Tank draining, pump and non-starting questions

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MatthewH
Posts: 5
Joined: Sat Sep 04, 2021 10:46 am

Tank draining, pump and non-starting questions

Post by MatthewH »

Hi All,
I have a South African BMW E12 518i automatic that has been sitting in my garage unused for a few years.
It had not been in the family long when it was parked, having developed (if I recall correctly) hot starting issues.
I now want to get it back on the road and would welcome any advice.
Here’s what I have done so far and my thoughts and queries...
First off, I charged the battery.
The engine turned over pretty well but would not start; not a splutter.
I pulled off a plug lead and held it to ground and noted a blue spark when the engine swung.
I suspect fuel issues.
Would like to drain the tank of all old (two or three-year-old plus) petrol, so I disconnected the outlet hose from the pump. But when the key was turned the pump did not respond.It had ceased making the clicking noise it had done earlier during testing.
Tested wires to pump with a multimeter – no voltage.
Tested pump on bench (very briefly) with an independent power supply. It runs.
I read somewhere (perhaps on this site) that there is a (combo?) relay that powers the pump and other vehicle functions but I'm not sure which relay it is. Please see attached pictures. Hoping some can tell me which it is and what they all do.
Also, I have read that there is a switch in the air flow meter/sensor (not sure about terminology here) that triggers the pump relay and that this may have some bearing. I am fairly ignorant about fuel injection but did watch a few Youtube videos on the K Jetronic system (am assuming this is the system in use) so have only a very rough idea of the broad principles.
Should also mention that a second filter (does not look original) had been plumbed into the system after the pump and it was full of debris. Removed and replaced it with a new filter of a similar size by a reputable brand.
Any pointers on what I should do next?
Kind regards,
Matthew
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BMW-518i-fuse-box-and-relays-2021---3.jpg
Fuse-box-518i.jpg
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Mike W.
Posts: 2653
Joined: Wed Aug 30, 2006 12:12 am
Location: Sonoma County

Re: Tank draining, pump and non-starting questions

Post by Mike W. »

Most of the info here is on US spec cars with M30 6 cylinder engines and L jet injection, so it's confusing and wrong for your application as you have K jet which is much different. We/I will help all we can, but for the engine/fuel injection an E21 forum might be of more use as they got K jet. For most body/suspension/electrical this would still be the right place.

The double relay is for L jet, I don't believe you have it, nor will opening the flap on the AFM do any good as that's again for L jet. The fuel pump is switched by either the engine cranking or getting a pulse from the ignition telling the relay it's turning fast enough to be running. There may or may not be a brief 1 or 2 second prime function when you turn the key to on. But there isn't a way I know of to manually engage the fuel pump relay, you have to pull it and put in a testing jumper into the right contacts in the base. Kind of a pain, but doable. Short of tracing out wires, look for the two thick ones that carry current and don't just turn the relay on. I think the relay, #3 in the image will be the right one. They are somewhat failure prone so don't be surprised if it is bad. That site is also very helpful. https://www.realoem.com/bmw/enUS/showpa ... Id=12_0341

K jet kind of runs off fuel pressure being a mechanical injection system, so pressure is essential. I had it on E21s so I'm somewhat familiar with it, although 15 years removed. One problem I had that was maddening was I neglected to properly tighten a hose clamp on the supply to the fuel pump one time. It never leaked, but it would allow the pump to suck air and often make starting very difficult. Since SA is a warm area keep that on your radar as the rubber supply hoses can break down at the ends.
Mike W.



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tlake
Posts: 417
Joined: Wed Feb 03, 2010 6:33 pm
Location: WA

Re: Tank draining, pump and non-starting questions

Post by tlake »

You need to get in touch with Taylor of www.outmotorsports.com

He spent a lot of time getting his 1983 320i K-jet car working. He would know. 8)

Taylor's e21 320i
MatthewH
Posts: 5
Joined: Sat Sep 04, 2021 10:46 am

Re: Tank draining, pump and non-starting questions

Post by MatthewH »

Thanks tlake and Mike W for your advice.
I will get hold of Taylor and the E21 forum.
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