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Old 03-11-2016, 03:21 AM
Thaiwake Thaiwake is offline
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Fuel system re-design problem MCX

I had another fuel pump pack up on my 2004 X Star with 5.7l MCX. I am in Thailand and wanted to see if I could get a replacement pump here. My mechanic told me the current system was bad with the pump in the tank. I can certainly agree with him there but I don't like what he has done as a replacement.

He took a fuel pump, I think from a Lexus that sits outside the tank. He has bypassed the entire fuel module and taken a hose from the tank to the pump then to a fitler and into the injector rail.

I am now getting over 100PSI pressure at the rail which is way too much, it should be 53-58PSI.

He says it doesn't matter if there is too much pressure as the ECU will only demand what is needed and will send the excess fuel back into the tank.

I haven't run it much as I don't trust the system but I ran the engine out of gear to hear how it runs. It seems fine at low RPM's but above 4000RPM the engine starts popping like there is a lack of fuel. It doesn't sound good and can't get the power over 5000rpm. Pulled the plugs and they are black and sooty like it is running rich.

I think he should have at least included the fuel pressure regulator at the top of the tank. Would this help reduce the pressure??? If I did this with a pump outside the tank, I would have to drill another hole in the top of the fuel module, run a line into the pump from the tank, then out of the pump back into the fuel pressure regulator on the module then from the module to a filter and into the injector rails.

I know it is a pretty cowboy system but not sure I want to go back to the original design as the pump fails too regularly.

Any suggestions or advice would be appreciated.

Thanks
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  #2  
Old 03-11-2016, 07:48 AM
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CantRepeat CantRepeat is offline
 
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He did this without consulting you first? I wouldn't have let him touch it.
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  #3  
Old 03-11-2016, 11:08 AM
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mikeg205 mikeg205 is offline
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no the ECU does not regulate the fuel pressure the fuel pressure regulator does.. at 100psi you will be running way rich.. at minimum you need to get a fuel pressure regulator to get that pressure down... he prolly bypassed the regulator and that is why pressure not sitting where its supposed to be.
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Old 03-11-2016, 11:43 AM
KyleNowad KyleNowad is offline
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Sounds like he shouldn't be your mechanic.
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  #5  
Old 03-11-2016, 12:27 PM
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JimN JimN is offline
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Quote:
Originally Posted by Thaiwake View Post
I had another fuel pump pack up on my 2004 X Star with 5.7l MCX. I am in Thailand and wanted to see if I could get a replacement pump here. My mechanic told me the current system was bad with the pump in the tank. I can certainly agree with him there but I don't like what he has done as a replacement.

He took a fuel pump, I think from a Lexus that sits outside the tank. He has bypassed the entire fuel module and taken a hose from the tank to the pump then to a fitler and into the injector rail.

I am now getting over 100PSI pressure at the rail which is way too much, it should be 53-58PSI.

He says it doesn't matter if there is too much pressure as the ECU will only demand what is needed and will send the excess fuel back into the tank.

I haven't run it much as I don't trust the system but I ran the engine out of gear to hear how it runs. It seems fine at low RPM's but above 4000RPM the engine starts popping like there is a lack of fuel. It doesn't sound good and can't get the power over 5000rpm. Pulled the plugs and they are black and sooty like it is running rich.

I think he should have at least included the fuel pressure regulator at the top of the tank. Would this help reduce the pressure??? If I did this with a pump outside the tank, I would have to drill another hole in the top of the fuel module, run a line into the pump from the tank, then out of the pump back into the fuel pressure regulator on the module then from the module to a filter and into the injector rails.

I know it is a pretty cowboy system but not sure I want to go back to the original design as the pump fails too regularly.

Any suggestions or advice would be appreciated.

Thanks
First, ALL fuel injected cars and trucks have the pump inside of the tank because it provides the proper pressure & volume and prevents vapor lock. The reason pumps in boats fail is because the Coast Guard won't allow non-vented tanks. If it was sealed the way cars and trucks are, with vapor recovery, few of the pump failures we see would have happened.

Water/other contaminants and the low profile cause the failures, not the design. If they could have a bladder in the tank or if the tank was tall/narrow, I doubt we would see the failures- when the fuel sloshes, it can leave the chamber where the pump is housed and running it dry kills the pump.

If you have run the tank dry, you need to know that this is the main reason these pumps fail. The fuel cools the impeller.

As far as the mechanic- RUN!

Excessive pressure DOES matter.
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Old 03-11-2016, 01:13 PM
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mikeg205 mikeg205 is offline
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Quote:
Originally Posted by JimN View Post
First, ALL fuel injected cars and trucks have the pump inside of the tank because it provides the proper pressure & volume and prevents vapor lock. The reason pumps in boats fail is because the Coast Guard won't allow non-vented tanks. If it was sealed the way cars and trucks are, with vapor recovery, few of the pump failures we see would have happened.

Water/other contaminants and the low profile cause the failures, not the design. If they could have a bladder in the tank or if the tank was tall/narrow, I doubt we would see the failures- when the fuel sloshes, it can leave the chamber where the pump is housed and running it dry kills the pump.

If you have run the tank dry, you need to know that this is the main reason these pumps fail. The fuel cools the impeller.

As far as the mechanic- RUN!

Excessive pressure DOES matter.
amen...
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  #7  
Old 03-11-2016, 09:47 PM
Thaiwake Thaiwake is offline
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Thanks for the replies guys. Yeah thought as much, will have to order a new in tank pump from the states and go back to the original system. I am out in the sticks here in Thailand and the choice of mechanics is pretty limited. Thank God this forum is here so I can speak to you guys
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  #8  
Old 03-11-2016, 10:31 PM
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osmonet osmonet is offline
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Quote:
Originally Posted by Thaiwake View Post
Thanks for the replies guys. Yeah thought as much, will have to order a new in tank pump from the states and go back to the original system. I am out in the sticks here in Thailand and the choice of mechanics is pretty limited. Thank God this forum is here so I can speak to you guys
We need pictures of you jumping over siamese crocodiles or something.
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  #9  
Old 03-12-2016, 01:41 AM
Thaiwake Thaiwake is offline
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haha, thankfully no croc's but the jellyfish can help to keep you up on the board that's for sure

Got another question if you guys can help:

I just went down to review some of the other work the mechanic has done and there was another thing that didn't sit right with me. Next to the battery isolator switch there is a small square black box that I think is the voltage regulator. There are 2 red wires on either side that go to the battery switch and a black wire that comes from the middle pin on the box. This black wire was detached from the engine and I didn't know where it came from. The mechanic told me I don't need it and to leave it detached. Now I am starting to question his wisdom, to be fair the engine was running ok without it but I would like to know where it is supposed to attach to??

I think it might come from the alternator but not 100% sure and also not sure if it goes to the positive or negative terminal. Can you guys enlighten me?
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  #10  
Old 03-12-2016, 03:28 AM
chrislandy chrislandy is offline
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He sounds like a butcher rather than a mechanic
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