jpitman2

Ignition box? Everything works fine, starts etc, EXCEPT only the pre crank short run of the pump. I have a spare relay of same spec I will swap in and see if that changes anything. Why would it be so hard to actually find out if the relay has the short run capability built in to it ? I had a BL car in the 80s with L-jet, and it had the pump prime at turn on, and it was audible if the ambient noise level was low. It also had a feature of giving all injectors a squirt if the throttle was snapped open, and once when I had a thermotime failure I used this feature to achieve cold starts by snapping the throttle a few times before cranking to get enough fuel to fire.

Another thought. At turn on, with no pulse at the tach input, what can make the relay close the pump circuit, then open it again after a brief period? Current charging a cap ? More complicated circuitry than this would seem overly complicated to me. I might try testing the spare relay on the bench to see what I can hear.

jp 83 Euro S AT 55k.

jpitman2

Back again. Just tested a brand new KAE , and an older 92861511301 branded fuel pump relay. IF these were going to fire the pump briefly on turn on, to my thinking, applying 12V across 15-31b should have at least briefly closed the contacts audibly. Neither relay uttered a peep. Is there something wronmg with my logic here?
I checked resistance across all contacts, and the only one that gave me a reading was 15->31 (tach signal, small pin) - >100k ohms. This reads to me that the tach signal is needed to enable the primary circuit (15->31b) to complete.
Not the expected behaviour, especially after the OP achieved correct operation - what make was that relay please ?
jp 83 Euro S AT 55k

rockatansky

The full story is that I have had to change 3 or 4 fuel pumps since I bought the car. Final conclusion was that they get clogged with debris from the bottom of the tank (found a lot when I removed the tank). I already change the tank, fuel lines, etc, last February and everything worked fine since then.

Among my doubts about the fried pumps failure, it was the relay and the electrics, at least until I removed the tank. Well this are the relays I have had installed and their behavior:

1-previous owner: KAE-3.300.100. Don't know why it was there (it's for an audi or vw). It starts at pre-crank position and never stops, until key off. That was the reason of opening the thread, to know why it didnt stops after 2 seconds.

2-February 2012: Bought to http://stores.ebay.es/suppersellstor...p2047675.l2563 a brand new KAE 3.308.200. It worked fine and did the 2 seconds stops (you can see it working at post #6 in this thread). This kae part match with 928.615.113.01. It worked until february 2013. It died at the same time my fuel pump died. At the bottom I post a picture of this relay.

3-March 2013. While doing the full fuel circuit renewal, I bought an old and used (but geniuine) 928.615.113.01 Porsche relay from an ebay seller that was selling two relays from a '82 in this page: http://www.ebay.com/itm/80S-PORSCHE-...item5400b97a19 I already bought the fuel pump relay and now he have edited the page and is only selling the wipers relay. This one is also working fine and doing the 2 secs push perfectly since then.

Also, here's a link I have archived with a guy testing a fuel relay, if it helps in any way:

rockatansky

...forgot to mention that if you ask me the reason of changing from the KAE to a genuine porsche relay, I must say I read this at some forum:
---------
I think I've stated KAE is crap no fewer then 50 times throughout the years.. Pure chinese crap (most likely w/ a high lead content..hell, you should throw it IN your tank!)
---
A KAE will generally last one year, an OEM will last twenty!

- Steve
---

...that's why I went for a genuine in the second try.

By the way, 928intl are in the middle of the 1/2 sale off for used parts on christmas. That will be just $12.50 for the relay if they have one in stock (and with 1 year warranty):

http://www.mailordercentral.com/928i...615%20113%2001

dr bob

The "complcated" part of the fuel pump relay is a few small resistors and caps with a single transistor. Radio Shack parts I'm sure. Or go high-tech and put a 555 timer IC in there with a couple resistors and a timing cap. Then the simple "working" part is the relay itself. It wouldn't be at all tough to make the "smart" part and tuck it under a common 53B relay. That way the part that wears is separate from the part that's smart. The later cars have the FP relay smarts in the engine controllers rather than the relay cans, undoubtedly to ultimately save build money.

I only got about 25 years and 100k miles out of the FP relay (53B type) in my S4; should have just replaced all the critical ones at once when I bought all the spares. Instead I found the weak one at the bottom end of the driveway. On the way to visit GB and Rob E for lunch one day. Coincidence?

jpitman2

I found a post somewhere where a guy said they had a 555 timer chip, set up so the pump kept running as long as pulses came faster than an r/c circuit oscillated . he worked out that the r/c time was ~ 0.5 sec to allow for cranking speed. But where do I find a relay that will do the short prime run at turn on now , when the supposed replacement KAE units dont do it ?

jp 83 Euro S AT 55k

jpitman2

Just retested the spare NEW KAE relay . I thought about it a bit, and saw that the pulse pin is connected to Coil ground. So I shorted 31 and 31B together. Then when I apply 12v across 15->31b, I do get a click of closing, followed by opening again in about a second or two. Next test - check the relay in the car for the same effect. Its not very old usage wise, under two years old time wise.
The old 92861511301 branded relay (replaced because it got hot in use - burnt contacts probably) DID NOT behave this way.


UPDATE 7Dec - KAE relay in car IS firing the pump for second or so...just needed sufficient quietness to detect it, and a while since last tried.

jp 83 Euro S AT 55k.

Fronkenstein

I haven't put a scope to the relay yet but it derives a pulse from the same circuit as the tach. I suspect (I say suspect because I cannot hear my relay due to loud exhaust) that as the RPMs increase so does the relay cycling. If this is true I am baffled as to how they regulate pressure for higher horse power ROW S2s because if the circuit is tuned for a 78 low HP shark that would be inadequate for a 315 HP shark not to mention one that is piped. I will post my results - if I remember.

Fronkenstein

jpitman2

The relay doesnt cycle with the pulses - it just closes once it sees pulses, and opens when the pulses cease. The pump can deliver more than twice the engine's needs, and the pressure is regulated by the pressure regulators on the fuel rail. The fuel need is supplied by opening the injectors for different times depending on the ECU's reading of demand.
jp 83 Euro S AT 56k

Kiln_Red

Euro S2 uses a simple 53 relay for the pump.

Fronkenstein

Ah I was speaking to CIS, sorry about that.

Fronkenstein

GlenL

I just got a KAE (Kaehler) relay and was surprised, having read this thread, that it was stamped "Made in Germany" on the box and the relay. It worked fine but, truth be told, was replacing another KAE relay.

For those who think your fuel pump relay is a problem, try replacing with the regular horn relay (928-615-117-00). The little tang on the fuel pump relay is the feed from the spark controller and that holds the relay ON when running. The horn relay just turns on with ignition switch and has no connection for the spark box. This works great for testing and in a pinch but the relay is ON and the pump is running whenever the key is in the RUN position. This means the pump runs when the engine stops, which is a fire hazard, and the pump is eating through the battery when the key is in RUN. It's not ON if you're just using accessories, though.

So... If you're not getting any pump action, try the horn relay. If that works, you know to order a new fuel pump relay. BTW - the pump won't "bump" for a couple of seconds every time you turn the car on. It takes a while for the capacitors to discharge so the relay will click ON with RUN again. I haven't figured out how long the wait time is. Just don't think the relay is bad if you don't hear the pump hum every time you try to start it.

James Bailey

on CIS system pressure is set by the bypass valve on the fuel distributor which has shims on a spring to adjust if needed. Thee relay and fuel pump run constantly while the engine is running and all the excess fuel simply returns to the fuel tank. The injectors spray constantly while the fuel distributor varies the volume to meet engine needs using control pressure to adjust the movement of the metering plunger....The "warm-up" pressure regulator on the front of the engine adjust the control pressure to compensate for temperature, altitude, engine vacuum, etc. The brains of a brainless injection system but all mechanical.

Fronkenstein

Wow this thread is ancient. I found the issue months ago Thanks though

Fronkenstein