Wrong engine wiring harness?

[M3Gonz]

Hey all,

im working on finishing an M50 swap that I bought as a half complete project. Is it possible that this might have a wrong wiring harness?

I cannot find a plug on the harness for the crank position sensor, the cam position sensor on the engine is a male plug and the wire on the harness marked “Cam” is also a male plug.

I’m wondering if I’m just an idiot or if this is something that’s come up for someone else before.

Thanks!

[e30austin]

you need to peel the boots back on each individual connector and confirm the wiring colors for yourself. relying on someone else's "handiwork" doesn't always work out - ask me how i know.

below are the wiring colors (and their respective hosts), that are primarily found on OBD1 E34/E36 wiring harnesses. once you lay the wiring harness out, it will be a little more clear which plug goes where.

oil pressure sensor - BRN/GREEN or BRN/GRY
blue (DME) coolant temp sensor - BRN + RED/BRN
gauge coolant temp sensor - BRN/YEL + BRN/VIO
crank position sensor - YEL
cam position sensor (female plug) - YEL + RED/WHT + BRN/ORG
VANOS solenoid - RED/WHT + GRN/BLU
knock sensor 1-3 - BLK PIN 70 (DME)
knock sensor 4-6 - BLK PIN 69 (DME)
throttle pos sensor - BRN + BRN/BLK + RED/YEL
intake air temp - BRN + GRY
idle control valve - WHT/YEL + RED/WHT + WHT/GRN
evap purge solenoid - BRN + RED/WHT

[M3Gonz]

That's super helpful, thanks a ton for the info!

It sounds like a best bet might be to just pull the entire harness out, unplug everything, then check all the plugs and wire colors to re-label everything and see if I'm missing a plug or have any incorrect plugs. As the info above states, the cam position sensor should be a female plug, but the one on my harness that's labeled "cam" is a male plug. I also still have not located the crank position sensor plug.

[e30austin]

that's why i said you need to peel the boots back and check each one. do that and report back.

[ForcedFirebird]

Yup, sounds like you "might" have an OBD2 (1996+) harness. I find the easiest way to identify is to continuity test the sensors back to the ECU connector.

[e30austin]

Yup, sounds like you "might" have an OBD2 (1996+) harness. I find the easiest way to identify is to continuity test the sensors back to the ECU connector.

or look for the giant coil pack harness connector on the exhaust side.

[ForcedFirebird]

or look for the giant coil pack harness connector on the exhaust side.

Sorry, meant for the identification of the sensor connectors since they are all 3 pol Bosch. Yes, 96+ will have the coil pack connection (round), <96 will have the integrated coil pack connectors (the cam sensor connector is also reversed to indicate VR vs Hall)

[M3Gonz]

that's why i said you need to peel the boots back and check each one. do that and report back.

Will plan on that. Unfortunately won't be until most likely next weekend, this project is at my father-in-law's shop over an hour away, and I won't be able to get back to work on it again until most likely next weekend. I'll snap a few pictures of the entire harness if that helps anyone else ID it. It does not have the giant coil packs on the driver side, it has the individual blocks. I have an S52 M3 also, which has the different wiring harness for sure.

Thanks!

[89_325i]

I had a similar issue. My M50 NV had a 413 ECU and what I thought was the corresponding harness. Turns out the engine has the proper harness. I confirmed it by testing several pins on the ecu, its pretty easy just to look at the pinout for the NV vs Vanos engine and test different ones for continuity.

Now I have a different issue, which is to confirm which wires the hamfisted PO cut and re-run them.

[M3Gonz]

that's why i said you need to peel the boots back and check each one. do that and report back.

Ok, I’m at the shop working on the car and have the wiring harness pulled. All the wire colors on the chart provided line up, however the cam position sensor plug in this harness is male, and I’m missing the crank position sensor plug entirely.

Based on my picture, does anyone see right away any issues or a way to tell what engine harness this is?

Thanks!

[e30austin]

looks like the correct harness to me, based on the fact that you have the correct knock sensor connectors. seems very perplexing that you don't have a crank position sensor connector. can you dig into the harness coverings and see if anything has been cut?

[M3Gonz]

I got some more info from a local E30 guy that knows the person who "built" and sold that harness, sounds like the person who put together that harness and sold it is kind of an unreliable flake, so it's not at all surprising that it's missing plugs and has the wrong plug.

I just purchased a used correct harness from an M50 that I'll be swapping out the main connector and this way I know it's the right one.

Also, I just found out there's a '95 E36 with the M50 engine that just showed up at a local parts yard, so I'll be heading out to grab whatever I can off that, including the harness, headers, and whatever else looks appealing.

[M3Gonz]

Alright, let me ask this another way, and perhaps I'm showing my lack of understanding of the basics of how engines work (aka this may be a dumb question)

Does the M50 require both the crank position sensor and the cam position sensor? The harness that came with this car was missing a crank position sensor wire entirely, and the cam position sensor plug was backwards (male, when according to the info here should be female)

The M50 sitting in the car when I got it (not running, PO never finished swap) did not have the crank position sensor installed on it.

Finally, I went ahead and bought another wiring harness entirely, it came from OBD1 w/vanos M50. It arrived and I worked on it today and guess what? No crank position sensor wire, and the cam position sensor wire plug is backwards (male, when it should be female according to the info here).

Help!

[jbontke]

Alright, let me ask this another way, and perhaps I'm showing my lack of understanding of the basics of how engines work (aka this may be a dumb question)

Does the M50 require both the crank position sensor and the cam position sensor? The harness that came with this car was missing a crank position sensor wire entirely, and the cam position sensor plug was backwards (male, when according to the info here should be female)

The M50 sitting in the car when I got it (not running, PO never finished swap) did not have the crank position sensor installed on it.

Finally, I went ahead and bought another wiring harness entirely, it came from OBD1 w/vanos M50. It arrived and I worked on it today and guess what? No crank position sensor wire, and the cam position sensor wire plug is backwards (male, when it should be female according to the info here).

Help!

Most cars with sequential EFI use a cam and crank sensor. Instances I have seen one crank sensor and cars uses a batch fire fuel system. This 'new harness' you bought, was it an OEM harness that worked before? I suggest you get a Bentley manual for the engine you have.

Haltech documents the engine as having two sensors:

https://support.haltech.com/portal/en/kb/articles/m50-engine

[ForcedFirebird]

Engines with coil on plug need a cam sensor to know when the piston is TDC on compression stroke (4 stroke engine), so, yes, the m50 needs a cam sensor to run properly.

When you go to the yard, note out the OEM situation and copy it on your e30.