12 replies to this topic

[saturnxjc]

I recently bought a 1987 Mallard motorhome with a 454 engine.

The fluids are good and check out good.

I put new spark plugs and spark plug wires on, new rotor and cap, new intake, air and fuel filter.

My question is, when I first started I drove for about 5 hours and at 65 miles per hour and and all of a sudden it slows to 40 miles per hour. When this happened I filled it up with gas and it was fine for a few more hours then I parked it overnight. The next day I ran all day with no problem. I thought it was fixed, but again I drove a half a day and it began to slow again and I filled it up but that did not work. The only thing I did not do was put in a new fuel pump but when I turn the key I can hear it turn on.

[wolfe10]

Might be worth pulling the fuel filter and verifying that it is not clogged. Also, many rigs have a sock-filter in the tank. It could be clogging. Fueling may knock the debris off the sock.

[hermanmullins]

saturnxjc,

Welcome to the Forum.

To go along with what Brett said,how long did the M/H sit without being started? How much fuel was in the tank when you filled it the first time? If the tank was low on fuel and had sat for a long time there could be alot of debris that comes from rust, condensation, bad fuel and on & on. If you can safely remove the fuel filter and run a hose from the tank into a bucket. Turn on the key (electric fuel pump) and let the fuel run into the bucket til its about half full. turn off the key and wait a few minutes to let it settle and see what kind of debris you have in the fuel. if you find a lot you might consider draining the tank and start with a new filter and fresh fuel. You may have to change the filter several times to catch all of the debris.

[saturnxjc]

Fuel filter and pump are good. I let it set for a day and started it up and drove for 50 miles everything was working great.

I stopped and put $40 of gas in it. I drove two blocks and the same thing started again and it will only drive 35 to 40 mph.

I am wondering if this has a sending unit in the tank and could this be the problem?

[hermanmullins]

Just because you can hear the pump come off and on with the key doesn't mean it is working enough to provide adequate pressure to fuel your throttle body injector. I would still get fuel out of the tank and check for trash. I started to say I wouldn't put in too much fuel* until I found the problem but I see you said you put in $40.00 worth of gas and by today's standards isn't much fuel. You could take it to an shop and let them run a test to see how much pressure your pumps is providing and see if when the key is turned off does the pressure drop quickly.

*(Note a empty tank is easier to drop them a full one)

[aztec7fan]

I agree with the previous posts that you may have some junk in the tank and it occasionally is causing blockage in the fuel pump, or possibly another filter in the tank. Another slight possibility, could it be temp related? You seem to have the problem only after driving for a while, albight sometimes for a long while. Is a heat sheild near the fuel pump loose or missing? could the pump be getting warm and after the coach sits, the heat builds up more in the fuel pump area? Have your mechanic check fuel pressure after the coach has run for a while.

Also possibly an vapor lock problem?

How long did the coach sit? is it possible some of the old fuel varnished? I wouldn't think so since you've filled it several times, but there might still be some pockets of bad fuel in the tank.

I have a 1989 Southwind with the 454 engine and performance so far is great. I do need to change my fan clutch though, and I'm just waiting for the time, $$$, and warmer temps to do so.

[OkieDave]

Not sure this will help, but check the fuel cap. As fuel is pumped out, you have to get air in there somehow. If the engine has a closed system, then the return vent is possibly stopped up.

[RonNewsam]

I had an '87 Allegro on a Chevy P 32 chassis for 14 yrs. The spark plug wires have to be dressed a certain way. Very important!
There are also heat shields on each individual plug.
On my '87 Allegro there was a ceramic fuel filter at the Rochester carb where the fuel line enters. There was also another one halfway between the fuel tank and the engine. Mine was located behind the rail just behind the entrance steps.
Hope this helps.

[DickandLois]

There are fuel filters in the Carberator ( 454 =s a large guadrajet) at the front of the carb. and an inline filter, generally located just forward of the rear axle.

If your coach is like my old 87, it may have two fuel filters in the very last pod area on the curb side. One pre auxiliary fuel in the fuel line to help prevent vapor lock and one post pump. This gave me a total of 4 fuel filters.

There maybe some foreign material in the fuel tank that has fouled the filter(s).

New in 2010 to FMCA. Driving a Class C, A and AD sense 1973. They just got bigger over the years !!!

**** ---F415802

[Deacon]

I just disposed of an 86 Mallard and the fuel line and filter ran up the inside of the left chassis rail. It was a carburated 454 that ran like a dream after I put a remanufactured engine in it. But, I'm in Oh. and the rig was in Az.

[dwightginnyputzke]

I have seen the same condition before they went to the sock on the end of the fuel line at the bottom of the tank. A flake of rust can be drawn into the pipe and cause a fuel blockage. The fuel line can be disconnected behind the fuel filter and air pressure blown back into the tank to clear the obstruction. Remove the fuel filler cap before using the air pressure.

[hermanmullins]

Dwight, Although you can blow air back through the fuel line going into the tank. Too much air pressure can damage the filter sock on the pick up tube or fuel pump. This can cause problems for either one of them.

[DickandLois]

The small filter is in the carburetor body, It is easy to strip the threads in the aluminum casting (Do not over tighten). There is a small plastic seal between the filter nut and the casting to prevent fuel leaks. Should be changed with filter! it is hard to see unless you are looking for it.

The larger cylindrical metal filter is the in line fuel filter. AC part # 509.

The large cartridge filter (AC # 147) is in the fuel line, mounted near the inline electric fuel pump that keeps positive pressure on the input to the mechanical fuel pump mounted on the lower right corner of the block. Passenger side. This helps to prevent vapor lock when the engine is running hot.

Not all chassis have this pump if you have one. The Manufacture was (is) Carter. Wish I could remember the number.

Pictures of the fuel filters used on P-32 Chassis with a Quadarjet Carb. 1980’s ...