81 351 spits and sputters but...

[imderrickjed]

81 ford platform for my Shasta Motorhome. I am having problems driving. Starts up find, Will idle for hours if you let it (shop says). But after driving it 2-5 it spits and sputters like there is no gas. I can cut the engine off wait about 1 min and start it back up then go 2-5 miles again (sometimes more). And mine will do it when it is cold as well, Cold or warm start it seems to do the same. As for a fuel system it has a large alumium cell (has been in place for years). Line goes right to the machanical fuel pump and right to the carb. Ive seen this same issue posted about a fuel injected engine, but not a carb. Shop found nothing wrong with it sitting in the shop, but said if they drive it and get stuck Im paying the tow bill. I drove it this weekend and found that I can get it to the speed limit of 45-55 and a few miles later when it spits and sputters I shut off the engine and coast. By the time Im down to 30MPH I fire it back up and Its running great for how ever many miles it wants. This seems to work better then pulling over and waiting. I know its not the safest.

[DaHose]

I have had similar sputtering on my 1983 Jamboree with a Ford 460. Idles fine, seems to run ok, but eventually would sputter. I just pulled the A/C compressor to upgrade it and noticed that I didn't put the vacuum advance hose back on the distributor diaphgragm when I changed out the ignition parts. I plugged the hose back in and it runs much better. Didn't sputter at all the last couple times out (in town usage). See if you have a vacuum leak somewhere.

Jose

[jamesa403]

Before you go to the expense and time to replace the fuel pump, replace the fuel filter(s), as this also sounds similar to water in the fuel filter, keeping the gas from flowing when it is sucking a lot of gas. The filter won't let water through when it is sucking hard, blocking off the gas from getting into the engine.

[gkainz]

The only way I found to DEFINITIVELY troubleshoot a similar problem on my (now gone) '83 Tioga E-350 460 with Motorcraft/Holley 4V was to put a fuel pressure gauge on it where I could see it, and drive it. Observe the fuel pressure when it starts behaving badly. Mine dropped to 1 psi or less when it acted up.

Mine turned out to be the hot fuel diverter valve (the aluminum V Block that has fuel line in, and 2 fuel lines out - one to the carb and one back to the tank).

Prior to this, troubleshooting/futile swapping of good parts included replacing an electric fuel pump (it really went bad... the start of the misbehavior but coincidental), replacing the fuel filterS - yeah, plural ... including the brass strainer in the base of the carb), adding more fuel filters suspecting junk/gunk in the tank, removing, cleaning, reinstalling the fuel tank (didn't really need it).

In desperation, I added a mechanical fuel pump inline with the electric fuel pump (my electric was not in the tank, but external) which provided enough capacity to overcome the hot fuel diverter valve. Having said that, I sold it before replacing that valve. I still cannot say definitely that it was the sole source of the problem, but it's still what I point my finger towards.

Not sure how much of what I experienced with my 460 is relevant to your 351, but something to ponder or investigate. I also found a lot of good info on Ford Trucks forums

[jdog]

Engines in 1984 were designed to run on "LEADED" gas to lubricate the valve stems and to prevent knocking which will burn the valves. Lead is not there anymore. Newer motors have different valves made from material to take more heat.

[imderrickjed]

j-d wrote:
Several of our guys have done that on Fords. More specifically, add to, or replace, the in-tank electric pump with an external pump. The aftermarket electric pumps don't seem to last all that long. And that's just not the $39 ones, it's the $139 ones too.

This one already has the original tanks removed and replaced with a 6' long aluminum fuel cell. Based on what Im hearing Ill replace the fuel pump with a solid inline electric one and hope all is well.

Then its onto fixing that plumbing leak!

[j-d]

Several of our guys have done that on Fords. More specifically, add to, or replace, the in-tank electric pump with an external pump. The aftermarket electric pumps don't seem to last all that long. And that's just not the $39 ones, it's the $139 ones too.

[imderrickjed]

Sounds like Im better off adding an electric fuel pump.

[Harvard]

We had an 84 GMC Suburban with a engine mounted mechanical fuel pump. When the fuel pump was heated by engine heat the fuel pump housing would expand and allow the high pressure to leak back into the low pressure (within the pump itself).

So, when ever we stopped for a quick burger we would have to go through a slow speed recovery and cool down period. Changing the fuel pump and replacing it with a "genuine GM" fuel pump did not fix the problem. Had to go with a 3rd party pump to fix.

[imderrickjed]

Its odd because this has happened at high speeds, Low speeds and even coasting (pretty much) down hill, yet each and every time I turn the key off for 1 min (maybe 30 seconds) it fires up and is good to go at any speeds. Plus we just bought it a couple months ago and drove it and hour and half home.

[PaulJ2]

Weak fuel pump or a restriction some where. You are using a bit more fuel than the fuel pump can supply. What happens is it can't keep up and as the carburator bowl gradually emties it then sputters and stalls.

[j-d]

We had a Dodge van with a similar fuel system. Simply a tank and an engine mounted mechanical pump. Had it 21 years, so several fuel pump failures. The trickiest one to figure out was one that went "weak." Didn't leak, didn't quit, just inadequate volume to pull a load.
Driving without towing, OK. Towing the boat, though, it'd so through the first two gears OK then starve in 3rd/high while still accelerating. Replaced and OK.
My theory is that in the lower gears it had the RPM to keep the fuel flowing. When it got to 3rd and the load was still there, the RPM wasn't and it couldn't deliver.
I'd change any filters it has, be sure to check carburetor inlet, and if that doesn't work, put another fuel pump on it. Can't be that difficult or expensive.