Fuel Pump Relay Failure

[jaustinmd]

During a major rebuild of my '82 911SC, the previous owner replaced the fuel pump in January, 2014. The car was not driven much until I acquired it in March, 2014. About a year later, (this spring), the fuel pump relay failed (Chinese generic?) and I replaced it with a "genuine" Porsche relay. Within about 6 months, this relay failed, too! At the time it failed, I had been driving on the interstate for about an hour - when I pulled the failed relay, it was pretty hot - not painfully hot, but quite warm! Luckily, I had a backup relay in the glove box, popped it in, and it has run perfectly since.

My tech, a Porsche specialist, initially said that the two relay failures could be a sign of faulty fuel pump, which is under warranty 'til Jan 2016. However, after a 2 hour drive the other day, I left the car running and felt the relay and it was cool - in fact, some of the other relays felt a bit warmer! After telling the tech the relay was cool after a 2 hour run, he said "let's wait and see if it acts up/fails again before replacing the fuel pump."

Of course, you know what will happen ... if the relay fails again and the pump is suspect, it'll likely be the month AFTER it runs out of warranty! Ha!

The question is - Is it likely I've just had bad luck with a couple of relays or is the pump really suspect or should something else entirely different be checked???

John

[tirwin]

My first thought is it's likely the relays and I'm basing that on the fact that people report high "infant mortality" with newer relays. And consider that with older wiring you have an increased likelihood of corrosion which creates additional resistance.

Just an idea but to check the fuel pump go for a drive and then get the car on the shop's lift and drop the belly pan to access the pump. If it feels too hot then maybe you can get it replaced under warranty.

[boyt911sc]

Originally Posted by jaustinmd

During a major rebuild of my '82 911SC, the previous owner replaced the fuel pump in January, 2014. The car was not driven much until I acquired it in March, 2014. About a year later, (this spring), the fuel pump relay failed (Chinese generic?) and I replaced it with a "genuine" Porsche relay. Within about 6 months, this relay failed, too! At the time it failed, I had been driving on the interstate for about an hour - when I pulled the failed relay, it was pretty hot - not painfully hot, but quite warm! Luckily, I had a backup relay in the glove box, popped it in, and it has run perfectly since.

My tech, a Porsche specialist, initially said that the two relay failures could be a sign of faulty fuel pump, which is under warranty 'til Jan 2016. However, after a 2 hour drive the other day, I left the car running and felt the relay and it was cool - in fact, some of the other relays felt a bit warmer! After telling the tech the relay was cool after a 2 hour run, he said "let's wait and see if it acts up/fails again before replacing the fuel pump."

Of course, you know what will happen ... if the relay fails again and the pump is suspect, it'll likely be the month AFTER it runs out of warranty! Ha!

The question is - Is it likely I've just had bad luck with a couple of relays or is the pump really suspect or should something else entirely different be checked???

John

John,

Ask your mechanic to test the fuel pump. It would take a few seconds to determine the current amperage and delivery pressures. Getting the car up on a lift and preparing the car would be longer than the actual tests. If the FP failed the tests, send it back ASAP before the warranty expires.

Tony

[OsoMoore]

I had two relays fail in sucession, and no problems since. On your next PP order throw a couple in the cart. They are cheap and small, so there's no harm in keeping a spare in the smuggler's box and another in the toolbox.

Also it is a handy way to steal-proof the car if you're leaving it overnight in a public area. Few people will know why it won't start, or that they can flip one of the other relays into its spot in a pinch.

[T77911S]

first i would clean up the fuse block.

disconnect battery
remove each wire one at a time. clean the ends of the wires with a wire brush.
clean the ends of the screws. try to clean the hole the wire goes in.
remove fuse. clean the contact points for the fuse.
clean the ends of the fuse

do this for all the fuses and wires.

if you have a MM, set it to measure amps
remove the fuse for the FP
connect the MM in place if the fuse to measure the current of the FP
should be around 7 amps.

take a look at the socket for the relay. see if you can clean the contacts for the relay.

[jaustinmd]

Originally Posted by T77911S

first i would clean up the fuse block.

disconnect battery
remove each wire one at a time. clean the ends of the wires with a wire brush.
clean the ends of the screws. try to clean the hole the wire goes in.
remove fuse. clean the contact points for the fuse.
clean the ends of the fuse

do this for all the fuses and wires.

if you have a MM, set it to measure amps
remove the fuse for the FP
connect the MM in place if the fuse to measure the current of the FP
should be around 7 amps.

take a look at the socket for the relay. see if you can clean the contacts for the relay.

The more I research it, I agree that a general clean-up of the fuse block and relay socket might be in order! If I go to all that trouble, I'm very tempted to just bite the bullet and upgrade to Pelican's ATO fuse block upgrade!

[85911]

For clarification, my '85 does not have a separate fuel pump relay. The DME provides this function, correct?

[tirwin]

Originally Posted by 85911

For clarification, my '85 does not have a separate fuel pump relay. The DME provides this function, correct?

Correct

[85911]

Tim: Thanks. I have stocked up on some spares as recommended by Pelican forum members and they include a spare DME, a red (round) multi-purpose relay, and a black ( round) multi-purpose relay as well as a number of the normal bullet fuses. I wanted to make sure I didn't incorrectly interpret the manual regarding the fuel pump relay.

[wilsonlaidlaw]

I too am suffering from the fuel pump relay failure issue. I have a 1977 Group B 3.3L tarmac rally 911. Some 7 years after its last major rebuild, the fuel pump relay failed last year. I got going temporarily by moving the horn relay into the fuel pump relay socket. I bought a new red relay and fitted. The specialist dealer recommended I also buy a spare, on the basis that although the originals were somewhat prone to failure, the more recent ones seem even more fragile. After less than 10 hours use, the replacement failed yesterday. It was slightly warm but not hot. I am reluctant to keep buying these defective and expensive relays and would prefer to go for a more permanent solution. Can one buy better quality relays in the multi-pin original fitting or is the best thing to engineer a total replacement using a heavier duty remote mounted relay?

Wilson

[rwest]

Originally Posted by wilsonlaidlaw

I too am suffering from the fuel pump relay failure issue. I have a 1977 Group B 3.3L tarmac rally 911. Some 7 years after its last major rebuild, the fuel pump relay failed last year. I got going temporarily by moving the horn relay into the fuel pump relay socket. I bought a new red relay and fitted. The specialist dealer recommended I also buy a spare, on the basis that although the originals were somewhat prone to failure, the more recent ones seem even more fragile. After less than 10 hours use, the replacement failed yesterday. It was slightly warm but not hot. I am reluctant to keep buying these defective and expensive relays and would prefer to go for a more permanent solution. Can one buy better quality relays in the multi-pin original fitting or is the best thing to engineer a total replacement using a heavier duty remote mounted relay?

Wilson

You might also try eBay or similar to find an old German made relay.

[proporsche]

Hi..i have been working on 911 for many many years ..never had a problem with burning out relays, but as you can experience the quality of the relays is gone..i suggest to find and original Wehrle relay..that will solve your problem.Even new relays are made in China unfortunately so find an old stock..i have plenty of them but am over the pond.....

Ivan

[wilsonlaidlaw]

I have bought a pair of new genuine OEM Porsche relays. These are still made in China (like seemingly everything else nowadays) but not by Üro. Hopefully these might last a bit longer and that the Chinese assembler was in a good mood, the day he made them.

Wilson

[HaroldMHedge]

Bought one of the red relays from Porsche and used it for my 87 factory oil cooler fan. Sad to say, it failed after about 3 months. Luckily, I was able to get my dealer to replace it under
warranty. Who knows how long the replacement will last.

Harold
87 Carrera Coupe

[Mark Salvetti]

Originally Posted by proporsche

Hi..i have been working on 911 for many many years ..never had a problem with burning out relays, but as you can experience the quality of the relays is gone..i suggest to find and original Wehrle relay..that will solve your problem.Even new relays are made in China unfortunately so find an old stock..i have plenty of them but am over the pond.....

Ivan

Ivan, what is that black relay at lower right with the LEDs and the switch?

Mark

[wilsonlaidlaw]

One of the problems is that the Üro relays look identical to the Porsche ones and it would not be a total surprise to find some dealers selling Üro as OEM ("Shall I get rid of that box for you sir?) I have bought some Porsche OEM ones from a reputable parts dealer in the UK who also sells the Üro ones at half the price. He said that the Üro ones are not advised for the fuel pump. I have sent a message to Wehrle asking if they still have Porsche round pin relays, made in Germany. I used to use an aerospace spec relay on my Ralt F2 car for the HP fuel pump. If I am still having issues, I will cannibalise a dead 5 pin relay and make it into a plug for the relay socket and fit an external 25A aerospace relay. I will use 5 core trailer wiring cable.

Wilson

[wilsonlaidlaw]

I have found a wiring diagram for the relay. I would intend to fit a Hella solid sate 22A 12V relay in the place of the original electromechanical relay.

Wilson

[timmy2]

Use the correct Fuel pump relay schematic, correct wire colors and includes the diode.
This is from the ‘78 schematics.

[proporsche]

Mark.. it is a factory relay set up for checking the idle on Carrera models.Some people use a wire i use this tool.


and here also tests on 944

[wilsonlaidlaw]

Originally Posted by timmy2

Use the correct Fuel pump relay schematic, correct wire colors and includes the diode.
This is from the ‘78 schematics.

My car was originally a 1977 911S not an SC, albeit I am now running gas flowed Motronic fuel injection on a big bore block but with 3.3 Turbo crankshaft. I wonder if that makes a difference? Is the diode inside the standard red 5 pin relay or external? The black relay from the horn circuit, which is I believe a simple make and break relay not a changeover, works OK (at least in the short term) on my car in the fuel injection relay socket.

Wilson