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[1724-U-W924]

Hello, I have an early 1977 924 and my fuel pump relay died, and the relay that came in the car is the SHO 477 906 059 which from what I could find isn't made anymore. I was wondering if there is a relay from another car that uses the same fuel system could be used in my 924.

[Beartooth]

I'm in the same boat. One fit is the KAE 3.300.300. https://www.pelicanparts.com/More_Info/433906059.htm?pn=433-906-059-INT&SVSVSI=724&DID=67831 I'm not sure if KAE is the OEM; either way, it's apparently also a fit for a few VWs and Audis, but unfortunately seems to be out of stock everywhere. List price is around $40; the only place you might be able to get a new one right now is ebay, for $150 or so... A plain relay will plug in and work, but would probably only be advisable in a "get you home" scenario. Since it's not clear if or when they'll be available again, I'm trying to figure out what the extra circuitry in the OE relay does; it might be possible to substitute a different relay.
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1980 931 diamond in the rough

[Eliza]

The KAE 3.300.300 is a direct replacement for 433.906.059 and won't help the thread starter I'm afraid. The old relay 477 906 059 is a six-prong, the later 433 906 059 is 5-prong.

What makes both these special is they're tachymetric, i.e. they need to see an ignition pulse to stay energized so in case of a crash and dying engine, fuel supply will be cut as a safety measure.

Elsewhere on this board there is a schematic for the 433 906 059, so it could be rebuilt at relatively low cost. Just a couple if resistors, capacitors and an NE555 in there.

I was lucky ( prudent? ) enough to stock a few when they were still available, although I switched to a KAE 3.308.200 ( 92861511301 ) from a K-Jet 928 because that is a direct fit AND consistently primes the pump for a second or two at ignition-on. This makes the car start at the first turn of the key, every time. Brilliant. These are still occasionally for sale at ridiculous prices.

Soooo.. might we consider between us 924 owners to produce our own relays? How hard can it be?

For the thread starter, you might want to open the relay and try reflowing the solder points. Or have someone look if any of the caps or resistors need replacing. If the circuit board itself isn't broken these can usually successfully be repaired. Yell if you need help with this.

Eliza
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1985 924 NA RoW
1981 931 S2 RoW

[Carrera RSR]

I contacted this guy a few times to produce a solid state relay for 924/924 turbo some years ago. Chased a few times but got no contact back - https://www.ftech9.com/new-products/993-ssr-pp may be worth bombarding him with requests so he can take a view if commercially viable
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1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
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[Eliza]

With the current semiconductor shortages I don't see solid state relays for our cars coming any time soon.

In the coming months, I'll play some more with my electronics starter kit to see if I can make my own relay. Just because

The only real challenge I see is making it small enough to fit into the socket. Nice winter project this.

If any of you feel like chiming in - how cool would a DIY relay be?
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1985 924 NA RoW
1981 931 S2 RoW

[scm924s]

It really doesn't have to be small enough to fit into the socket. If manufactured with a flylead with a plug to suit the socket, the relay can be mounted remotely.

Good luck with finding a solution.
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1984 n/a Ruby Red Metallic
1988 924S Guards red- sold
1986 924S Guards Red - sold
1984 n/a Black - sold
1980 n/a Le Mans#1 - sold
1980 n/a Le Mans#2- sold
1977 Martini - sold

[Fasteddie313]

Doesn’t the early NA just have a metering plate position switch for its safety?

If it closes when the plate moves you could just use that is your relay ground, and use ignition key on power for its signal positive, and the relay would only engage and give fuel pump power when the key is on and the plate moves..
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80 Turbo - Slightly Modified

[Eliza]

I was under the impression that the early relay has an extra pin that energizes via the starter to prime even before the first ignition pulse. Reliable info on the web is scarce and fuzzy though. If it were my car, I would try a repair of the existing relay first..
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1985 924 NA RoW
1981 931 S2 RoW

[Eliza]

I found the info the thread starter was looking for on the German Porsche forum. For future reference:

The later relay 433 906 059 can be used instead of the NLA 477 906 059 after the following changes to the relay board of a 77 car:

Wire 31b ( originally connected to the metering plate switch ) needs to be connected instead to the green wire from ignition coil to tach ( 1b ).

An inline fuse of 16a needs to be spliced into the hot wire ( 30 ). The early relay has its own fuse, the later one doesn't.

Terminal 50 of the relay socket remains empty with the later relay and can be left alone.

All other terminals ( 15, 31, 87 ) can stay as-is.

HTH,

Eliza
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1985 924 NA RoW
1981 931 S2 RoW

[Beartooth]

Didn't realize the NA and turbo were different; sorry for the bad info...

It sounds like the 928 relay would be a minor upgrade, and there might be others. My Mercedes' have similar circuitry that primes the system; the also have a rev limit cutout. One of those might actually work with minor adaptations, but it'd have to be a four-cylinder version. Some digging into the service manual indicates that it counts impulses per second from the tach signal and shuts off when that's exceeded. So a six or eight cylinder version would take 50% higher or twice the advertised cutout; a six-cylinder version set to cut at 6000 would instead not cut until 9000. Anyway, there might be some options from different VWs and Audis. I'm sure there are other fuel pump relays that you could somehow rig up to have the same no spark, no run functionality. A final thought on a substitute is the 944 relay. I'm guessing it has a similar energize on tack signal functionality, but it looks like it adds something else to the mix. Maybe it's similar to the 928 version? Seems to be availability on those...

It is pretty frustrating that such a simple part is unobtanium. I notice in digging up part numbers for other VW, Audi, and Porsche relays that we're far from the only ones NLA. Definitely don't throw out those old relays; most could be fixed. It's probably the semiconductor that's the limiting factor, with everything in such short supply. If that's not the part failing, the other stuff should be easy to replace, and sometimes the problem is just corroded contacts or a bad solder joint. It'd be nice if that guy Carrera RSR mentioned could help us out. Ultimately, it'd be nice to have a plug-and-play relay with priming and a rev limiter. My understanding is that ignition-based RPM cutouts are better (especially ones that randomly cut out cylinders), but some protection is better than nothing...
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1980 931 diamond in the rough

[Eliza]

Hi Beartooth,

turbo and n/a share the same relay 433 906 059. It's only the cars up to MY 1979 that have the early relay 477 906 059, and that's because the earlier ignition setup is different so a running engine was determined in another way than in the 1980 and later cars.

Rev-limiting on the turbo is already dealt with by the overboost switch, no need for a rev-limiting relay? ( at least on the series 2 turbos ).

Yep, it's a shame that one unavailable relay can cause such grief, but essentially we're lucky that after 40-plus years, so many parts are still available.I just noticed that after years of non-availibility, the wiper switch for the later cars can be bought new again - for a whopping 363 EUR ( not to worry, I have a spare in my parts box ).
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1985 924 NA RoW
1981 931 S2 RoW

[Rasta Monsta]

Overboost has nothing to do with rev-limiting
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Toofah King Bad

• WeiBe (1987 924S 2.5t) - 931 S3

[chuck21401]

Are you missing a genuine part?

With our form, you can query the availability of Porsche Classic genuine parts online.

https://www.porsche.com/usa/accessoriesandservices/classic/genuineparts/notesonavailability/

(enters 433 906 059)

We're sorry, but the genuine part that you requested is currently unavailable.

Your request has been automatically passed on to the Porsche Classic product management team.

We regret that we are unable to respond to you personally. Your request will be checked for technical and economic feasibility.
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1981 Porsche 931 w/S1 engine & g31 transmission. Water-cooled intercooler

[chuck21401]

[Carrera RSR]

Anyone have any idea if the KAE 3.300.300 relay has any kind of rev limiting feature? I have this relay in my car and just thinking aloud of something I have experienced

FYI this KAE relay on my car primes the pump most times I turn the ignition to on. On cold start ups I tend to turn a few times to hear the pump prime a few times and then it starts on first kick of the start (without the need of 5th injector connected ) If I don't prime it takes 2-3 cranks more for the fuel to reach pressure and fire up.
_________________
1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
Now www.924board.org/viewtopic.php?t=34690
Then www.924board.org/viewtopic.php?t=31252