Rear Fuel Line Replacement - Drain Tank?

[kris159357]

Hi,

I'm looking at replacing the rear pressure fuel line from the tunnel to the accumulator on my '79 SC.

From what I have read so far on various searches, there was no mention of draining the tank. Does the fuel pump have a check valve in it, making it only necessary to collect what is in the pressure line?

Thanks

[Steam Driver]

Personally I would drain the tank. Not to do so would be just looking for trouble.

[ossiblue]

The fuel pump check valve only stops the flow back into the pump, not away from the pump, so fuel would likely flow out under gravity with the pump off and the line disconnected. However, if you lift only the rear of the car to do your work, the fuel would not flow out because liquids will not flow uphill. Safety dictates that the tank be drained.

[Jdub]

You should replace both lines since you are "in there". Drive the car until gas is almost exhausted (Reserve +). Disconnect battery at both terminals and remove from car (strongly recommended) or as a minumum cover both posts with non-conductive caps.

Drip method is perfect, in open area with plenty of air not assisted by anything electrical. This gas is ideal for two-stroke mixup so keep it for the tiller/weedeater/?. Add new gas as 1 gallon (only!) and check for leaks on startup. When satisfied drive to station and fill up, being sure to have a look under the car, just in case!

Replace gas filter as well if not already done very recently and scribe mileage and date on the filter body.

[LEAKYSEALS951]

I'd go ahead and drain the tank. Here's why: You might get by if the tank is low AND the rear is jacked up so the height of the rear tunnel line is higher than the gas tank( I don't know if that's possible or not), but it's gonna be messy, why? because all the gas from the rear line to accumulator is going to be splattering on your face when you disconnect the rear line from the tunnel. That's expected, but you don't want to be wondering "is this fuel from the rear line soaking me, or fuel from the gas tank? These are unpleasant things to ponder, and retighting that line in limitted access is a pain- not too fun with gas leaking from everywhere. Take the extra time to empty the tank. Good luck
Ron

p.s.- while you are contemplating emptying your tank, go ahead and order some vacuum line from our host, so when you rip your current vacuum trying to replace your fuel lines, it will already be in the mail!!!!! (ask me how I know)
http://www.pelicanparts.com/cgi-bin/smart/more_info.cgi?pn=N-020-353-5-M21&catalog_description=&%2533%252E%2535%2520X%2520%2537%252E%2530mm%2520OD %2520%2528quantity%2520as%2520needed%252C%2520pric ed%2520per%2520meter%2529%2520%2520

pss-ALSO, if you get ambitious and decide to replace your brake booster vacuum line (like I decided to do)- DON'T- unless you are a glutton for punishment. I replaced mine, but in retrospect, the old one was okay

[boyt911sc]

Originally Posted by kris159357

Hi,

I'm looking at replacing the rear pressure fuel line from the tunnel to the accumulator on my '79 SC.

From what I have read so far on various searches, there was no mention of draining the tank. Does the fuel pump have a check valve in it, making it only necessary to collect what is in the pressure line?

Thanks

Kris,

If you are replacing the delivery line/s after the FP, there is no need to drain the fuel tank provided you have a good working FP. However, if you are replacing a section of the return line/s, you have to drain or empty the gas tank. Why? There will be residual fuel in the fuel line/s and FP, after draining the line, fuel from the gas tank won't pass through the FP. Test it if you disagree!!!

To drain the fuel tank, I do a controlled drip method by loosening the return fitting at the fuel tank and allow it to drain. Or disconnect the delivery line at the FA and test run the FP till you empty the tank. The dirt or debris inside the tank won't get to the FP because of the in-line filter in the fuel tank. Which ever method you use, one thing you have to remember. Work safely and keep away any sources of sparks or ignition while during this job.

Tony

[boyt911sc]

Kris,

It seems like I killed your thread after my post. There were four (4) successive posts with the same recommendation or suggestion of draining the fuel tank to replace a section of the delivery line. No post appeared after mentioning that it was not necessary to do so. This is probably another myth busted.

Below are some pictures of a CIS set-up that would demonstrate the overhead fuel tank delivering fuel to the FP and shows no fuel flow after the pump. I left this set-up for more than 12 hours now and will close the shut-off valve later tonight after 24 hour demo.

Overhead fuel tank with shut-off valve at open position:


Fuel lines from gas tank to FP:


Fuel line disconnected from the fuel accumulator:


The curved fitting was actually allowed to hang to the floor to observe any fuel flow through the FP, not a trace of fuel except for the residual fuel after shutdown:


Tony

[LEAKYSEALS951]

^^^WOW! That is the coolest CIS diagnostic station I have ever seen! Nice work! - or do you use this to test fire engines out of the car?
If there is a spring or something to keep the pump closed, more power to you!
Ron

[boyt911sc]

Originally Posted by LEAKYSEALS951

^^^WOW! That is the coolest CIS diagnostic station I have ever seen! Nice work! - or do you use this to test fire engines out of the car?
If there is a spring or something to keep the pump closed, more power to you!
Ron

Ron,

I use this set-up for testing and calibrating WUR's, FD's, and fuel injectors' operating pressures. However, I did use it before to run a friend's engine for a start-up. For testing and running a complete engine after a rebuild or major work, I prefer an engine test stand like this:







The first version of my engine test stand made from scrap metals in the 90's and had several revisions later.

Tony

[T77911S]

Originally Posted by boyt911sc

Kris,

If you are replacing the delivery line/s after the FP, there is no need to drain the fuel tank provided you have a good working FP. However, if you are replacing a section of the return line/s, you have to drain or empty the gas tank. Why? There will be residual fuel in the fuel line/s and FP, after draining the line, fuel from the gas tank won't pass through the FP. Test it if you disagree!!!

To drain the fuel tank, I do a controlled drip method by loosening the return fitting at the fuel tank and allow it to drain. Or disconnect the delivery line at the FA and test run the FP till you empty the tank. The dirt or debris inside the tank won't get to the FP because of the in-line filter in the fuel tank. Which ever method you use, one thing you have to remember. Work safely and keep away any sources of sparks or ignition while during this job.

Tony

its been a long time since i replaced my fuel line in my 77s, but i think tony is right.
when i first saw this i was thinking that when i did mine i was surprised that no fuel was coming out of the fuel pump. i guess the fuel cant leak past the pump.

IE, i did not drain it. i might have run it down, plus you will need to jack the car up and i may have had the rear higher than the front...just in case.

[Robey5]

I am in the middle of this job right now. I have the rear of the car higher than the front - and I have very little gas in the tank.

In my case, I prepared for the fuel face-wash by having a cup handy when I cracked the fuel line connections near the trans carrier. Because I did not mark the lines from inside the car, I am going to run the FP for a couple seconds to see which one is the return, and which is the feed line - and to push the debris out that may be present. After all of that, I will drain the tank (maybe) from the drain point to see if there is any other 'stuff' in the tank that is of concern.

After all of this work, I would consider it a prudent measure to drain the tank - but that is up to you... I'd suggest it.

[boyt911sc]

Originally Posted by Robey5

I am in the middle of this job right now. I have the rear of the car higher than the front - and I have very little gas in the tank.

In my case, I prepared for the fuel face-wash by having a cup handy when I cracked the fuel line connections near the trans carrier. Because I did not mark the lines from inside the car, I am going to run the FP for a couple seconds to see which one is the return, and which is the feed line - and to push the debris out that may be present. After all of that, I will drain the tank (maybe) from the drain point to see if there is any other 'stuff' in the tank that is of concern.

After all of this work, I would consider it a prudent measure to drain the tank - but that is up to you... I'd suggest it.

Bryant,

You don't need to run the FP to determine which is the delivery and return lines for your engine set-up. If you don't realize which is which, stop and refer to the schematic diagrams. The line that goes to the fuel accumulator is the DELIVERY line. The other line is the return. Do you remember how many times you had come to me for help? And spoke over the phone? Draining the fuel tank is not a bad idea but is it necessary? It is your choice.

Tony

[kris159357]

Guys,
Thanks very much for the responses.

Tony thanks for taking the time to load the photos, its very informative. I wont end up draining the tank which is good news. Its on jack stands at the moment for cv boots and bearings, its also 3/4 full so I don't have the luxury of driving till almost empty.

On another note what do you think of those hose clamps, you are using in the photos? My delivery line thats being replaced is original, I was going to take it to a hydraulic shop to be re crimped. The return looks to have been replaced recently by the previous owner, with these clamps. If I was draining the tank i was going to take this off and have some crimps put on as well, but you seem to be using similar ones.

Kris

[boyt911sc]

Kris,

I used the OEM fittings with barb section and used the metal band and crimped them. Your local hydraulic shop has several options to crimp these hoses. Most important is to use fuel hoses rated for fuel injection and securely crimped them. Although the return line is not subjected to high fuel pressure like the delivery lines, it could be exposed to severely high fuel pressure in case of clogging or restriction in the line. So treat both delivery and return lines as high pressure lines.

If you need quality fuel lines, contact Len Cummings (aka BoxsterGT). He makes beautiful replacement fuel lines as good as OEM lines. If you don't have the ability and confidence to build your fuel lines, don't feel bad. Get them from the pro's. This is some piece of work you can not afford to fail.

Don't forget when you break the fuel line fitting/s, that there will some residual fuel in the line and highly recommended to allow atleast 6 or 8 hours or more after you ran the FP. The residual fuel pressure would drop to ZERO over an extended idle time.

Tony

[kris159357]

I completed this work on the weekend just gone and wanted to confirm that Tony is correct.

The supply line could be removed without draining the tank, with only the small amount of fuel in the line draining out.

Cheers
Kris