Looking for confirmation that I need a new fuel pump
06-25-2011, 08:25 PM
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Looking for confirmation that I need a new fuel pump
Greetings,
As I'm writing this I'm realizing I just should buy a new fuel pump, but what the hell, I'll ask anyway.
Background:
Twin 1991 Mercruiser 320 5.7L EFI engines. Both have been sitting for three years. Starboard engine is in the shop being rebuilt. While it's there, i'm trying to get the port side engine going.
Assume I've done everything you'd do to prepare an engine to start after sitting three years, including evacuating all of the old fuel from the tank, and replacing the fuel filter. When I first tried to start it, the fuel pressure sensor was leaking. So I replaced it with the one that was on the starboard engine, just to see if I could get it to run.
The engine starts, and runs for about 5 seconds. Actually sounds pretty good. Not a rough idle. But after five seconds it dies. I can turn the igntion off, then back on, wait 15 or 20 seconds, start again, and it does exactly the same thing. I can also throttle it up, and start it (after waiting) and it revs right up, then slowly dies. It takes about 4 or 5 seconds for it to die. This is totally repeatable, over and over. If it had a carb, I'd say the float was sticking because that's exactly how it behaves - like it's running off of the fuel in the bowl, but can't get more.
I took the fuel line off of the electric pump. When I turn the key on, no fuel comes out (I gather this is normal). When I start it, fuel does come out, but not the amount I would expect. At least not the amount I'm used to seeing from a mechanical pump. It just sort of burbles out while the engine is being turned over.
Next I checked the pressure. I turn the key on, wait a full minute, then turn the engine over. When the key is on and the engine is not turning, there is no pressure. When I turn it over, the pressure runs up to about 30, and it starts, and then you see the pressure start falling (after a few seconds) and as it falls, the engine dies.
So I'm guessing this is a fuel pump problem, especially since it's had gas sitting in it for three years. Am I right? I'm also kind of wondering if the pressure sensor or the pressure regulator play into this kind of problem. I don't know what those two devices do (other than what their name implies).
This was the pump I was thinking of getting. I don't need high performance, I just need it to be a decent pump:
http://www.offshoreonly.com/classifi...o35544-en.html
Thanks for any and all advice/comments!
Stan
As I'm writing this I'm realizing I just should buy a new fuel pump, but what the hell, I'll ask anyway.
Background:
Twin 1991 Mercruiser 320 5.7L EFI engines. Both have been sitting for three years. Starboard engine is in the shop being rebuilt. While it's there, i'm trying to get the port side engine going.
Assume I've done everything you'd do to prepare an engine to start after sitting three years, including evacuating all of the old fuel from the tank, and replacing the fuel filter. When I first tried to start it, the fuel pressure sensor was leaking. So I replaced it with the one that was on the starboard engine, just to see if I could get it to run.
The engine starts, and runs for about 5 seconds. Actually sounds pretty good. Not a rough idle. But after five seconds it dies. I can turn the igntion off, then back on, wait 15 or 20 seconds, start again, and it does exactly the same thing. I can also throttle it up, and start it (after waiting) and it revs right up, then slowly dies. It takes about 4 or 5 seconds for it to die. This is totally repeatable, over and over. If it had a carb, I'd say the float was sticking because that's exactly how it behaves - like it's running off of the fuel in the bowl, but can't get more.
I took the fuel line off of the electric pump. When I turn the key on, no fuel comes out (I gather this is normal). When I start it, fuel does come out, but not the amount I would expect. At least not the amount I'm used to seeing from a mechanical pump. It just sort of burbles out while the engine is being turned over.
Next I checked the pressure. I turn the key on, wait a full minute, then turn the engine over. When the key is on and the engine is not turning, there is no pressure. When I turn it over, the pressure runs up to about 30, and it starts, and then you see the pressure start falling (after a few seconds) and as it falls, the engine dies.
So I'm guessing this is a fuel pump problem, especially since it's had gas sitting in it for three years. Am I right? I'm also kind of wondering if the pressure sensor or the pressure regulator play into this kind of problem. I don't know what those two devices do (other than what their name implies).
This was the pump I was thinking of getting. I don't need high performance, I just need it to be a decent pump:
http://www.offshoreonly.com/classifi...o35544-en.html
Thanks for any and all advice/comments!
Stan
06-25-2011, 09:13 PM
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Three years sitting and I'll bet you have build up in every place in the system. If a blended gas was left to sit for a few months you may have the same issues, as I did. I would suggest pulling some fittings and inspecting them to rule that out first. If you find that you have some build up run a cleaner through as much as you can. You can push it through with air. I would check it well before making the assumption of a fuel pump. I am a bit limited on the mechanics side but I seem to remeber the the EFI requires 8 psi sustained or it will code out. I do not know if it will shut you down but others will chime in and help you with the details on that. Start with the feed side to the EFI and clean clean clean!
06-27-2011, 09:00 AM
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Thanks for the advice. Yes I agree about the fuel pump. I don't any evidence of buildup, but I'm running seafoam through there anyway. The service manual says I need at least 35 psi on the fuel lines.
But I have other suspicions about what is going on now.. I also have no/low oil pressure. I thought the problem was the gauge. But now I think the ECU could be detecting a "no oil pressure" condition and shutting the engine down. So I've got to resolve the oil pressure issue first. There was sludge in the oil when I changed it (I bought this boat used). The previous owner claimed he did regular oil changes, so I don't know how the sludge got there. Maybe from sitting for three years. I'm going to clean out the engine and oil cooler good and put on a mechanical oil pressure gauge and make sure I've got oil pressure before moving further.
The starboard engine is in the machine shop. I'm half tempted to just pull this one and take it down there too.
But I have other suspicions about what is going on now.. I also have no/low oil pressure. I thought the problem was the gauge. But now I think the ECU could be detecting a "no oil pressure" condition and shutting the engine down. So I've got to resolve the oil pressure issue first. There was sludge in the oil when I changed it (I bought this boat used). The previous owner claimed he did regular oil changes, so I don't know how the sludge got there. Maybe from sitting for three years. I'm going to clean out the engine and oil cooler good and put on a mechanical oil pressure gauge and make sure I've got oil pressure before moving further.
The starboard engine is in the machine shop. I'm half tempted to just pull this one and take it down there too.
