I would like to remove the outer case from this MFI pump, to soak the case in rust dissolver and paint or plate it.
Can anyone that has opened one up please tell me what to expect?
e.g. will it all come out from the case as one unit if I remove the 4 slotted screws on the hose end, or will bits fly everywhere? There is some kind of stud/closed rivet on both sides of the outer case that makes me think it might not be so easy to remove the pump from the case...
Also, while I have it open, will I be able to tell by looking if it is in good condition (I know it works and pressure is in range but at the low end), and is there anything that I should soak the pump in to remove any old petrol residue or varnish that wont cause it harm in any way? isopropanol? acetone?
Perfect, thanks, but all the talk of O-rings put me off opening it up. It works and doesn't (didn't) leak so I think I'll just clean it and paint it with POR15!
Do yourself a favour and rig it up and test before you put it back on the car. There is a procedure in the workshop manual for testing the flow delivery. I had a perfectly nice working pump on mine but it didn't deliver enough flow to activate the main MFI pump. Ended up buying new from Porsche... Ouch.
Isn't it just as easy to test it on the car though, especially if it was previously running OK?
In my case, I have a pressure gauge that I can attach in the engine bay. The last time I ran the engine, the pressure was at the low end of the range (I don't remember the numbers are, but recall that it was at low end), and the engine was idling OK. I didn't drive the car though....
Just looked up the pressure range: 14.2 psi +- 2.9, so it must have been running around 11 or 12 I suppose... perhaps its a little gummed up, or commutator is not so clean.
My 2d..
Works on the car at tick over, wot is another thing, esp if the load on the engine is sustained and engine demand has to be matched by the pump.
I would clean it up, get some fresh petrol through it and run it on the car when you can.
If it is weak then it is not so difficult to remove and replace.
Iirc the outer body is crimped locally to assemble the pump and seal it so disturbing that assembly may be the death of the pump, re assembly will be harder to do and keep it petrol tight?
A leaking pump where it is located is not a good thing, very close to the exhaust tubes.
73T 911 Coupe, road/hillclimber 3.2L
Lola t 492 / 3.2 hillclimb racer
Boxster 987 Gen II 2.9
911hillclimber wrote: ↑Fri Jul 07, 2023 1:45 pm
My 2d..
Iirc the outer body is crimped locally to assemble the pump and seal it so disturbing that assembly may be the death of the pump, re assembly will be harder to do and keep it petrol tight? A leaking pump where it is located is not a good thing, very close to the exhaust tubes.
I think you are dead right here, thanks for sharing your opinion
deano wrote: ↑Fri Jul 07, 2023 9:58 am
Isn't it just as easy to test it on the car though, especially if it was previously running OK?
In my case, I have a pressure gauge that I can attach in the engine bay. The last time I ran the engine, the pressure was at the low end of the range (I don't remember the numbers are, but recall that it was at low end), and the engine was idling OK. I didn't drive the car though....
Just looked up the pressure range: 14.2 psi +- 2.9, so it must have been running around 11 or 12 I suppose... perhaps its a little gummed up, or commutator is not so clean.
What do you think?
I don't know your situation, if it's on the bench you can test it on your own. 2 person job in the car. do whatever is easiest.
The fuel pressure in the circuit is dictated by the pressure control valve in the fuel filter housing return pipe fitting. If the pressure is low then either the pump is weak in its pressure delivery or the valve spring is weak. It is more likely to be the valve spring than the pump in my experience of chasing fuel pressure issues as they must weaken over time. I fitted an 84-89 carrera bosch pump that you can buy off the shelf for ~£50-£60 and it runs fine at 11psi - as dictated by the pressure control valve. There is no need to be spending hundreds on these pumps or relying on ancient pumps that can leave you stranded IMO. I have a brand new pump in the car and carry a new spare for a total of ~£100.
Last edited by knapmann on Tue Jul 11, 2023 11:14 pm, edited 1 time in total.
knapmann wrote: ↑Tue Jul 11, 2023 12:03 pm
The fuel pressure in the circuit is dictated by the pressure control valve in the fuel filter housing return pipe fitting. If the pressure is low then either the pump is weak in its pressure delivery or the valve spring is weak. It is more likely to be the valve spring than the pump in my experience of chasing fuel pressure issues as they must weaken over time. I fitted an 84-89 carrera bosch pump that you can buy off the shelf for ~£50-£60 and it runs fine at 11psi - as dictated by the pressure control valve. There is no need to be spending hundreds on these pumps or relying on ancient pumps that can leave you stranded IMO. I have a brand new pump in the car and carry a new spare for ~£100.
Interesting.... I see that D911 have fuel pressure regulators and repair kits at crazy prices, but cannot see one for our cars anyway. I suppose that the inline type Bosch 2-hose pump would have to be repositioned slightly for rear pump cars as it would not fit into the cradle, and new fuel hoses made up and wiring. That's all do-able, but do we know what needs to happens to the 3rd hose that the MFI pump has (I'm not sure what its for - the parts diagram doesn't show where it goes and I cannot remember - I think there are only two pipes going thru the tunnel to the fuel tank).
deano wrote: ↑Tue Jul 11, 2023 12:52 pm
Interesting.... I see that D911 have fuel pressure regulators and repair kits at crazy prices, but cannot see one for our cars anyway. I suppose that the inline type Bosch 2-hose pump would have to be repositioned slightly for rear pump cars as it would not fit into the cradle, and new fuel hoses made up and wiring. That's all do-able, but do we know what needs to happens to the 3rd hose that the MFI pump has (I'm not sure what its for - the parts diagram doesn't show where it goes and I cannot remember - I think there are only two pipes going thru the tunnel to the fuel tank).
Yes you need to make up a mount of some kind and do some minor mods to the hoses and wiring. The third pipe isnt required, the pump is simply plumbed into the tank->filter housing line, while the return line goes direct from filter housing to the tank. Just dont get the tank take off and return connections the wrong way around and fill your pump with crud like I did...
I looked at getting a new pressure control valve fitting as mine was sticking causing erratic pressure but they are stupid money like £200 or something so I prised mine open and repaired it. It still gives lower than "optimum" pressure but the car runs fine. That said mine is a 2.0l, maybe if you have a 3.0 MFI engine at full revs it would require the full pressure/flow delivery, I cannot say, I would think 11PSI is sufficient generally.
