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| Fuel pressure gauge acting wierd. https://slantsix.org/forum/viewtopic.php?t=27083 |
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| Author: | Sam Powell [ Sat Feb 09, 2008 6:21 am ] |
| Post subject: | Fuel pressure gauge acting wierd. |
The Dart has a sending unit fuel pressure gauge which registers in the dash. Until a few days ago, when I went to start it, I would flip the fuel pump switch, and you could watch the fuel pressure build. When it got to 40lbs I would turn the key, and it would start, most of the time on the first or second try. Once in awhile, I would goof up the procedure, and it would take some cranking. But that is another story. Now, when I flip the switch for the fuel pump, I hear the pump running, and hear its pitch go down as it gets up to pressure, but the fuel pressure gauge does not move. Then when I crank it, and it fires, the fuel pressure gauge jumps up to 40lbs at idle. So what gives here? Could the engine start with zero fuel pressure? It seems not. And if it is not registering any pressure while cranking, why does it work fine once it starts? Any thoughts about diagnostics here? I could put the mechanical gauge back in the line under the hood, and see if that is registering pressure. I am just wondering if there has been an inconsistancy in fuel pressure that has added to its quirky starting behavior. While it is driving, the fuel pressure indicated on the gauge is exactly what you would expect. The pressure goes up as vacuum goes down. I have been thinking about building a new fuel tank set up to eliminate the surge tank, but will bring that up in another thread later. Sam |
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| Author: | Pierre [ Sat Feb 09, 2008 5:41 pm ] |
| Post subject: | |
It may do that if the sender is sticking. May need a couple seconds of pressure until it unsticks? What happens if you just power up the pump and run it continuously without the engine? Jumper the pump straight to the battery. If it registers no pressure while cranking and cranking.... do you have the gauge power ran to an always on source or on only in run? |
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| Author: | emsvitil [ Sat Feb 09, 2008 5:43 pm ] |
| Post subject: | |
I think you could test for a sticky sender by giving a tap with a wrench.............. |
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| Author: | Sam Powell [ Sat Feb 09, 2008 7:36 pm ] |
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I THINK the gauge is powered by the same source as the pump. I will check that. Thanks for the thoughts. I assume the answer to "will it start with no pressure?" is no. Sam |
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| Author: | Pierre [ Sat Feb 09, 2008 10:37 pm ] |
| Post subject: | |
Sam without any pressure I don't think any fuel will come out the injectors. Pulse widths in the ms range, I doubt gravity will have time to pull any fuel thats left in the rail through the tiny injector openings. If the gauge is powered from same source as the pump I would expect it to show pressure during cranking unless theres some sort of warmup time needed by the sensor/gauge, its sticking, or maybe draw from the starter causes voltage to drop low enough the gauge shuts down? The fuel pump will keep running, although at a slower pace, if voltage dips however the gauge may have electronics that implicitly/explicitly shut it down if incoming voltage is too low. |
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| Author: | 65Dodge100 [ Sun Feb 10, 2008 11:07 am ] |
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I noticed in another thread that you said your surge tank goes dry sometimes. Is there any chance that the pressure gauge sender is in a pocket of trapped air until the engine sucks it up or the pressure reaches a limit where the regulator relieves it into the return line? I’m thinking if something is wrong that is allowing air into the system after shut-down, from the return line or the surge tank, maybe the pressure sender doesn’t pick up air pressure. Maybe it could cause some flaky cold starts also. Danny |
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| Author: | Sam Powell [ Sun Feb 10, 2008 7:29 pm ] |
| Post subject: | |
I am thinking the same thing. I was wondering if a low pressure electric pump could be installed in the rear to supply the surge tank, but this seems like too many band aids to me. In another thread I am discussing a new tank assembly to eliminate the need for the surge tank. Sam |
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| Author: | Matt Cramer [ Mon Feb 11, 2008 12:08 pm ] |
| Post subject: | |
Quote: I am thinking the same thing. I was wondering if a low pressure electric pump could be installed in the rear to supply the surge tank...
That is more or less what I have on my Dart. It is unnecessarily complicated and I may go to a single in-tank pump or sumped tank in the future.
Sam |
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