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Thread: Fuel Pump Relay Issues

  1. #1
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    Fuel Pump Relay Issues

    Hi guys,

    I recently bought a 1981 320i. It ran fine when I bought it. However, it died on me a couple of days ago. I was able to diagnose that the carb (it has a carb conversion) was not getting fuel. A buddy and I removed the fuel pump relay and jumped it with a paper clip. With the paper clip in place of the fuel pump relay, I switched the car to ON and I could hear the pump switch on. I therefore ordered a new fuel pump relay thinking that a new relay would be the solution. I get the new relay and install it. I go to turn the car on, and the fuel pump did not prime/switch on and the car would not start. However, if I put the same paper clip in place of the relay, the fuel pump switches on. I am clueless on what it could be at this point and would appreciate any help. Thanks!

    Sidenote, how hard would it be to convert the car back to fuel injection?

  2. #2
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    Quote Originally Posted by edestrella97 View Post
    Hi guys,

    I recently bought a 1981 320i. It ran fine when I bought it. However, it died on me a couple of days ago. I was able to diagnose that the carb (it has a carb conversion) was not getting fuel. A buddy and I removed the fuel pump relay and jumped it with a paper clip. With the paper clip in place of the fuel pump relay, I switched the car to ON and I could hear the pump switch on. I therefore ordered a new fuel pump relay thinking that a new relay would be the solution. I get the new relay and install it. I go to turn the car on, and the fuel pump did not prime/switch on and the car would not start. However, if I put the same paper clip in place of the relay, the fuel pump switches on. I am clueless on what it could be at this point and would appreciate any help. Thanks!

    Sidenote, how hard would it be to convert the car back to fuel injection?
    The fuel pump relay is unique in such a way that a good 'running' signal(pulse) is required for the relay to stay 'closed' (on). This signal(pulse) wire is between the relay socket 31b and the ignition coil "-". I'm not sure of the exact location of the connection at the coil end, it may or may not be on the coil -see the attached electrical manual (save a copy). Check that 31b wire, check the 31 ground wire, and make sure all the relay socket terminals are clean and tight.

    electric manual, 81-83
    http://www.findmymerchant.com/images..._1981-1983.pdf

    click pics to enlarge...

    reference picture (thanks GDAus)
    F Pump relay Sock04.JPG

    another reference picture
    e21-fp-relay-bottom.jpg

    ---
    the other question should be in a different thread
    ---
    Tbd

  3. #3
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    Thank you!

  4. #4
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    The Fuel Pump Relay used often is KAE 3.304.100, what I have installed. Pin 31 is unique its very small. Pins 15 and 87 is the 30A Coil,Pin 31 is ground and Pin 1 receives the pulses from the Ignition Coil( blk-Black Wire) which keeps the coil on which keeps the fuel pumps running, the wur and the air auxillary valve are on the same circuit-Key in run position-battery bus line. Need to check the wiring of the socket in the fuse box and trace out the lines. 80-83's 320i's use the KAE and BMW fuel pump relay with the pins as shown to fit the socket. There is confusion on the internet about fuel pump relay,,some sellers list the Lambda or Main Relay as Fuel pump relay, it is not fuel pump relay, it powers the frequency modulation valve not the fuel pumps. Gus's diagram does not fit 1980-83's BMW e21 320i's-North American Versions,,Euro,England, South African,Australian versions--- not seen those. Not sure what 77-79 320i use as fuel pump relays. I use a fused 8 amp line to jumper 87 and 15 line with 6.3 mm spade terminals,much better jumper, safety built in against shorts, the other jumper is good as well so long as the wiring is good.
    DSCI0009t.jpg

    Robert which fuel pump relay does your car use ?


    s-l225.jpg12631277245.jpg


    Randy
    Last edited by 320iAman; 03-25-2018 at 09:17 AM.

  5. #5
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    Hi Randy, The 77-79 fuel pump relays are the same as the 80-83, except there are both 20A and 30A available, and (20A)relay pin "31b" is marked with a "1" on the (30A)relay. The relay socket is the same too, except the pre 80 socket has an extra 'unused' connector. And like you, I'm also not sure if there are any other variants in other parts of the world...

    The pre '80 fuel pump relay was rated at only 20A vs the 30A relay that you posted. The pre '80 e21s were originally designed with only one fuel pump and no Lambda system. Awhile back, we came to the conclusion that the 20A relay must have been installed to many e21s that were equipped with the 2nd fuel pump and Lambda system, which was the cause for many fuel pump relay failures, ie: too much electrical load for the 20A relay to handle properly. Interesting, nonetheless.

    My '78 fuel pump relay is the 20A version - on two '78s, neither car got equipped with the 2nd fuel pump (the recall-fix was not done on them - I'm glad). I just noticed that one parts supplier offers the 20A relay for '77-83 and another parts supplier offers the 30A relay for the '77-83.

    Anybody with two fuel pumps - be sure to replace with the 30A relay!

    Quote Originally Posted by edestrella97 View Post
    Thank you!
    You're welcome.
    Tbd

  6. #6
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    The 80-83 Fuel Pump Relay runs the in tank and exterior tank fuel pumps, the Air Auxiliary Valve , Warm Up Regulator and provide signal voltage and amperage to turn on the Lambda or Main Relay. I call it the work horse relay, thats why I brought up the introduction of another relay to cut the load down,, the Hella upgrade,, Hella is the Company that sold the car wide wiring harness to BMW and even Hella had a subcontractor making them for them, sometimes.. Hella designed the upgrade and actually sold a kit for a while, here in the USA, I have been running the Hella upgrade , I made a Kit and installed it and posted the details. Hella makes racing wiring harnesses for BMW Racing Teams or did then, these are not easy to get until the cash is on the table and they were not cheap. Think of Hella as Professional Auto Electricians, thats how I approached them and successfully got what I bargained for.


    Randy
    Last edited by 320iAman; 03-25-2018 at 07:55 PM.

  7. #7
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    "work horse" relay is a better name for it

    I remember your thread about the kit, I'm glad your pleased with the results!
    Tbd

  8. #8
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    This one? https://www.bimmerforums.com/forum/s...T-BUSY-Part-II

    I think Tom is still waiting for a response...
    '81 E21 320i / '90 E30 325i / '̶9̶2̶ ̶E̶3̶4̶ ̶5̶2̶5̶i̶t (sold) / '15 Toyota XW30 / '̶̶8̶0̶ ̶E̶2̶1̶ ̶3̶2̶0̶i̶A̶ (sold)

  9. #9
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    “Workhorse” Relay .... seriously ? It’s not even breathing heavy, let alone breaking out in a sweat !

    And this should be obvious if anyone ever looked at the circuit diagram. The fuel pump circuit branch is protected by a 16 Amp fuse in the fuse box. So even under the worst case scenario, the relay is only trying to switch 80 % of its full load rating.

    Here’s some real world numbers ... some years ago I tested the currents in different circuits on my ‘81 318i Australian spec 1.8 litre. And Yes .. the fuel pump circuits are the same around the world, except for a minor variation in the pump relay on the earliest models (the pump relay had an extra pin out that wasn’t used) and the extra connection for the lambda circuitry in the NA models.

    I remembered that the fuel pump circuit was a bit under 8 amps maximum .. but I retested it at lunch today just to make sure. So I pulled the pump relay .. stuck an ammeter between sockets 15 and 87 and started her up.

    I let the engine warm up a bit and at about 2,000 RPM to get a stable 13.9 Volts at the battery
    ... the current was 7.65 Amps.


    That’s Fuel Pump + WUR + AAV currents.

    A bit of calculation ... the resistances of the WUR and AAV ... 22 + 50 ohms approx.

    This gives current for the WUR & AAV as 0.64 + 0.28 = 0.92 A

    So the 2 fuel pumps are pulling a run current of 6.73 A & 0.92 A for the WUR + AAV

    If you add in the lambda relay.... for a typical 12 volt relay of that type, the coil hold in current is typically 0.10 ~ 0.14 Amps .. so for a worst case scenario you end up with a total current of -----

    ~ 7.8 Amps, which is only 39 % of the standard relays 20 amp capacity !

    So there is no earthly reason for changing a good existing relay for a 30 Amp version, nor for adding an extra relay (and an extra layer of complexity) to power the WUR, AAV (& lambda relay if fitted) to reduce the load on the existing relay contacts by at most, 1 amp! (give or take 10 milliamps)

    Oh and as to using an in-line fuse in a jumper across terminals 15 & 87 ... the switch in the relay simply shorts out the 2 terminals so there is no need for a fuse. But if you feel the need to use an 8 amp fuse to protect the 16 amp fuse in the fuse box ... go right ahead.

    Quote Originally Posted by amarino View Post
    This one? https://www.bimmerforums.com/forum/s...T-BUSY-Part-II

    I think Tom is still waiting for a response...
    Aren't we all

    Cheers
    hmm .. Wonder what happens if I do this ...

  10. #10
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    So as stated elsewhere here:

    .... using a jumper across terminals 15 & 87 ...

    If someone was to bottom-line the "fix" for having to jump the relay terminals, what would be the cause for such a need to "jump" the terminals to make the pump work?

    Ruling out the relay itself:
    Could it be a short in the WUR?
    Is it a wire missing from the coil?
    Perhaps a bad ignition contact?
    thoughts? This seems like it's a common issue with a simple solution.

    What are the most probable items to verify if the pump(s) work when jumped.
    Last edited by blacky77; 03-27-2018 at 01:09 AM.

  11. #11
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    Thanks for your testing GDAus, that's always great information. Maybe the 30A relay does not get as hot as the 20A relay, thus possible eventual damage to the IC chip (75C max?)?

    Quote Originally Posted by blacky77 View Post
    So as stated elsewhere here:

    .... using a jumper across terminals 15 & 87 ...

    If someone was to bottom-line the "fix" for having to jump the relay terminals, what would be the cause for such a need to "jump" the terminals to make the pump work?

    Ruling out the relay itself:
    Could it be a short in the WUR?
    Is it a wire missing from the coil?
    Perhaps a bad ignition contact?
    thoughts? This seems like it's a common issue with a simple solution.

    What are the most probable items to verify if the pump(s) work when jumped.
    *shorts could indeed cause a problem, and remember the relay is fused.

    Make sure all the socket terminals are clean and tight (look at notes in the 2 pics I posted). Check the ground and signal(pulse) wires/connections. In another case, the fuse contacts are the issue.

    The relay can be tested too, ie: the IC chip inside the relay. The signal(pulse/trigger) is very sensitive (as noted in one of the pics). If the relay contacts are burned, may be able to clean them, or just use it as a spare/tinker-with and replace it with a new one.

    test rig (use a bigger load if test requires 'load' testing).
    click to enlarge...
    e21-fp-relay-test-rig.jpg
    Last edited by epmedia; 03-27-2018 at 02:03 AM.
    Tbd

  12. #12
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    Quote Originally Posted by epmedia View Post
    "work horse" relay is a better name for it

    I remember your thread about the kit, I'm glad your pleased with the results!
    works perfectly,, I'll stick with Hella update, I can see its an improvement in the wiring harness and running these devices.

    Randy
    Last edited by 320iAman; 03-27-2018 at 03:06 PM.

  13. #13
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    Quote Originally Posted by epmedia View Post
    Thanks for your testing GDAus, that's always great information. Maybe the 30A relay does not get as hot as the 20A relay, thus possible eventual damage to the IC chip (75C max?)
    Hi Robert ...
    Actually the biggest source of heat inside a relay comes from the current through the relay coil. There are two accepted temperatures for the coils, 80C & 85C.
    As for the 555, yes it has a temp rating of 70C, but the virtual junction temp .. ie. inside the chip is 150C. So in the real world they are a lot more temperature tolerant that their basic specs would indicate.

    As for the heating in relay contacts .... basically the contact resistance should be virtually 0. I've got my E21 off the road at the moment doing some rust repairs .. so i had a chance to check out the relay in the car and a spare I have. The best of my meters is capable of measuring down to 0.0005 Ώ and it couldn't measure anything with the contacts manually closed in either of them.. Similarly, doing a voltage drop test across the closed contacts gave zero as well (meter capable of reading down to a 0.001 volt drop). So the heating effect on the switch contacts is very very small ...unless they are heavily overloaded ! But the E21's standard relay has a load rating of 20 Amps ... that is a continuous rating and under normal circumstances it is only carrying less than 8 Amps!

    The main heating effect the switch contacts have to cope with is produced by the arcing when the contacts open. Again ..the FP relay is not constantly cycling on and off ... there should be minimal wear and tear on the contacts. I have a spare used relay and the one in the car ... both German SK brand one has the BMW logo on it. Under 60 X magnification, the spare has no discernible discolouration or arc damage, the other, which is probably the original has slight grey area with an only just visible amount of wear pitting. That one I did a quick cleanup on the contacts with some 600 grit wet & dry something like 7 years ago and I can't see any deterioration since then. Some abrasives are electrically conductive .. so wash out with a contact cleaner after doing this !

    Cheers
    hmm .. Wonder what happens if I do this ...

  14. #14
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    The 555 Timer is NE555P by Texas Instruments, a few other companies makes these as well, with slightly different lettering, at least the 30A Models are Ti NE555P. I have 2 dozen SE555P which are the Military Grade 555 Timers. Can read about the data differences here and specifications of the other lesser models. There are also two cases for the 555 timers one epoxy and the other metal, metal being superior.

    http://www.ti.com/lit/ds/symlink/ne555.pdf

    As too the relays rated and actual output that is another entirely different issue and the upgrade to these relays, I did testing on relays and published a few items on this including my circuit that ups the ante on these relays so that rated and actual is equal for all intensive purposes and then sum and more solid than the Rock of Gibraltar , a very long time ago. I did this for commercial applications and the left the military wanting ,,I tested for the armed services in my earlier years and was told I got the highest score recorded in all tests in electronics ever.

    Randy
    Last edited by 320iAman; 03-29-2018 at 03:56 PM.

  15. #15
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    Great info, GDAus and Randy. The 555 was one of my tinker hobbies awhile back, I had lots of fun with them and the 556,, great memories. I was just peaking at my (now, 40 years old) spare fp relay - with NE555P (Texas Inst) chip, some burning on the contacts, still works, cleanable. I'd imagine also that not all aftermarket relays are created equal and then there's some variables that can be thrown in- to 'observe' the relay's behavior (ie: aftermarket fuel pumps, dirty fuel filter, higher fuel system pressures, etc.). I suppose the ultimate experiment would be to test the components of the 'failed' fp relays! To know what's really going on in there - or maybe the 'failed' relays are fine and something else is wrong!

    Hey, who wants to send us some failed fuel pump relays? for science purposes, of course.
    Tbd

  16. #16
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    Here is the Ti SE555P Timers, The Ti NE555P timer and socket, and the SE555P timer and Socket installed, upgrading the fuel pump relay made by KAE, BMW,Hella, Bosch, et cetra, I removed the NE555P, installed the socket and then tested the NE555P and then removed it with tweezers and installed the SE555P timer, I ran both in my car and both work no problems. When the 555 Timer goes out I replace it in seconds. The SE555P is Military Grade -55 to 125 C operating temperature, the NE555P 0-70 C operating temperature, ect. My solder station is inexpensive,, may be Weller will give me another solder station for free again.. ,,,desoldering and soldering, no problem.. How sweet it is.. The socket future proofs the 555 timer in case the SE gets updated as well,,.
    SE555PDSCI0266.JPG, NE555P and SocketsDSCI0267.JPG and the KAE FP Relay with SE555P installedDSCI0268.JPG,DSCI0269.jpg

    Credit where Credit is due..


    Randy
    Last edited by 320iAman; 03-30-2018 at 08:56 PM.

  17. #17
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    Way cool projects, Randy!

    And only cost about 45 cents each, I love those things, can do so many things with them!
    Last edited by epmedia; 03-31-2018 at 12:09 AM.
    Tbd

  18. #18
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    Indeed Robert, they have many applications been around since 1971 or so. In this style of work the 555 Timer is elevated above the socket fully secured and inserted allowing free air underneath, the sides, and front and back ends with the 555 timer soldered to the circuit board free air is not available to all these places, another upgrade.

    So in Upgrades over Bosch, KAE , BMW and whom ever.

    1.) The Timer is SE Military Grade in data.
    2.) The Timer is in a Socket Interchangeable without desoldering
    3.) The Timer is elevated from the socket better cooling , more access to free air available.
    4.) Cost saving to replace the timer rather than the whole relay
    5.) Reserved

    I'm running the KAE FP Relay with the SE555P installed above picture, I'll make another later probably from brand new KAE.



    Randy
    Last edited by 320iAman; 04-02-2018 at 06:52 PM.

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