1981 bmw e12

Post your E12 technical questions and comments here. Please, no off-topic posts.

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winged1775
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1981 bmw e12

Post by winged1775 » Wed Feb 05, 2020 4:45 pm

Hello i have a 81 e12 with a swapped 3.5l and the engine harness has seen better days. When i bought the car i got it to run after clearing old gasoline and putting new fuel lines. I'm having issues getting it running and if i do get it to run it will fire but die with in seconds. I have Fuel and spark.

I'm thinking some of the cables are needing replacement especially the one green cable that is connected to the distributor.

I have a bosch 0280001122 ECU and need help finding a engine wiring harness that would go with the engine and ecu. any help would be greatly appreciated .

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keehn
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Re: 1981 bmw e12

Post by keehn » Thu Feb 06, 2020 1:16 pm

Winged1775,

Would you mind posting some photos of the wires in question? I'm a bit confused on a 3.5l conversion that is still using L-Jetronic (which is what your ECU part # matches up to).

Mike

winged1775
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Re: 1981 bmw e12

Post by winged1775 » Thu Feb 06, 2020 5:08 pm


they way i understand this the ecu uses the signal from distributor to send a signal to injectors?

PatinaBeforePolish
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Re: 1981 bmw e12

Post by PatinaBeforePolish » Thu Feb 06, 2020 6:02 pm

That ECU part number was specced for E12s, 23s and early 24s all with L Jet. You say you have fuel and spark and it ran at one time. I assume you have compression. Did you change the fuel filter when you cleaned the tank and lines? Have you done any work since it last ran? Wouldn't hurt to replace the wire but that may not be the issue.
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winged1775
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Re: 1981 bmw e12

Post by winged1775 » Thu Feb 06, 2020 7:25 pm

yes new filter, every time i touched that wire i can get it to run or start but now it just cranks

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Lock
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Re: 1981 bmw e12

Post by Lock » Fri Feb 07, 2020 2:13 am

Sounds like it's running on the cold start injector, that's spraying when cranking and giving it a bit of fuel. I'd unplug that for troubleshooting. If it doesn't fire at all, maybe it's fuel. Have you confirmed it' sparking on all leads when you crank?

I also like to jumper on a 12v LED onto injectors when testing. I'd do that to check that they're actually firing, that will narrow down if it's fuel or spark.

That green wire is the inductive pickup from the distributor, it's just a little coax cable (single inner wire and shield outer). It goes over to the ignition unit by the washer tank. you can run a multimeter from it to the ignition unit plug to test if it's not sending the signal and if so fix or replace the wiring. I have part of the original ignition wiring harness (I cut some parts out) so might be able to help.

Also does your tach needle move at all when cranking? The ECU needs the ignition output for timing, without it it won't fire the injectors.
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winged1775
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Re: 1981 bmw e12

Post by winged1775 » Mon Feb 10, 2020 2:48 pm

Lock wrote:
Fri Feb 07, 2020 2:13 am
Sounds like it's running on the cold start injector, that's spraying when cranking and giving it a bit of fuel. I'd unplug that for troubleshooting. If it doesn't fire at all, maybe it's fuel. Have you confirmed it' sparking on all leads when you crank?

I also like to jumper on a 12v LED onto injectors when testing. I'd do that to check that they're actually firing, that will narrow down if it's fuel or spark.

That green wire is the inductive pickup from the distributor, it's just a little coax cable (single inner wire and shield outer). It goes over to the ignition unit by the washer tank. you can run a multimeter from it to the ignition unit plug to test if it's not sending the signal and if so fix or replace the wiring. I have part of the original ignition wiring harness (I cut some parts out) so might be able to help.

Also does your tach needle move at all when cranking? The ECU needs the ignition output for timing, without it it won't fire the injectors.
I think you're right about starting on the cold start injector... i will be checking the spark on all spark plugs this weekend thanks for the help.

winged1775
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Re: 1981 bmw e12

Post by winged1775 » Mon Feb 10, 2020 6:06 pm

actually not getting any spark. if anyone could point me to the right direction how to troubleshoot this issue.

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Lock
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Re: 1981 bmw e12

Post by Lock » Tue Feb 11, 2020 9:52 pm

Sent you a PM but the ECU relies on the ignition circuit working, so focus on that first.

Might be the coil failed, distributor sensor failed, green sensor wire broken, wiring somewhere else is broken, or the ignition unit has failed (most common).

Trace that you get voltage from the distributor sensor when it cranks. Make sure that voltage is getting to the ignition unit. Make sure the ignition unit is producing voltage for the coil to run, and that the coil is okay.
1979 528i 5-speed conversion G260/6, Motronic 1.3 179
1980 Honda CX-500

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keehn
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Re: 1981 bmw e12

Post by keehn » Wed Feb 12, 2020 11:29 am

I second Lock on his advice.

Regarding the wiring, I would recommend you perform continuity checks on the wires from start to end (or end points where continuity is expected). This will allow you to rule out wire issues. With the image you shared of the green wire, that...has seen better days, and I would recommend you change it with a new green 12-16awg (? on awg) wire.

Additionally, cleaning end connection points will help reduce resistance throughout the circuit. Vehicle (*cough* Volkswagen *cough*) exposed wire connectors WILL corrode over time, increasing resistance, and cause phantom electrical issues throughout various systems.

Also, not sure if you have perused the "Technical FAQ" portion of this site, but http://firstfives.org/faq/ljet/528i_Ljet_schematic.PDF is a good electrical diagram drafted up by Peter Florance I'd recommend you look over while you troubleshoot.

Lastly, to add on Lock's advice, use a test light to probe if voltage is coming from the distributor sensor while cranking.

Mike

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