Do not use the in-tank pump... EVER
08-27-2015, 04:29 PM
#136
Customer wants stock so stock he gets. But it's all going to be new. New intank, new external, new hose, new S-pipe, new filter. I'm not going back in there again so it's good that he's one that likes to do things the correct way.
08-27-2015, 05:38 PM
#137
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Since you are going with the nuke-it-from-orbit approach you might as well pull the sender while the tank is drained and check the filament and float for corrosion and free movement. Otherwise... guess what... the next complaint will be a gas gauge that's not right. BTDT.
08-27-2015, 06:12 PM
#138
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The external pump that pairs with the in-tank pump is different from the single-pump pump. Should one decide to replace the in-tank pump with a strainer, the correct external pump should be installed at the same time.
Sean -- What hose are you using between the in-tank pump and the bulkhead fitting?
Sean -- What hose are you using between the in-tank pump and the bulkhead fitting?
08-27-2015, 08:09 PM
#139
Do not use the in-tank pump... EVER
Bob, the factory one. 928-356-550-04
And yes, if you are putting the strainer in instead of the pump I use the 87-88 fuel pump. After seeing the price of the new in tank pump, I'm sure more will opt that direction.
And yes, if you are putting the strainer in instead of the pump I use the 87-88 fuel pump. After seeing the price of the new in tank pump, I'm sure more will opt that direction.
05-17-2019, 03:09 PM
#140
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Interesting data point from my 79 to add to this discussion. I'll try to keep this brief 
Keep in mind, for whatever reason I never pondered the idea of my 79 having an in-tank pump. I was never aware these early cars had them....otherwise my plan of action would have been different.
September 9, 2017 my 79 wouldn't start. I had just driven it a couple days prior. Diagnosed failed fuel pump relay. Noticed the white plastic is a big discolored under this relay. Check the female terminals for tightness, all feel normal (had another 928 where similar issue was a damaged female terminal making a bad connection).
2018 drove the 79 quite a bit, normal year, no issues.
Sometimes towards the end of the year I went to start up the 79 for winter storage and move it on the lift. No start.....diagnosed another dead fuel pump relay. Installed my jumper wire, pump whirred to life, started the engine for a quick drive before on the lift and parked until winter.
Spring 2019 finally getting around to figuring out what is up with the 79. My first step every spring is to install my jumper wire in place of the fuel pump relay and check under hood for fuel leaks. When I went to remove the wire it was hot so I pulled the CE panel to thoroughly check it over. While it was out, cleaned up all the contacts with DeOxit, pulled the spade terminals for the relay and again inspected them for any issues. Zero corrosion, all tight etc... nothing obvious.
Plug in a different relay and start the car. A few minutes later the car died, well this isn't good. Install the jumper wire and this time no pump, just a "fump" sound of the pump trying to spin and a quick check with my amp meter...it's drawing over 20 amps. Figuring my fuel pump is waving good-by, jammed or dead, I took the rear cover off and much to my surprise I see an in-tank pump! As stated above this was news to me or I would have investigated this back in September of 2017.
I crimped off the fuel line, pulled the external pump and soaked it in some solvent thinking maybe a chunk of that rubber hose came off and jammed it. After a day in the sauce, tried spinning the pump forwards and backwards to see if it would un-stick. No go, it's locked up tight. Time to drain the tank and pull the in-tank pump.
The fuel tank was over 3/4 full too.
I put the fuel line that comes off the in-tank pump and run it into a gas can and it's just a trickle of fuel coming out. Keep in mind I'm working off a lift, the car is 6' up in the air and the gas can is directly below, this should be gushing out like a garden hose.
It took almost an hour to drain the tank, that's how much the in-tank pump has been restricting flow for God knows how long!!!
Once I finally got all the fuel out and pulled the in-tank pump, much to my surprise the short hose is 100% in-tact. Test the pump with my 12V source, it's locked up too, no movement forward or backwards.
Order a strainer, hose, pump, and filter - back on the road!!!
What's the moral of this story? My car ran fine (I have a WBO2 gauge in the car) with the in-tank pump locked up causing a major restriction to the external pump, until it died from over use having to suck that hard against the dead pump.
After this experiment, I'm convinced more than ever the in-tank pump is not needed and any possible tiny benefit from said pump isn't worth the risk. Had I realized this car had an in-tank pump back in 2017 I would have pulled it for a strainer and probably saved the original pump. Thank goodness I wasn't 100 miles from home when everything decided to die.
Again, think about it. My car ran fine, on hot days running to red line many, many times under full load having to suck fuel through that dead pump. Now I have a free flowing strainer with a large feed nipple.
Maybe if I lived in Bahrain and expect the car to run WOT at top speed for hours on end in 140F ambient temps I'd change my mind.
Keep in mind, for whatever reason I never pondered the idea of my 79 having an in-tank pump. I was never aware these early cars had them....otherwise my plan of action would have been different.
September 9, 2017 my 79 wouldn't start. I had just driven it a couple days prior. Diagnosed failed fuel pump relay. Noticed the white plastic is a big discolored under this relay. Check the female terminals for tightness, all feel normal (had another 928 where similar issue was a damaged female terminal making a bad connection).
2018 drove the 79 quite a bit, normal year, no issues.
Sometimes towards the end of the year I went to start up the 79 for winter storage and move it on the lift. No start.....diagnosed another dead fuel pump relay. Installed my jumper wire, pump whirred to life, started the engine for a quick drive before on the lift and parked until winter.
Spring 2019 finally getting around to figuring out what is up with the 79. My first step every spring is to install my jumper wire in place of the fuel pump relay and check under hood for fuel leaks. When I went to remove the wire it was hot so I pulled the CE panel to thoroughly check it over. While it was out, cleaned up all the contacts with DeOxit, pulled the spade terminals for the relay and again inspected them for any issues. Zero corrosion, all tight etc... nothing obvious.
Plug in a different relay and start the car. A few minutes later the car died, well this isn't good. Install the jumper wire and this time no pump, just a "fump" sound of the pump trying to spin and a quick check with my amp meter...it's drawing over 20 amps. Figuring my fuel pump is waving good-by, jammed or dead, I took the rear cover off and much to my surprise I see an in-tank pump! As stated above this was news to me or I would have investigated this back in September of 2017.
I crimped off the fuel line, pulled the external pump and soaked it in some solvent thinking maybe a chunk of that rubber hose came off and jammed it. After a day in the sauce, tried spinning the pump forwards and backwards to see if it would un-stick. No go, it's locked up tight. Time to drain the tank and pull the in-tank pump.
The fuel tank was over 3/4 full too.
I put the fuel line that comes off the in-tank pump and run it into a gas can and it's just a trickle of fuel coming out. Keep in mind I'm working off a lift, the car is 6' up in the air and the gas can is directly below, this should be gushing out like a garden hose.
It took almost an hour to drain the tank, that's how much the in-tank pump has been restricting flow for God knows how long!!!
Once I finally got all the fuel out and pulled the in-tank pump, much to my surprise the short hose is 100% in-tact. Test the pump with my 12V source, it's locked up too, no movement forward or backwards.
Order a strainer, hose, pump, and filter - back on the road!!!
What's the moral of this story? My car ran fine (I have a WBO2 gauge in the car) with the in-tank pump locked up causing a major restriction to the external pump, until it died from over use having to suck that hard against the dead pump.
After this experiment, I'm convinced more than ever the in-tank pump is not needed and any possible tiny benefit from said pump isn't worth the risk. Had I realized this car had an in-tank pump back in 2017 I would have pulled it for a strainer and probably saved the original pump. Thank goodness I wasn't 100 miles from home when everything decided to die.
Again, think about it. My car ran fine, on hot days running to red line many, many times under full load having to suck fuel through that dead pump. Now I have a free flowing strainer with a large feed nipple.
Maybe if I lived in Bahrain and expect the car to run WOT at top speed for hours on end in 140F ambient temps I'd change my mind.
05-17-2019, 03:22 PM
#141
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Interesting data point from my 79 to add to this discussion. I'll try to keep this brief
Keep in mind, for whatever reason I never pondered the idea of my 79 having an in-tank pump. I was never aware these early cars had them....otherwise my plan of action would have been different.
September 9, 2017 my 79 wouldn't start. I had just driven it a couple days prior. Diagnosed failed fuel pump relay. Noticed the white plastic is a big discolored under this relay. Check the female terminals for tightness, all feel normal (had another 928 where similar issue was a damaged female terminal making a bad connection).
2018 drove the 79 quite a bit, normal year, no issues.
Sometimes towards the end of the year, went to start up the 79 for winter storage, move it on the lift. No start.....diagnosed another dead fuel pump relay. Installed my jumper wire, pump whirred to life, started the engine, quick drive before on the lift and parked until winter.
Spring 2019 finally getting around to figuring out what is up with the 79. First step every spring, install my jumper wire and check under hood for fuel leaks. When I went to remove the wire, it was hot so I pulled the CE panel to thoroughly check it over. While it was out, cleaned up all the contacts with DeOxit, pulled the spade terminals for the relay and again inspected them for any issues. Zero corrosion, all tight etc... nothing obvious.
Plug in a different relay and start the car. A few minutes later the car died, well this isn't good. Pull the jumper wire and this time no pump, just a "fump" sound of the pump trying to spin and a quick check with my amp meter...it's drawing over 20 amps. Figuring my fuel pump is waving good-by, jammed or dead, I took the rear cover off and much to my surprise I see an in-tank pump! As stated above, this was news to me or I would have investigated this back in September of 2017.
Crimped off the fuel line, pulled the external pump and soaked it in some solvent thinking maybe a chunk of that rubber hose came off and jammed it. After a day in the sauce, tried spinning the pump forwards and backwards to see if it would un-stick. No go, it's locked up tight. Time to drain the tank and pull the in-tank pump.
Over 3/4 of a tank in the car too. I put the fuel line that comes off the in-tank pump and run it into a gas can and it's just a trickle of fuel coming out. Keep in mind I'm working off a lift, the car is 6' up in the air and the gas can is directly below, this should be gushing out like a garden hose.
It took almost an hour to drain the tank, that's how much the in-tank pump has been restricting flow for God knows how long!!!
Once I finally got all the fuel out, pull the in-tank pump and much to my surprise, the hose is 100% in-tact. Test the pump with my 12V source, it's locked up too, no movement forward or backwards.
Order a strainer, hose, pump, and filter - back on the road!!!
What's the moral of this story? My car ran fine (I have a WBO2 gauge in the car) with the in-tank pump locked up causing a major restriction to the external pump, until it died from over use having to suck that hard against the dead pump.
After this experiment, I'm convinced more than ever the in-tank pump is not needed and any possible tiny benefit from said pump isn't worth the risk. Had I realized this car had an in-tank pump back in 2017 I would have pulled it for a strainer and probably saved the original pump. Thank goodness I wasn't 100 miles from home when everything decided to die.
Again, think about it. My car ran fine, on hot days running to red line many, many times under full load having to suck fuel through that dead pump. Now I have a free flowing strainer with a large feed nipple.
Maybe if I lived in Bahrain and expect the car to run WOT at top speed for hours on end in 140F ambient temps I'd change my mind.
Keep in mind, for whatever reason I never pondered the idea of my 79 having an in-tank pump. I was never aware these early cars had them....otherwise my plan of action would have been different.
September 9, 2017 my 79 wouldn't start. I had just driven it a couple days prior. Diagnosed failed fuel pump relay. Noticed the white plastic is a big discolored under this relay. Check the female terminals for tightness, all feel normal (had another 928 where similar issue was a damaged female terminal making a bad connection).
2018 drove the 79 quite a bit, normal year, no issues.
Sometimes towards the end of the year, went to start up the 79 for winter storage, move it on the lift. No start.....diagnosed another dead fuel pump relay. Installed my jumper wire, pump whirred to life, started the engine, quick drive before on the lift and parked until winter.
Spring 2019 finally getting around to figuring out what is up with the 79. First step every spring, install my jumper wire and check under hood for fuel leaks. When I went to remove the wire, it was hot so I pulled the CE panel to thoroughly check it over. While it was out, cleaned up all the contacts with DeOxit, pulled the spade terminals for the relay and again inspected them for any issues. Zero corrosion, all tight etc... nothing obvious.
Plug in a different relay and start the car. A few minutes later the car died, well this isn't good. Pull the jumper wire and this time no pump, just a "fump" sound of the pump trying to spin and a quick check with my amp meter...it's drawing over 20 amps. Figuring my fuel pump is waving good-by, jammed or dead, I took the rear cover off and much to my surprise I see an in-tank pump! As stated above, this was news to me or I would have investigated this back in September of 2017.
Crimped off the fuel line, pulled the external pump and soaked it in some solvent thinking maybe a chunk of that rubber hose came off and jammed it. After a day in the sauce, tried spinning the pump forwards and backwards to see if it would un-stick. No go, it's locked up tight. Time to drain the tank and pull the in-tank pump.
Over 3/4 of a tank in the car too. I put the fuel line that comes off the in-tank pump and run it into a gas can and it's just a trickle of fuel coming out. Keep in mind I'm working off a lift, the car is 6' up in the air and the gas can is directly below, this should be gushing out like a garden hose.
It took almost an hour to drain the tank, that's how much the in-tank pump has been restricting flow for God knows how long!!!
Once I finally got all the fuel out, pull the in-tank pump and much to my surprise, the hose is 100% in-tact. Test the pump with my 12V source, it's locked up too, no movement forward or backwards.
Order a strainer, hose, pump, and filter - back on the road!!!
What's the moral of this story? My car ran fine (I have a WBO2 gauge in the car) with the in-tank pump locked up causing a major restriction to the external pump, until it died from over use having to suck that hard against the dead pump.
After this experiment, I'm convinced more than ever the in-tank pump is not needed and any possible tiny benefit from said pump isn't worth the risk. Had I realized this car had an in-tank pump back in 2017 I would have pulled it for a strainer and probably saved the original pump. Thank goodness I wasn't 100 miles from home when everything decided to die.
Again, think about it. My car ran fine, on hot days running to red line many, many times under full load having to suck fuel through that dead pump. Now I have a free flowing strainer with a large feed nipple.
Maybe if I lived in Bahrain and expect the car to run WOT at top speed for hours on end in 140F ambient temps I'd change my mind.
Some had an in-tank fuel strainer, a "combination sucking/pusher sump" (very close to the strainer/tank) and the same pressure pump, behind the right rear tire.
There was always some sort of pump "feeding" fuel to the pressure pump.
None of these '78/'79 cars had one pump.
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Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
greg brown
714 879 9072
GregBBRD@aol.com
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
05-17-2019, 03:24 PM
#142
Chronic Tool Dropper
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My personal experience in other '70's CIS cars in SoCal is that the internal pump is essential. No reason to believe that LH is any different as far as fuel pump requirements with boiling, so the internal pump stays.
Maybe if I lived somewhere where the weather doesn't include any 90+ days, .and. I was absolutely sure that I and all future owners would never drive the car on a 90+ day with less than half a tank, I'd consider swapping the two-pumps for a single pump. But that requires a clairvoyance I don't have.
For over seven decades now, Porsche has been known for adding extra cost, weight, potential failure points and unneeded complexity to their cars. The dual pump system is obviously one of those $bloat opportunities, taking advantage of the fact that the inner pump is in fact hidden out of sight in the bottom of the tank. Stuff like this was added so they could charge more for the cars, making them more exclusive and packing the bottom line.
Maybe if I lived somewhere where the weather doesn't include any 90+ days, .and. I was absolutely sure that I and all future owners would never drive the car on a 90+ day with less than half a tank, I'd consider swapping the two-pumps for a single pump. But that requires a clairvoyance I don't have.
For over seven decades now, Porsche has been known for adding extra cost, weight, potential failure points and unneeded complexity to their cars. The dual pump system is obviously one of those $bloat opportunities, taking advantage of the fact that the inner pump is in fact hidden out of sight in the bottom of the tank. Stuff like this was added so they could charge more for the cars, making them more exclusive and packing the bottom line.
05-17-2019, 05:09 PM
#143
Pro
While I'm not a master of Porsche engineering mindset by any means, I have worked on MB CIS equipped cars for years, and found that they only used a single Bosch fuel pump for many of the CIS years. Only in the late '80s did they go to a twin pump arrangement, and that was parallel pumps for fuel flow on the larger 5.6L engine.
The spring loaded pressure accumulator and check valve were intended to prevent vapor lock, no added pump is required for that purpose.
Looking at my '78 928, I have not found a second pump yet, but now I'm curious and will be hunting this weekend, to see if there is one present. There was only a filter in the tank, from my inspection through the fuel sender hole.
The spring loaded pressure accumulator and check valve were intended to prevent vapor lock, no added pump is required for that purpose.
Looking at my '78 928, I have not found a second pump yet, but now I'm curious and will be hunting this weekend, to see if there is one present. There was only a filter in the tank, from my inspection through the fuel sender hole.
05-17-2019, 10:54 PM
#144
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While I'm not a master of Porsche engineering mindset by any means, I have worked on MB CIS equipped cars for years, and found that they only used a single Bosch fuel pump for many of the CIS years. Only in the late '80s did they go to a twin pump arrangement, and that was parallel pumps for fuel flow on the larger 5.6L engine.
The spring loaded pressure accumulator and check valve were intended to prevent vapor lock, no added pump is required for that purpose.
Looking at my '78 928, I have not found a second pump yet, but now I'm curious and will be hunting this weekend, to see if there is one present. There was only a filter in the tank, from my inspection through the fuel sender hole.
The spring loaded pressure accumulator and check valve were intended to prevent vapor lock, no added pump is required for that purpose.
Looking at my '78 928, I have not found a second pump yet, but now I'm curious and will be hunting this weekend, to see if there is one present. There was only a filter in the tank, from my inspection through the fuel sender hole.
Absolutely 100% guarantee.
08-30-2019, 10:41 PM
#145
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Geeeeez,
I have not removed Snow White's in tank fuel pump... Time Bomb!
>
I have not removed Snow White's in tank fuel pump... Time Bomb!
>
08-31-2019, 08:52 AM
#146
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78/79 cars all came with 2 pumps as Greg stated.
1) In-tank pump plus external pump mounted on the outside of the tank
2) External pump on the outside of the tank plus another pump mounted in the fender of the right rear tire. Opposite side to the filter/accumulator.
1) In-tank pump plus external pump mounted on the outside of the tank
2) External pump on the outside of the tank plus another pump mounted in the fender of the right rear tire. Opposite side to the filter/accumulator.
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Does it have the "Do It Yourself" manual transmission, or the superior "Fully Equipped by Porsche" Automatic Transmission?
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928 Owners are ".....a secret sect of quietly assured Porsche pragmatists who in near anonymity appreciate the prodigious, easy going prowess of the 928."
Does it have the "Do It Yourself" manual transmission, or the superior "Fully Equipped by Porsche" Automatic Transmission?
George Layton March 2014928 Owners are ".....a secret sect of quietly assured Porsche pragmatists who in near anonymity appreciate the prodigious, easy going prowess of the 928."
08-31-2019, 09:57 AM
#147
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I bought one of the new Bosch in tank fuel pumps for my 89, it lasted maybe a hundred miles. A complete waste of a $1,000.00!
08-31-2019, 10:50 AM
#148
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08-31-2019, 01:06 PM
#150
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Repairing the hose doesn't matter if the pump is seized. I have pulled seized in-tank pumps with split hoses. I don't think I've seen a seized pump with an intact hose.