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F350 losing power..... Help!

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86-350-460-dually

F350 losing power..... Help!

F350, 460 4 speed manual. 1986.

Hey everyone. I recently towed a 40' travel trailer from 88 miles away to close to my destination and I did not make it. In fact, I shouldn't have hooked up to the trailer, because I was having issues going to them. They lived over two mountain passes and I was losing power on my way there going uphill. I am fine on flat ground though.

After hooking up, I had all the power in the world taking off and at low speeds. On the freeway, I couldn't sustain my 55 mph on any incline. As I approached the steep mountain, I dropped to 15 mph in 2nd gear around 3000 rpm. That was it. Third and fourth gear had no power at all, even going 55 mph approaching the mountain.

Since, I have changed the clutch, checked the timing one the truck and adjusted it to 11° without distributor advance, tuned the carb to a quarter turn from idle drop, and have the idle speed screw set to 900 rpm (seems where she is happiest).

A buddy of mine keeps suggesting that my new 4 barrel carb might not be opening up all the barrels at those higher speeds. Is there a way to check that and what other thoughts would you have to check?

Unfortunately I am pressed on time. In just 2.5 weeks in am towing my 12k lbs tiny house 4 states over and there's even worse mountain passes on this trip.

Adam

1986 F-350, Dually 4WD, C/C with the 460/7.5L

Gary Lewis

Re: F350 losing power..... Help!

Administrator

Bummer!

So, tell us a bit more. First, what carb do you have? Do you have a mechanical fuel pump or electric? Dual tanks?

Second, what were the symptoms? Any missing, rough running, backfires? Or just sagging and no power?

I'll suggest that the problem either a lack of enough fuel or weak spark. But let's see what others say and what your answers are.

Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

86-350-460-dually

Re: F350 losing power..... Help!

Gary,

So there was not any roughness, or backfires. Aside from going up steep hills, she ran great. It just slowed down.

I do have new plugs and wires from December.

It is a ln electric fuel pump in the front tank. The rear tanks fuel pump doesn't work.

Carb is the Edelbrock 650 cfm AVS2, installed in December.

Adam

1986 F-350, Dually 4WD, C/C with the 460/7.5L

86-350-460-dually

Re: F350 losing power..... Help!

Here is the 40' trailer hooked up.

Adam

1986 F-350, Dually 4WD, C/C with the 460/7.5L

86-350-460-dually

Re: F350 losing power..... Help!

If it matters, my vacuum advance from the distributor is hooked up to the ported side of my carb.

Adam

1986 F-350, Dually 4WD, C/C with the 460/7.5L

grumpin

Re: F350 losing power..... Help!

Have you checked for a vacuum leak?

Dane
1986 F250HD SC XLT Lariat 4x4 460 C6-Sold
1992 Bronco XLT 4x4 351W E4OD
1998 GMC Sierra SLE K1500 350 4L60E
Arizona

86-350-460-dually

Re: F350 losing power..... Help!

Grumpin,

Do you have a good way or checking for a leak? I did find a major leak in December, but that was just an uncapped spout.

Adam

1986 F-350, Dually 4WD, C/C with the 460/7.5L

1986F150Six

Re: F350 losing power..... Help!

Administrator

Does the truck have catalytic converters? When you replenish fuel and remove the cap, do you hear a swooshing sound?

86-350-460-dually

Re: F350 losing power..... Help!

I don't hear a swooshing sound, no. I honestly don't know about a catalytic converter. I do know that all the emissions pumps were removed from the engine bay.

Adam

1986 F-350, Dually 4WD, C/C with the 460/7.5L

86-350-460-dually

Re: F350 losing power..... Help!

I don't know if I mentioned this before, but the truck has plenty of towing power in first and second gear. We totally forgot to remove the wheel chaulks on the trailer and in first gear I towed the trailer right over them. Starting from a stop was not a problem. It feels like higher speeds and gears is where I am losing power.

Adam

1986 F-350, Dually 4WD, C/C with the 460/7.5L

Gary Lewis

Re: F350 losing power..... Help!

Administrator

I've seen a lack of fuel cause those problems, and I've seen a weak spark cause those problems. In both cases the vehicle did better in lower gears.

The reason a weak spark can do it is that taller gears cause lower RPM but the same load. That creates higher cylinder pressure (BMEP) and at high pressure the spark just won't jump across the gap.

But I lean to a fuel system problem. One test I'd be inclined to do is to adjust the opening point of the secondaries. That's easy on that carb and should show in the instruction manual. Try it where they open earlier and open them later and see what happens.

However, I think you are just running out of fuel. Perhaps put a fuel pressure gauge on the system and put a phone under the hood to watch it and Facetime to another phone in the cab? Or, if you have an Apple Watch, put the phone under the hood and see it on the watch. I think you'll find that the pressure drops.

Gary, AKA "Gary fellow": Profile

1986F150Six

Re: F350 losing power..... Help!

Administrator

Or, the rubber fuel line from the tank could be collapsing or sucking air?

86-350-460-dually

Re: F350 losing power..... Help!

In reply to this post by Gary Lewis

Thanks Gary! For clarity, do you suspect that the fuel pressure drops or doesn't increase?

I have the wrong ignition coil on the truck now. I do have the stock one on hand from a junk yard, but I just haven't done the swap yet. That wouldn't explain the lack of spark, correct?

Adam

1986 F-350, Dually 4WD, C/C with the 460/7.5L

Gary Lewis

Re: F350 losing power..... Help!

Administrator

David - It is possible the fuel lines are causing a problem. But this truck should have the nylon lines rather than rubber. Still, there could be an air leak that would kill the pressure.

Adam - I expect that the fuel pressure is low and then drops. But the reason it drops is that the floats in the carb drop and the needles open up as you open the throttle, so the flow should increase. But if the pump is weak then it can't keep up with the needed flow and the pressure drops.

On the coil, it would depend on what coil you have in. But I doubt that you have a coil so poorly matched to the system that it can't supply a high output voltage. On the other hand, if you have the right coil then put it on and see what happens.

Gary, AKA "Gary fellow": Profile

86-350-460-dually

Re: F350 losing power..... Help!

Thanks Gary. I will have to examine the fuel pressure.

Adam

1986 F-350, Dually 4WD, C/C with the 460/7.5L

85lebaront2

Re: F350 losing power..... Help!

Administrator

Ok, a couple of items, first, does your truck have a mechanical fuel pump or the electric in-tank pumps? In either case, if the "socks" (fuel strainers) in the tanks are dirty they will restrict the flow of fuel. Do you know what gear you have in it? How heavy is the 5th wheel? I towed a 10K one with Darth and I will say acceleration in 3rd wasn't anything to brag about, never had a problem losing power even towing up 7 mountains grade in PA, was down in 2nd at 37 mph (FWIW, guy with a Chevy pulling an identical 5th wheel was down in 1st at 22 mph on the same grade).

Do you still have the stock exhaust on, or has it been changed, the original was dual 2.5" pipes to the muffler, then what looks like 3" out and opens up to around 4" with two screens in the end.

I would start with a fuel volume test, it should be a pretty good stream, I can't find the exact spec for it, pressure is 5-7 psi though.

Bill AKA "LOBO" Profile

"Getting old is inevitable, growing up is optional" Darth Vader 1986 F350 460 converted to MAF/SEFI, E4OD 12X3 1/2 rear brakes, traction loc 3:55 gear, 160 amp 3G alternator Wife's 2011 Flex Limited Daily Driver 2009 Flex Limited with factory tow package Project car 1986 Chrysler LeBaron convertible 2.2L Turbo II, modified A413

Notch5oh

Re: F350 losing power..... Help!

Sounds like fuel starvation. Could be a clogged filter. If the truck has one.

Cool rig though!

86-350-460-dually

Re: F350 losing power..... Help!

In reply to this post by 85lebaront2

Lebaront,

It has the in tank electrical fuel pumps. It has 4.56 gears. That trailer in the photo was 14k lbs, and the trailer I will be towing in 2 weeks is 12k lbs. Regardless, I was losing power going up the same hills without the trailer though. I couldn't sustain 55mph empty. I probably dropped to 35 mph on the freeway going full throttle.

I have 2.5" pipes going to the muffler and then one 2.5" or 3" pipe coming out. Other than that, I have no clue if it's stock or not.

Adam

1986 F-350, Dually 4WD, C/C with the 460/7.5L

grumpin

Re: F350 losing power..... Help!

In reply to this post by 86-350-460-dually

86-350-460-dually wrote

Grumpin,

Do you have a good way or checking for a leak? I did find a major leak in December, but that was just an uncapped spout.

You can use brake cleaner or starting fluid, but starting fluid can give false indications if it's near the carb inlet.

They will give you a rise in RPM.

Also you can use a cigar! Google Scott Kilmer, I believe is his name.

What about your clutch? Know the history? As in last time it was replaced.

Dane
1986 F250HD SC XLT Lariat 4x4 460 C6-Sold
1992 Bronco XLT 4x4 351W E4OD
1998 GMC Sierra SLE K1500 350 4L60E
Arizona

ArdWrknTrk

Re: F350 losing power..... Help!

Administrator

In reply to this post by 86-350-460-dually

I have the same carburetor on my 460.
With 4.56 gears you shouldn't have a problem pulling that trailer, let alone just getting the truck going at 55 mph.
That's what a rig like this was made for.

You say "mountains". Is altitude a factor where you live?
Carburetors don't compensate well for thin air, but rich is not the same as running lean.

There is no catalytic converter on your truck.

You should check for fuel volume at the carburetor (after the vapor separator T, if it's still there)
Bill can better explain how to jumper the fuel pump circuit to enable this test.

But I think your friend is on to something.
Given your symptoms the secondary throttle plates may well be blocked from opening.

Let me ask. If the AIR pumps and emissions have been removed, is there still an EGR spacer under the carb?
Check for clearance by removing the carb and looking to see if the base gasket is clear of the rear pair of venturis and then seeing if the intake ports do not obstruct that same gasket in any way.

I know I was unable to find a spacer that worked with this carb and had to resort to a die grinder to open up the rear ports for the butterflies to clear.
If the fuel volume test goes well this is the next thing I would check.

Just my 2c.
Good luck with your trip and your new tiny home.

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.