Our purpose is to support owners in their use and maintenance of the Porsche 928 and to foster camaraderie among owners throughout the world.
Welcome, Guest
Username: Password: Remember me

TOPIC: Fuel pump question

Fuel pump question 04 Apr 2017 15:02 #19623


  • Posts:5
  • new928's Avatar
  • new928
  • Junior Forum Member
  • OFFLINE
  • Karma: 0
Hello there. I'm brand new to the 928 family and have loved Porsche for as long as I can remember. That being said, I have zero experience with Porsche and the 928. I have only worked on VW bugs. This 928 seems quite a few notches above working on a bug. Anyway, It's a 1979, and has no service history. It's been off the road for 3 or 4 years the previous owner thinks. He got it from someone in his neighborhood but hasn't done anything with it. He's removed the fuel tank, cleaned it out but that's about it. I see that new in tank fuel pumps are pretty pricey. Are there any alternatives that people have used with success or should I plan for $600 - $800 for the in tank pump? I'm sure I'll be posting a few things. I'm looking forward to trying to get this car up and running again. When I get the car I'll post a picture.
The administrator has disabled public write access.

Fuel pump question 04 Apr 2017 20:23 #19624


  • Posts:157 Thank you received: 5
  • joejabq's Avatar
  • joejabq
  • Senior Forum Member
  • NOW ONLINE
  • Karma: 1
Hi and welcome! I went through the same thinking process with my '79. Let me tell you what my strategy is./was. After talking to Roger at 928sRUs, I replaced the external fuel pump and put a filter in the tank instead of the internal pump. It was enough to get the car running so that I could keep working on it. I figured that I could always add the internal pump if I really need it. Roger says that this is a pretty standard approach with these older models.
The administrator has disabled public write access.

Fuel pump question 04 Apr 2017 23:01 #19626


  • Posts:5
  • new928's Avatar
  • new928
  • Junior Forum Member
  • OFFLINE
  • Karma: 0
Thanks for the reply. I'm interested in learning why the 2 pump setup was used in the first place. Obviously it's there for a reason. But if I can at least get the fuel moving using just the external pump for now then I might try that option first to at least see what's up with the engine. There's going to be a lot of research for sure. I'll know more when I pickup the car on Saturday and hope all the parts the previous owner took apart are still around. Thankfully it looks like he didn't do too much dismantling.
The administrator has disabled public write access.

Fuel pump question 09 Apr 2017 11:06 #19628


  • Posts:110 Thank you received: 5
  • Rich928's Avatar
  • Rich928
  • Administrator
  • OFFLINE
  • Karma: 3
We don't know the decision making process for Porsche. The 1978 - 1979 CIS cars had two Fuel pumps. Later, some cars had two, some didn't. My 1993 GTS has two fuel pumps. There are theories that for hot climates the in-tank pump helps reduce the chances of vapor lock ... we don't know.
Rich
Membership Chairman
Charter Member
1993 928 GTS Cover Girl
1987 928 S4
1979 928 5-speed rescue
1979 928 5-liter track beast
The administrator has disabled public write access.

Fuel pump question 09 Apr 2017 20:10 #19633


  • Posts:157 Thank you received: 5
  • joejabq's Avatar
  • joejabq
  • Senior Forum Member
  • NOW ONLINE
  • Karma: 1
Rich928 wrote:
We don't know the decision making process for Porsche. The 1978 - 1979 CIS cars had two Fuel pumps. Later, some cars had two, some didn't. My 1993 GTS has two fuel pumps. There are theories that for hot climates the in-tank pump helps reduce the chances of vapor lock ... we don't know.

That's my understanding as well. Everything that I've read hints that the two pumps are to avoid vapor lock when running hard in hot locations.
I'm going to dig into my CIS this summer. One of the tests is the fuel flow rate with one or two pumps. I'll be sure to report what I find.
The administrator has disabled public write access.

Fuel pump question 09 Apr 2017 23:50 #19634


  • Posts:5
  • new928's Avatar
  • new928
  • Junior Forum Member
  • OFFLINE
  • Karma: 0
IMG_20170408_170501040.jpg


IMG_20170408_194551089.jpg

Being in Washington state we at least don't get the heat very often up here. I'll probably lean towards the single pump set up for now unless I come across a reasonable priced option for in the tank. Just picked up the car on Saturday and haven't had a chance to start going at it.
Last Edit: 10 Apr 2017 00:04 by new928. Reason: add photo
The administrator has disabled public write access.

Fuel pump question 14 Apr 2017 18:16 #19638


  • Posts:5
  • new928's Avatar
  • new928
  • Junior Forum Member
  • OFFLINE
  • Karma: 0
So I finally had some time to get the car up on ramps and take a look underneath the back end. The previous owner had removed the tank and cleaned it out. I've found some pictures online of the fuel system but still don't understand it a whole lot yet and I don't want to start putting things back yet. Do the 2 pumps work in unison all the time or does one work while the other doesn't depending on the fuel in the tank? I see a large rubber fuel hose that goes from the external pump up and around the passenger rear wheel well and there seems to be a filter attached in the wheel well. I'm assuming this is a stock setup? Then at the top of the tank there's a fuel line that runs straight under the car towards the engine.
The administrator has disabled public write access.

Fuel pump question 14 Apr 2017 21:26 #19642


  • Posts:157 Thank you received: 5
  • joejabq's Avatar
  • joejabq
  • Senior Forum Member
  • NOW ONLINE
  • Karma: 1
new928 wrote:
So I finally had some time to get the car up on ramps and take a look underneath the back end. The previous owner had removed the tank and cleaned it out. I've found some pictures online of the fuel system but still don't understand it a whole lot yet and I don't want to start putting things back yet. Do the 2 pumps work in unison all the time or does one work while the other doesn't depending on the fuel in the tank? I see a large rubber fuel hose that goes from the external pump up and around the passenger rear wheel well and there seems to be a filter attached in the wheel well. I'm assuming this is a stock setup? Then at the top of the tank there's a fuel line that runs straight under the car towards the engine.
Nice looking 928!
Ahh, I did this job on mine last year.
I'm pretty sure that Both pumps run at the same time, but I didnt put the inside pump back in. What you describe is what I have on my 79. There's an accumulator in the wheel well too that keeps some fuel line pressure so the car starts quickly. The top line is the fuel return line coming out of the fuel distributor (if I remember right).
Roger (928sRus) sells a fuel line replacement set. You might consider changing the lines now since everything is out and because there's nontrivial pressure in the lines.
When you get to the old lines in the engine compartment, it's really hard to take off the coupling next to the firewall so Roger suggested that I use a dremel and cut the line and leave the coupling In place. Then attach the new line back on the coupling. Hope that makes sense! Have fun! I may some pics in my post. (Joe's 79)
The administrator has disabled public write access.

Fuel pump question 14 Apr 2017 22:58 #19643


  • Posts:8
  • Balz's Avatar
  • Balz
  • Junior Forum Member
  • OFFLINE
  • Karma: 0
Just a heads up on all this fuel discussion. I have a very experienced Porsche mechanic friend who once worked for Peter Greg on his 917. the guy is an aeronautical engineer and probably the smartest Porsche car guy I know. He nearly burned up his racer and garage by having a dud fire extinguisher close by when working on a fuel cell and pump. Fortunately he had three extinguishers in the garage. Two turned out to be duds. Fortunately for him, his car and his garage number 3 was the charm. PLEASE, no matter how smart you think you are, before engaging in fuel related repairs make sure you have triple redundancy on the extinguishers (and none of those bitty bottles for oven fires). Best insurance you'll ever have is placing them prominently around your garage. My friend said he performed olympic high jump across the car to get to number 3. Very, very lucky man. Be safe out there and drive'm like you stole'm... safely of course!
The administrator has disabled public write access.

Fuel pump question 15 Apr 2017 00:11 #19644


  • Posts:5
  • new928's Avatar
  • new928
  • Junior Forum Member
  • OFFLINE
  • Karma: 0
Great point Balz. When I get to the point of adding fuel to the tank I'll definitely do that.

Ok, so this is starting to make a bit more sense to me. I'm thinking I can add one of these (in the picture) into the tank instead of the pump. That goes from the tank to the external pump and then through the filter (I might have that backwards) , then to the accumulator in the wheel well towards the engine. Then there is a line that comes from the engine back to the top of the tank in the sender unit?
Attachments:
The administrator has disabled public write access.

Fuel pump question 15 Apr 2017 05:03 #19645


  • Posts:157 Thank you received: 5
  • joejabq's Avatar
  • joejabq
  • Senior Forum Member
  • NOW ONLINE
  • Karma: 1
new928 wrote:
Great point Balz. When I get to the point of adding fuel to the tank I'll definitely do that.

Ok, so this is starting to make a bit more sense to me. I'm thinking I can add one of these (in the picture) into the tank instead of the pump. That goes from the tank to the external pump and then through the filter (I might have that backwards) , then to the accumulator in the wheel well towards the engine. Then there is a line that comes from the engine back to the top of the tank in the sender unit?

Yes, you got it! Just to be perfectly clear, working from the tank forward, the rubber hoses part of the lines that you described, eventually connects to hard lines going forward to the engine compartment. The rubber hoses pick up there next the the firewall. All of these rubber hoses are of a particular rating for the pressure. You can't use just generic rubber fuel lines! Just get the kit from Roger. It has the right grade hoses already cut and clamps.
If you have any questions, just post and I can send you pictures from my 79.

When you get it all put back together, you can locate the fuel pump relay and the right terminals to jump so you can test that power is going to the pump(s) properly check for leaks and such without having to crank the engine.
BTW, I had to replace my sending unit too because it was frozen. hopefully yours works, but don't be surprised if it doesn't.

Martinss shared this with me when I started and it was incredibly useful:
"I find the pictures in PET invaluable Joe. Mostly I go to the Autoatlanta site and 'Shop hard parts' for the correct model year; yours would be: www.autoatlanta.com/porsche-parts/928-78...orsche_928_parts.php

The full PET Catalog is available in PDF for each model (www.porsche.com/canada/en/accessoriesand...ginalpartscatalogue/) and I have it saved locally on my computer, but while it is more complete, most times the Autoatlanta site is more convenient."
The administrator has disabled public write access.
Moderators: mm928
Time to create page: 2.020 seconds