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Discussion Starter · #1 · (Edited)
Thought I had the fuel presser bleed down solved but nope! I do have a new fuel pump on the way, but putting the old one back in has not solved the issue and I did not have this problem when the old pump was in before. I believe there is a check valve in the pump itself, and I'm thinking there is a second one in the fuel regulator. Am I correct on this? Does anyone know, are there any others, and if so where?

Thanks in advance,
Jim
 

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Discussion Starter · #2 ·
Anyone know where I can find a diagram that might show the check valves in the fuel system?

Thanks,
Jim
 

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Discussion Starter · #3 ·
If there are only 2, and putting the old pump back in doesn't solve the problem, then it would seem I should be ordering a replacement fuel filter/regulator right away? No?

Not wanting to throw parts at it, and not sure how many check valves there are in the system I'm kind'a at a loss as, "I can't tell the players without a program."

Jim
 

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Discussion Starter · #4 · (Edited)
OK, I think I have a plan. From the book, "Bosch EFI systems." (Thank you QSilver7) :) I am thinking the pinching off needs to be done at the fuel filter/regulator to pinpoint the problem. Not as I did, at the fuel pump.

"The engine should remain pressurized even when the engine is stopped. This permits quicker restarts, and helps to prevent vapor lock. With the pressure gauge connected as described above, run the engine briefly, then shut it off (or energize the fuel system with the engine stopped). The pressure should not drop below about 14 psi for at least 20 minutes after shut-down. A loss of residual pressure may be caused by an external leak, one or more leaking injectors, a defective pressure regulator, or the fuel pump check valve. To check both these last two, re-pressurize the system and, immediately after shutting down the engine (or disabling the pump), pinch shut the supply line from the pump to the regulator. If the residual pressure now holds, the regulator is defective; if not, the pump check valve is leaking. If all this fails to stem the drop in residual pressure, about the only remaining candidates are one or more defective injectors, and the cold start valve."

I can also move my defective fuel pressure gauge around the system as I pinch things off. (it may read 20# low, but it reads) Put it just after the pump, clamp and watch the pressure. Then move it to the regulator, clamp and watch. That way I think I can spot where the pressure is escaping to. I"m expecting it to be the new fuel filter/regulator, not the pump, and perhaps it was just a coincidence that it started when I was in the tank. We'll see.

Jim
 

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Discussion Starter · #5 · (Edited)
Ugg, seems to me the test above is wrong. If put a gauge on the fuel rail, pressurize the system, then pinch off the supply line to the fuel regulator. If the pressure now holds it's the fuel pump check valve, not the regulator because you have removed the fuel pump check valve from the system, not the regulator.

I think I'm going to put the gauge on the out line from the pump, pressurize the system then block off the fuel line just past the gauge. If the pressure holds, the pump check valve is good. So the pressure loss is down stream of the pump and the next thing to check is the fuel regulator.

Next, check the regulator by moving the fuel psi gauge to the fuel rail. Pressurize the fuel system and block off the supply line to the fuel rail. If the pressure now holds the problem is the fuel filter/regulator. If the pressure still drops the problem is down stream from the clamp, either a leaking injector or in the cold start valve.

I guess it also can be done by putting the gauge on the fuel rail and, starting just down stream of the pump, progressively moving the clamp on a pressurized system, and repeatedly checking the pressure until you come to the place where it no longer looses pressure. That is probably the easiest way to do it.

If I am in error on this, looking at this wrong, or just plane bassackwards, please let me know.
Jim
 

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Discussion Starter · #6 · (Edited)
OK, FIXED!!!

The fuel test gauge decided to work today and a new fuel pump showed up in the mail so I was able to get out in the garage and do some work.

Decided not to mess around! Put the fuel test gauge straight on the fuel pump, (no line to the motor) and turned on the ignition. The pressure would spike at 60psi, then drop by itself, with the key still on, to zero. When I started the motor with the gauge now on the fuel rail same thing, pressure would spike at 60 then drop to zero. I got 47# eventually, started the car, and then clamped off the fuel line. Pressure stayed at 27 for a long time then very slowly started to come down. There it was for sure. Not only did the new pump have a bad check valve but the old pump that I thought was good and put back in, also had a bad check valve. Really drove me up a wall trying to figure out what what happening!!

With the new (3rd) pump in it, it starts perfectly. Holds pressure well. All is fixed.

Was a real brain teaser for me, I figured out the 2nd pump was bad, but had no idea the old pump check valve was also bad.

I believe there are 2 check valves in the fuel system, on on the fuel pump, and another on the fuel regulator. If you are having loss of residual fuel pressure, my suggestion is, start at the fuel pump, check to see if pressure is building and holding there, then if it is, work your way forward clamping off the line until you find the source of the leak.

Jim
 

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Discussion Starter · #8 ·
Turn the key to ign1 a few times?
When the pump check valve was broken even though I turned the key to position 2 several times it was not enough to build pressure in the system. It took the starter turning over the engine for prolonged periods 2 - 3 times before there was enough pressure to start the motor. I think it takes around 25 - 30# of pressure to start the motor, and it seems to maintain 47 running.

Jim
 

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Discussion Starter · #9 · (Edited)
I have to say I don't really understand the system completely, but below is what I have found and surmised.

I think the regulator operating on vacuum, closes the pressure to a limited 50# as vacuum builds. Therefore if vacuum gets low in the motor, say a vacuum leak, it will not impede the flow of fuel at high rpms.

There are 2 lines on the rearward portion of the fuel filter and only one fuel line going out. This is I think is the return system. Any pressure higher than #50 causes the regulator to return fuel to the tank. I do not believe there is any fuel check mechanism in the fuel filter or regulator.

Upon reflection, I believe there is only one check valve in the system and it is integrated into the fuel pump. Were there a second one in the fuel regulator (and I think there should be) I would think that even when the check valve in the pump has failed, there would still be plenty of pressure in the rail to start the car. This is not the case. If the check valve in the pump fails, pressure in the rail will rapidly drop to 0 when the motor is shut down, then require much effort by the starter and fuel pump to re-establish pressure in the rail.

So your car is hard to start, check fuel pressure at the rail. After starting, then shutting the motor off, the rail should hold 15# for 20 min. If it doesn't, I think the pump is the culprit. It is quite easy to remove, I will include pics later on the easy way to do this and the tricks I have learned having to do this several times.

The failed pump check valve can be confirmed by putting the fuel psi gauge directly on the pump out line, turning on the pump for just a couple of seconds or until the pump builds about 50# of pressure, shut off the pump and you will see the psi rapidly fall to zero. This means the pump check valve is bad. Replace the pump.

A fuel pressure gauge that will work nicely can be had on ebad for as little as $30. I suggest buying one before it is needed to help solve problems when they arise. Fuel pumps, like alternators, starters, etc., are wear items and need to be replaced when they fail or bout every 150K - 200K. But without the proper diagnostic tools one will be left wondering why the car is hard to start or won't start and being quite frustrated at being stuck on the side of the road.

I think a tip that a fuel pump is getting ready to quit all together is misfire at high rpms and inability to move fuel from the drivers side of the saddle tank to the passengers side where the pump is located (this can be monitored on test #7). When fuel is getting low the sucking jet should be able to bout empty the L tank, and all the fuel should be on the right side. This is accomplished by the pump sucking up the fuel on the L while pumping fuel to the motor. When the pump gets week it doesn't do the fuel transfer well.

Don't forget, once you d/c the fuel level sender you may need to go in to test #21 to re-calibrate the fuel level system. If you don't do this you may get all kinds of strange fuel level readings after you close the system up again and think all should be working well.

Jim
 

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Thanks for sharing your knowledge!
I am having fuel system symptoms. Seems like my car needs extra turns of the crank to fire up lately.
 

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Discussion Starter · #11 · (Edited)
Thanks for sharing your knowledge!
I am having fuel system symptoms. Seems like my car needs extra turns of the crank to fire up lately.
I'd suggest ordering a fuel pressure test gauge if you don't already have one. There is a good kit on ebad for $28 w free shipping!
Could be many things but, "You can't tell the players without a program." (Yogi Berra) :)

Jim
 

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I'd suggest ordering a fuel pressure test gauge if you don't already have one. There is a good kit on ebad for $28 w free shipping!
Could be many things but, "You can't tell the players without a program." (Yogi Berra) :)

Jim
Thanks for the recommendation, there are so many for sale on ebad.
I want to make sure I get one that will work

was this the one you saw?
http://www.ebay.com/itm/New-Fuel-In...:g:qXoAAOxyxmJSN9NY&item=331025066056&vxp=mtr

The seller's description says it's for " most fuel injection equipped vehicle (Except for CIS-Jetronic, Bosch and GM throttle body systems)
 

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Discussion Starter · #13 · (Edited)
Thanks for the recommendation, there are so many for sale on ebad.
I want to make sure I get one that will work

was this the one you saw?
http://www.ebay.com/itm/New-Fuel-In...:g:qXoAAOxyxmJSN9NY&item=331025066056&vxp=mtr

The seller's description says it's for " most fuel injection equipped vehicle (Except for CIS-Jetronic, Bosch and GM throttle body systems)
Ya, that's the one, but on closer look I'm not wild about it because:
There is no purge valve. This is quite helpful when working on the rail if there is air in it.
On the bigger kits there is a fluid tight quick release in the hoses. That way you can screw on the Schrader section without loosing fluid, then add the gauge, again without loosing psi or fluid. Which is also a good way to put the fuel gauge on. Works much better this way than putting the whole thing together then trying to screw it on the Schrader valve.

Guess I'd still go for a bigger kit, either this:
http://www.ebay.com/itm/FUEL-INJECT...:g:7FIAAOSwDwtUm014&item=351271502098&vxp=mtr or,
http://www.ebay.com/itm/0-100PSI-Fu...:g:kqcAAOSwLs5XLF6I&item=401116719654&vxp=mtr

There a whole lot more stuff in it than you will probably ever use, but still, the price is so low. I borrowed my friends very old and simple SnapOn gauge that is still running $100 for a used one on ebay, the big ebay kits do the same stuff and a lot more for half the price. His SnapOn doesn't even have the ability to "T" into a line.

I had/have a problem with mine, but it's the crimp on the Schrader adapter, not the gauge. Bet this doesn't occur on 1 in a 1000 or more. Right now the hose is working fine and I"m thinking about either replacing it for $20 or just taking some epoxy and making sure it doesn't slip back to the way it was impeding pressure flow. The company has completely turned a def ear to me and won't send me a new tube or replace the kit. Actually they are ignoring my emails all together now but reading their reviews it seems to be their policy that if they sell a defective product, "sorry about your bad luck". No matter, I still like the gauge and the price.

Jim
 

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After a little research I have learned that the early e39's like mine have no Schrader valve in the fuel rail. Instead I need connectors that fit the quick disconnects.
 
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