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Old 09-07-2013, 03:52 PM   #1
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Fuel-pump pressure on 8.1 Liter V-8 gas.

I have a Itasca 38J with a 8.1 Liter GM gas V8 engine. We recently returned from a 5978 mile road trip. During the trip I experienced a lack of power when pulling a grade so upon our return I sought the advice of a well-respected local mechanic. After extensive testing he told me the fuel-pump was not producing the required pressure, that it was 6 pounds low. He says a new pump is about $450.00 and labor is $375.00 since the pump is located in the fuel tank. My question is this: Is it possible to install a "external fuel pump" in order to boost the pressure? David S.
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Old 09-07-2013, 04:01 PM   #2
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You should post this in the Workhorse Chassis forum for the best results. I don't know the answer to your question.
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Old 09-07-2013, 04:06 PM   #3
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We had a Newmar KS with the 8.1 and the fuel pump had to be replaced about the middle of our 3500 mile trip. I wish my bill was $450 plus $375 labor as I paid about $1100 for the same thing----the coach had very weak power.

I think your mechanic is charging a very fair price. If it were me, I would pay his price and have it done. JMHO
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Old 09-07-2013, 04:39 PM   #4
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Quote:
Originally Posted by David S View Post
I have a Itasca 38J with a 8.1 Liter GM gas V8 engine. We recently returned from a 5978 mile road trip. During the trip I experienced a lack of power when pulling a grade so upon our return I sought the advice of a well-respected local mechanic. After extensive testing he told me the fuel-pump was not producing the required pressure, that it was 6 pounds low. He says a new pump is about $450.00 and labor is $375.00 since the pump is located in the fuel tank. My question is this: Is it possible to install a "external fuel pump" in order to boost the pressure? David S.
The pressure "at the rail" should be ~58 to 62 PSI for normal operation. What is yours??? Are you sure the lack of performance was not due to altitude?

The price and part number of the pump is different for some model years. Depending on your chassis year you may require at Workhorse only pump, or you may be able to use an aftermarket pump at much lower price. Pump replacement does require dropping the tank.

I've not heard of anyone adding a secondary pump as a "booster". I'm not sure how that would work in a fuel system that returns excess fuel to the tank....
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Old 09-08-2013, 10:11 AM   #5
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I've been using an external boost fuel pump on my diesel for 8 years now. Got it at NAPA. With the plumbing and extra fuel hose, it came to under $100. Found an ign wire at the engine to power it.

Have friends with gas engines that use them too. Saves the expense and time of dropping the tank.

The fuel return system is separate and doesn't seem to be bothered by an external fuel pump.
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Old 09-11-2013, 11:03 AM   #6
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Thank You very much. I am going to look into this right away. David S.
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Old 09-11-2013, 11:20 AM   #7
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Quote:
Originally Posted by David S View Post
I have a Itasca 38J with a 8.1 Liter GM gas V8 engine. We recently returned from a 5978 mile road trip. During the trip I experienced a lack of power when pulling a grade so upon our return I sought the advice of a well-respected local mechanic. After extensive testing he told me the fuel-pump was not producing the required pressure, that it was 6 pounds low. He says a new pump is about $450.00 and labor is $375.00 since the pump is located in the fuel tank. My question is this: Is it possible to install a "external fuel pump" in order to boost the pressure? David S.
And the Number one problem with ele fuel pumps is? The owners allowing the fuel level to get very low thus not giving enough fuel in the tank to keep the pump from getting hot. Yes, I'm a ASE Cert Gm Parts Guy and the best way to keep them pumps alive is to keep the tanks at least half full and make darn sure its good fuel as well. Not only have i been around a lot of this, I also owned a Towing Company (Wrecker Service) Up in Michigan for over 12 years plus 13 years working for the other guy before that. This affects anything with fuel injection gas powered auto/truck, bottom line, never ever run the fuel level below a quarter of a tank. Good Luck Y'all.
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Old 09-11-2013, 12:31 PM   #8
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Originally Posted by Jim_HiTek View Post
I've been using an external boost fuel pump on my diesel for 8 years now. Got it at NAPA. With the plumbing and extra fuel hose, it came to under $100. Found an ign wire at the engine to power it.

Have friends with gas engines that use them too. Saves the expense and time of dropping the tank.

The fuel return system is separate and doesn't seem to be bothered by an external fuel pump.
JIM: on Workhorse chassis since 2004 the "excess" fuel is returned to the tank at the filter, which is inside the chassis rail and very close to the tank. I can't imagine where there is room to install an aux. pump to boost the pressure prior to the return. Are you saying a pump between the return and the engine a workable solution for front engine gassers?
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Old 09-12-2013, 12:29 AM   #9
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JIM: on Workhorse chassis since 2004 the "excess" fuel is returned to the tank at the filter, which is inside the chassis rail and very close to the tank. I can't imagine where there is room to install an aux. pump to boost the pressure prior to the return. Are you saying a pump between the return and the engine a workable solution for front engine gassers?
Without seeing what your talking about, I can't address your question directly. The pump wouldn't have anything to do with the return line. Except indirectly. Unless I misunderstand you.

Of course I'm not familiar with every RV out there, but, the rigs I am familiar with that have installed external fuel pumps didn't have a problem finding an appropriate place to mount them. After all, they are only 2" in diameter and 3.5" long. In my case, I had to add 6' of fuel hose in order to mount the external pump to a frame rail in a convenient place. Placed it where I could actually see it. Then, since the inlet and outlet were smaller diameter then the fuel line, had to adapt it with brass fittings.
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Old 09-12-2013, 02:18 AM   #10
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Have you cleaned the MAF sensor and replaced the air filter? Had a similar problem with loss of power and surging on my 8.1. Runs like a champ now.

You shouldn't have to add any extra pumps.
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Old 09-12-2013, 05:39 AM   #11
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Get a second opinion on the fuel pressure. It should not even run down the road at 6psi.

joe
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Old 09-19-2013, 12:37 PM   #12
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I believe the OP said the fuel pressure was six pounds low, not six pounds total. This must be low enough to cause performance problems if the mechanic is correct.

If it were me, I would remove the in-tank pump and leave just a pickup tube, and then install a fuel pump on the rail where it can be reached easily. Then, any future pump problem can be fixed within a small fraction of the time and expense compared to the in-tank placement, which I dislike for those reasons.
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Old 09-19-2013, 01:41 PM   #13
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Six pounds below minimum is probably not the fuel pump. It may be the fuel pressure regulator which is located on the rear of the intake manifold at the end of the fuel rail. The regulators usually have a failure in the diaphram which allows fuel to leak past the seal into the vacuum hose on the regulator. This will cause fule to run down that hose into the intake manifold flooding the # 8 cylinder. The computer sees this as a rich mixture situation and starts reducing the ammount of fuel injected intothe cylinders to compensate. This causes lack of power, missfiring, and occaisonal pinging on grades and heavy acceleration. This also cuases teh pump to put out maximum pressure to try to compensate for low rail pressure, but the regulator continues to leak off the fuel. Vicious circle. To check you neeed to remove the dog house(engine cover) inside you coach, locate the pressure regulaotr, it looks kinda like a miniture brae booster, or bell. that has a vacuum line sitting at the top of it. Pull off the vacuum line and turn the key on without starting the engine. If you see fuel dripping out of the port on the regulator the seal inside has gone bad and what I have described is happening. Repalce the regulaotr and all should be fine.
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