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Old 12-14-2014, 07:51 PM
damienk damienk is offline
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Exclamation fuel starvation challenge

alright. If anyone can solve this one, I will be immensely grateful. My A4 dies shortly after starting (suddenly, like if the ignition was turned off) and it is fuel related. To make it simple:

- if I disconnect the fuel line from the tank and hold it in the air and keep it filled with gas, it runs perfect and forever.
- if I connect it to the tank, or if I LOWER the fuel line , it dies (it dies within seconds when lowered at the level of the fuel tank).

I would say fuel pump of course, but voila: I tried it with 2 different new fuel pumps, no difference. I tried everythingween: The fuel pump is new. New fuel filter. Rebuilt carb. New fuel lines. Even a new freaking fuel tank (when I realized it ran when disconnected but not when connected, I assumed it was the fuel tank, until I noticed - today - that how high I hold the fuel line matters).

I don't know what else to do. I am desperate. There is no leak in the fuel lines. No fuel leak anywhere. The pump is new, and works (if I disconnect between the carb and the pump and start the engine it fills a cup of gas in no time). The pump is 1.5 to 4 PSI, which I understand is what is required. And it is not like I relocated everything recently, everything is where it used to be.
I have no idea what to do next. I am pissed at all the parts I bought for no reason, and I am clueless. Any suggestion, apart from hiring someone to hold the fuel line up in the air and fill it as it goes?
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Old 12-14-2014, 10:50 PM
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I chose to reply in this thread because it has more information than the other in the troubleshooting section.

Sounds to me like you have a fuel system leak but not the kind that drips fuel. I bet you're sucking air through a clamp, fitting or seal somewhere (we've heard of fuel filter seals that cause this before). The entire fuel system is under negative pressure up to the fuel pump and positive pressure thereafter. A leak ahead of the pump that allows air into the system will stop the fuel flow.

Raising the fuel line and pouring in fuel changes the gradient ahead of the pump from negative to positive pressure and the problem temporarily disappears.

The only other thing that comes to mind is a stopped up tank vent. As a test try running the engine with the fuel fill cap removed. That will provide good venting for sure. If the engine dies again we can forget the vent as a possibility.
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Old 12-14-2014, 11:18 PM
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Two questions -

Are you reading a fuel pressure gage, or is your pump (s) rated at 1.5 - 4 psi?

Pump test done with normal fuel line position, normal tank, and you only took the hose off the carb inlet barb, no other changes?

PS - internal hose obstruction? There was a weird post on here a while back where someone found a piece of plastic inside their fuel line. Troubleshooting nightmare 'cause it's so random. It could be that moving the fuel line is the issue, not the coincident change in elevation.
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Last edited by BunnyPlanet169; 12-14-2014 at 11:29 PM.
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Old 12-15-2014, 08:22 AM
damienk damienk is offline
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Thanks for the suggestions.

BunnyPlanet: the pump is rated 1.5 to 4 PSI. I don't own a fuel pressure gauge.
Therefore, I haven't done any pump test. With everything in normal position, the pump spits a healthy cup of gas when starting the engine (hose disconnected at carb) . With everything connected in normal position, it doesn't work. With hose disconnected at tank level in normal position, it doesn't work. With hose disconnected at tank level and raised above normal position (above tank level by 2 inches at least), it works flawlessly.

Also, no internal hose obstruction. (hoses are new, tested, and I also checked each hose separately multiple times, by blowing, sucking, and testing the flow of gas through each of them.

Ndutton: fuel tank vent is fine, I tested it, and also removed it (cap open) to rule it out. A leak was my next guess too, but...where? I checked all clamps (all double clamped), all hoses, the fuel filter housing is the same as before and I checked it multiple times. No bubbles anywhere, no fuel leak...

I was thinking that maybe the pump isn't powerful enough, and that my carb is finicky with the PSI? Could it be low pressure? What does 1.5 to 4 PSI (fuel pump range) mean? That the pump delivers 1.5 when it is having a bad day, 4 on good ones? What makes it be at one end or the other of this range?
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Old 12-15-2014, 09:23 AM
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Take care to avoid assuming everything is good when something clearly isn't.

How about a test with an outboard fuel tank and single hose from it to the fuel pump, tank positioned at the same level as the main tank (eliminates all fuel system components up to the pump)?

Engine runs fine - add components back into the system one at a time, testing after each addition.

Engine quits as before - get after the pump and carb.

Hey wait. Do you have an oil pressure safety switch for the fuel pump power? How many terminals on the switch? Have you bypassed it by placing a jumper wire across the terminals?
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Old 12-15-2014, 09:25 AM
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I went absolutely nuts tracking down a few fuel issues.
Lesson 1 is YOU NEED GAUGES!
I ended up with a fuel pressure gauge and two vacuum gauges - one on the input side of my filter and one on the output side.
My issue turned out to be debris in the tank that would clog the pickup tube, cause fuel starvation, and fall back off when the suction dissipated. Drove me nuts until I figured that out
Lesson 2 came awhile later - liquid filled gauges are very nice because the needles don't jump around. What I didn't know was they change readings with temperature if you just use them as received. You need to mount them with the little rubber stoppers facing up and cut the ends of the stoppers so the gauge is no longer air tight. THEN they read correctly after they get hot.

As for your issue, I can't say for sure yet but I believe an air leak has been mentioned. That might be it. I would get a gauge or two and get some measurements. Fuel pumps are sold with pressure ranges, not a fixed number. The output will vary with the load on the pump, voltage, and maybe temperature. 1.5 to 4 PSI is the correct range for an A4. My pump sits rock-steady at about 3.8 - 3.9 PSI.
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Old 12-15-2014, 10:31 AM
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What is getting me is the "dies suddenly" and "dies within seconds" part. Post #1. There should be fuel in the line, filter, pump, carb bowl.
Even if you turn off a petcock the engine still runs for awhile right?
What is the relative elevation of the filter to the fuel level in the tank? Just thinking back to my filter at the highest point that slowly filled with air, due to a leak, and led to shutdown.
Reaching but. Could misaligned floats play into this. Floating to high/sticking and stopping the flow. Only allowing fuel to flow when the "extra" head, negative to positive, pressure is added by raising the line as mentioned in post 2. ??????
Dan S/V Marian Claire
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Old 12-15-2014, 01:28 PM
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I agree that a pressure gauge would help. I have a cheapy from Amazon made by Mr. Gasket (#1561)..it was $13. I installed mine just before the carb..The engine will run even around only 1 PSI of fuel pressure, but a gauge at the carb will confirm or eliminate a fuel delivery problem forever. My mechanical pump delivers right around 2.75-3 PSI.

Neil, good thought with the OPSS!
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Old 12-15-2014, 05:44 PM
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If you have a fuel filter/separator make sure you have not reversed the input and output connections. When spinning the cartridge on I like to apply a thin coat of machine oil to the gasket to ensure a tight seal.
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Old 12-15-2014, 09:28 PM
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Is it possible to pressure test the fuel system from say the pump inlet and back?
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Old 12-15-2014, 09:39 PM
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Quote:
Originally Posted by damienk View Post
alright.

I would say fuel pump of course, but voila: I tried it with 2 different new fuel pumps, no difference. I tried everythingween: The fuel pump is new. New fuel filter. Rebuilt carb. New fuel lines. Even a new freaking fuel tank (when I realized it ran when disconnected but not when connected, I assumed it was the fuel tank, until I noticed - today - that how high I hold the fuel line matters).
What kind of tank?
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Old 12-15-2014, 09:49 PM
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Sure, you can test but that's what the gauges the guys are talking about will do on the system in situ. Ahead of the pump = vacuum gauge, after the pump = pressure gauge.
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Old 12-15-2014, 09:54 PM
Rbyham Rbyham is offline
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I look forward to hearing what resolves this. Nothing comes to ind here except that you will be happy once it is solved because you now have a completely new fuel system. Having bought a 48 year old boat with original A4, one thing I did right was pull all fuel components out and replace including tank. I have enjoyed 18 months now of zero issues in a boat and engine of that age and which had been in storage 8 years when I purchased. The day is coming soon when you will be glad you handled it this way...
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Old 12-15-2014, 11:33 PM
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Quote:
Originally Posted by damienk View Post
Thanks for the suggestions.

BunnyPlanet: the pump is rated 1.5 to 4 PSI. I don't own a fuel pressure gauge.
Therefore, I haven't done any pump test. With everything in normal position, the pump spits a healthy cup of gas when starting the engine (hose disconnected at carb) . With everything connected in normal position, it doesn't work.
Damien - can you elaborate on this please? Everything normal, the pump spits gas.... For how long? Like, can you fill half a liter? Spits, or steady pulsing stream? Are you sure the pump is plumbed correctly? It has a distinct inlet and exit. Most of these small pumps are rated approx 30 gallons per hour, so you should get a quart milk jug every 30 seconds.

If you have a oil pressure safety switch (USCG required with an electrical pump) you can bypass it temporarily and then just turn on the ignition for 15 seconds to test.

Last weird thought - does moving the hose around for testing brush against other stuff? Like a wiring bundle, or the wiring to the OPSS? I've had situations where one plausible solution was in fact the physical interaction with the actual, unrelated, problem.
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Old 12-16-2014, 01:37 AM
JOHN COOKSON JOHN COOKSON is offline
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The fuel pump is weak or not working. When it is gravity fed everything is fine. When the fuel pump has to pump the fuel it is to weak to do so.
How much electricity are you getting to the fuel pump?
Try running a jumper wire from the boats battery to the fuel pump, bypassing the boats wiring & OPSS, and see what happens.

TRUE GRIT

This assumes the tank, filters, and fuel lines are not the problem.
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Old 12-16-2014, 11:03 AM
jwmurphy jwmurphy is offline
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FWIW, This past season I experienced fuel starvation issues on my 40 Year old A4. The fuel system: hoses, tank, pump, filters etc. checked out OK. But, what I did discover when I took the carb apart for cleaning (no dirt found) was that although the float was operating properly the float valve needle was sticking in the shut position. This was easily confirmed when blowing (by mouth) into the fuel inlet wasn't enough pressure drop down/open the needle. I replaced the needle and seat assembly (supplied by our host) and had no further issues.
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Old 12-16-2014, 01:52 PM
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Red face

Sounds like you best get that pressure gauge and start at the carb and work back to the pump itself. FWIW, an electric fuel pump can be "working", that is, pulsating but still not be delivering any pressure, typically because it is wired backwards. Damhikt.
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Old 12-16-2014, 03:39 PM
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Alright! Thank you all for your good advices. I solved the problem today, but might have been creating a new one

So I was about to get a fuel pressure gauge, but reluctantly, as I did check meticulously every connection and I would have bet my life I had no leak whatsoever. Also, all was plugged right, and clean, and new. I knew for a fact the issue wasn't the carb (I cleaned it like a freak, spent hours on it, rebuilt it with new parts), or the filter, or the pump, or the tank, or the fuel lines,.... which leaves nothing, right?
But what triggered the solution is the visit to my boat of a neighbor who also happens to be a very experienced mechanic: despite anything I could say, is answer was: fuel pump. I told him I tried 3 different fuel pumps and had the current one cycling all night in my garage, he was sticking to his guns: it is fuel pump related. He said, somehow, the fuel pump isn't doing its job. I didn't get it as fuel was coming out of the fuel pump when turning on the engine, but at that point, I figured I had nothing to lose trying to go his way.
So I figured that if the fuel pump was good but not working good... (lots of thinking there)... it had to do with the fuel pump power supply. I looked further into it, shook the connection to the oil pressure safety switch... and the plug from the OPSS came with the wire, all corroded from the inside!! Very excited at that point as I had the perfect culprit, I wired my pump directly to my battery with a clamp and started the engine: purring like a newborn kitten. 1 minute. 2 minutes. 10 minutes. 30 minutes. It was a bad OPSS connection. That simple, and I had replaced the WHOLE fuel supply system...
BUT, I still have some questions to be answered, and also need to find a proper fix:

1- As it was, obviously, an electrical issue (the fuel not getting power), how come that the fuel pump was still spitting gas when I was turning on the engine? With the fuel line disconnected from the carb, I was getting a full cup of fuel in like 2 seconds from the fuel pump just by starting the engine. Without starting the engine, no fuel was coming out of the fuel pump. For me, this meant that the fuel pump was getting power and working. Obviously, it wasn't. So what the ..? I don't understand that part.

and 2 - How should I solve this issue cleanly? I currently have a very hardcore solution: I connected a wire to the pump wire, turned the ignition on, and went around looking for a hot spot with my wire. I got a spark somewhere, so I attached my wire there and done. Obviously, this isn't exactly a "by the book" solution, so... What should I do?
I know that the real "by the book" solution would be to replace the OPSS. However, here is the thing: this thing is like soldered into the engine block by 30 years of rust and corrosion. It looks like a really bad idea to try to take it out, if it is even possible (and a very poor access doesn't make it easier). And I am very, very weary of creating new issues where there currently isn't any (I can see it coming: oil leak, or damaged threading so I can't put a new one in, etc...). So, I am looking for a way to bypass this OPSS. Where is a good place to connect my pump to (if not to the OPSS)? And I know the USCG requirements is to have an OPSS, but I am not going to go that road, for the above mentioned reason. So, what's the next best solution?

Thank you all for your help so far, and your help to come! Today is a happy day, my boat is running again!
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Old 12-16-2014, 03:55 PM
damienk damienk is offline
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And 2 thumbs up for john Cookson who got it right thanks!
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Old 12-16-2014, 04:01 PM
damienk damienk is offline
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And also: this forum is awesome and people here are great, and I don't even count the times I came here looking for answers in the past, although it is the first time I actually post about my own issue. So thanks, again.
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Old 12-16-2014, 04:32 PM
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I believe there are three places on the carb side of the A-4 that give you access to the oil pressure passages, the term is escaping me. One forward of the flame arrester, one midway behind the carb and one over the oil pressure adjustment. I believe any of them can be used for the OPSS.
Dan S/V Marian Claire
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Old 12-16-2014, 04:57 PM
JOHN COOKSON JOHN COOKSON is offline
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damienk
Is there a wire that is co joined to the wire that goes to the fuel pump that goes around to the starter motor?
Late model engines had this feature so the fuel pump & carb will prime while the engine is being cranked.

Someone will have a picture for you R\E optional OPSS locations.

TRUE GRIT
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Old 12-16-2014, 05:08 PM
JOHN COOKSON JOHN COOKSON is offline
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And One More Thing

I want to take the opportunity to remind when trouble shooting electrical devices it is important to check the device AND the associated electrical circuit.

TRUE GRIT
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Old 12-16-2014, 09:32 PM
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Exclamation

John, exactly.

damien, You solve it by installing a mechanical fuel pump..
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Old 12-16-2014, 11:49 PM
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+1 with Shaun on the mechanical pump.

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