PO nonsensical coolant temp sensor

[E30volk]

Hello R3V, this is my first post here and unfortunately it's a bit of a bizarre one.
Lately my 88 325is has been running a bit rich, so I decided to replace my coolant temp sensor to see if it would help. I went out to take a look and make sure I was ordering the correct part, and found this:

Where the wire comes out of the loom and into the female connector, it seems that somebody has changed out the connector from the normal oem 2 prong to a three prong. Along with that, there's an additional wire attached to the connector which snakes through the engine bay until it leads to what I believe are some fuses? (the ones found under the rectangular cover on the drivers side of the engine bay, pics included) also the sensor definitely is not oem because it's got 3 prongs as well to match up with the connector, and it's black instead of blue.

Does anybody have any idea what the PO was going for here by doing this? and any idea what I should do now? I'm thinking of taking off the 3 prong connector and getting a proper oem 2 prong connector, and then taking off the additional wire and installing an oem sensor. I just want to make sure it's not going to mess anything up. The car runs fine the way it is now, other than running a bit rich.

[digger]

seen a few ebay performance improvements which just alter the signal from this sensor to change the fueling. no idea if that is what it is. there are few sensor variations perhaps just an early model one

[E30volk]

seen a few ebay performance improvements which just alter the signal from this sensor to change the fueling. no idea if that is what it is. there are few sensor variations perhaps just an early model one

I'll have to check out the wires on the fuel relay side, but it would make sense that that's what it is. After further inspecting it after work it seems that the fuel relay wires (all of them, not just the random wire coming from the sensor) have old electrical tape around them like the connector, which would make me further believe that it's an ebay upgrade.
I'm pretty much sure it's not an older model sensor set up either, as the wire looks like it's been bodged in by a kangaroo or something else without opposable thumbs

Nice sig pic btw

[nando]

that coolant sensor looksl ike it's from an E36 or something.

it should be a 2 pin sensor with a blue connector. for absolute certain, you want to put the correct sensor in there.

yes, you can force the DME to run a bit richer by making it think the engine is cold, but this is a bad idea - it forces open loop mode, retards your timing, and a bunch of other things you wouldn't want 100% of the time.

[E30volk]

So after a bit of messing around with the wires around the fuel relays and being confused, I did a bit of research and realized that there are apparently only supposed to be 3 relays underneath the rectangular cover, and that the fourth relay is just a random ass relay installed by the PO to connect the temp sensor into.
Can someone please confirm for me that there are only supposed to be three relays underneath the rectangular cover??

[nando]

yeah, there should only be three.

I have NO idea why you would install a relay inline with a sensor.. temp sensors are passive.

[Swanny]

Still a mechanical fan? Perhaps PO tried to run an electric fan at some point using that sensor as a switch...things you'd love to go back and ask them.


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[E30volk]

Still a mechanical fan? Perhaps PO tried to run an electric fan at some point using that sensor as a switch...things you'd love to go back and ask them.


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I don't think it has anything to do with the fan as it's got no physical connection to it and the fan is the original stock fan. Would make sense though if it were an electric fan.


I think I've finally got it figured out thanks to you guys. I took a look at the 4th relay and figured out that it's in no way directly connected to the DME. It's only connected to the temp sensor by the bodged in wire. I took the 4th relay out and ran the engine, with no significant effects or changes. I couldn't really tell if it was running any leaner, but that's besides the point right now.
Now that I know that the relay and everything else isn't connected to the DME, my plan of attack is to remove the 4th relay and extra wiring completely, get rid of the black 3 prong connector and install an oem 2 prong, and then put in an oem temp sensor the way it should be. I'll keep you guys updated

[E30volk]

Think I finally got this thing figured out. A buddy and I went to rip out the extra relay and wiring, but realized that there was another couple wires coming off the temp sensor, ending attached to the starter. After a bit of research I came across this on the e30zone wiki:

"Despite their technical knowledge, BMW had problems with cold starting on some M20 engines. To cure this without a fundamental redesign, a Cold Start Relay was devised to fool the ECU into thinking that the engine was already warm.
To identify whether your car was fitted with a Cold Start Relay, look for an extra relay fitted to the outside of your fusebox.
This relay is connected so that it switches on when the starter motor engages, and connects a resistor in parallel with the temp sensor, artificially raising the level of the coolant data to the ECU."

After reading that I decided to pull the extra relay and see what would happen after driving for a few weeks. I also replaced the main relay while I was at it since it still had the original from '88 installed. It reacted by leaning out on the first day after about 20km driving (went from 16.8l/100km down to around 11l/100km, and the exhaust smelled a lot better). I also got the chance to test out how it would start in the cold with the relay removed. Started up really well in cold all the way down to -35C so I'm happy.
Did some research on the black 3 prong pigtail connector and found out that it was made by TE connectivity, a company that didn't start producing anything until 2007, so it is a more recent mod. I assume the car ran fine in the cold for the 19+ years before, and it's been a local car all it's life.
If I was to take a guess I'd say one of the previous owners had cold starting issues and either added this in themselves or had it done by a mechanic hoping it would fix it, but without resolve since it had a whole host of starting issues when the most recent PO (my buddy) bought it.

So, now that I've driven it for a few weeks with the extra relay out, it's started to run a bit rich again. It's running at 14.6l/100km, but it doesn't smell as bad as before. I'm going to pull the plugs and see what they look like, but I think the richness is coming down to the old 3 prong temp sensor, oxygen sensor+holey exhaust, and possible vacuum leaks. I'll update after I take a look at the plugs

[E30volk]

Forgot I never really updated/summed up this thread, but basically the extra wiring and three prong sensor did end up being an official BMW fix to some cold start issues. The problem I experienced is that I could no longer replace the coolant temp sensor with an OEM bosch E30 one when it needed replacing. After removing all additional wiring+relay, splicing in a new pigtail and installing a new coolant temp sensor, the car has been running and starting perfectly for some time, including in -30C weather.