HELP - swapped in S52 from M50NV this week and engine won't stay running, TPS code CL

[singh336]

Need some help or ideas if anyone has any...


here is what happened...


I had a 1990 325i E30 with a M50NV i swapped in earlier this year...


Then last weekend I got a good deal on an OBD 1 S52 on ebay so i went to check it out..


the motor was in the car and running perfectly... and I helped pull it...

it took me two days to take mine out, and swap that one in and then since the last few days all I have been doing is troubleshooting why it doesn't start.


The engine will start sometimes and run like is running out of gas. So here is what I did...



Checked fuel lines supply and return, they are correct, fuel pressure is great, yes the car has fuel.

Checked vacuum lines, found ICV hose was real cracked bad so taped it up for the meantime until I buy one, but it doesn't leak now. All lines and hoses etc are hooked up correct.

I checked harness entirely to make sure it was all plugged in, when I pulled the running motor I did not disconnect anything on the motor, only disconnected whatever was connected to the car...

checked grounds, motor is grounded well, fuel injectors grounded well.


changed spark plugs with brand new ones, old ones were ...old.

I read the CEL light which gave me code 1216... throttle potentionmeter.. okay...


Checked OHMs of sensor, in spec.. swapped it out with a spare anyways.. no good. Chased wires back to ECU, all of them were correct on the pin outs and none of them were broken in the middle.

TPS gets 5V as spec, reads 1k ohms closed and 4k ohms open... so all good there... ECU is correct and same one the motor was running with before i pulled it....




Got the car to start and run for a maximum of about 20 seconds... had to keep throttle on it heavy but not steady, had to feather it... thats not correct... so i let it die.



Also disconnected MAF, then plugged it back in, disconnected TPS, plugged it back in, disconnected both for the hell of it too. the car did same thing everytime.



I took the intake manifold off almost a dozen times now, everything under there is perfect... grounds are there... fuel is there... spark is there...


wtf? crank shaft sensor works , saw the rpms move on the dash...


Not sure what else I can do and wtf why a TPS code?



I can take and upload a video tomorrow

[328ijunkie]

What harness/ecu you running?

[Wizard13]

It's a 403 with an obd1 harness, i believe.

[singh336]

It is an obd1 harness off of who knows what with a 413 ecu.

We fixed it last night so for anyone searching in the future I can tell you we found that the FPR was bad on the fuel rail.

What happened was we unplugged the temp sensor on the head and the car started to run better ... But I knew the temp sensor couldn't go bad from the swap, I guess anything could happen but it's unlikely.


Then I remembered , the car I took the engine out of had some fuel pressure gauge mounted in the shock tower which was probably a regulator too now that I think of it... I didn't take that and I think that's why the engine ran perfect in the donor car vs my car.


I thought my car was running out of fuel... But it was actually getting too much fuel... We plugged temp sensor back in and pinched fuel line while it was running and it ran better and sustained an idle. LOL.


It was my fault for not taking note on that extra FPR the guy had mounted externally from the motor.

Is a shame because I had this motor in the day after I took the m50 out. I could of been up and running in no time.


now I have some random idle searching which is pretty serious but most of the time it idles good so I'm going to put hose clamps on whatever doesn't have one for vacuum line I know under the icv that hose has no clamp.

Everything is good tho, swap was worth every dollar and hour of time because car pulls HARD. Really love this motors power.