turbo fuel pump amp draw

[inaminit]

Helping a friend with his turbo, It is a 76 with a 77 engine or a 77 with a 76 engine-I cannot remember which. It started blowing 16 amp fuses on the fuse that leads to pin 30 on the two fuel pump relays, and when we put a 25 amp fuse in, a couple of wires got hot. Combined draw through the fuse was 21-24 amps. Then I measured a 13 amp draw to the front pump, and 8 amps to the rear. Grounds seem good, but I don't know where the actual ground connections are. Some questions:
1. What is the ampere capacity of 2.5 mm wires?
2. Is a pump that is drawing 13 amps failing or is the rotor locked or rotating with a lot of rotational drag?
3. What is a typical fuel pump amp draw?
4. Where are the fuel pump ground points on this car?
My friend has ordered a new front pump, but I think it is important to have a better understanding of the situation before we just start to throw parts at the problem.
Thoughts or suggestions?
Thanks in advance

[Schulisco]

To me it looks like the pump is stuck (does the car sits long time? How old is the fuel? Have a look inside the tank, it may be corroded!) On SCs the fuel pump has a draw of about 9amps. I suppose the pumps of a 930 barely take the same draw, probaly a bit more as they may be stronger than those of SCs, don't know.
2.5mm² wires can take up to 25amps if installed in free air (they will get warm with such a draw)
The fuel pump does not have a particular ground on the housing, its got two terminals being attached as shown in the wiring diagrams (+12V from the fuel pump relay and ground).

Here's a brief product info page about these pumps being used on SCs and others, but not 930's:
https://www-ezt--autoteile-de.translate.goog/motor/kraftstoff-system/bosch-benzinpumpen/72938/bosch-kraftstoffpumpe/benzinpumpe-0-580-464-126-198-l/h?_x_tr_sl=de&_x_tr_tl=en&_x_tr_hl=de&_x_tr_pto=wapp

Thomas

[wazzz]

There is this pdf document available online with specifications for Bosch fuel pumps. Amp draw vs. pressure and flow for various fuel pump types is shown in line charts at the end of document.

[spuggy]

930 factory wiring runs both fuel pumps through a single fuse. Many have had issues with the relays/fuses running hot, and a common modification is to run a separate/dedicated fuse for the second pump, which improves reliability, eg: 930 Fuel Pump Fuse Overload - The Solution

Apparently, you can no longer buy the fuel pump pigtails/relay base with the thicker wires - they're now all supplied with the thinner ones. Dennis can make them to the original spec - or Kroon may be a source.

You can, in fact, run a stock-ish 3.3 930 with a single 911 pump, as it meets factory spec for flow/pressure just fine. Well, my 230K mile 911S pump did, anyway.

Even a modified CIS 930 making substantially more power than stock will usually run perfectly well from a single Bosch 044 motorsport pump - also pretty common as these typically out-perform both factory-fitted pumps at a fraction of the replacement cost of either factory pump:



At least some parts listings suggest that the superceded 930 front pump model is interchangable/equiv with the 911 pump. An SC front pump 0.580.254.053 is rated 11.5A for 175 l/hour @ 5 bar, according to the Bosch "Motorsport components" document. That same document lists the 044 as 15.5A for 200 l/hour @ 5 bar... So I'd take these ratings as conservative - except for max power consumption...

More recently, Bosch are rationalizing their fuel pump range again. Not only are the original pumps probably NLA (except perhaps NOS), the 044 itself is also superceded - Bosch fuel pumps - 0580 464 200 versus 0580 254 044

Some have had good results with the AEM pump as a replacement for the 044: AEM 400LPH (AN) INLINE HIGH FLOW FUEL PUMP

HTH.