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Hello everyone, I just bought a 1980 320i in pretty good shape. No rust, good body, good interior, 170k on the clock. However, I bought it not running. The car has electrical issues, which I will be chasing down with a multimeter hopefully soon. The previous owner replaced the engine wiring harness because the old one, which came with the car, burned up a bit. There is one extra sensor plug that is unused, and I don't see any sensor to plug it in to. Anyone know where this guy goes?



And, if anyone has any ideas on what to check first with the bad electrical let me know. Some things work, some things don't. The positive cable gets warm, which indicates a bad ground somewhere. Most of the lights work, but the windshield wipers and blower motor do not. I think the reason it doesn't run (I haven't actually tried to start it because I'd like to ensure I don't have an electrical fire) is because it sounds like the fuel pump turns on for a second, then stops. The spark plugs fire when I crank it over, so it has spark. Perhaps not fuel. Any help would be appreciated, and thanks in advance. Kyle

And my car is a 1980 US 320i 5 speed with AC

Hi there and welcome!!!

So you have the 1.8 injection (m10 b18) engine. Where about are you based, US?

If it had a spark, than it is likely you have two problems.

1: electrical, sounds like ground or wrong connections or plain old shortage, worn wires or so.
2. Engine problems. To run an engine needs fuel, air and spark. I think you lack the first and have the seconden and third.

the missing plug may connect to a sensor (which may not be present on your version) is on of the sensors in the coolant elbow yellow? you see the brown plug connected to the brown sensor, there would be a yellow one to mate that to but its likely it has been omitted from your engine.
the earth problem will cause you no end of issues so you are best off searching out where that problem is first. check all the earth cables and make sure one hasn't been connected to something silly like the starter solenoid or something.
When the previous owner replaced the loom due to fire did he give a cause? I only ask as perhaps one of the existing components (alternator, fuel pump, starter, etc) may have failed internally causing the short and resulting in the fire?

I see it is a M10 with K-jet injection. The only parts where the original Boschplugs go in are:

* Coldstartinjector.
* Extra airslide
* WUR.
* Temperature switch for the could start.

I see that your coldstart and airslide are already installed and i believe the brown connector is already at a temperatureswitch?

That leaves the WUR unit to be connected.

Thanks for the replies everyone!
Uwburrman, mine is the mechanical fuel injection version,and I'm in Sacramento CA. I agree that is is most likely a fuel issue because it does have spark. I'm hoping to track down most of the other electrical problems before trying to get it running, because I don't want to have the same issue of melting wires.

Steed and Peter, thanks very much for eliminating what sensor that extra boschplug goes to. The WUR has one plugged into it already, so my guess is that the replacement wiring harness is from a different year that used an extra sensor. Maybe the 77-79 version? I don't know, but if it goes to nothing that is one less thing to track down. The previous owner got the car from a friend of his and it was his intent to get it running and make it a daily driver, but he was too lazy to try and fix the electrical gremlins. The old wiring harness was in the trunk, and a few wires had the insulation melted off them. So it doesn't appear to have been a massive electrical fire, more of a small melting incident and the easiest thing to do was to replace the entire harness. The fuel pump is new, so I can probably rule that out as a problem. The starter seemed fine when I was cranking it over without the plugs in to bring up the oil pressure, but I won't know for sure till I have time to really dive into it.

Basically I need to bribe my electrical engineer friend and we need to check things with the test light to try and find a bad ground. That shouldn't be too hard to do. Hopefully. Then I can see how well it runs and drives.

Hi
I assume, you have the harness version for US emission control. The white plug should be connected to a frequency valve. I don't know what it does, but I can send you a link where you may get some useful info about that and schemes, etc.
M.

Update time!
I finally got some time to fiddle with the car, and its good news. I noticed when I would turn the wipers on they would move at first, then nothing. Long story short, whoever installed them wasn't too smart. They were installed in such a way that they were trying to move into the engine compartment instead of over the windshield. That made me think that maybe my problems were not a bad ground or bad wiring. So I force fed the engine some starting fluid and it fired up for a second. Obviously it wasn't getting gas, and the external fuel pump made noise, so I checked the internal pump and it was kaput. I bypassed it for now, and tried to start it again... Nothing. So I took the external pump off, and tested it. It sure sounded like it was pumping, but nothing was coming out. I got a new one ordered, installed it, cranked it over, and its leaking gas. I traced it to the hose from the filter to the steel line leading to the fuel distributor. Looks like Pelican Parts has it for 30.50. At least I have fuel pressure now...

Almost there, looking promising. Apparently wiper mechanism was fitted the wrong way, that's can be sorted out quickly as well...

Another update:
It runs!!!!

Poorly... Seems to be running very rich, its quite smokey and smells like gas. It won't idle and stalls if you let it drop below 2000rpm. So I pulled the plugs and they are black and sooty, so it seems like my diagnosis is correct. I'm wondering if the cold start valve or the warm up regulator is dumping fuel into the engine. Anyone have any advice?

On the plus side, all 4 cylinders have 150+ lbs of compression, and it sounds like its running on all 4 when its revved up. Just gotta figure out why its running rich.

One step closer! With new plugs also make sure ignition dizzy and rotor arm are pretty clean and the its perhaps time to work on the mixture through the fuel dizzy. They may have set it richer to compensate for a fuel pump on its way out. WUR could play a role indeed, have a spare you can try? Watch out for fuel leaks though.

So, I went to the junkyard to grab some parts and I found something interesting. My car doesn't have this on it, the junkyard car did. I don't know what this is or what it does. It is located under the intake runner for cylinder #1.


The banjo fitting screws into the fuel distributor, and the other end goes to the return fuel line. (I think, I actually don't remember. I was in a hurry as it was raining on me at the junkyard) It makes sense, because the return fuel line has a bolt in it as pictured here. And, the replacement wiring harness has an extra plug as shown in my original post. That extra plug probably goes to this thing.


What does that thing do? Why is there (as far as I can tell) no provision for me to screw it into the fuel distributor? And could this be the cause of it running very rich?

I'm getting closer to solving the mystery....

could this be a fuel bypass valve/solenoid? reducing the pressure in the injector rail at ECU predetermined conditions?

Hypothetically could it be for reducing the fuel pressure at lower revs to reduce the amount of fuel injected (returning it to the tank). the may explain why its dying at lower revs from over-fuelling?

That injector is indeed located under the intakemanifold and looks to me that is the coldstart injector.

So, that thing is the frequency valve, which as I have read helps regulate excess fuel pressure in the fuel distributor and will send excess fuel back to the tank. It certaintly seems like this (or lack of it) is causing my problems. I simply don't see anywhere where there is a hole or fitting on my fuel distributor to screw in the banjo fitting. Does anyone else not have one on their 320i? I'm wondering if somehow someone replaced the fuel distributor with the wrong one or something. Its quite puzzling.

Upon further research, it looks like the 77-79 cars don't use the frequency valve. So now I am thinking that maybe I have a 77-79 fuel distributor on my 1980. Which is a bummer if that is the case. If so, anyone, know of a way to get it to run properly without replacing the whole thing?