How many fuel pumps?

[Channing]

I have a 1987 Holiday rambler aluma-lite XL 27 ft motorhome. I have a mechanical fuel pump. Do I also have an electronic fuel pump in the tank? I went under the motorhome under the tank had my wife turn the key I heard nothing turn on. Does that automatically mean I don't have one? From what I read online it seems to be true. But couldn't there be one in there that's not working? Makes sense right? I do not have a fuel pressure sending unit with a positive and negative terminal that I can bypass to see if I could hear it come on in the tank. I have a oil pressure switch which is a plug with a single wire coming out of it. Does that mean I don't have one in the tank? I've got about six wires coming out of the tank area don't know which color wire it would be. Just want to know if there's a way I could tell. Is it the length of the motorhome? Do longer ones you need an extra pump? Is it too far for just a mechanical pump to be able to pull it all the way up to the carburetor? is mine long enough to where it needs one or not? Please help.

[Nick-B]

With 6 wires coming from the gas tank you most likely have a pump back there.
Just to help others give relevant help, which engine/chassis do you have under your HR motorhome?

[Channing]

Originally Posted by Nick-B

With 6 wires coming from the gas tank you most likely have a pump back there.
Just to help others give relevant help, which engine/chassis do you have under your HR motorhome?

454 - 7.4
As far as I know it's a p-30
I put a new mechanical fuel pump on last night. Still getting no fuel to the carburetor.

[Channing]

???

[Lowflyer1]

Originally Posted by Channing

454 - 7.4
As far as I know it's a p-30
I put a new mechanical fuel pump on last night. Still getting no fuel to the carburetor.

All the fuel pump/senders I worked on at Ford in the 90s had a tank mounted fuel pump/sender assembly and 2 set of wires: 2 for fuel level sender and 2 for the pump. These were continuous flow systems to also cool the pump as well as the fuel rail. So two fuel lines also.
Not sure about your engine of that era.

[amosnandy]

Originally Posted by Channing

I have a 1987 Holiday rambler aluma-lite XL 27 ft motorhome. I have a mechanical fuel pump. Do I also have an electronic fuel pump in the tank? I went under the motorhome under the tank had my wife turn the key I heard nothing turn on. Does that automatically mean I don't have one? From what I read online it seems to be true. But couldn't there be one in there that's not working? Makes sense right? I do not have a fuel pressure sending unit with a positive and negative terminal that I can bypass to see if I could hear it come on in the tank. I have a oil pressure switch which is a plug with a single wire coming out of it. Does that mean I don't have one in the tank? I've got about six wires coming out of the tank area don't know which color wire it would be. Just want to know if there's a way I could tell. Is it the length of the motorhome? Do longer ones you need an extra pump? Is it too far for just a mechanical pump to be able to pull it all the way up to the carburetor? is mine long enough to where it needs one or not? Please help.

When you say you have a mechanical fuel pump, you mean one that bolts to the side of the engine, and has a rod or lever that operates off the camshaft? Correct?

If the engine is original, it should have a throttle body injection. It looks like a carburetor but instead of sucking gas through jets, it directly sprays fuel into the venture. The normal pressure for a TBI should be at least 13 psi, but some of the bigger motors on trucks had up to 30 PSI. It will not have the 50psi that a rail type fuel injection has. The mechanical pump has a vacuum line to it that regulates the pressure.

On a rig like yours, you may also have a pump in the tank.

If I was upgrading this, I would eliminate the mechanical pump. You can buy a cover plate that covers the whole where the mechanical pump goes.

How hard is it to drop the tank? If it has an electric fuel pump it will install from the top. With the tank out, pull the fuel pump out, make note of where all the wires go, especially the + and - for the pump. It should be pretty obvious, as one should go to ground near the tank and the hot runs off into nowhere land. Blow it off well so there is no gas in or around it. Apply 12v to the positive and negative, just for a couple seconds. You should hear it start and run. If it runs but you don't think it is pumping, you can just put it in a bucket of water, an ice cream bucket works well, apply power and see if it pumps. You need to clean it well to make sure you get all the water out before you reinstall it. I use carburetor cleaner But to be honest, on a rig that old, if it has an in tank pump I would replace it. They are like $50.

If you don't have an electric pump in the tank, and it just has pickup tubes going in for fuel, it should have a round plate on the top. This is also the fuel level float. Pull it out and make sure nothing is plugged and clean it good.

Now that you have gotten that far, and eliminated the mechanical pump, either way I would put an electric fuel pump in it. It just goes in the line. Make sure you get one for the TBI not the injection type as they have too high pressure. You can put it anywhere in line, but I like to keep them close to the fuel tank, down on the frame rail somewhere that is protected. Then you just need to find a hot wire that comes on with the ignition. If you check your fuse block, there is probably an extra slot for more fuses. You might have to take the fuse block off to make a connection on the back, but many will already have an empty spot marked "Ignition" with a spade connector under it. Make sure it is fused. The aftermarket in line pump should have a built in regulator, so when it get the 13psi you need it shuts down. I also recommend putting it on the tank side of any filters it either has or you install.

We do this kind of install all the time on hot rods, old cars, classics. It is very dependable

[Gary RVRoamer]

The Chevy P30 chassis manual should answer your questions. Get a free one at

https://www.gmcmi.com/wp-content/upl...sis-Manual.pdf


You could always insert an electric pump near the tank and suck out the fuel to send onward to the engine pump. There is no downside to that except the pump cost & your labor.

[yeloduster]

The P30 motorhome chassis with the 7.4L (454) engine was carbureted until 1990. The 1987 P30 chassis with the 7.4L engine had both mechanical and electric fuel pumps. The mechanical pump on the engine had a fuel return line port that connected to a line returning fuel to the tank to help alleviate vapor lock problems. It also had an in-tank electric fuel pump. An oil pressure switch assured that there was no voltage to the electric pump if the engine was not running.

If you turn on the ignition and short the one wire on the oil pressure switch to ground you should hear the pump in the tank run.

Somewhere near the engine is a fuel pump control module that decides when the electric pump runs.

The engine should run with either the electric pump or the mechanical pump. However it may not be able to run full throttle for very long on just one pump and may be prone to vapor lock it either pump is not working or is weak.

[THenne1713]

If carb engine vs injected, pretty safe bet no electric pump if you have mechanical, but worked on 240z once w/ BAD electric beside tank and mechanical on engine and FOUR CLOGGED FUEL FILTERS BETWEEN THE TWO, and bad/ loose inline fuse holder at drivers knee feeding pump.

[yeloduster]

Originally Posted by THenne1713

pretty safe bet no electric pump if you have mechanical,

Factually incorrect. These 1980's P30 motorhomes had two fuel pumps. An electric pump in the tank with an adjustable pressure regulator mounted to the right rear frame rail and a mechanical fuel pump on the right side of the engine block. I had a 1988 and I am much more familiar with the Quadra-Jet carburetor and fuel delivery system that I would like to be.

I eventually eliminated the mechanical pump, added a high capacity electric external pump back at the tank and switched to a Holley 650 CFM spread bore carburetor. That worked much better, more power, smoother engine and better economy.

[Channing]

Originally Posted by yeloduster

The P30 motorhome chassis with the 7.4L (454) engine was carbureted until 1990. The 1987 P30 chassis with the 7.4L engine had both mechanical and electric fuel pumps. The mechanical pump on the engine had a fuel return line port that connected to a line returning fuel to the tank to help alleviate vapor lock problems. It also had an in-tank electric fuel pump. An oil pressure switch assured that there was no voltage to the electric pump if the engine was not running.

If you turn on the ignition and short the one wire on the oil pressure switch to ground you should hear the pump in the tank run.

Somewhere near the engine is a fuel pump control module that decides when the electric pump runs.

The engine should run with either the electric pump or the mechanical pump. However it may not be able to run full throttle for very long on just one pump and may be prone to vapor lock it either pump is not working or is weak.

I put a new mechnical pump on it. I hooked up my jumper cables from my jeep to the motorhome and started the jeep just to make sure the cranking power was there cuz I knew he was going to take time to get the fuel up since the filter the lines and the pump were all dry and I wanted to make sure there was at least 12 volts going the whole time I was cranking. I pumped the heck out of the gas and crank it over and over and over didn't even get fuel to the filter cuz when I disconnected the line it was still dry.
No I'm still not 100% sure if I have an electric pump I cannot get it to come on where I can hear it but if I have a fuel pump relay switch then doesn't that mean I have an electrical fuel pump? It's next to the engine under the doghouse mounted to the firewall I googled the numbers and it is a fuel pump relay switch and it clicks when I turn the key on.

[Channing]

Originally Posted by Gary RVRoamer

The Chevy P30 chassis manual should answer your questions. Get a free one at

https://www.gmcmi.com/wp-content/upl...sis-Manual.pdf


You could always insert an electric pump near the tank and suck out the fuel to send onward to the engine pump. There is no downside to that except the pump cost & your labor.

I have one. I'm pretty sure anyways, and it has helped me tremendously but it does not specifically tell me if I have an electronic fuel pump. On page 7-29 under the paragraph titled "fuel pump" the last sentence says "some units are built with both mechanical and electric in tank pumps." It also tells me the wire at the ignition is tan and white. I found a brown and white one. I don't know . How dark does tan have to be to be brown? And it's way to small it's like 20 gauge that's not going to carry the current it's going to need to. Anyway, I just cannot find an answer on the fuel pump anywhere. I'm just going to have to drop the tank. We live in it and we park where we can so I kind of have to be quick about it. I dropped one tank once on a Ford tempo and that took me some time that's why I'm not wanting to drop this tank. Could put one on externally but I still have to find the line. Mabye that's where my answer is.

[yeloduster]

Let's back up a little. Have you had this engine running? How long ago did it run?

There are a hundred reasons why it won't start and you need to weed out some of the more obvious. It is possible that at cranking speeds you can't get enough suction on the fuel line from the mechanical pump to get fuel to the engine.

Dribble a little gasoline down the primary bores. Then try to start the engine. If the timing, compression and ignition system are good the engine will start and run for a few seconds. That eliminates everything but the fuel system.

If the engine starts the fuel delivery system is the issue. If it doesn't start something else is wrong...too!?

If it were me I would start there.

[Channing]

Originally Posted by yeloduster

Let's back up a little. Have you had this engine running? How long ago did it run?

There are a hundred reasons why it won't start and you need to weed out some of the more obvious. It is possible that at cranking speeds you can't get enough suction on the fuel line from the mechanical pump to get fuel to the engine.

Dribble a little gasoline down the primary bores. Then try to start the engine. If the timing, compression and ignition system are good the engine will start and run for a few seconds. That eliminates everything but the fuel system.

If the engine starts the fuel delivery system is the issue. If it doesn't start something else is wrong...too!?

If it were me I would start there.

I've done a lot more than dribble a few drops. Where talking keeping it running for 30 seconds with a squirt bottle. And it wasn't a leaky squirt bottle or a hot engine. If I could just find out if there's a electronic fuel pump in the tank. I'm going to get back underneath there and I'm going to probe every wire with my voltmeter while my wife turns the key no when she just turns the key on my voltmeter should have a reading if there's power going to it is there anything else back there that might fool me the power goes back to when the key is turned on?

Can you answer me one question?

If there is a fuel pump relay switch does it mean that there's an electronic fuel pump?