944 Relay problem

Corse · 09-24-2007, 03:27 PM

I just bought a beautiful excellent condition low mileage 944 (35k miles). It ran beautifully for 2 hrs, stopped and started a couple of times with no problems. Then when arriving home it wouldn't start. I found a spare relay in the glove compartment - no idea what it was but I replaced a similar unit under the dash thinking that this was for the fuel pump. The relay was noisy but the car fired up. Ran it to the garage without a problem. Now it won't start at all although I have lights and power. Is there a common problem with these relays, fuel pump or perhaps the dash itself?

Ernest Hill · Ernest Hill's Garage

sounds like a battery (or loose alternator belt) problem, get it tested; carrying a spare fuel or fuel/DME relay is just wise, a lot of us do it, and Porsche (& even VW, 83-84) electrical systems are the best. your car probly sat a while and Porsches do NOT like to sit, so expect a lot of 'teething' problems. get a 60K service done, expensive but necessary, Porsches require regular maintenance

Corse · 09-25-2007, 08:00 PM

Thanks for the info, one more question, should the fuel pump be buzzing/primed with ignition switch on before starting?

TibetanT · TibetanT's Garage

Cory:

Yes! When you first turn the key to the "ON" position, the fuel pump should be running. The reason for this is to get the pressure up so the injectors will fire.

I always get in, turn the key to "ON" for a few seconds...like ten or so, then turn key all the way over for ignition. I find it does help keep the fuel rail supplied and the starting idle a little smoother.

Hope this helps.

mjadair · 09-26-2007, 08:27 AM

I guess that depends on what year. My 83 does not run the fuel pump with the key just on, but the moment that it starts cranking the pump spins up.

looneybin · 09-26-2007, 09:14 AM

Porsches have a built in safety feature that prevents the fuel pump from running unless the engine is also turning. It is to keep fuel from dumping into a bad situation ie: if you wreck the car, causing a fire.

Tidybuoy · 09-26-2007, 10:33 AM

Another thing to consider: While your car is low mileage, it's still 20 years old.

I bought an '88 with 17k miles and it was as mint as they come. But, I had to replace the hoses, belts, fluids, and filters.

When I replaced the Fuel Filter, I also replaced the fuel tank screen - it was clogged quite a bit.

It's always possible that your relay problem is caused by a bad fuel filter which is causing the fuel pump to overwork itself.

Lastly, which you will probably hear from everyone on this board - change the timing belt. At 35k miles, it's due (unless it was just done). If that snaps, you'll have big problems.

Vern

Corse · 04:50 PM

It just had a $2k full service incl belts... that reminds me that I need to change the belts on my Ducati for the same reasons!

Thanks for the replies- a wealth of expertise! going to start testing with a meter this Friday.

Brando · Brando's Garage

Quote:

Originally Posted by TibetanT

Cory:

Yes! When you first turn the key to the "ON" position, the fuel pump should be running. The reason for this is to get the pressure up so the injectors will fire.

I always get in, turn the key to "ON" for a few seconds...like ten or so, then turn key all the way over for ignition. I find it does help keep the fuel rail supplied and the starting idle a little smoother.

Hope this helps.

Maybe an older carbureted Porsche 911, but most certainly not a 944. All 944s are setup so the fuel pump is only running as the car is cranking or running. In fact, all new cars (to my knowledge) are the same way.

Now, if someone has messed with your wiring, bypassing the relay to have +12v from the ignition switch, something is amiss.

Ernest Hill · Ernest Hill's Garage

as soon as you turn on the ignition your 944 will bring your fuel pressure to the proper level, before you start cranking. (if you don't believe me, Brando, open your fuel line and turn on your ignition-- that is how you test your fuel flow as opposed to pressure.) ideally your check valve is holding your pressure so that the pump does not actually need to pressurize; my 83 &84 both loudly ran when i turned on the ignition, but i cant hear it in my 951, so i dont know what to say about whether or not it indicates a problem. but if you contiue to have problems, 1. they may go away, & 2. look to your fuel lines first since your car sat. 2X on the fuel tank filter screen cleaning advice, then, fuel pump check valve, fuel pressure regulator & dampener, fuel injectors are all possibly toast. buy a fuel pressure gauge and a good manometer so you can start testing components, otherwise you will get nickel-and-dimed sorting this out

onZedge · 09-27-2007, 06:44 PM

Quote:

Originally Posted by Brando

Maybe an older carbureted Porsche 911, but most certainly not a 944. All 944s are setup so the fuel pump is only running as the car is cranking or running. In fact, all new cars (to my knowledge) are the same way.

Now, if someone has messed with your wiring, bypassing the relay to have +12v from the ignition switch, something is amiss.

Yes, yes, I agree. On the 924Ss and 944s, the DME cuts out the fuel pump below starter cranking speed (something like 200-400 RPM), so fuel is not continuously pumped after the engine quits like after a wreck!

I knew a guy who spent big bucks restoring an MGB. First time he drove it, the fuel line at the carburetor came off. He had an aftermarket electric fuel pump wired to the ON position of the ignition. It was at quitting time on a Friday at a large industrial company parking lot exit. QUITE SPECTACULAR to say the least!

It was what we all call a CAR-B-Q down heah.

earlr85944 · 09-27-2007, 07:27 PM

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as soon as you turn on the ignition your 944 will bring your fuel pressure to the proper level, before you start cranking. (if you don't believe me, Brando, open your fuel line and turn on your ignition-- that is how you test your fuel flow as opposed to pressure.)

THAT IS NOT THE FACTORY WIRING FOR THESE CARS. Other model\years yes but not these. As Brando said:All 944s are setup so the fuel pump is only running as the car is cranking or running.
But:

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In fact, all new cars (to my knowledge) are the same way.

is not correct, most new cars will pressureize the system with the key on.

TibetanT · TibetanT's Garage

Brando and others:

Point well taken, regarding the fuel pump and it running with the ignition switch in the "ON" position.

I have been restoring this 1987 944 AND did find a mess in the wiring from the fuse box and under the dash. My original problem stemmed from the fuel pump not running at all, even with a new ECU and DME Relay installed. Go figure, after installing a brand new sunroof relay, the pump came on and then the car started with no trouble. These two relays don't even have anything to do with each other as far as I can tell??

Here, I thought I was done, but it sounds like I need to go back through my wiring and ensure this isn't happening.

Thanks!

PorchFile · 09-27-2007, 08:49 PM

and search under garage manual - select 'd' for DME and look at the troubleshooter for DME relay. The pdf file shows how to make a 'jumper' that will a) allow you to test your relay, and b) get you home if it goes out suddenly. When you jump the contacts on the block, the fuel pump will immediately begin running.

PorchFile · 09-27-2007, 08:50 PM

Sorry - lost the link when I tried to paste it in.

http://www.clarks-garage.com/

Corse · 07:15 PM

Well after 2 months of sitting I went out to the car fitted the DME relay and it started first time! I couldn't believe it! so I loaded up the system , AC , heated window, lights , radio, brake lights to see if drop in current would affect the running of the car and possibly cause it to stop. However it ran fine. I changed the DME to secondary spare and it ran again! now I am concerned as with it running I have no way to trace the problem, and if I take it out it may stop running anywhere. It doesn't seem to be a DME problem but I am buying anew just in case.