'83 633CSi - running so rich it stalls

[Fedaykin633csi]

Grasping at straws for a solution here, hoping the collective can help. At the beginning of lockdown I sent out my injectors to get rebuilt as I was chasing an on-throttle jerky acceleration issue. I had eliminated the common culprits and thought what the heck, I'll do the injectors.

Fastforward to reinstalling them, and it sure seemed like my fuel rail was over pressurized, but just a guess (I would test fuel pressure by a gauge, but who knew this was specialist equipment!? None of my local auto parts stores have them). Injector #1 sprung a leak from the body seal, but it may have come back from service like that. Got a new injector, hooked it all up. No leaks, started fine but definitely choking - black smoke, etc. Stalls. Wet spark plugs. Hmm.

One by one with no change I: verified injectors weren't leaking, replaced FPR, verified fuel return is flowing by running it into a jerry can with no change, unplugged thermotime switch, capped supply to CSV. Cap, rotor and wires are new. Unplugging O2 doesn't do much if anything, ditto CTS.

As far as I can tell, no appreciable vacuum leaks. AFM flap is moving freely, but I will double check. What else is there that could give it so much fuel it drowns??? Is there some way the fuel supply system could burn out the DME? (they are the same low-impedance injectors I sent out for service).


Any wise words would be appreciated, I just put new tires and wheels on this car and have yet to drive it. Cheers!

[Ralph in Socal]

My 82 633 would only start when cold and run very rich. Would not restart after shutting down as the engine was drowned in fuel

Turned out the Coolant Temp Sensor feed to the ecu was not connected so the ecu defaulted to cold start and run rich.

To prove my point to myself, I ran a separate wire bypassing the harness from the sensor to the ecu. The car runs well now. Restarts easily when warm and recently passed CA smog inspection.

Your car may also have the dealer installed resistor inline tucked inside the sensor boot. A broken connection there will cause your rich condition also

Ralph

[Fedaykin633csi]

Ralph, can't wait to check this out. You used the ETM to find the CTS input to the DME?

Would be great if it wasn't a mystery over pressure situation.

[Ralph in Socal]

Check resistance between the sensor post and ground. Sensor is blue, white or light brown on the thermostat housing

Then check resistance of sensor input at ecu and see if you have the same value. Yes the ETM will detail which terminal is the CTS at the ecu. Good luck

Ralph

PS - I removed the inline resistor. No longer necessary

[Fedaykin633csi]

Well there's your problem right there



It's going to be a couple of days before I can solder this back up sans resistor, but thank you Ralph for pointing me this way!

[Ralph in Socal]

Easy peasy. Well done

Ralph

[cornwallis]

Enjoyed reading this post! Lots of good info in here.

[songzunhuang]

Easy peasy. Well done

Ralph

Hmm, I just came across this Ralph. I didn't check mine before sending it off to the shop since i didn't know about it a few days ago.
Is there a way to bypass this sensor so that the cold start injector never comes on? I'm just wondering if I can tell the shop to test it quickly without burning into their very spendy hourly rate.

[Ralph in Socal]

No Song. This sensor (CTS) provides input to the ecu for running conditions at startup or while at running temp.

Symptoms you described indicated fuel supply cut off.

The cut wire results in poor running from too much fuel as the ecu defaults to full rich to prevent engine damage

Ralph

[songzunhuang]

No Song. This sensor (CTS) provides input to the ecu for running conditions at startup or while at running temp.

Symptoms you described indicated fuel supply cut off.

The cut wire results in poor running from too much fuel as the ecu defaults to full rich to prevent engine damage

Ralph

OK, the shop called an told me my plugs are fouled and they say my car is running rich. Confusing as it seems to me that it's not getting fuel and that's why it's dying, but I'm second guessing myself now. I had someone in another post tell me they disconnected their cold start injector and it ran great for over a year now. Oh well, this is why it's in the shop. Thanks.

[Ohmess]

I too have a rich running condition on my 1979 635csi, and would like to conduct the sensor test that Ralph suggests. The suggestion is to check resistance between the sensor post and a ground to obtain a measurement that is then compared to the measurement at the ECU. It looks to me like the sensor has two outputs, so I would think I would be measuring resistance across these two terminals.

Ralph - Can you straighten me out?

[songzunhuang]

Well there's your problem right there



It's going to be a couple of days before I can solder this back up sans resistor, but thank you Ralph for pointing me this way!

So, it turns out that I just experienced this exact same thing. My car was put on a flatbed to a shop, who ultimately found this same condition in my car. Sheesh. Wish I had come across this last week.

[Ralph in Socal]

I too have a rich running condition on my 1979 635csi, and would like to conduct the sensor test that Ralph suggests. The suggestion is to check resistance between the sensor post and a ground to obtain a measurement that is then compared to the measurement at the ECU. It looks to me like the sensor has two outputs, so I would think I would be measuring resistance across these two terminals.

Ralph - Can you straighten me out?

You are correct. At the sensor check resistance between terminals. At the ecu connector, resistance reading is at terminal 13 against ground.

Ralph

[Ralph in Socal]

Well there's your problem right there



It's going to be a couple of days before I can solder this back up sans resistor, but thank you Ralph for pointing me this way!

So, it turns out that I just experienced this exact same thing. My car was put on a flatbed to a shop, who ultimately found this same condition in my car. Sheesh. Wish I had come across this last week.

Not what I expected but excellent you found it. Shop costs are outrageous these days. Sorry Song

Ralph

[Ohmess]

Thanks a ton Ralph.

A follow-on question. What was the purpose behind adding the resistor?

[GRNSHRK]

I too have a rich running condition on my 1979 635csi, and would like to conduct the sensor test that Ralph suggests. The suggestion is to check resistance between the sensor post and a ground to obtain a measurement that is then compared to the measurement at the ECU. It looks to me like the sensor has two outputs, so I would think I would be measuring resistance across these two terminals.

Ohmness, unfortunately I don't have an answer to your question, but I did want to point out that in your "79 635 (presumed to be a Euro) you would have L-jet injection, not Motronic, which is what these guys are dealing with

But I do have a couple of manuals and can take a look, see what I can come up with

Maybe you should start a new thread, so that you can obtain information more suited to your model

[Ralph in Socal]

Thanks a ton Ralph.

A follow-on question. What was the purpose behind adding the resistor?

The TSB referenced in this thread provides the answer

https://bigcoupe.com/phpBB2/viewtopic.php?t=32967

As Bobbo pointed out, this would not apply to your series 1 car

Ralph

[Ohmess]

Thanks a ton Ralph. I'm new to this particular car, and am learning about early BMW fuel injection.

[Ralph in Socal]

The silver relay would not have been done to your car but the coolant temp sensor test does apply. Same location on the thermostat housing but may be different ecu input terminal

Ralph

[RossDinan6]

For a factory fix it is quite the kludge. Resistors are not designed to tolerate the vibrations they receive in this application. While they last a long time in the wild, all of them will eventually break. Anyone that has this resistor should probably consider replacement before failure.

Can it be eliminated? I am running standalone so am not up on Motronic in quite a few years. Mine failed way back before the Motronic replacement.

[oilcooler]

my 84 635 euro is also having random dying/stalling, and just replaced the reference sensor cables (eventhough they tested fine), replaced the fuel pressure regulator (because i have an extra), swapped the ecu (since i have both usa and euro ecu's), and my car is still stalling/dying. i will check for the inline resistor tomorrow.

i like that knowledge is shared on this forum.

[songzunhuang]

The silver relay would not have been done to your car but the coolant temp sensor test does apply. Same location on the thermostat housing but may be different ecu input terminal

Ralph

For what it's worth, I have completely removed the mystery silver relay and driven my car the better part of 510 miles in all kinds of situations without a hiccup. I keep it in the glovebox just in case, but I really don't think I'll be needing it. One day I'll trace all the wires coming out of it and remove them.

[oilcooler]

figured out the random stalling/dying issue by process of elimination...it was the main relay! a $20 relay caused loads-O-worries. it wasn't the reference sensors, wasn't the fuel pressure regulator, wasn't the fuel pump, wasn't my two ECU's, wasn't the fuel pump relay...it was a simple and easy to replace main relay.

my 635 runs well again!

[86_6series]

Thanks for posting the solution.

Bob V