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Old 07-30-2011, 11:09 AM
formosa formosa is offline
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Lt1 external fuel pump issues

Hi,

I just replaced my 95 LT-1 external fuel pump with the Carter cross reference. The boat ran for 1 minute or so then died. I could not get it to restart. Not having a gauge, I pulled the fuel filter to see if the pump was putting fuel into a bucket. It was not. I then disconnected and blew out all the fuel lines from the tank to the pump. All were clear, did not see any junk. Pump ran during key on, but nothing pulling from the tank - not priming.

Thinking I had a "leak" pulling air which would prevent the pump from priming, either in the return system (either at the stainless return connection into the pump) or the return line back into the tank - pulled both and I put my finger over both fittings (the threaded and the barbed) that go into the pump return inlet, and wha-la the pump then immediately pulled from the tank and put fuel into the bucket.

I spent hours on this - if the return connections are "plugged" at the pump - the pump and the motor run - if the return side is hooked up into the pump - the motor doesn't prime and get any fuel and it's evident when looking at the in line clear fuel filter coming from the tank (doesn't fill up with gas). Continuing on, put the return side directly back into the tank and plugged the return "inlet" on the fuel pump and the motor ran - up to 3,000 rpm.

I'm obviously not going to run the boat like this....

The question is how can this pump design work in the first place, when it simply will pull air from the return side and therefore never build up any suction to pull gas from the supply side of the tank? I get that the return side should in theory put fuel back into the pump directly - and the return line into the tank simply be an overflow --- but that ain't happening. I just don't see how this little pump will prime from the tank in 1-2 seconds when it will just pull air from the return line. If it's just pulling from the tank line it primes immediately.

My limited knowledge only comes up with three possibilities - 1. The new pump is too weak to pull from the tank unless it has complete suction - so it's a bad pump (1 minute old). 2. The return system has an issue (I lost a check valve or something when disconnecting the old one?) 3. It's something else entirely.

Hours on this and the boat was (I thought) ready to launch after a year out of the water.

Can someone please sanity check me that the return side is used as an input to this fuel pump? And there is no check valve on the return side to keep the pump from pulling air from the return side? Thanks much.
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  #2  
Old 07-30-2011, 01:44 PM
formosa formosa is offline
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Update. Yes, I confirmed with the mechanic at the dealer's that the return side from the engine is part of the loop and I didn't just hook something up very wrong. After I went through the 5 minute explanation --- he took out his Indmar pump and blew into the fittings clearly one side had a check valve or didn't pass air (thus would cause suction and enable the prime). This was not the case on my Carter pump from NAPA - both openings at the bottom of the pump passed air in either direction.

Then the idea of putting in a check valve into the return line itself .... went to West Marine and bought an anti siphon valve and put it inline into the return line to the tank. Hooked everything up to the pump as designed (engine return back to the pump, et al). Wha la, the engine primed, started and ran no issue (with fuel). It's now overheating but that's a separate issue.

When my boat was stolen the return line was "cut" to drain all the fuel when it was sunk ... was there originally an anti siphon on the return line and the priming issue only showed up when putting in the Carter vs. Indmar pump. Bottom line it's working now.
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Old 09-11-2011, 09:33 PM
mmthorn mmthorn is offline
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Interesting. Was your pump mounted to the block? Did the return line from the TBI/MFI enter a Y-fitting (with a check on one of the branches) or did it enter the block on the engine and exit in two places (again....was there a check valve in this block)?

I have a pump with two inlets and while I don't think I have your problem I think you are correct that there must be a check valve to keep the pump from drawing air from the return line to the tank. I am not sure where the check valve is.
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Old 09-13-2011, 09:17 AM
mmthorn mmthorn is offline
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Took the pump off my 1998 Maristar and talked to a tech at my local mastercraft dealer. There is one inlet and two outlets to these pumps. It appears at first glance that there are two inlets but the angled port (at the bottom) returns air/bubbles in the line to the tank. There is a check valve in this port to keep the pump from drawing air during operation.
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Old 09-13-2011, 09:25 AM
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JimN JimN is offline
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Quote:
Originally Posted by formosa View Post
Update. Yes, I confirmed with the mechanic at the dealer's that the return side from the engine is part of the loop and I didn't just hook something up very wrong. After I went through the 5 minute explanation --- he took out his Indmar pump and blew into the fittings clearly one side had a check valve or didn't pass air (thus would cause suction and enable the prime). This was not the case on my Carter pump from NAPA - both openings at the bottom of the pump passed air in either direction.

Then the idea of putting in a check valve into the return line itself .... went to West Marine and bought an anti siphon valve and put it inline into the return line to the tank. Hooked everything up to the pump as designed (engine return back to the pump, et al). Wha la, the engine primed, started and ran no issue (with fuel). It's now overheating but that's a separate issue.

When my boat was stolen the return line was "cut" to drain all the fuel when it was sunk ... was there originally an anti siphon on the return line and the priming issue only showed up when putting in the Carter vs. Indmar pump. Bottom line it's working now.
The anti-siphon is supposed to be placed at the pump, in case the fuel line is cut. It's not a high pressure device, so I'm not sure I would use this if it was my boat. The OEM pump was a Chrysler part, IIRC.
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Old 09-13-2011, 05:21 PM
Jorski Jorski is offline
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Boat: 1993 190 with LT1
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Here is a source for replacing that pump...much cheaper than M/C or skidim:

http://bpi.ebasicpower.com/c/INDFP/Fuel+Pumps+Indmar



This is for the LT1 only.
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Old 09-14-2011, 10:29 PM
mmthorn mmthorn is offline
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I wonder if the ebasicpower part would also work on the TBI. I spoke with my mastercraft parts guy and he said they only have one p/n for the MFI and the TBI. This is possible because the fuel pressure regulator handles controlling the pressure/flow.
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Old 09-14-2011, 10:48 PM
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_fng_ _fng_ is offline
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Quote:
Originally Posted by Jorski View Post
Here is a source for replacing that pump...much cheaper than M/C or skidim:

http://bpi.ebasicpower.com/c/INDFP/Fuel+Pumps+Indmar



This is for the LT1 only.
I put that model in my TBI and haven't had issue with it yet *knocks on wood*
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