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E12 ECU question

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Sechserreihe
Posts: 46
Joined: Sun Jun 26, 2016 7:10 pm
Location: Columbus, OH

E12 ECU question

Post by Sechserreihe » Wed Feb 14, 2018 2:48 pm

Hi,

I'm very close to getting my 1981 US spcec 633CSi that's been converted to Euro spec including a 1978 635CSi M90 motor and all running gear, to start.

I can get the motor to spring to life for barely a second and then it dies. I can do this over and over again. Runs for a second and dies. I can't hear any pumps but it is getting fuel when I crank (had hose connected to Pressure Regulator outlet to check). I believe it to be fuel pump / pump relay(s) / ECU related. I have a hunch the ECU isn't connected completely. I took a picture of the ECU that I've routed into the location above the glove box. It has 3 wires coming off the main harness that need a home. They have odd looking connectors. Is there a relay / connector these connect to?

The previous owner of the car had pulled the motor and ECU for a swap into his E12 5 series. I'm not sure if he pulled any relays associated with the ECU from the glove box area.

Thanks for any input.

Mark
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Sechserreihe
Posts: 46
Joined: Sun Jun 26, 2016 7:10 pm
Location: Columbus, OH

Re: E12 ECU question

Post by Sechserreihe » Thu Feb 15, 2018 10:55 pm

been at it some more and made a little progress. I switched out my 12 pin double fuel pump relay as it was not triggering the fuel pumps when opening the MAF door with the key in the ON position. By coincidence, my '87 Alfa Milano 2.5 has the same Bosch fuel pump relay as I was able to get the fuel pumps working when I cracked open the MAF door. I thought I had it licked. Not so.

The engine still only springs to life for a second or two and then dies. At that point I checked for voltage at the injectors thinking that it's my Cold Start Injector that's causing the brief rev of the motor. I was right...no Voltage at any of the six injectors.

I'm still convinced that the three wires on the harness right at the ECU that have nothing to plug into are the culprit. Can anyone advise as to what gets plugged in these various sized male spades?

And lastly, there is still one unidentified wire after the engine install that I need to figure out where it goes. Can someone please advise? It runs off the lower passenger side wiring harness and exits directly below the AC evap canister.

Thank you,

Mark

'78 M90 in an '81 US 633csi.
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Brucey
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Re: E12 ECU question

Post by Brucey » Fri Feb 16, 2018 5:34 am

the most likely reason for your symptoms is that you have cold start injector function but not main injector function. The most likely reason for that is that the main relay is knackered (on a motronic car) but on an L-jet car there may be other causes.

I would suggest that you at least test that the main injectors are not jammed shut; they should click open when powered.

FWIW on BMWs of this vintage the wires are best identified by wire colour and location (rather than plug type). All the wire colours are indicated on the relevant ETM which you can download for your model, for free.

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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hornhospital
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Re: E12 ECU question

Post by hornhospital » Fri Feb 16, 2018 8:25 am

Sechserreihe wrote:
Thu Feb 15, 2018 10:55 pm
At that point I checked for voltage at the injectors thinking that it's my Cold Start Injector that's causing the brief rev of the motor. I was right...no Voltage at any of the six injectors.
That is a large clue. The injectors have 12 volts on one leg continuously any time the key is in the run position. The ECU fires the injectors by GROUNDING them. The ECU could be working fine, but if there's no power to the positive side of the injectors, there's nothing to fire the injectors when the ECU grounds them.
Ken Kanne
'84 633CSi "Sylvia"; '85 635CSi "Katja";'87 325is "Odette"; '93 325is "Elvira"; '95 M3 "Ashlyn"

Sechserreihe
Posts: 46
Joined: Sun Jun 26, 2016 7:10 pm
Location: Columbus, OH

Re: E12 ECU question

Post by Sechserreihe » Sat Feb 17, 2018 1:41 am

Thanks guys but I'm still working on this issue. I did check the injectors and I am indeed getting 12v on the pins. Sorry, that they were dead at first. But what I'm really thinking is going on here is a missing wire from the tach. From what I've read and seen on the schematics, there should be a wire that runs into the glove box area to hook into the Number 1 pin of the ECU. I have checked with a multi-meter and the wire attached to the harness (one with the naked spade and heavier gauge than the other two) does run into Pin 1. But it's not hooked up to anything. Is this what's not sending a signal to the injectors?

I've looked and looked under the dash and cannot locate a suitable wire to plug into. There is what looks like the perfect candidate just inches away but it runs into a blank slot in a multi connector! duh!

Please shed some light on this if you could.

Oh, and lastly, what is going on with this mess at the bottom radiator coolant temp sensor? Don't understand the multiple wires for a two prong coolant sensor. Is this correct? I know that it's an integral part for the ECU to operate properly.

Many thanks for the help.

Mark
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Brucey
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Re: E12 ECU question

Post by Brucey » Sat Feb 17, 2018 10:38 am

pin 1 is (I think) the wire that grounds the coil and thus provides spark. If this is not connected correctly you will get no spark. If it is not connected to the tachometer then it probably won't stop the engine from running, but you won't get any tacho reading, obviously.

The injectors are fired by six high current connections (in two banks of three, typically) in most bosch ECUs of that vintage.

If the injectors are not opening then causes include

- bad 12V feed (test that volts hold up on the feed under load with a 20-30W bulb)
- jammed injectors that won't open
- no primary signal to the ECU (in which case there will be no spark either)
- no injector signal (which could be a ground wire fault or an internal ECU fault etc)

BTW if the fuel pump doesn't run when the AFM flap is moved (or the fuel supply is badly clogged) then you may get the engine to fire but then it will quit running after a few seconds as the fuel rail depressurises. You can verify fuel pressure by temporarily fitting a pressure gauge.

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Sechserreihe
Posts: 46
Joined: Sun Jun 26, 2016 7:10 pm
Location: Columbus, OH

Re: E12 ECU question

Post by Sechserreihe » Sat Feb 17, 2018 9:44 pm

Got it figured out. It was the missing wire that gets plugged into that wire off the harness by the ECU. I ran a wire from the Ignition module plug (16 - black double wire) and ran it straight to the wire at the harness. Fired right up!

Thanks for all the input and pointers. I appreciate it.

Mark

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