Fuel Pump Rebuild?

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Texas710
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Fuel Pump Rebuild?

Post by Texas710 » Tue Mar 15, 2016 11:25 am

Hello all.

Been dealing with the standard "the truck is hard to start after sitting" issue and when doing some research on this site, I came across some information that said if the pump's internal check valves are working properly, you should not have much of an issue.

I replaced all the fuel hose/clamps/filter this last weekend with some gates line and SS fuel injector clamps, hoping this would solve the issue. Ran the truck on Fri/Sat and then last night (Mon) and it took 10-15 seconds of cranking (after initially jumping to life) to get the carbs full enough to start (truck is kept in garage), it's close to 20+ seconds if the truck has sat for a while. With the new hose/clamps, I am starting to suspect the fuel pump needs some attention. Other than the back flowing fuel, the truck runs fine once it gets idling, so it's pumping fine.

Is there a good way to test this theory, or should I just go ahead an rebuild? I think i'll be ordering a replacement kit anyways, good thing to have in the spares. 1 other thing, might be unrelated, when I took off the fuel filter, there was a small dime sized piece of white thin plastic (almost like a grocery bag) in the filter. Could this be one of those check vales?

I have thought about an electrical fuel pump in the past, but I am kind of a sucker for stock things, keep it simple...

Any help is always appreciated, Thanks.

kdiqq
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Re: Fuel Pump Rebuild?

Post by kdiqq » Tue Mar 15, 2016 11:38 am

You might want to just throw in a new unit. There is a VW unit available at NAPA.

Before you do that, try cranking with the fuel line going in to a bucket. Make sure it's moving fuel. If you want to be even more thorough, hook it up to a fuel pressure gauge.

Sounds like a fuel pump though.
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pcolette
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Re: Fuel Pump Rebuild?

Post by pcolette » Tue Mar 15, 2016 1:30 pm

The rebuild kit does not include new check valves and they are not readily available as a seperate item. They are part of the upper half of the pump. I would check with Jim L. and see what he suggests.

Did you use metric fuel line? Although there are SAE sizes that are close, they still allow air to leak even with the better quality injector clamps you used. I've been through this a few times and still don't have it ideal even with a new pump, new metric line and new clamps. :(

Part of the problem is that modern gasoline evaporates much faster than the gas of 30-40 years ago. On "closed" fuel injection vehicles this doesn't matter much but with our wide open carbs it seems that the fuel disappears quickly. On both my 710's, if they sit for 3 or more days I can count on 15 seconds of cranking even though both have all new parts.

EDIT: Sorry - Meant pump, not carb in second sentence.
Last edited by pcolette on Tue Mar 15, 2016 5:28 pm, edited 1 time in total.
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Hotzenplotz
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Re: Fuel Pump Rebuild?

Post by Hotzenplotz » Tue Mar 15, 2016 4:31 pm

save the time to rebuild and get yourself a VW fuel pump
Volkswagen : 113 127 025 C - 113 127 025 B - 113 127 025 A

tested and working, see http://pinzforum.kiruna.de/viewtopic.ph ... mpe#p72668
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Texas710
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Re: Fuel Pump Rebuild?

Post by Texas710 » Tue Mar 15, 2016 4:58 pm

I did not use metric, 5/16 and 3/16. I figured they were close enough, the 3/16 is smaller than 5mm so should not be an issue... Should...

Do the VW pumps have check valves? Might be easier to swap out for one of those and rebuild another time.

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pcolette
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Re: Fuel Pump Rebuild?

Post by pcolette » Tue Mar 15, 2016 5:33 pm

Yes, the VW pumps have the check valves. NAPA has carried 2 different brands of the VW pumps under the same part number. IIRC one of the forum members indicated that one brand seemed a bit lower quality.

BTW, I also remembered that one time I had a fuel pump rebuilt professionally it was pointed out to me that the brass inlet & outlet tubes had become loose and air was leaking out (or in) at those points. A careful application of JB Weld took care of it.
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Jimm391730
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Re: Fuel Pump Rebuild?

Post by Jimm391730 » Tue Mar 15, 2016 7:21 pm

All fuel pumps have valves; when the pump sucks in fuel, it must pull fuel from the tank (and not "backwards" from the carbs) so one valve prevents the flow backwards from the pump outlet. When the pump pushes fuel out, it must push the fuel out to the carbs (and not "backwards" to the tank) so another valve prevents flow backwards from the pump inlet.

To say it differently, the pump just moves fuel in and out of the pump as the diaphragm moves in and out. One valve is in the inlet side that only allows fuel into the pump (not out); the other valve is in the outlet side that only allows fuel out of the pump (not in).

These valves are not super high precision and can allow a tiny bit of fuel to leak in the wrong direction; this can allow the fuel in the pump to drain back to the tank when not running (the pumped fuel volume when running is much, much more volume than the valves leak). Once the pump and valves are dry, they don't pump much and it can be a b***h to get fuel flowing again. Some have bandaided this by adding additional check valves external to the pump, but additional valves add resistance to the flow of fuel and should not be needed if the internal pump valves are working as they should. It is better to rebuild/replace the pump and its internal valves than keep a substandard pump and kluge other things to try to get back the performance that is missing.

And yes, the gas can and will evaporate from the carbs. It can and will take some cranking to refill them, but even if the carbs are empty they should refill with just a few seconds of cranking. I find that "pumping" the pedal while cranking will use the accelerator pumps to move sufficient amount of fuel into the engine to help it to catch sooner (even if it does not run smoothly yet) but once the engine starts to catch, run faster, the pump pumps faster and in a few more seconds the carbs are full. Without pumping the pedal it just might take 15 seconds or more to "catch" without any assistance.
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Re: Fuel Pump Rebuild?

Post by pinzinator » Tue Mar 15, 2016 7:54 pm

I used a VW pump in my 710 for many years without a problem. Recently I installed a 24v electric fuel pump which works great, and has practically eliminated cold-start cranking. http://real4x4forums.com/PinzgauerBBS/v ... =12&t=9790

Texas710
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Re: Fuel Pump Rebuild?

Post by Texas710 » Tue Mar 15, 2016 9:16 pm

I have read a lot on this issue and rebuilding or replacing seems like the best idea. I wanted to start simple with the hoses and see what happened after that. I had the thought of check valves, but restricting a 5mm hose anymore seems like a bad idea. Still hard to believe that is the correct size hose...

Pinzinator: I know, I drool over that particular post. I just am not ready to start changing all that just yet, I like simple and mostly stock for now. But, not to say I would rule that out in the future.

Pcolette: you might have just pointed me in another direction, when I was replacing the hose, the brass inlet moved some, I assumed this was normal, but maybe not. I will be getting into this tomorrow. God bless JB weld!

I think a trip to Napa is in order.

Oh, and I will try the different starting technique, I have so far been a non-pedal pumper but will try something different.

Thanks again guys, any other thoughts are welcome.

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Re: Fuel Pump Rebuild?

Post by audiocontr » Thu Apr 28, 2016 5:14 am

I had a no fuel scenario on the beach with a rising tide once. I flipped the diaphragm over and the pump worked great since.
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Pinzcat
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Re: Fuel Pump Rebuild?

Post by Pinzcat » Thu Apr 28, 2016 10:50 am

I was tired of cranking a long time before starting (the starter too...). So I've installed a hand pump (the same as for outbord motors): so I press a little to fill in the carbs... and the engine runs immediately.
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Texas710
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Re: Fuel Pump Rebuild?

Post by Texas710 » Thu Apr 28, 2016 8:50 pm

I ended up pulling the pump, opening everything up and cleaning everything, plus I did the JB trick on the brass intake/outlet, just to be safe. Put it back together and it all seems fine for now. I did order a replacement, SAV was running a special on NOS pumps, didn't cost much more than a VW one, and now is in the spares box.

Testing tomorrow, have to move a 1000 gallon rainwater tank to the top of a far off hill, bout 200 miles round trip. First time without a top/flat bed mode, I have to say, I like the look.

Pumping the pedal also has been helping to catch earlier.

Pinzcat! Man, I had this thought awhile back but was to chicken to try it. I like it, seems very easy. Any issues with that? I wouldn't think so, but you never know.

Pinzcat
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Re: Fuel Pump Rebuild?

Post by Pinzcat » Fri Apr 29, 2016 3:16 am

@ texas 710:
No problem with this system. I am not the only one to use it, I found the idea on the german Pinz forum!
http://pinzforum.kiruna.de/viewtopic.php?f=3&t=8935

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montieth
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Re: Fuel Pump Rebuild?

Post by montieth » Wed Sep 26, 2018 12:42 am

Why don't these fuel pumps have a hand priming lever? The British vehicles I'm used to have them though they're in arguably MUCH harder places to reach than on the pinz.


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