glack

I'm curious how likely it would be for a fuel pump to all of the sudden fail.

The '85 Euro S started up just fine today as it normally does. I drove it 8-10 minutes at ~35mph. Parked it for 20 minutes. Started up just fine, drove it back for another 8-10 minutes at ~35mph. Parked it for 15 minutes, got back in and it cranked started, got up to 1200rpm and just died. Cranked again, got up to 1000rpm and just died. No response from giving it gas. Now it just cranks and cranks (as in turning over and trying to start). It has 1/4 tank of 91 in it.
I assumed it isn't getting fuel and was able to initially make it up to 1000-1200rpm just from the gas that was already in the system.

The fuel pump is no longer making a buzzing/humming sound when the ignition is turned on so I checked the fuse and swapped the relay - still nothing.

Would a fuel pump just die like this?

Any ideas?

Any help would be very very very much appreciated.

Old & New

I think the first step is to temporarily bypass the relay to check for a failure there. Do a search for one of the fine posts detailing this procedure.

SteveCo

glack;
In the very early days with my car, I had a similar experience: Car started and ran fine for about 10 minutes. Then on acceleration up a highway onramp, the car died just as I merged into traffic. Luckily I was able to direct the car to the side of the road. Cranked the engine....nothing. Lots of spark and fuel in the tank, but no sound from the fuel pump.

My problem was a simple one: the fuel pump circuit fuse was blown. I later found that the blown fuse was the wrong rating (too small)....and I did not have much equipment with me to diagnose the problem at the roadside. So a $50 tow truck ride later I find the solution is a $0.50 fuse! Needless to say, I now carry a few spare fuses and a small circuit tester (have not needed either since this incident however).

So if you suspect the fuel system is the problem, start with the basics: fuses and relays. I seem to recall that some research after my incident indicated that the relay failure is a common thing and that a jumper wire was another good item to carry onboard...just in case.

Check fuse #42 and Relay XX (you can jumper out the relay or swap it with relay VIII or XII as a test...just make sure that the swapping relay is working if you go that route!).

Regards,
SteveCo in St. John's

Jim bailey - 928 International

Yes fuel pumps can just die . Often they will become louder and louder prior to departing . You might check the pump by dropping the cover under the fuel tank and use a spare length of wire to jump from the battery + to the fuel pump + . Also with a test light or mutimeter you can check to se if there is power in the normal wire to the pump . Your 1985 Euro is an LH car and LH computers control the power to the fuel pump . Start with testing the pump , relays etc.......it how ever may be the L H brain

John..

I've had several pumps just stop working one day for no reason and without warning. It is not uncommon. The worst is the pump that works one day and refuses to the next.

Rufus Sanders

Oh yes, they fail in a hearbeat. Mine died in the driveway last time luckily. It's easy to replace and actually fun since it doesn't involve removing the tank on most of the cars. Some repairs are a testiment to how the Porsche engineers thought out the design of this car. Gotta appriciate that! - Ruf

glack

As I said, I checked the fuses and swapped the relay (with Horn XII) immediately. Horn works so relay must be fine.

Anyway, I have 12 volts at terminal 30 of relay XX. I inserted relay back into XX and checked for power at fuse #42. I have no power at fuse #42.
Interestingly, I went through each fuse and found that I have no power at fuses #29-45. The ignition was on when I checked them.
The weird part is that some of the accessories work, i.e. the parking lights work, the indicators work, etc.


I'm guessing I must have some sort of problem behind the central power panel but I'm clueless as to what.

If anyone can lend some guidance, I'd be much appreciative.

SteveCo

Sounds like we might need WallyP on this one. I think you will need a good printout of the wiring diagram to help you figyre this one out (I did and a couple of highlighter markers to trace things out!!).

On the fuse power issue, all the fuses on the '85 up to and including Fuse 29 are linked in common power busses. That is to say, groups of fuses draw their power supply from several common battery feeds. All the fuses from 30 onward are more or less independant...and most draw their power through relays (ie: they are not powered unless the relay supplying them is activated).

Using the fuel pump circuit as an example, if Relay XX was not activated (for some reason), then there would be no power on either side of Fuse 42. It appears on quick review that most of the remaining higher position fuses in the panel follow the same process (ie: are downstream fused circuits).

Back to the fuel system electrics: Relay XX draws direct battery power at relay terminal 30, then feeds this through relay terminal 87 on to Fuse #42 and then on to the fuels pumps. As Jim bailey mentioned earlier, Relay XX is activated by the LH fuel computer (terminal 17 on the LH brain) and draws battery power through central electrical panel buss "15". There are no fuses in the activation circuit that I can see.

So, here's what you can check:
1. Pop Relay XX and check for:
- battery power at terminal plug 30 (key position does not matter);
- battery power at terminal plug 85 (ignition "off")
- battery power at terminal plugs 85 & 86 (ignition "on")
- assuming this is OK, continue on....if not trace down the wiring to find out what's wrong.
2. Jumper relay XX terminals 30 and 87 and the fuel pump should work. If it does not, then I suggest you follow Jim Bailey's advice and try powering the fuel pump directly to determine if the fuel pump is toasted or if you have a wiring/computer issue.
3. If the pump does work when the relay is jumpered, but the car does not start, I think it is highly likely your LH fuel computer is toasted. John Speake on the board has a service to rebuild these or one of the Big 3 can provide you with replacement options.
4. You could try to temporarily ground terminal W15 on the central electrical panel...this simulates the switching on of the fuel pump relay by the LH fuel computer. If the pump runs and the car starts/runs, then you have some form of wiring/electric gremlin in this circuit. If no run, again it points to an LH failure.

Hope this helps...I'm not an expect here, just reading the diagrams and attempting to return some of the troubleshooting knowledge gained from others on the forum.

Regards,
SteveCo in St. John's

glack

Okay, so I discovered the problem and am wondering if anyone has ever encountered this before.

After testing the fuel pump directly as Jim suggested from the battery, I was relieved to hear it buzz away.

I then fashioned a jumper for terminals 30 and 87 and noticed that upon inserting the spade into terminal 30, the female side of the connection backed out!!

I removed the screws from the central power panel and carefully positioned a couple fingers behind relay XX to support the wires while I inserted the jumper. The shark fired right up!

I then removed the jumper and firmly replaced the relay with my finger still stuffed roughly behind the wire for terminal 30 and badabing!
Wow that felt good. No fried LH brains, not toasted fuel pump, just a sneaky female connection on relay XX that kept backing up.

Thank you guys so much for your help.

SteveCo

Glad to here it was something simple...well, sort of. Maybe the loose female terminal is the result of the infamous previous owner syndrome?

Regards,
SteveCo in St. John's

Jim bailey - 928 International

Yes watch those sneaky female connections............

glack

SteveCo,

Previous Owner Syndrome (P.O.S.? ) is definitely ailing my shark. I found 12 fuses that were the wrong amperage and 3 relays look like they were removed with a pair of pliers.
Anyway, I appreciate the write up. It was extremely helpful.

John Struthers

In addition to above replies.
How old is the filter?
Pull the check valve; clean ball and seat, if necessary, of shellack. If stuck open fuel pressure can bleed off- back drain down-.
If filter is clogged restriction can fuel starve the engine .

SteveCo

glack;
I avoided the POS acronym...someone might get the wrong idea on the reference reading this post in the future! The PO may have bene a POS, but definitely not the car. I am constantly amazed at how well though out and built these cars are, if you can just think like the people who created them.

Seriously, there have been a number of people that have found very crazy and creative electrical novelties in 928s, particularly with the central electrical panel. I figure that most cars lost their fuse panel diagrams very early in their lives and for-hire repairers simply guessed at fuses rather than look them up. I found a 25amp fuse in the interior lighting circuit that had resulted in burning off the terminal for that circuit in the CEP wiring harness! I figure the lights were not working and the repairer kept sticking in bigger and bigger fuses when smaller ones would blow. The problem? A common short in the front headliner light. Fixed this and the circuit works fine with the speced 5amp fuse. Took me about 10 hours to figure this one out.

On the relays, I destroyed one the first time removing it, then figured out that you really need a purpose-build tool to do this job properly. I have since fashioned one, but you can buy them fairly inexpensively. The CEP is really a fine piece of work, once you really look at it and understand it's execution...looks like you have had this experience at this point.

In any case, it is a very good idea to take some time, pull all the fuses, verify the correct amperage, clean the contacts and reseat them. I guess the same thing should be done with the the relays, but I personally have not had much problem with them.

I have been the gratefully recipient of lots of good advise and technical expertise on the List in the past year or so. Specifically on the electrical systems and wiring diagrams, I have learned alot and have applied a significant amount of what I have learned. I am happy to pass on what I know, but keep in mind, I am a relative newbie...there are others far more knowledgable and experienced out there. This is a long way of saying that a second opinion is often a good idea!

Regards,
SteveCo in St. John's

T_MaX

If you haven't done a ground and connector clean-up yet, you may want to schedule that PM at your earliest convenience.

Many times when connections and ground points get dirty, they will create hot spots in the electrical system. Being the CEL is the main distribution point for most of the 928 's electrical system, this will some times be the first place you will start seeing the effects.

A prime example of this is after you have discovered that one of your window switches has been sticking or you have held the button down to long by accident (cd case, M-phone or your hand/arm pressing on switch while driving). That relay gets so hot you can't touch it! Trust me, I know!

Now what ends up happening over time, is the plastic that holds the female spade connectors in place starts to melt. Not much, just enough to allow the single tab lock, on the female spade connectors to back out or loss their forward tension (so to speak).

The Fix?

Sorry, I have'nt gotten that far yet (maybe this winter). I did what you did and just push them from behind while inserting the relay. It works for now, but not "The Fix".

P.S. I gubbered up my Fuel pump case the last time I removed it. When I put it back in I just left the cover off to help dispense the heat. As an added bonus, if you don't think your fuel pump is not working you can just reach in and push the contact closed with a finger.