how much fuel pressure is to much?

[gorskined]

hello all still trying to sort out some intermittent issues with my 76 3.0l row turbo
i was wondering can any one tell me what the fuel pressure on the main line just before the fd should be? mine is currently 155 psi just before the final strainer going into the fd. My fd adjusted supply system pressure is 85 lbs and my adjusted control wur pressure is within the manuals wur cold pressure curve and the warm is spot on also.

i am running two Bosch 044 pumps i know over kill for a stock 3.0l motor but i was curious if i may have too much pressure entering the fd.
I'm running into some intermittent issue that i think may be caused by excessive fuel volume randomly to each cylinder. seeing as its basically a stock motor i am considering only running a single 004 pump.


Thanks in advance
Regards Ned

[sigchuck]

I don’t know the answer to your question, but on my SC I run one 044 pump in the front and it passes the system pressure and return tests just fine for ‘78-‘79 model years. I don’t recall those values top of head, but imagine they’re close to the ‘77 values.

[tops911]

I have a 1982 turbo with two 044 fuel pumps, I checked the pressure when I first installed them and they were in spec with the pressures of the stock system (I think the lower side of the limit), but I dont remember what it was. No issues for me.
Sorry not much help

[356911930]

Hi Ned,

From the workshop manual (WSM) the system pressure should be:

Testing value 6.0 to 6.7 bar (kp/cm )
Adjusting value 6.2 to 6.5 bar (kp/cm2)

The is for 1976-1985.

Hope this helps,

Rahl

[Mocker]

1 bar = 14.5 psi

6.0-6.7 bar = 87-97 psi

6.2-6.5 bar = 90-94 psi

[gorskined]

The pressure everyone is referencing is the regulated pressure on the Fd I'm looking for the un regulated pressure, the pressure that is entering the Fd . This pressure can't be tested by the gauge that you adjust the wur with . I had to add a gauge block before the Fd to get this pressure readings. I can't find a reference any place for the standing head pressure after the pumps and before the Fd. My regulated pressures are perfect . I'm wondering if possibly the high unregulated pressure if in fact it is high I don't know...my be causing the intermittent fuel issue.

Thanks

Thanks

[dos531]

Originally Posted by gorskined

The pressure everyone is referencing is the regulated pressure on the Fd I'm looking for the un regulated pressure, the pressure that is entering the Fd . This pressure can't be tested by the gauge that you adjust the wur with . I had to add a gauge block before the Fd to get this pressure readings. I can't find a reference any place for the standing head pressure after the pumps and before the Fd. My regulated pressures are perfect . I'm wondering if possibly the high unregulated pressure if in fact it is high I don't know...my be causing the intermittent fuel issue.

Thanks

Thanks

That's because it really doesnt matter. Unless youre getting pressure drop from insufficient supply, the regulated pressures arent going to change with different pumps.

[spuggy]

Originally Posted by dos531

That's because it really doesnt matter. Unless youre getting pressure drop from insufficient supply, the regulated pressures arent going to change with different pumps.

+1 ^^^ This.

From the Bosch Motorsport Components application sheet:

Modern electric fuel pumps are “Positive Displacement” type pumps, this means that the pump cannot produce pressure unless it is acting upon a restriction. The only restriction in the system should be the fuel pressure regulator. The regulator controls the system pressure; the pressure ability or flow volume capacity of the fuel pump will not alter the system pressure.

You could use an 044 with carbs if you wanted. It'd just move the fuel around 10x or 20x as much

[356911930]

Hi Ned,

One check you can make is the pressure at the incoming fuel line to the rear fuel pump. Disconnect the fuel line going into the rear fuel pump. Install your fuel pressure gauge set. Pressure must be between 2 and 4 bar. If less than 2 bar, the first pump (front) is defective. If more than 4 bar, the second pump (rear) is defective.

This should verify that your fuel pumps are working correctly.

Best of luck,

Rahl

[gorskined]

I am sure my pumps are working correctly.I have about 10 bar 150 psi off my rear pump going into my fd..... Is 150psi to much pressure entering the Fd?????? ? I'm assuming the original pumps didn't have this much pressure. im wondering if this would cause an intermittent blow by or something inside the FD.

[heliolps2]

I agree with everyone here, I had 400 hp 930 engine in my 76 911 with one 044 up front, I did install a rear 044 but it made my car to lean and the system pressure was to high and no way to adjust it to where I needed it to be. Remember to more fuel pressure in these CIS 930's the leaner they get the opposite of EFI. Just saying I had that car for 20 years of playing with it.

The other issue you need to address is the fuel lines which most people don't discuss. The turbo cars have bigger fuel lines. I recommend you change those to get the fuel you need. not another fuel pump.

[Alan L]

Your 2 044 pumps will be doing the same as everyone else's 044 pumps - and presumably they would have 155lb entering the FD also. Not sure how you are measuring this but I am guessing you are completely blocking the exit for the fuel with a gauge on the line to the FD. That doesn't really matter. The FD pressure is controlled by the bleed off at the system pressure valve. And yours is in spec. Which means the FD is capable of bleeding off the extra fuel. So everything should work just fine as far as that side of things go. You could only have too much pressure if the system pressure valve was unable to regulate the SP.
Regards
Alan

[gorskined]

[QUOTE=Alan L;12151813]Your 2 044 pumps will be doing the same as everyone else's 044 pumps - and presumably they would have 155lb entering the FD also. Not sure how you are measuring this but I am guessing you are completely blocking the exit for the fuel with a gauge on the line to the FD. That doesn't really matter. The FD pressure is controlled by the bleed off at the system pressure valve. And yours is in spec. Which means the FD is capable of bleeding off the extra fuel. So everything should work just fine as far as that side of things go. You could only have too much pressure if the system pressure valve was unable to regulate the SP.
Regards
Alan[/QUOTE

Alan
Thanks for the reply This is why I'm frustrated. The intermittent 155 psi is not with an obstructed return line. The 150 psi is just before the the FD . i originally replaced all my fuel lines with an6 lines. I can installed a an6 gauge fitting pretty much any where, so i placed one just before the hard line entering the fd. where i made a custom fitting to connect the an6 to the Porsche hard line .
When i use my test gauge manifold the pressure is good and my control hot and cold are good the system pressure is about 85psi I've seen it as high as 95 (good) and the line entering the FD is 150 psi when the problem is happening..... i even swapped gauges to rule out a gauge issue. .
After i removed the Fd and connected the supply line to the return and pumped directly back into the tank. The gauge barley moved but its a 200psi gauge. when i slowly bend the the return line the gauge will start to rise and pins at 200psi hard, like it has quite a bit more pressure than 200psi . When i do the same test with a single pump it will run up to 145 -150psi .. I'm convinced something is off with the fd.
i just boxed everything up and sent it out to flowthech. after about 50 hours of testing and checking I'm at the point were I'm pretty convinced its not anything I'm doing wrong . i even drained the new tank put in bore scope to make sure there were no issues with the return line in the tank. Then i removed all my an6 fittings to be sure when i inserted the line into the fittings i did it correctly (no ripped or folded internal liner flapping around ) all good . ill let you know what flowtech says

Thanks again always appreciate your knowledge

Regards Ned

.

[Alan L]

So you have intermittent 155psi. I didn't pick up on that. The other thing I would have done is check the flow volume out of the FD.
But I guess we wait now and see what Flowtech come up with.
Regards
Alan

[gorskined]

Originally Posted by Alan L

So you have intermittent 155psi. I didn't pick up on that. The other thing I would have done is check the flow volume out of the FD.
But I guess we wait now and see what Flowtech come up with.
Regards
Alan

i did check the fuel volume more than once it was good within factory specks on the high side i don't recall the actual #s .
The car runs really good a blast to drive when it runs than all of a sudden not so much, hesitation no power reacts like its running on 4 cylinders ..

i was so fed-up with the car last week after putting everything back together. I ran it for 5 minutes running perfect, i went to take it out. When left the driveway I realized had taken the 10lb halon extinguisher out of the car . i actually said to myself screw it if it catches fire problem solved, its insured. glad it didn't and two miles later it started running awful .

i must have at least 200 hours into this issue one good thing. i am really starting to get a full understanding of how everything works and how one thing directly effects the next.

Regards Ned

[908/930]

Hopefully Flowtec can find something. Looking at the schematics it sure looks like system pressure would be the same as the pressure entering the distributer, depending on how the primary pressure reg bleeds off the excess, but have never tested pressure there. I do not think this is your problem but did you check the fuel accumulator to make sure it is still functioning?

[Alan L]

I feel your pain and frustration. I think most of us who have had a 930 long enough have gone thru this. When I bought mine (from Japan) it was a freshly rebuilt engine ready to go. 'Yeah right' as the down under saying goes. Took me months to get it to go, then the transmission/clutch problems showed up etc. And a rats nest of wiring issues, jumped relays etc. Freshly built engine = 1 2nd hand P/C + 1/2 lb of RTV. I was at such a loss at parts of the process I seriously conmsidered parting it, because after months of work I still didn't have a functioning car. But with a handful of the cars in the country that wasn't much of an option so I perservered - in too deep now.
What does come out of this tortuous process, as you say is a good understanding of where the gremlins are. You can trouble shoot them quick time. Which makes ownership of the beast so much better further down the track.
lets see what Flowtech come up with. Those intermittent issues are a nightmare. I had a bouncing airplate for a while . Could not cure it. Dumnno what I did. But it went away. But I do suspect the fuel presure issue is not the key to this. A coil breaking down?
Regards
Alan

[flightlead404]

Originally Posted by gorskined

i must have at least 200 hours into this issue one good thing. i am really starting to get a full understanding of how everything works and how one thing directly effects the next.

Regards Ned

That part is good. I must caution you though, when you're "absolutely 100% convinced" where the problem lies, it usually isn't but you blind yourself to other possibilities.

true for everything, not just 930 maint

[gorskined]

Originally Posted by 908/930

Hopefully Flowtec can find something. Looking at the schematics it sure looks like system pressure would be the same as the pressure entering the distributer, depending on how the primary pressure reg bleeds off the excess, but have never tested pressure there. I do not think this is your problem but did you check the fuel accumulator to make sure it is still functioning?

yes replaced it new fuel accumulator

[gorskined]

Originally Posted by Alan L

I feel your pain and frustration. I think most of us who have had a 930 long enough have gone thru this. When I bought mine (from Japan) it was a freshly rebuilt engine ready to go. 'Yeah right' as the down under saying goes. Took me months to get it to go, then the transmission/clutch problems showed up etc. And a rats nest of wiring issues, jumped relays etc. Freshly built engine = 1 2nd hand P/C + 1/2 lb of RTV. I was at such a loss at parts of the process I seriously conmsidered parting it, because after months of work I still didn't have a functioning car. But with a handful of the cars in the country that wasn't much of an option so I perservered - in too deep now.
What does come out of this tortuous process, as you say is a good understanding of where the gremlins are. You can trouble shoot them quick time. Which makes ownership of the beast so much better further down the track.
lets see what Flowtech come up with. Those intermittent issues are a nightmare. I had a bouncing airplate for a while . Could not cure it. Dumnno what I did. But it went away. But I do suspect the fuel presure issue is not the key to this. A coil breaking down?
Regards
Alan

i originally thought it was electrical. The first thing i did prior to digging into the fuel was i borrowed and swapped out the ecu coil wires and distributor and spark plugs from a running car .it made no difference.