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Great detail. That was an eye opener. I did not realize the difference between summer and winter gas. I could easily wind up with winter gas in the summer as I sometimes travel for 2 or 3 months.
This discussion reminds me of a conversation I had with a friend long ago. He had driven his (carbureted) Jag through Death Valley in the summer and had to stop on the road to fix a tire. It was brutal hot. He heard funny sounds from the gas tank and opened the cap to find the gas was boiling.
Local Porsche service shop suggested that I put 104 octane race gas in the car if it is going to sit for a month or 3.
Just as an update, the following 2 part numbers are in the car right now.
928 608 801 300 Internal FP
928 608 810 403 External FP
Not sure if the 403 pump is the best choice if changing to a single pump configuration. Does anyone know?
I am happy to be the dissenting opinion in the in-tank pump discussion. The usual problem is that the little molded-rubber connector hose gets eaten by modern gas and splits, easily replaced. The motor for the in-tank pump is also connected by a couple of skinny wires which can get compromised especially, if the connecting hose has split.
That is a small part of an epic thread on this topic. Our 88s4 didn't have an intank pump from the factory of course, but after that incident it does now. That was our only such failure in 30 years and 90K miles, and also happened in unseasonably hot weather in eastern Washington, in the early spring. So not common, but not acceptable for us. And it could well have been winter gas, we filled up in the flats before heading over the mountains and into much warmer climates.
Our 90GT had an intank pump from the factory, and still does-- fixed once by us (split factory connector-hose) and replaced at least once by the various POs. It now has a Bosch 043 fuel pump (to feed bigger power) and still fed by the intank pump. I am sure an 043 with a strainer would be fine, but honestly for a stock-ish motor I think a stock pump would be the better choice if you are going to ditch the intank pump for a strainer.
The reason is this: Suction is the enemy, negative gauge pressure at the pump inlet. With a strainer nothing is pushing, so with higher flow (e.g. 043) you would get lower pressure at the pump inlet and a higher likelihood of cavitation and/or vapor-lock. You want a pump that is reasonably matched to the engine's needs, excess flow just heats up the fuel unnecessarily. But if you want to fit a larger pump, then the intank pump becomes even more important, to avoid negative pressure at the main pump inlet.
The "regulator" is a "self regulating pressure control valve" referenced to the pressure inside the fuel rail. The device drives tight shut until the pressure builds to that required and then the diaphragm force balance causes the thing to progressively open to maintain a constant set pressure in the rail. ... I suspect you well understand this just the nomenclature I used.
Yeah. We're talking about the same thing: A purely mechanical system - helped a bit via manifold vacuum with one 'goal' designed-in. Calling it a 'controller' implies way too much 'smarts' in my book. This is especially true in today's new cars where everything is modulated by software. Oil pressure, fuel pressure, engine temperature etc., are no longer purely a result of a cleverly-designed (or not) mechanical (perhaps electro-mechanical) system. These days it is indeed more appropriate - but somewhat imprecise since the logic is integrated with the 'rest' of the system - to call something regulating <a something> a controller.
Great detail. That was an eye opener. I did not realize the difference between summer and winter gas. I could easily wind up with winter gas in the summer as I sometimes travel for 2 or 3 months.
This discussion reminds me of a conversation I had with a friend long ago. He had driven his (carbureted) Jag through Death Valley in the summer and had to stop on the road to fix a tire. It was brutal hot. He heard funny sounds from the gas tank and opened the cap to find the gas was boiling.
Local Porsche service shop suggested that I put 104 octane race gas in the car if it is going to sit for a month or 3.
Just as an update, the following 2 part numbers are in the car right now.
928 608 801 300 Internal FP
928 608 810 403 External FP
Not sure if the 403 pump is the best choice if changing to a single pump configuration. Does anyone know?
Still researching inline coolers.
Frank
Frank,
The winter gasoline spec also has an end user purpose in that it helps the fuel to atomise in more extreme cold conditions. I suspect this issue is more a problem for carburetted vehicles but does fuel injected vehicles no harm for sure.
I am aware that some later models have a different fuel pump spec but without the pump datasheet it is not possible to understand what the differences might be. If both types are still available on the market then that would suggest there are model specific differences rather than developmental mods intended to improve the general build quality.
Not sure why you were advised to store the fuel with a higher octane brew in the tank. I suspect it was probably to ensure that when you returned to the car the fuel might still have a credible octane left in the tank after the light end components had preferentially vapourised over time.
On a slightly different but nonetheless relevant point, if the pressure controller fails to hold system pressure in the fuel rail this will cause problems at gas stations when one shuts down the motor in a hot condition. If the rail loses pressure in such condition the engine heat soaks into the fuel rail and if the pressure drops too much the fuel will likely boil up at the elevated temperature and then you can probably forget being able to start. This happened to me once at a gas station in the middle of nowhere during a hot summer afternoon. We pushed the 928 away from the pump , parked it with the bonnet open and went for a cup of tea and something to eat. Half an hour or so later it fired up straight away. I immediately replaced the regulator and both dampers and the problem never reappeared. Thus why it is important that both the regulator and the check valve are in tip top nick.
I can tell that a stock 1990 GT external pump is good enough to supply a 434rwhp motor in my race car. Internal pump packed up years ago and was replaced with a strainer. Car has been raced in 26C external temperatures - no issues whatsoever... The only thing was that when the car was being build I fitted a brand new BOSCH OEM pump purchased from JDS in Cambridge...
I had a similar issue wirh my 93 GTS. Car was running fine then at a bbq restaurant, no start. Would catch for just a second then nothing. I checked relays, fuses etc. no go so had her towed home.
Checked voltages at both pumps and had 12v, could feel and hear the external pump running but little to no fuel pressure at the passenger rail. The external pump was about 5 months old. However It had an original internal pump so I wanted to check to see if it or the little hose had failed. Pulled the end of the hose off at the external pump, stuck it in a bucket and applied 12v to internal pump, flow was good. I then pulled the external pump out and put a hose on each end with input in a gas can and output in a bucket and applied 12v, flow was a trickle. Tried reversing polarity to see if something might have gotten into the pump but no luck.
I replaced the external pump and car started immediately and has had no problem sense replacement. I have the 87-88 external pump and strainer on the shelf I got from Roger and that will be installed this summer.
Moral of story, just because you replaced it doesn't mean it's working. Good luck!
Well I got the strainer and the required hose and got down to finally getting this changed over to a single pump. But have run into some problems.
Sorry for scale of the pictures. I don't know how to resize.
Recap:
Car has been sitting ~ 3 years in no start condition with ~ 1/2 tank fuel.
Prior ot no start, the car had been driven ~ 900 miles after having tank flushed and both fuel pumps. fuel filter as well as the small interconnecting hose replaced.
1. I siphoned ~ 8 gal of gas out of the tank before starting to loosen hoses
2. I loosened hose at the external fuel pump first and was surprised that no gas came out.
Their appeared to be what looked like grease just inside the nipple on the external pump. But later learned it was just some of the damp crystals.
Residue inside nipple.
The hose however was filled with dry crystals. Yep bone dry. So I figured maybe a stoppage in the hose was holding back some gas and I used a stiff wire to clear out the crystals in the hoes that I may break through to the liquid fuel. But after clearing as much as I could, still no residual fuel came form the tank. Note that the large crystals on the left were in the hose and the abrasion of the wire to clear the hose created the finer crystals to the right. t . It was very easy to crush the crystals to a fine powder in your fingers.
Then I tried to loosen and remove the hose from the internal fuel pump in prepartion to remove the pump. I had been warned to be careful with the internal pump removal lest I damage the tank. So I loosened the hose clamp and was using the tip of a flat screwdriver between the hose and the body of the the pump to break the bead on the hose so I could slip it off. I had barely applied any twist and the entire end of the fuel pump fell off.
The question is how to remove the internal pump. Can I grab the outside of that protruding black ring? Do I have to grab it by its insides? I don’t want to damage the tank but not sure it that protruding ring is part of the tank.
Wow, that is a mess!! You've got a lot bigger problems than the in-tank pump. The threaded aluminum sleeve is toast, you can see part of the outer (knurled) surface still attached to the fitting. The pump itself is buried in crap.
I would start by pulling the fuel level gauge (from inside the rear hatch area, under a large plastic cap) and see just what sort of mess you have down there. My guess is that the tank will want to come out for a thorough cleaning.
Yes, just got back inside. knurled sleeve is supposed to be bonded to the tank. I just unscrewed it off the end cap of the pump. Destroying that ring is what I was warned not to do by a couple of people. But the sleeve is totally disintegrated... like eaten by acid. Just a bit left on the end. I did not even put a socket on it. I was just using screwdriver blade to get the rubber hose off when it fell off the end of the pump.
Looks to me like the threaded collar on the in-tank pump separated from the end of pump. (Never, ever have I seen that before. Don't think I've heard of it either.) If you are lucky, after cleaning out, as much as possible, the port in the tank you may be able to twist-out that threaded collar from the tank's port.
You won't be able to withdraw the rest of the intake pump through the port until you get the threaded collar out of the port.
You can, probably, remove the level sender (as per Jim--^) and then withdraw the in-tank portion of the pump out that way. Then you might have enough room to get the threaded collar out from the outside.
This, all under the assumption that the threads of the collar haven't corroded irrevocably to the threaded port insert.
Car was always in the garage so no likely tampering. Tasted a grain of the powder to see if was caustic or acidic. ..no taste. It's not brown sugar either.
Here are some better pics of what is left. Looks like a lot of missing aluminum. Like something ate it. The Aluminum threaded part of the pump as well as the the aluminum tank ring are corroded away. The pipe nipple on the "wet" (in tank) side of the bulkhead is corroded right through.
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