Should I Replace electric fuel pump with original manual pump?

[HandyDan]

I have a 33 ft. 1984 Holiday Rambler Imperial.  It came to me with an electric fuel pump installed in the front wheel well by the previous owner.  The manual fuel pump had been removed.  When I drove it the 150 miles to my home last year, it would not run well at all when the secondaries on the carb would open up.  After reviewing the Chevy Chassis Manual, it suggests putting an electric fuel pump back by the fuel tank and retaining the manual pump on the engine.  This was to prevent vapor lock.  They also stated that electric fuel pumps are designed to push fuel but do not pull it very well.  Therefore having it installed in the front wheel well meant having to pull gasoline almost 20 feet before pushing it into the carb.  I have removed the electric fuel pump and reinstalled it back by the fuel tank.  I am wondering if I need to reinstall the manual fuel pump.  Shouldn't it run just fine on just the electric one?  I haven't tried it on the street, yet, since it is out of license at the moment.  Does anyone have both pumps installed?

[fgutie35]

My Winnebago Elandan rides on the same chassis as yours, and mine has two pumps. One electrical on the back, and the mechanical on the front. If you measure the pressure close to the carburator, then you can replace the mechanical pump for an electric that will deliver the same pressure. In your case, two things may have happened. Either the previous owner, put an electrical pump that cannot meet the demand of the carburator, or he removed the one from the back, and installed in the front. Regarless of what he did, you need two pumps. One to "throw" the fuel from way back there, and one to lift it up to the carb with enough pressure.

[ClydesdaleKevin]

I'd say to go ahead and reinstall the mechanical fuel pump and run it on the two pumps.  Mechanical fuel pumps for our RVs are pretty cheap.  Just hope the previous owner left the pushrod in place when he removed and capped off the old fuel pump.  I'm not sure how difficult it will be to find a replacement pushrod (its only a couple inches long) if its missing.  That said, if its all there and you replace it, a neat trick to keep the pushrod up in the engine (it will want to slide out while you are putting in the new pump because its at a downward angle) is to slather it in wheel bearing grease...that way it stays where you want it while you put the new pump on.  Engine oil will wash away the grease as soon as you start the engine and all will be well.

Kev

[DaveVA78Chieftain]

As described in the Chevy P30 Chassis manual (pg 7-40), they did not start installing the factory electric pump until 84 1/2.  That was due to a large number of Vapor lock complaints.  The recommendations for pre factory installs were:
1. Add a electric fuel pump and pressure regulator outside of the frame rail back by the rear gas tank.
2. Power the new fuel pump vai a oil pressure safety cutout swtich.
3. Add a by-pass line around the new electric fuel pump with check valve to allow the mechanical pump to continue working if the electric pump fails.  The electric pump presurizes the fuel from rear to carb do the mechanical pump becomes a backup pump.
4.  Install a new 1/2" metal fuel line outside of the frame rail from rear to front.  Prevents the exhaust system from heating up the fuel line creating vaporlock.

Factory installs (84 1/2 and later) had pump inside fuel tank with a regulator on the frame rail.

Lots more detail in the Chevy manual write up but thats the jest of it.

Dave

[bluebird]

I would NOT replace the mechanical pump. Pushing fuel to a mechanical pump with an electric pump is hard on the electric pump. It's just a restriction that the electric pump wasn't designed for. You only need 5 to 6 psi pressure at the carb. Anymore than that and the needle won't be able to keep it from flooding. The electric pump does need to be as close to the tank as possible. Make sure you install a good filter after the pump. Most electric pumps are made to push not pull. Again if you're using an electric pump you must check the fuel pressure at the carb. If more than 6 psi you must install a regulator, and it can be mounted close to the carb. I would carry an extra pump with me if it is an after market pump. Also make sure you install a fuse for the pump, so you don't end up causing an electrical fire.

[Oz]

Since electrical pumps can be purchased which delivered the the required PSI, or adjustible ones which can be dialed-in to it, then how would an electrical pump, delivering the same PSI to the mechanical pump as the mechanical pump puts out, be hard on it unless the pressure from the electric pump is either higher or lower?

How is there a difference between what a pump pulls or pushes?  I can understand having a higher draw (pull) of fuel to the pump to ensure adequate supply to it, then regulated to the proper output (push) which would explain a pump designed to pull, but if a fuel pump is designed to push the fuel instead of pull, what does that mean in terms of the difference between push and pull?  The pull suction obviously can't be less than what needs to be pushed, so is the initial pressure at the exit end of the pump to the connecting fuel line actually higher so that it is the proper pressure at the end of it?  I'm just not grasping that concept,  I would think the pressure would be the same from exit to end.  So, how can a pump be designed to push, rather than pull?   i??

[Island_winnie]

I installed an electric pump by the selector valve 2 years ago. It's on a switch and is usually turned off. It's a 6 psi pump and if the output is restricted, the stroke just reduces. It's made for that. I use it for starting after long layoffs, and it's there as a backup if needed. Fuel prices here run between $1.00 and $1.60 per litre, so I fill up when the price is low, and then use the electric pump to fill the car. It's like having a tanker in my driveway. The mechanical pump doesn't care if it's on, both the valves in that one just pass through fuel is pressure is applied from behind.

[bluebird]

Mark, most automotive pumps are what they call vane pumps and don't have much suction. A diaphram pump will have much more suction than a vane pump but won't have as much gpm as a vane pump.  I probably shouldn't have said it would be hard on the elec pump, but it is a restriction. Guys have tried this in the drag racing world, and most have found out it actually reduces flow. A mechanical pump is all that is needed for our coaches, but if a fellow is having trouble with vapor lock he should remove the mechanical pump and install a electric pump as close to the tank as possible. I run a Holley black pump on my race car. It doesn't have much suction but it'll flow 140 gph@14psi. I have it regulated to 7psi, but I run stainless needles and seats made for ethanol. I have a $400.00 pump to install in My sons car and the instructions wants it as close to the tank as possible, but it has to have a return line plumbed back to the cell.  There is another reason to remove the mechanical pump. If it has a diaphram failure, the electric pump can fill the crankcase full of fuel. Don't have to tell anybody what that will do.  Remember Murphy's law?

[HandyDan]

Well, I reinstalled the mechanical fuel pump and all was running well.  I got up early Monday morning to take the MH to the local Chevy Truck Center to have the safety inspection completed.  Wouldn't you know it, half way to the truck center, the electric fuel pump quit working.  I was in the middle of the road with no power.  The mechanical pump was doing nothing.  I assume it could not suck fuel past the electric pump.  Anyway, the truck center sent a tow truck an hauled it in.  They said the wire to the pump had been burnt by the techs that installed the mufflers and was shorting out on the chassis.  While at the truck center they not only fixed the pump, completed the safety inspection, but installed a new Edelbrock carburetor and converted the AC from R12 to R134a.  It works well now.  Took it for a shakedown cruise to Truman Lake (about 100 miles) and it ran great.  It could use some more power, but it purred right along.  However, the bill for all the work about equaled what I paid for the MH to begin with.