'83 633CSi - running so rich it stalls

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Fedaykin633csi
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'83 633CSi - running so rich it stalls

Post by 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!
Last edited by Fedaykin633csi on Wed May 20, 2020 6:15 pm, edited 1 time in total.
1983 633CSi 5-speed Burgunrot, a slow burn 645CSi project
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Ralph in Socal
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Re: '83 633CSi - running so rich it stalls

Post by 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
There is a very fine line between "Hobby" and Mental Illness.

85 635csi Zinno Auto
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Fedaykin633csi
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Re: '83 633CSi - running so rich it stalls

Post by 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.
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Re: '83 633CSi - running so rich it stalls

Post by 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
There is a very fine line between "Hobby" and Mental Illness.

85 635csi Zinno Auto
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Fedaykin633csi
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Re: '83 633CSi - running so rich it stalls

Post by Fedaykin633csi »

Well there's your problem right there

Image

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!
1983 633CSi 5-speed Burgunrot, a slow burn 645CSi project
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Ralph in Socal
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Re: '83 633CSi - running so rich it stalls

Post by Ralph in Socal »

Easy peasy. Well done

Ralph
There is a very fine line between "Hobby" and Mental Illness.

85 635csi Zinno Auto
84 528i Euro
83 635 Euro Arktik
81 528i Kastanien 5-speed
88 528e Bronzit (Granpa Car)
86 535i Auto (For Sale)
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Re: '83 633CSi - running so rich it stalls

Post by cornwallis »

Enjoyed reading this post! Lots of good info in here. =D>
Hector :twisted:
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Re: '83 633CSi - running so rich it stalls

Post by songzunhuang »

Ralph in Socal wrote: Wed May 20, 2020 5:25 pm 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.
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Re: '83 633CSi - running so rich it stalls

Post by 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
There is a very fine line between "Hobby" and Mental Illness.

85 635csi Zinno Auto
84 528i Euro
83 635 Euro Arktik
81 528i Kastanien 5-speed
88 528e Bronzit (Granpa Car)
86 535i Auto (For Sale)
81 633 csi (retired)
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Re: '83 633CSi - running so rich it stalls

Post by songzunhuang »

Ralph in Socal wrote: Tue Jan 17, 2023 1:16 am 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.
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Re: '83 633CSi - running so rich it stalls

Post by 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?
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Re: '83 633CSi - running so rich it stalls

Post by songzunhuang »

Fedaykin633csi wrote: Wed May 20, 2020 1:27 am Well there's your problem right there

Image

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.
-----
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Ralph in Socal
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Re: '83 633CSi - running so rich it stalls

Post by Ralph in Socal »

Ohmess wrote: Tue Jan 17, 2023 5:43 pm 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
There is a very fine line between "Hobby" and Mental Illness.

85 635csi Zinno Auto
84 528i Euro
83 635 Euro Arktik
81 528i Kastanien 5-speed
88 528e Bronzit (Granpa Car)
86 535i Auto (For Sale)
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Re: '83 633CSi - running so rich it stalls

Post by Ralph in Socal »

songzunhuang wrote: Tue Jan 17, 2023 11:12 pm
Fedaykin633csi wrote: Wed May 20, 2020 1:27 am Well there's your problem right there

Image

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
There is a very fine line between "Hobby" and Mental Illness.

85 635csi Zinno Auto
84 528i Euro
83 635 Euro Arktik
81 528i Kastanien 5-speed
88 528e Bronzit (Granpa Car)
86 535i Auto (For Sale)
81 633 csi (retired)
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Re: '83 633CSi - running so rich it stalls

Post by Ohmess »

Thanks a ton Ralph.

A follow-on question. What was the purpose behind adding the resistor?
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Re: '83 633CSi - running so rich it stalls

Post by 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 [-o<

Maybe you should start a new thread, so that you can obtain information more suited to your model \:D/
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Re: '83 633CSi - running so rich it stalls

Post by Ralph in Socal »

Ohmess wrote: Wed Jan 18, 2023 6:45 pm 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
There is a very fine line between "Hobby" and Mental Illness.

85 635csi Zinno Auto
84 528i Euro
83 635 Euro Arktik
81 528i Kastanien 5-speed
88 528e Bronzit (Granpa Car)
86 535i Auto (For Sale)
81 633 csi (retired)
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Re: '83 633CSi - running so rich it stalls

Post by Ohmess »

Thanks a ton Ralph. I'm new to this particular car, and am learning about early BMW fuel injection.
1972 3.0 CS - Annabelle
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Re: '83 633CSi - running so rich it stalls

Post by 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
There is a very fine line between "Hobby" and Mental Illness.

85 635csi Zinno Auto
84 528i Euro
83 635 Euro Arktik
81 528i Kastanien 5-speed
88 528e Bronzit (Granpa Car)
86 535i Auto (For Sale)
81 633 csi (retired)
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Re: '83 633CSi - running so rich it stalls

Post by 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.
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Re: '83 633CSi - running so rich it stalls

Post by 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.
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Re: '83 633CSi - running so rich it stalls

Post by songzunhuang »

Ralph in Socal wrote: Wed Jan 18, 2023 9:59 pm 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.
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Re: '83 633CSi - running so rich it stalls

Post by 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!
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Re: '83 633CSi - running so rich it stalls

Post by 86_6series »

Thanks for posting the solution.

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Re: '83 633CSi - running so rich it stalls

Post by tschultz »

oilcooler wrote: Sat Mar 18, 2023 7:25 pm 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!

Agree with Bob V! May be a problem I have run into recently as well!
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