Marti

I was heading out to do some data logging to test a new ignition map and boom, car dies and I pull into the side of the road a couple of streets away from home. Tried restarting, nothing happening.

I first looked at the CE panel and checked the fuel pump fuse, all good. Next I "felt" the fuel pump relay, it seemed to be switching ok but still no starting.

I was now starting to feel a bit down as my testing is not going to plan and I know I am going to have some work to do to get this sorted. Just then I lovely american blonde walked by and paid the car a great compliment saying "I love your car" - I stopped being mad at the car and thought it's not too bad.

I hoof it home and picked up my electrical kit so I could jump the relay and get my head down by the fuel pump. I went ahead and jumped the relay and low and behold nothing from the pump, I disconnected the wire from the pump to check it was getting power and it was, this thing was definitely seized.

I removed the pump and took it home to see if I could unblock it. Turning it upside down a bunch of small black chips fell out and after 20 minutes of trying back and forward it finally spun into life.

Seems I have classic in tank pipe failure so I guess I will be pulling the in tank pump and replacing the small pipe that connects to the screw fitting.

Does anyone know the size of the pipe and what material should be used when doing this job?

Funny, if the car was running I probably would have offered that girl a lift home in it - probably best it was not running

dr bob

Stay away from American blondes. They get dirty too quick.

The in-tank pump may not have failed. the bits you see may easily be the short connecting hose between that in-tank pump and the tank nozzle fitting. It's only thirty years old now, you'd think stuff from a Porsche would last a little better. Seriously, the in-tank pump is a very simple single-stage, not prone to failing on its own unless it's been sludged or varnished.

FredR

The in tank pump is made of white plastic bits [likely yellowish by now] - the black bits will indeed be shards of petrol degraded hose that break off when the hose gives up..

Not sure what size the hose is but I can measure the OD of the nipple it fits over if that helps at all. Given the hose is exposed to fuel on both the inside and the outside it may well have a special spec. I used a regular hose as I had nothing else at the time [two years ago] but I am thinking of pulling the pump to check how my DIY revamp of the cables and hose is getting on.

Whilst the in tank pump is out give it a little "bump" with power to make sure it is viable

polecat702

Just curious, does any one know how many amps a good working external fuel pump pulls while running normally?

FredR

It should pull about 2 amps when running normally. This assumes it is pumping 2.5 litres per minute, develops a differential pressure of 48 psi [3.3 bar] ,has a pumping efficiency of 60% and a motor efficiency of 95%.

Fuse 38 that covers the fuel pumps and the O2 sensor for those models so equipped is rated at 15 amps. The in tank pump should normally take about 0.2 amps assuming it produces about 5 psi max. The fuse rating has to consider the starting current for the two pumps that is likely in the region of 6 times the normal current so when the motors fire up the likely current to the fuel pumps will be about 13 amps- sounds about right!

Wisconsin Joe

I'm going to disagree with Fred on this.

I had an intermittent fuel pump failure earlier this summer. Wasn't sure if it was the pump or the relay.

I put a Snap On diagnostic tester on it. I used a 'loop around' inductive pickup attachment that plugged into the box, and it let me see amperage draw by the pump.

The idea was that if the pump was failing, it would show irregular and 'spiky' power consumption.

It showed an amazingly flat line of 5.6 amps when running (average - high was 6.3. low was 4.9).

This isn't a brand new pump, but it's not all that old.

Turned out to be the relay.

FredR

Joe,

An interesting challenge. I had something in my head that was telling me 5 amps was the number I should expect to see thus why I qualified my calculated number with the parameters I used in lieu of hard defined info.

I suspect the motor efficiency I used was optimistic given 95% is for a brushless motor design that I assumed they would use for this type of device - that number would drop to about 80% if these things have a brush type motor design . I did find a data point that suggested the pumps are rated for 4 bar differential pressure at the rated flow - what that suggests is that the pump will flow more than the rated capacity when operating at rail pressure. Putting these numbers into the calc would suggest a current of 3 amps- still some margin from your measured values that I cannot explain.

On the other hand if 5 amps is a more realistic current draw, then I wonder what the starting current may be. My assumption is that they are direct starting but maybe they have some kind of starter circuit resistance built into the electronics to control the inrush associated with DC motors?

I have seen various numbers quoted for fuel pumps that I tend to take with a pinch of salt until I see verifiable data. The only other thing I can think of is if the "conservative" factors I used are still overly optimistic. I spent ages trying to find some data for the in-tank pump never found anything. Its flow capacity at the very least has to match the pump it feeds - I assume it will generate about 5 psi of pressure.

polecat702

My pumps are new, less than 120 miles on them. I measured the draw at the pumps while the car was on the lift. 10 amps. New relays and a different CE Panel. the relay gets hot as hell, and kicks out. Got a wiring harness problem some where in the car. I have a spare harness that looks better than the one in my 89. Gonna change it all out, looks like a bitch of a job, but it's cooler here now. Perfect time, and a top end refresh too.

Don Buswell, and daughter, did my intake and valve covers. They look fantastic! Gonna get my shark back up and running. I hope!!!

jcorenman

ID of the connector hose is the universal standard of 12.7mm

Try this thread: https://rennlist.com/forums/928-foru...ml#post9863710

merchauser

roger has a hose kit replacement, with modern hose, and new clamps. might be a lot easier to buy from him?

Marti

merchauser

great news! compare to all the other things you have done, this is cake. let us know the outcome.

Marti

Marti

merchauser

great news congrats