Early CIS fuel pump with late CIS engine?

Adidas · 12-22-2010, 02:56 PM

1974 911 with an 82 3.0 engine installed. The fuel pump is also a Bosch 1974 911 unit as well. Engine runs fine with no issues. Should the pump be changed to the later 80-83 pump to match the engine? Not aware of any different fuel pressures in these pumps but I'm sure the fittings will be different. Just leave it as is? Thanks

jmitro · jmitro's Garage

check the specs on fuel pressue and flow rate for the different pumps

Gogar · 12-22-2010, 04:51 PM

Is it a "sidewinder" pump in the driver's rear wheel well? Definitely different fittings, I'm not sure about the specs.

I know this isn't your question, but if it is in the rear wheelwell, you could do well to relocate the pump to the front crossmember and run a new high-pressure line from the pump back to the accumulator. Pain in the ass, but not really 'difficult', and helps your warm starts immensely.

You could get some good coin for that '74 CIS pump too.

In my opinion any good CIS pump is fine, I know in my 2.4 CIS motor I used a VW CIS part number from a '80s Golf. Some of the Bosch pump #s have been superceded also and they only make 10 pumps or something instead of a zillion which in some cases is good because it brought prices down.

T77911S · 12-23-2010, 04:27 AM

here is a chart some one else posted, yea, i stole it.

Adidas · 12-23-2010, 07:03 AM

Gogar. Yes the pump is mounted in a metal cradle inside the driver's rear fender. By mounting under the fuel tank up front will warm starts be improved by getting the pump away from the hot engine and heat exchangers and helping the 'vapor lock" problem.

77911 S. The part number on my pump is 0 580 254 985. Don't see it on the table above. Probably need to post another topic and get this info. Thanks.

ossiblue · 12-23-2010, 07:45 AM

Quote:

Originally Posted by Adidas

Gogar. Yes the pump is mounted in a metal cradle inside the driver's rear fender. By mounting under the fuel tank up front will warm starts be improved by getting the pump away from the hot engine and heat exchangers and helping the 'vapor lock" problem.

77911 S. The part number on my pump is 0 580 254 985. Don't see it on the table above. Probably need to post another topic and get this info. Thanks.

Moving the pump forward will help keep the pump/fuel cooler but you may have another issue if you have hot start problems. "Vapor lock" is a misnomer for this--if the fuel accumulator is doing its job and the fuel pump check valve is working, you should not have hot start problems with the pump located in the factor position.

I would recommend moving the pump forward as it saves it from the extremes of the engine heat and should make it last longer, but it probably won't cure your hot start problems.

Tsunamiboy · Tsunamiboy's Garage

My 1979 SC has the stock fuel pump supplying a 1987 3.2 Motronic engine. No problem!!!!

spuggy · 12-23-2010, 08:25 AM

Quote:

Originally Posted by Adidas

The part number on my pump is 0 580 254 985. Don't see it on the table above. Probably need to post another topic and get this info. Thanks.

The table above are the specs for the Bosch motorsport fuel pumps. Bosch don't publish an equivalent for the "regular" pumps that I've ever seen, although the "universal fuel pump" interchange document is useful, and so is the vehicle cross-reference (showing what Bosch part #'s are fitted to what cars). I posted links in this forum several times to these documents on the Australian Bosch site. Other sites have them too.

Any CIS pump should work, if it meets your flow/pressure requirements, then it's just a question of fittings. (In fact, any CIS pump should be fine for EFI as well). If yours is in spec and works, I'd leave it.

If you need to change it, the 044 motorsport pump is very cheap by comparison to some other pumps as it is very widely used, and it out-performs all the factory-fitted pumps by a wide margin. Worth a couple of hours and $30 worth of fittings to adapt to the factory hoses.