Just got back from a trip with the RV, a 1986 E350 carbureted 460 powered cut-away.

I started losing power in the mountains. At 5,000' altitude, pulling a grade in 2nd at 2,700 RPM's it started cutting out. At first I thought it might be ignition but it was almost like I was running out of gas...I pulled over and it idled great and the motor reved right up smoothly.

I pulled back out and floored it and after a long sputtering while it finally got to 3,200 RPM and into the secondaries. It seemed to be getting gas.

But cruising along it would cut out and lose power and I topped the pass crawling at 20 mph in 1st gear...if I tried to give it more gas it would just stumble.

Fortunately the other side of the pass is all down hill for the next 30 miles and when I stopped to get gas I calculated 6.6 MPG for the last 114 mile leg, including coasting the last 30 miles down hill. Normally get about 8 MPG.

At this point I was under 1,000' of elevation and it ran like a champ for the next 120 miles (including 90 miles of freeway at 65 mph) all the way home.

First on my list is to change the fuel filter but I also wonder:

1) Would a failing in tank fuel pump act like this?
2) How about a bad carb in need of a rebuild. As I said it idled just fine but maybe the power circuit is messed up causing it to be way too rich at high altitude (causing bad MPG and flooding at cruise?) but okay at lower altitude?

At this point I'm really scratching my head. What the heck happened? Thoughts and advice would be greatly appreciated.

 

I think low vacuum is causing your problem, and the powervalve is staying open.
The 4180 comes with a two stage power valve, but the only one Holley sells on their site is a 125-207.
It starts at 10" and fully opens at 5"

The combination of thinner air, a carburetor jetted for sea level, and possibly a worn timing chain are just too much.
Maybe there's a vacuum leak somewhere else that is contributing too?

It would be interesting to install a vacuum gauge where you can see it while driving and try to recreate the problem.


EDIT:
The jetting spec's for 4180's are listed in the gray bar across the top of pages 15-16 of the numerical listing on Holley's website.
http://www.holley.com/data/TechServi...%20Listing.pdf

 

You will have some problems with it at high altitude, as in slightly running rich. There is no way to get around it, it can't compensate for that drastic an altitude change.

But it should not have cut out like that. I would try the fuel filter first like you suggested. If you have the gizmo at the carb with the return line, I would also take it off and make sure it's clear. I had a co-worker with a 460 and he had a cutting out problem, and it turned out this gizmo was clogged with little pieces of plastic. He found out the pieces came from the sock in the tank that had disentegrated.

 

Any chance you got some bad fuel (or have some water in the tank from sitting between vacations)? Did it start running rough on day one of the trip - or did it start running bad after a couple of days of driving without issue?

 

Maybe when he 'finally reached 3,600 rpm' the engine was moving enough volume to accept the amount of fuel/air being offered.

It would be the secondaries opening too soon that causes it to struggle.
Vacuum holds the plate closed against spring pressure.

 

All good suggestions as far as things to look at.

Just want to say that I operate at 5,300 feet all day long, "high" elevations to me are 11,000+ feet....

 

Thank you all for the replies!

I've had the unit for about 10 years now and I've made the trip many times.

I started out with good gas but I could have picked up some bad gas along the way...

The last fill up was at the bottom of the 30 mile (and 4,000' rise in altitude) grade, and while it bogged like you'd expect, it didn't cut out.

Vacuum leaks. Wouldn't that also show up as a rough idle?

Vapor lock. Wouldn't that also show up as a rough idle?

Power valve porking too much gas. This is a new one to me. The exhaust certainly smells rich but no black smoke and it idles okay. Is this consistent with a bad power valve?

On the freeway it seemed like it didn't take much throttle to keep it at speed (perhaps less than usual?) and the throttle response was "laggy", meaning if I gave it more gas it would only slowly pick up speed...

 

Did you by any chance run through a large puddle of water at speed? Believe it or not, I have seen a number of vehicles with collapsed exhaust pipes. Starting in the late 60s with the advent of emission systems, Detroit went to double wall exhaust pipes due to the high heat levels from retarded timing, lean mixtures and air pumps.

At highway speeds, particularly in a heavy vehicle, the pipe gets red hot or hotter. Dump cold water on it, the outer layer contracts and squeezes the still soft inner layer collapsing it. Instant exhaust restriction and poor running at full throttle.

 

Yes vacuum leaks would cause a rough or high idle

Yes, vapor lock also would cause a rough idle/stall problem

Yes, that slight richness would be a sign of a leaking power valve. It doesn't cause drastic trouble when it leaks, it just makes the exhaust stink and it gets lousy mileage. The plugs also turn black from being rich. It's a common problem, usually caused by this crappy gas they sell now(alcohol in the fuel), and age. A rebuild would fix that part, though you might have to buy the power valve separately.

Since it has seemed to have cleared up, the bad gas theory might be what was wrong as far as cutting out(water in the fuel).

 

I can't see water in fuel.
Given the amount of alcohol now in U.S. road taxed gasoline it would seem improbable.

http://epa.gov/oms/regs/fuels/rfg/waterphs.pdf

 

Update,

I changed the fuel filter element (a canister type mounted to the frame rail) and it was very dirty. I think the last time I changed it was around 8 years ago...note to self, change fuel filter more often.

I'm fairly certain the dirty fuel filter was the source of my trouble and it seems to run a bit stronger now. Not sure why it ran okay once I got down out of the mountains, perhaps it was because I filled up and was running on a full tank versus a half tank?

Question for the group. This episode got me thinking about replacing the in tank electric fuel pump. I have an estimate for the job at a reputable shop (not a job I care to do myself) @ $225.00. For a 27 year old vehicle changing out the in tank electric fuel pump seems like a reasonable insurance policy to take out.

Thoughts and opinions?

 

Provided they get the correct pump.

 

Thanks LeBaron for something new to worry about! LOL (sort of).

I think he knows what he's doing though. I wanted a complete sending unit assembly but he told me he couldn't get a whole assembly ( Id also found this out at the auto parts store ), and even if he could, it still wouldn't be right because it would lack the extra fuel nipple for the generator ( it's an RV after all). Hmm I hadn't thought about that.

Since He also wanted to make sure I knew he didn't think my cutting out problem was the fuel pump, "they either work or they don't" was pretty much his advice, I reckon he's honest.

But I will quiz him some more about making sure we get the right pump. I may even ask for the packaging so I can document what went in.

Thanks.

 

I am not a big fan of changing parts just to be changing them. The quality of the newer parts now can be suspect. If it's working, I would not change it.

 

Boy oh boy ain't that the truth! It took me two tries to get a properly working fan clutch for the 460, and my quest for an instrument cluster voltage regulator, that holds the gauges steady, continues. Not to mention the "life time" warranty water pump I put in the Suburban (gasp!) that failed after only 5 years...good thing I kept the receipt or I'd have been out $129.00 for another one.

So as much as I'd like to stimulate the local economy by spending money needlessly, I think I'm going to take your (and others) advice and not try and fix something that isn't broken.