924Board.org

[CMXXXI]

I'm pretty ignorant when it comes to electrical matters. How or why are 924 and 931 fuel pump relays different? This photo shows the 924(L) and the 931(R) fuel pump relay. The only difference I see is that the far right-hand connector is labled "1" instead of "31b". The pin layout is the same, the schematic is the same.

Now, to make matters even more "quizzical", the 433.906.059 relay in the photograph is the actual relay that has been in my 931 ever since I bought it in Germany years ago (never been changed in all the time I've run the car). Does the fact that mine is a 79 Euro without the electronic ignition and lambda and "stuff" make the difference and allow me to use the "924 part number" relay?

(Click photo for larger image)

According to the 924.org Tech Section, there is another 924 fuel pump relay, PN 477.906.059. Is there a difference between it and "the other" 924 relay?
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'79 Eurospec 931

[Finbarr]

As far as I can tell, there's no difference at all between them. The parts catalogue shows the same part number for both models - 433 906 059 - and for all model years, so the only difference between these two units must just be the physical case size and the pin numbering.

However, looking at the wiring diagrams for early 924 models (up to 1978) shows a labelling the same as Smoothie's photo - 31 is connected direct to ground and 31a is connected to ground via a thing called an "air flow sensor contact". These early models didn't have a connection to the coil supply, so I'm guessing this air flow sensor is somewhere on the inlet manifold and cuts off the fuel if the engine stops.

I can only guess that the newer type of relay can replace the older one, so the original part with the old markings has been dropped and the new one specified as the replacement for all models.
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1980 931 (with the odd electrical quirk...)

[Smoothie]

[John Brown]

FWIW, I have posted pics of the two relays. You can see that the 924 is much simpler consisting of a single pcb featuring the venerable 555 timer ic; while the 931 is 2 pcbs with 2 1455 ics. Why the extra comlexity is anybodies guess. I always wondered if the cheaper part would work.

http://users.adelphia.net/~johnbrown3/parts10.htm

http://www.meridianelectronics.ca/gadgets/mc1455.htm
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John
80 931 - #931 44Cup
99 Escalade - tows track cars
gone but not forgotten: original 924.org car - 82

[Smoothie]

Clearly I got carried away there overthinking the testing procedure. While it might be interesting to know how the thing works, all that "what goes where" isn't needed to test it. Obviously, if the car runs with 30-87 jumpered and it doesn't run with the relay installed (and it's the correct relay for the car), somethings wrong with the relay. Just remove the jumper and plug the relay in - that's the test.

Well...except for the fact that the relay can be good, but the wiring to terminals 15, 31 and/or 31b(1) might be bad.
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"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[Lizard]

smoothie are you trying to confuse everyone?
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3 928s,

[Smoothie]

Hey! I got a sudden burst of energy..

For a 931, relay wiring:
31b (or 1) - to coil primary terminal #1 primary(-)
31 - to overboost pressure switch, then to ground (ground for testing off the car)
15 - to 12v(+)
30 - to battery 12v(+)
87 - to fuel pump fuse 25A, then on to both fuel pumps

For '78 na:
31b - to airflow sensor switch
31? - to ground (no terminal number given - guessing 31)
50 - to 12v(+)
15 - to 12v(+)
30 - to fuse, then on to 12v(+)
87 - to single fuel pump

For '79, '80, '81, '82 na:
1 - to coil terminal #1 primary(-)
31 - to ground
15 - to 12v(+)
30 - to 12v(+)
87 - to 25A or 16A fuse, then on to fuel pumps

Connections go to the same places for '79-'82 na and 931's, so it still looks like the cheaper na relay could work in a 931.
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"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[Finbarr]

The plot thickens! I've just checked my 931 and it's got the cheaper relay in (and always has as far as I know) - 433 906 059.

Inside it, almost to spite the words of John Brown, is a single PCB with a 1455 IC instead of the old 555.

The merest mention of the 555 has brought back so many memories of electronic projects from years gone by (sighs wistfully) that I'm going to make it my mission to trace the circuit and figure out how it works.

Somebody stop me if it's been done already!
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1980 931 (with the odd electrical quirk...)

[Smoothie]

Very nice. At $21.64, I think I can afford to carry a spare.
433.906.059 is available from www.thepartsbin.com for $21.64 as part number P2037-20302.
-And if that price is too good, you can get it from www.NAPAonline.com for $34.99 as part ECHAR292.

The gold plated 931 relay 931.615.113.00 made of unobtainium is at thepartsbin for $96.90.

The -'78 na relay 477.906.059 goes for $36.01 as P2037-20749 at thepartsbin.
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"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[swj]

Ah ha! So that's why the one I found in my glove compartment is the cheaper version too - thanks Finbarr.
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1980 931

[CMXXXI]

This "revealation" that the relays do in fact interchange should be good news to all us 931 owners. But curiosity still makes me ask "why are they different inside"? As John wrote: "Why the extra comlexity?" (I'm just glad that there are those of you out there that can make sense of all the electrical stuff. I can deal with the car's wiring diagrams in the manuals, but much beyond that, and it's all voodoo).
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'79 Eurospec 931

[Paul]

Maybe the more expensive one has a rev limiter. My car shuts down slightly above red line (80 931). I'm still using the factory installed original fuel pump relay.

[Smoothie]

Wow , the plot just thickened again.
But what about NA's - don't they have rev limiters?
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"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[Lizard]

the 931 rev limiter is the fuel pump relay,
the 924 NA doesnt have have a rev limiter, yah shyadup my peddle got stuck down once.
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3 928s,

[numbbers]

No, Lizard, thr '80 931 rev limiter is in the rotor in the distributer. It has a spring and steel ball contactor under the epoxy filled part. At approximately 6300 revs, the centrifical force causes the steel ball to overcome the spring tension, and open the spark circuit.
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1980 924 Turbo