluster will I get a working temperature gauge. On the original cluster I have no temperature displaying. But if I put the 88 Motometer cluster in, it won't start but the temperature will display.

[Gregs///M]

Ah so your car tries to start but fails to run.

In this case, something is inhibiting the injection electronics from entering the DME. It gets signal from the cluster too.

I would perform the electronic troubleshooting tests outlined in the Bentley manual for your car. Since you have a swapped the engine, there could be some mis matched wiring.

[strang3majik]

To make things even more interesting, with my original 84 318 cluster (the one that works)...if I pull the coding plug completely out of the back of the tach, it still works as it did. No difference. No temp, but tach still displays.


I'm seriously at a loss.

[strang3majik]

How come it would start with one of the three clusters then and everything except only the temp gauge work?

It has to be a different pinout for the newer clusters or something. Idk.

Going to try and run the temp sender straight from the sender to the body harness and bypass the engine harness to see if that works.

[strang3majik]

Temp sender didn't make a difference. Still no temp gauge.

And a few hours later now it wot start with the original cluster. Only if I unplug it.

[strang3majik]

I figured it out.

The SI reset/diagnostic wire were hooked up as per the diagram listed on Garigastics website. I cut that wire and all is well no. Apparently they should not be hooked together.

Temp gauge works now as well.