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Old 09-13-2008, 08:41 PM   #1
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1986 32' Excella
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Moho Fuel problems

77 Argosy-454 carburated.
Problem- when I floor the pedal the tranny kicks down and then the motor just shuts down. Like Off. After I muscle it to the side of the road it turns over and almost wants to start. This is an intermittant problem but has happened once to many times. After a few hour sit it has started up and run fine. Almost sounds like vapor lock but -who knows any idea's???
Thanks in advance- DG
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Old 09-14-2008, 12:32 AM   #2
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If the starter cranks strong when the engine is hot but barely fires then the fuel pump isn't providing enough fuel. That also sounds like what is happening when you punch it. Has the filter been replaced? I realize that you wrote that it only happens occassionally but that is my take given there are no other symptoms. Does the moho have it's fuel supply line with enough clearance AWAY from the block and exhausts?
Neil.
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Old 09-14-2008, 06:38 AM   #3
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Bizzare theory that I have seen happen a few times...
The suction hose from the frame to the fuel pump may be cracked. Since it is on the suction side, there would be little, if any leakage. But when you hit the gas, the torque of the engine will move it slightly, and open the cracks in the line, causing the fuel pump to suck air. It also allows the gas in the line to that point to run back into the tank.
After you coast off the side of the road, and you crank the engine, it will start pulling fuel out of the tank again, but will take some time to get all the way up to the engine again.
Or it could be a bad fuel pump, as stated above.
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Old 09-14-2008, 09:02 AM   #4
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I can vouch for the fact that what Terry is describing does happened because it happened to us in downtown Detroit on a Sunday afternoon. We found that the main rubber fuel suction line from the fuel tank to the engine had cracked just enough to cause sporadic engine outages.

My temporary fix was to tap into the suction feed line that the generator uses. Its located in a different spot and was not cracked. The drawback is its a smaller diameter line and doesn't reach as far down into the tank. But it worked, it got us from Detroit to Toronto back to Texas without a problem.

Been there done that....

Brad
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Old 09-14-2008, 10:33 AM   #5
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The problem is fairily common. As stated its a fuel issue, I would guess you have pressure but no volume.

In the past a pony pump back by the tank is added along with a new pump up front ( original replacement)

This issue you describe is more common on hill climbs, but can be simmulated with hard acceleration, as you have described.

A clogged fuel filter could also be the culprit or bad accelerator pump, however the engine would restart.

My advice is check fuel line preassure, and volume, and if thats it, replace pump and add a pony pump back by the tank (electric)

If it was a crack in the line, you would get a puddle under the unit when stalled. but stranger things can happen.
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Old 09-14-2008, 11:18 AM   #6
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In my experiance usually a fuel problem has a tendency to bogg spit and sputter then shut down. If it just shuts off it could be on the electrical side, ie; ign coil or distributor module and pick up. After these items cool off they will work fine and it will start again. If it doesn't get regular tune ups and the spark plugs and wires wear out it really works on the coil and module having to throw the spark farther.
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Old 09-14-2008, 12:02 PM   #7
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Good advice

The forum is great - the responses here most likely hit upon the problem. A local mechanic can do a pressure and volume test of the fuel supply system. It's my guess that you have two problems 1. a restriction in the fuel line between the tank and the fuel pump and 2. a vapor-lock situation.

These modern fuels have a much lower vapor point than the fuels of 1977 and that makes our old MO's highly susceptible to vapor lock. Most new vehicles have the fuel pump located in the tank and that eliminates the problem.

In any case, a good electric fuel pump located back at the tank is a worthy investment. Good luck and let us know the probelm and resolution.
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Old 09-14-2008, 12:29 PM   #8
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Don't mean to hi-jack this thread, but the diesel folk who have the same type of problems
should know our coaches have a "fuel pressure regulator" located on the frame rail
just behind curbside front wheel well. It drove us nuts until a old timer asked when I
last replaced it....not ever..did not even know I had one!
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Old 09-14-2008, 06:43 PM   #9
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Vapor lock can be a problem. Check the routing of the fuel line and take a close look anywhere it is close to the exhaust.

Do you have a rear fuel pump? I recently had a intermittent fuel starvation caused by an electrical problem. My MH would power out (much as you describe except that if I took my foot off of the throttle it would idle). Turned out to be an intermittent failure in either the ignition switch or the relay that controls the rear (electric) fuel pump. Not sure which since they were replaced at the same time (I was more interested in curing the problem than in knowing for sure what caused it).
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Old 09-14-2008, 06:55 PM   #10
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I'm getting ready to ditch the existing fuel system. Just need to know what to do, sort of.Presently have the mechanical pump on the block only. I'm thinking of pulling both fuel tanks, cleaning them out, scrapping the frozen solenoid selector valve and adding a manual valve, individual elect pumps and new lines all the way around. I have some AN fittings from another project that I may use!
What brands of elect pumps have some of you used with success? My on line research has prices all over the place--
When the PO added the aftermarket fuel tank, well it is a real hack job.
after sitting all nite, this morning - no start
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Old 09-14-2008, 07:03 PM   #11
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I used the Carter low-pressure vane-type fuel pump. They are a lot quieter and smoother than the old "pulse type". Some should have a regulator, check before performing the "smoke test":

CARTER P4070 CARTER ELECTRIC FUEL PUMP 4-6 $84.95 BUY ONLINE
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Old 09-14-2008, 07:13 PM   #12
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a shot of starting fluid will quickly tell you if it is a fuel or electrical problem.
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Old 09-14-2008, 07:18 PM   #13
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If you go with rear electric pump(s) you may want to run the control circuit through a oil pressure switch.

This was stock on the AS MH with rear fuel pumps and I recently added this to my set up. It had to be added since a PO had butched the rear pump wiring so that it ran directly off of the ignition. (I kid you not, there was a wire that ran from the distributor directly back to the rear pump).

I corrected this with a ignition switch controlled relay to power the rear pump but I only recently found out that the stock set up has the relay control running through an oil pressure switch.

My MH starts up just fine on the front (mechanical) pump alone, then as the oil pressure comes up, the rear pump kicks in. I feel much better knowing that in an accident (or a burned up engine) the rear pump will not continue to pump fuel to the engine compartment, where there could be a ruptured line.
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Old 09-14-2008, 07:21 PM   #14
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Quote:
Originally Posted by richinny View Post
a shot of starting fluid will quickly tell you if it is a fuel or electrical problem.
Intermittent ignition problems usually produce backfires.
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