LeonLewis

Hi Guys

I have a 1981 928 4.5.

Recently its been pretty cold down to -3. And the car has been left outside. I took her for a drive having left the car in this weather for around 3 days. After 10 mins the fuel pump fuse blows. I replace the fuse. Take the car back, put her in the garage. Leave it for a few days. Fill her up as the tank has also been running low a fair bit. And then she seems to be fine.

However after around a week or 2 and quite a lot of little drives. Same issue again (Car has been in the garage and with half a tank of fuel since the first fuse blow).

The fuel pump, fuel filter are newish (replaced <5000km). The injectors have also been cleaned. So the only thing I can think of is the fuel relay.

It seems strange to me however as the only variables that have changed have been the tank being on low. And the fact that I unusually left her outside in cold temperatures. However after filling her up and putting her back in the garage after the first fuse blow. I am getting the same problem.

Anybody have any ideas?

Thanks

Mrmerlin

could the fuel pump cover be touching the HOT wire at the pump or the saddle touching the hot wire?

Did you D100 all the fuse holders and make sure the tabs are tight that hold the fuses,
, added D 100 to the wires that plug into the back of the CE panel and the fuses, do you have quality fuses?
did you use any water remover in the fuel tank.
Is it possible the fuel is in freezing temps
NOTE leaving the tank at half full in freezing temps will increase the chances of condensation occurring,
its best to always fill the tank and keep it that way.
water can settle to the bottom of the tank and if you have enough of it,
then it could clog the strainer or inside the tank pump.

Petza914

It's also possible the fuel pump is just going bad and drawing too much amperage. Start eliminating possible causes. You can eliminate the relat as a possible cause by dring the car with a jumper installed. Connect sockets 30 and 87 where the really plugs in. This will make the pump run all the time so be ready to go once installing the jumper, or better yet, put a switch on it and wires long enough for you to reach the switch from the driver's seat. If it still blows the fuse when running on the jumper, it's not the relay.

928FIXER

Drop the fuel pump cover and look around for a short section of harness that would have gone to a in tank pump on earlier cars. I've seen them tucked behind the straps,left hanging cut off and wires left uninsulated with the hot wire rubbing on a ground surface.

LeonLewis

Thanks for the replies. I am currently going on the theory that there is water in the tank due to leaving it out in freezing temperatures on an almost empty tank. Prior to leaving it out i also noticed some shuddering. Which I understand could be consistent with the water in the tank theory.
So i am planning on draining the tank. By pulling the pipe connection from the fuel pump method. I reckon the tank could be quite dirty. Not aware of it every being cleaned. Should i try and give it a little clean in situ? Any ideas on how to do that. Can i just put a high pressure water jet down there? Maybe some detergent. Flush it out a bit?

Cheers,

Mrmerlin

drain it and report what you find first

LeonLewis

maybe i should try the water remover first? Does this stuff actually work?

Mrmerlin

If you suspect water it would be wise to drain the fuel first to confirm it if so drain the tank first

LeonLewis

So i poured a can of the water disperser in there. There was around 40 Litres of fuel in the tank (60L recommended for this product). I drove it quite a bit and revved it quite a bit (Which i realized after was probably a mistake). The fuse almost blew again. The next day I drained all the fuel (by releasing the hose that goes to the fuel pump). I did not notice any water however now that I had added the water disperser (And quite a high concentration). Perhaps I wouldn't notice it if it was there. I did notice some sludgy silt like deposit right at the bottom of the tank. There was a reasonable quantity but not significant enough to look like it would cause an immediate issue. Also worth noting none of it came out in the petrol whilst draining the tank.

Due to the fact this issue only arose after I left the car out in freezing temperatures I ruled the silt out as the major cause. Other than that the silt the tank looked in surprisingly good shape.

So after that i filled the car up to the max. It takes a hell of a lot of petrol I have rarely filled it passed half tank in the last 10 years.

So now it seems to run ok. After a short drive. I checked the fuse after the drive and the fuse is ok. It is a little warm to the touch but not boiling. Im not sure if that is normal?

Im not sure if this is going to work.. I am wandering if the filter has got clogged. Or the pump has got damaged with ice from the freezing temperatures. Perhaps they willl be my next points of attention if the issue continues.

copperstew

You can use a multimeter to check the amperage draw directly. Most multimeters require you to switch the lead to the fused amperage plug on the meter. I tested my fuel pump recently that way.

My blue Bosch pump (0580464017) is for a US-spec 1984 928S. It drew 6.5 amps. The spec was ~7 amps at 3 bar.

Alan

I don't understand this comment at all - what did you mean?

Alan

LeonLewis

Hey, I was looking at the fuse quite regularly and I noticed that it melted almost to the point of blowing

LeonLewis

So now I changed the filter aswell as It turned out I had a spare one sitting around. So next on the radar will be the pump. Thanks for the info, that will come in handy

LeonLewis

Hey, can you provide detailed instructions on how to do this? Sorry i still have a lot to learn!

LeonLewis

Hey, can you provide detailed instructions on how to do this? Sorry i still have a lot to learn!