Omitting intank fuel pump

Turbodime · February 21, 2014, 05:12 PM

I just picked up a new to me, '90 Holiday Rambler 34cs with a 1989 P30 chassis and 454ci. The 60gal tank is out to be cleaned. The pump and sending unit are shot. The engine has a new mechanical pump and I dont see why it needs a second pump at the tank, other then helping with vapor lock. Has anyone here ran their rigs with just the mechanical pump, and no electric tank pump?

Im looking at just repalcing the sending unit with a FG12p http://tinyurl.com/k5a7yp8
The unit that came out of the tank is an odd ball one, with three ports that no one seems to make anymore .
The previuous owner removed the tank so I didnt get a chance to run out the lines. The ports look to be a supply, vent, and maype a genarator pick up. The Gen pick-up is half the length as the main pick-up and pump unit. I imagine this is to keep the genset from suckin gthe rank dry. I have seen the third port on return line for EFI, but I wouldnt think this being a carbd RV would have a return.

If the FG12 will work, Im going to use this and just tee off the outlet fuel line to the genset. If i find a good reason to add an electric pump at the tank, I'll do that, but it will be outside the tank so I wont have to drop the tank to replace.

Thanks for any advice or info.

Aaron

legomybago · February 21, 2014, 05:45 PM

Yes you have a return line coming from your mechanical pump, your fuel return system should be running a loop from your intank fuel pump too and through your mechanical pump on the engine, then back to your tank. If you just run with the mechanical pump, you will have vapor lock issues somewhere down the road...that is why the electric pump is there.

M & J · February 21, 2014, 05:54 PM

Highly suggest you keep it as designed. Much easier to do it now than when you have to.

Froggy1936 · February 21, 2014, 07:09 PM

Aaron i agree with you If needed a electric pump outside the tank is a better option. Putting a fuel pump in the tank has always amazed me . Volkswagen (one of the first Fuel Injection) Mass users had external electric pumps for many years Then went to pumps in the tank. The only reason i can think of is cost (wich is what drives all things for manufacturers) If you find you need another pump down the road there are many many better options than the in tank pump You can get a pump that pumps 10 gal a min if necc ! Removing a fuel tank is not an easy task ! Frank

pvoth1111 · February 21, 2014, 07:18 PM

Having it in the tank...helps to keep the pump cool.....monies need to be spent to have a external pump that will last.... outside of the tank...

Stripe · February 21, 2014, 07:34 PM

While in contrast, a potential hazard of a tank-mounted fuel pump is that all of the fuel lines are under (high) pressure, from the tank to the engine. Any leak will be easily detected, but is also hazardous. electric fuel pumps will run whenever they are switched on, unless a safety device such as an inertial switch is fitted, which can lead to extremely dangerous situations if there is a leak due to mechanical fault or an accident. Mechanical fuel pumps are much safer, due to their lower operating pressures and because they 'turn off' when the engine stops running.

So you need to weigh the differences and decide which you'd prefer..

ClydesdaleKevin · February 21, 2014, 08:14 PM

Voice of experience, and heed me well, grasshopper! You WILL get vapor lock and your life, and road trips, will suck without an additional electrical fuel pump either in or near the tank!

If you feel you must absolutely dispense with an in-tank pump...which I would probably do if my 89 didn't allow access without dropping the fuel tank...then you need to install a good aftermarket fuel pump right at the tank, with a good aftermarket pressure regulator.

Or else you WILL get vapor lock, and you WILL curse the day you bought your rig...lol!

Kev

Rickf1985 · February 21, 2014, 08:24 PM

Not all electric fuel pumps are high pressure, only the ones designed for fuel injection. On top of that you usually use a regulator close after the pump to get the pressure down to the required 3-5 lbs. There are three main types of electric pumps, rotary vane, which runs all the time it is on but produces fairly low pressure. Rotary gear, which also runs all the time but produces high pressure and electromagnetic pulse pumps that only run when the pressure drops below a certain value. These are very low pressure pumps. Granted, any leak will be hazardous. The comment about the mechanical pump having a return line has me curious, why would it? None of the vehicles I have worked on over forty years have had it with the exception of a very few specialized vehicles made for off road. Is this something that is specific to the motorhome? I know the standard P30 chassis does not have it because I have worked on them in fleets.

Rick

ClydesdaleKevin · February 21, 2014, 08:29 PM

There is definitely a return line, at least in the late 80s P30 motorhome applications. Its what feeds the fuel to our Onan genny as well!

Kev

Rickf1985 · February 21, 2014, 08:34 PM

Kevin replied while I was slowly typing and he has a good point. I will expand on this a little bit. You can run a return line with a mechanical pump and depending on what type of pump you are using you may have to have a return with an electric pump. This is what you need to keep in mind, the carburetor needs 3-5 lbs. of pressure to operate. You have to make sure that the return is fed through an orifice that does not allow any more fuel more fuel to flow back to the tank that maintains the 3-5 lbs. at the carburetor at wide open throttle. That is usually not possible with the mechanical pump so there is not usually a return with the stock mechanical pump. The whole idea of the return is to keep the gas flowing so if it does start to boil in the line then the vapor will flow through and back to the tank, it will not get "locked" in the line. This is the specialized vehicle application I was talking about before.

Rickf1985 · February 21, 2014, 08:35 PM

Kevin, how does the genny get gas if the engine is not running so no return gas?

ClydesdaleKevin · February 21, 2014, 09:23 PM

The genny fuel line Tee's into the return line. As long as the line is primed from the engine having been run recently, the genny runs fine. Was a bit of a learning curve though...You have to start the engine on our rig for a few minutes to prime the line, then the genny will run fine all day. The return line goes to the sender unit on the tank and goes down to about an inch from the bottom of the tank, which is why I think they designed our rig this way. You still have a pickup that doesn't go to the bottom of the tank, but you don't have to install a genny specific pickup in the fuel tank.

Even with all new rubber hoses though, you definitely want to start the engine on ours first before starting the genny. Then you can turn the engine off and the genny will run happily all day long.

Kev

Turbodime · February 22, 2014, 02:43 AM

Holy crap, I can't belive all the great responses. It's 12:30am and I just got in from working on the rig. Never got underneath to find out where the lines go. I know the genset has a Facet fuel pump. In the morning my two oldest boys are going to clean the gen'e carb and change the oil and filter in the morning and I'm going to run down all the fuel lines .
I'll post more once I figure them out. Thanks for the advice I'll post pics of what I do.

Oz · February 22, 2014, 09:16 AM

Quote from: Turbodime on February 22, 2014, 02:43 AM
Holy crap, I can't belive all the great responses.

I know, right? I've always thought the sub-name for us should be, "The Eager Beaver RV Club"!

legomybago · February 22, 2014, 11:11 AM

This is the pump I've had on two 1985-1987 P30's. 3rd port is the return. Both of my rigs didn't come factory with the electric pump...but you change that!!

You can turn the electric pump on and listen to the fuel circulating though the system, you don't have to worry about the diaphragm in the mechanical pump bursting while electric pump is working...

http://www.mypartsgarage.com/carter-mechanical-fuel-pump-m6628.html

Sprdtyf350 · February 22, 2014, 12:53 PM

My 85 Southwind has a carburetor. Has a mechanical pump with a return line and an external pump on the frame rail back by the tank. There is also an oil pressure safety switch to keep the electric pump from running if the motor dies, or you crash. I found that after sitting for a while I would have to crank and crank until fuel filled the carb bowls. Not liking that I added a spring loaded switch that bypasses the pressure switch. Now I turn on the key, hold the switch for about 5 seconds, and the motor starts quickly.

You might be able to use the existing wiring for your in tank pump to run an external pump.

Here is the pump mine came with from the factory, and the pressure switch. I didn't get mine from these links but you get the idea.

http://www.summitracing.com/parts/crt-p4070/overview/

http://www.ebay.com/itm/JEGS-Performance-Products-11200-Oil-Pressure-Safety-Switch-/200720632712?pt=Motors_Car_Truck_Parts_Accessories&hash=item2ebbe1cb88&vxp=mtr

HandyDan · February 22, 2014, 04:38 PM

http://tristarrradiator.com/index.html

This company may be of help in finding or repairing the unit you have. I've never used them, but they have a nice website.
Dan

Stripe · February 22, 2014, 05:37 PM

That's not too far from my old stomping grounds in Upstate NY..

cook elandan · February 23, 2014, 09:04 PM

rickf,
just want to let you know that most of the cars that i have owned in the past all had a return line from the fuel pump. 79/84 pontiac trans am, 80 bonneville, 72 olds98. plus now the 2 elandans that i have.

Turbodime · February 23, 2014, 11:16 PM

Spent the last two days working on the rig. I love projects, and this one is really turning into a fun one. Here are some pics of my rear fuel/vent lines. Right off the left side of the tank is a fuel regulator. The 3/8" fuel supply line heads towards the back then wraps around to the right frame rail. It hooks up with the return line and vent line and all three stay on the right frame rail. Around the tranny one of the fuel lines has a tee. I spent some time looking to see if I could tell if it was the return or supply but couldn't get my fat head in a tight spot. I did find the mechanicsl pump and the return line was unattached. Previous owner was in the middle of the repair. Never did find a filter other then the carb filter. I'll be installing one back by the tank.

There is a separate port on the tank that looks to be a vent line. It travels through the right frame rail and connects to some type of check valve and from there the 3/4" tubing travels to the rear, and ends at the hitch. This seems like a huge vent. It already has a vent at the a sending unit and there is a vent at the fill line. I'm curios about the 3/4" vent, anyone know what's it for?

Still waiting on the rad shop to get the take clean. I have a funny feeling about this shop, owner is haying he's using caustic then dumping in muriatic acid. I asked him how that was working out because the two don't mix. He had no clue what I was talking about. I called an rv used parts outfit in PHX and they have a tank for $150. If the mad chemist can't get my tank clean I'll run down and pick up the $200 one.

Turbodime · February 24, 2014, 12:12 AM

Here's a pic of the tank vent check valve? I think.

DaveVA78Chieftain · February 24, 2014, 01:40 PM

From Chevrolet Motorhome Chassis Service Guide (Available in our Free Manuals section here on CWVRV):

1985 1/2 to 1989 stock carbureted P30 had an in tank electric pump, regulator outboard of the frame rail (aft of rear wheels; aft of tank), 1/2" steel line to filter (AC GF-509 located outboard of frame rail at tn transmission area), 1/2" steel line to mechanical fuel pump. Anything else and the system has been hacked. The 1/2" steel line was ran outside of frame rail to protect it from exhaust heat.

1990 - 1993: GM transitioned to TBI injection on the motorhome chassis so the fuel lines are pressurized (10-15 psi) by the in tank fuel pump all the up to the TBI unit (no mechanical pump installed). There should also be a fuel filter (GF-481) installed around the transmission area also.

While not positive, the brass device on the frame rail below the wires with the large hose in this picture sure looks like a regulator to me

Somebody has definently been working on your rig at some point because there are no stock clamps and zip ties in many places (plus the wire splices). Hard to know what has been done.

Make sure you look at your chassis VIN number to understand exactly what year the chassis is. It was not unusual for Winnebago to place this years model (i.e. 1990) on last years chassis (i.e 1989) because they had to order the chassis' early in order to recieve them for the next model year.

Dave

Turbodime · February 24, 2014, 05:17 PM

It's a '90 HR with a '89 chassis. The brass valve is the pressure reg. Im going to check the line that runs out of the chassis near the tranny. The rig only has 24k on it. Your correct about the butt-splice connectors I doubt they're factory.

Now I know it has a fuel return from the mechanical pump, I'm looking at the diesel sending unit as its a 3-port.

I really don't want to drop the tank in the future and I'm going to try and exhaust all my options first.

Thanks to those that have posted replays, you have given me a lot to think about.

I just figured out the password so I have lots to read.

DaveVA78Chieftain · February 24, 2014, 07:56 PM

Most of the relative information is in Appendix 7-7 starting on pdf page 135. There was a lot of research performed by GM regarding P30 chassis Vapor Lock issues so there is a lot of information in this section regarding the fuel system.

Dave

Turbodime · February 25, 2014, 02:39 PM

Thanks Dave, I was into 40 pages so im glad you directed me to the pages I was after. What a first rate manual.