1978 F150 Loses Power When Driving Uphill

Any way you can put it on a 30-35 degree or so incline to troubleshoot it?

Joe in Texas

Yes, are you thinking it may be a float problem in the carb?

First double check your timing. On a Chevy it 10 degrees above top dead center. Next check to be sure your distributor cap is not cracked and your points (if you have them) are set properly and not burnt. The chirping sound is probably a belt (could be the alternator starting to go bad.)

I''m just an "apple tree" mechanic! But it sounds like an electrical ignition problem. Do you by chance have a Carter or maybe an Eldebrock carburetor?

The truck has a new distributer and I inspectyed the cap and it looks good. There are no points and the carb is a few years old, it is an oe replacement from autozone. I also have timing set at 6 btdc as recommended with vac advance plugged.

You may find a sweet spot between 10 btdc & 13 btdc

It could also be a bad torque converter.

I have a manual trans with new clutch. The truck runs perfect otherwise.

Stop throwing parts at the problem, and test. You changed the muffler. How about the catalytic converter? Crawl under the truck, and pull out the oxygen sensor out. Try that hill again. If that exhaust leak helps, remove the cat-con. and retest. Let us know.

My truck has no cat or exhaust sensors.

Thanks, I will try it.

This sounds like a very good place to start.

Unlikely to be catalytic converter, since it is a 1978 model. Unless added afterwards, but why on a carburetted motor? I believe you need to check your needle and seat. It may be sticking and not allowing the full flow of fuel to the motor.

1978= no O2 sensor!

I suppose you do have the battery tied down properly and its not shorting out when it rocks back going up hill?

Fortunately we never got any of the "M" motors in Oz, our F trucks had Clevelands till the early 80's and then they went to Windsors. Except for those fitted with the inline 6's which were the canadian 240/300 or the later 4.1litre Oz crossflow but there are not many of those around.

If you have a full tank of fuel, does that make any difference? My F trucks either had the belly tank or the rear mounted flat tank. The belly tank could be cruel with only 1/4 tank of fuel going up hill because the fuel wouldn't be any where near the pickup.

What carburettor have you got installed? As you may have a float level issue.

The only other thing I can think of is that you may have a loose electrical connection or a wire that has chaffed and may be shorting out when you go up hill.

Thanks, I have a flat tank but I will check the other items you mentioned.

question ; WHERE is the " chirp sound " comeing from ? What area of the truck ?

the chirp sounds like it is under the truck, and it is not the exhaust.

Ok , "under the truck" is a good start , now, WHERE " under the truck" does it seem to be comeing from ?

From the front ?

From the middle ?

From the rear ?

Left side ?

Right side ?

Do you have someone who can stand on the side of the hill as you pass by to help narrow down the AREA " under the truck " the sound is comeing from ?

Does the " chirp sound " change speed or is it constant speed ?

Is the " chirp " sound FAST , like it is associated with the RPM's of the ENGINE ?

Is the " chirp " sound SLOW , like it is associated with the rotations of the wheels or drive shafts ?

Does the "chirp" sound CHANGE SPEED with the speed of the vehicle ?

Does the " chirp " sound Change speed with the speed of the engine ?

Does the " chirp " sound like metal on metal ?

There are a LOT of questions that need answering before I can give you ANY KIND of answer that would help !!

All of the driveline ujoints have been replaced but it only happens when the engine begins to loose power. At times it seems to be coming from the rotation of the wheels. I havnt changed the front drive ujoints but I will have someone listen for me. Thanks.

Well , a slower "chirp" that seems to be related to the speed of the wheels more than the speed of the engine , would tend to lead me in the direction of a lower drive train problem.

Does the problem of loss of power happen in BOTH 2 wheel and 4 wheel drive mode ?

When was the last time you checked the oil level in the trucks rear end ?

When did you last check the transfer case oil level ?

*** You probably think THIS is dumb but ... ---> Is the emergancy brake engaged or the Brake Cable Stuck ?? ***

I checked the fluid levels and ebrake, all are good.

You said the chirping gets louder when you go up a hill ? AND that the truck loses power at the same time. The sound seems to come from under the truck , and does not vary with engine RPMs ... The gear box and tranny oil levels are fine , and you checked the e-brake.

OK GOOD !! You have eliminated or narrowed it down beautifully !!

I suspect you have a FUEL PUMP that is on it's way out.

But he has already replaced the fuel pump.

Usually when the pump goes on these motors it usually sprays fuel all over the oilfilter. Also you get a more than usual smell of fuel under the bonnet. and your fuel consumption goes through the roof!

I am going to place a fuel guage on the line before the fuel filter and see what the psi is.

I was not aware that he had already replaced the fuel pump. This is one LONG thread and it's hard to read it all and remember it all.

I'm back to thinking it is SOME KIND of lower drive train problem then.

Take a sample of your gas, where it comes out of the fuel pump. It's possible you have debris or moisture in your fuel tank that is getting shifted and sent up to your engine on inclines.

I just dropped the tank and it was clean. I will try blowing ther line out and I just replaced the fuel filter.

My solution is to tip a bottle of spirits into me. Screw the car for now.

The tank is free of water and debris.

On second thought, a fuel problem, or ignition for that matter, will also produce a stutter or misfire, however if you have a vacuum problem, or stiff advance and retard linkage in distributor, you wont have splutter but loss/lack of power. The reason being that when you go uphill you have to feed in more gas which in turn will/should alter the ignition timing. If this does not happen you are trying to run uphill with retarded timing.

With a loss of power, I might look for a vacuum leak.

This is what I am leaning toward but I have checked all of the vac hoses and all is good. The only thing I had a problem figuring out is what hose went where. I followed the schematics but they do not specify for 1978.

What carb is on your truck? I think I can find the vacuum diagram for the truck. Do you have a dual diaphragm vacuum advance on the distributer?

On these units the vacuum port on the distributer closest to the center of the distributer is connected to manifold vacuum directly. The one further away is connected to ported vacuum, so that it only gets a vacuum signal when you step on the throttle. If these ports are not plumbed correctly, you could be loosing vacuum advance just when you need it the most. For testing purposes, ignore the thermal vacuum switches for now. ( three vacuum ports that are stuck into a water coolant passage on the intake ) Good luck.

I have a single vac advance with the 2150 carb.

That is some good news. The 2150 is a very user friendly carb. 6 Phillips head screws pointing up, the air cleaner wing nut stud, and a small screw in the side of the choke blade is all it takes to lift the top off.

If you want to check the fuel level in the carb, start the truck, and allow it to run for 2 minutes to stabilize the fuel level in the carb. Remove the above mentioned screws, and lift the top of the carb off. Measure how much fuel is in the bowl. But because the fuel jets are way in the back, it does not seem to me that fuel could run away from them on any hill.

Have you tried the fuel line enrichment yet?

Where is the fuel line enrichment line located?

That is the procedure I described in post #15. Gas in a bottle and a vacuum line to suck extra fuel.

I got it, I have it written down to troubleshoot still.

I will try it today, thanks.

You have brought up a good point, If the OP is able to connect a vacuum gauge to the engine as he climbs the hill, the loss of power should be at some specific reading on the vac gauge. He should get the same results by power breaking. CAUTION Full throttle power breaking generates 1 degree per second.

After driving for awhile get out and feel the centers of the front wheels, if they are real hot, it could be that your brakes aren't releasing completely, this would be exacerbated when going up hill. If that's the case it's time to look at calipers and the rubber connecting hose that runs from your metal brake lines out to your calipers, these can deteriorate over time and not allow brake fluid to travel back out of the caliper when the brakes are released, creating a situation where there is constant pressure being applied to the rotor.

Thanks I will look at that.

OK,

If we assume that draco is competent, which I do, then we have a level problem.

If the fuel pump/system is working properly, there are only two places where the fuel level can change. The float bowl and the gas tank.

In the float bowl, we have......the float. That is adjustable, yes? Have you checked it?

bob c can give us a hand here. Does the fuel, moving back in the bowl have some effect? Could it be so high as to choke the engine down when going up hill if the float is set too high??

In the tank, there's the fuel pick-up level. Could be a problem if it's at the front of the tank. I had a Chevy in '78 so don't know Ford details.

The chirp? I don't know.

The fuel pick up in the tank is angled toward the bottom center of the tank but problem still occurs when the tank is full. As for the adjusting the carb float I would need some help because I am not too familiar with this adjustment.

Well, if you can adjust your toilet bowl float, you could adjust your carb float. It's basically a float that opens and closes a needle valve to let in fuel. But I don't know why you'd need to.

This one's from a bike.

Good point about full gas tank.

Hey, Thanks everyone for your input. I will spend the next day or so double checking all of these potential solutions.

Let us know, I can't help but think that an improperly adjusted float would cause problems all of the time. I'm always intrigued by mystery automotive problems. I recently lost brakes and engine power simultaneously on my 86 GMC pickup. What the hell! I didn't even feel like dealing with it, and going directly to the bottle of spirits. Finally got to poking around and discovered a freaking squirrel had chewed out an elbow in a main vacuum line. It went to my vacuum assisted brake booster, disabling the brakes and creating a massive vacuum leak, making the engine run like crap. It was the acorn shells under the air filter housing that gave it away. Good Luck!

I will inform you all when I figure it out. Thanks.

I had a 1987 4x4 Ford Ranger. When unlocking my front hubs , I found the the right side wasnt fully releasing and would bind or pull the truck down (because the axle was fighting the Diff) as if the brake was on. Then it would release about a 1/2 mile down the road with a loud bang and the truck would drive normal again. Happened 3 times before I figured it out. I was on a flat highway though, no hills. Just wondering if it's your engine losing power or something holding the truck back like a binding axle or transfer case.....another suggestion to ponder....Good Luck....Rescue

I considered this but I checked the four wheel drive when engaged and disengaged and there doesnt appear to be any problems. I still think that the problem is due to a fuel problem. I am still troubleshooting some of the items addressed by the others but thanks for the input.

Oops.........forgot to ask...have you tried going up the hill backwards to see if it loses power that way..................Rescue

Good point, I will try it. Thanks.

This has all the symptoms of a fuel delivery problem. I recommend an unpressurized GPH test. Multiply the HP at WOT by .5 which is the approximate specific fuel consumption in pounds per HP per HR for a water cooled Otto cycle engine. Divide that result which is fuel burn in pounds per hour at WOT by 6 (the weight of one gallon of gasoline).The result is the amount of fuel in GPH that engine needs to produce maximum power. Typically fuel delivery systems are designed to provide twice that amount. Disconnect the fuel line from the suction side of the engine driven pump. Connect a rubber hose to the chassis line and place the other end into a measured jar (Mason's work fine but a gallon wine jug is better) sitting in a catch pan to prevent spillage. You are about to do a timed gravity feed fuel flow test. Divide the GPH figure by 60 to get the GPM value and start timing the unassisted flow from the main tank into the gallon jug. If the fuel flow starts to dribble or slow down, you haven't solved the problem but you now know where to look. Remove the gas tank cap and listen for s sudden inrush of air. If you hear one, then the problem is that the cap is not vented sufficiently and the building vacuum in the tank under WOT is loading the engine driven suction pump. If that is the cause, then look to see if the tank has been collapsed any from the atmospheric pressure. I would also reverse flow the fuel lines that run the length of the chassis and make sure by visual inspection that the line is not restricted by a crimp from trauma or too sharp a bend radius. I suspect the problem will go away when you install an electric boost pump at the tank and push the fuel to the engine the way it should be. Engine driven fuel pumps simply "suck"! Sorry. . . . . . . I couldn't resist the pun! I've a suspicion that what we are dealing with here is an engine swap where a smaller, less fuel demanding engine has been replaced with one significantly more powerful and the fuel system was not upgraded to keep up. If that suspicion is accurate, you may need to run a larger fuel line for the thirstier engine. Laughing Jaguar

Thanks for the info on the flow test, but you brought up an interesting point about the fuel tank cap. The old caps just have a rubber gasket that seals around the tank inlet hose. I wasnt aware that they could cause a vac in the tank but it makes sense. I will try the hill with the gas cap on loosly.

First of all, I want to offer to empty that wine jug.

Second, nice post.

Bob C wrote:" First of all, I want to offer to empty that wine jug. Second, nice post." Thanks Bob. I studied engine design and suspension systems for four years and ran a technical school for Porsche-Audi after I left MB. I worked briefly as a crew member for a Formula One team when things were a lot more simple. Needless to say I've skinned my knuckles more times than I care to recall, on machines with wheels and wings Diagnostic stuff like this is like offering a kid a box seat and a hot dog at a baseball game. L.J.

I also have a long and vast history of experience. I was a beer drinking drunk till I discovered wine. Then I graduated to cheap wine. But now that I am older, and more mature, I only drink hard liquor.

Nice rounded education if I do say so myself.

just my 2 cents worth. You say it is a new engine. Is it tuned for the fuel you are using? i.e. is the engine "pinging"?

The engine is flawless when not under a heavy load and there is no pinging. After I get on the throttle for about a mile or so, is when it begins to chirp very mildly underneath the truck and begins to loose power when driving uphill. Ironically I just remembered when I dropped the tank, I found the original locking cap broken in the tank where someone broke it to replace it. The cap it has is a metal cap that had a rubber gasket replaced on it, not allowing it to vent. I will replace the cap and try it again.

"After I get on the throttle for about a mile or so, is when it begins to chirp very mildly underneath the truck and begins to loose power when driving uphill." --

When you lose power going up hill do the engine RPMs stay the same or are the RPMs falling off as you ascend the hill?

In an earlier post you said you replaced the clutch. Did that include replacing the the flywheel or have it machined/checked to make sure it was not warped/worn?

Once the chirping starts, does it do it with the truck stopped and in running in nuetral?

I put my money on the chirping sound coming from the water pump.

I'm betting on smugglings birds.

The engin is running a 3/8 fuel line throughout. I will let you know if the fuel cap replacement fixes the problem.

Okay I'm coming into this conversation after it has matured and given advantage of former posts and idea exchanges I don't think it's a fuel delivery problem.

Is the suspension in the factory delivered condition; is the truck customized? And are the tires larger than factory spec?

How does the truck perform if under load when on a flat hi-way? Do the same symptom's occur as on a hill?

The suspension is from the factory but I do have 33s on the truck. The same chirp will occur on flat hwy but the power loss happens uphill.

I questioned the condition when under load because if the distributor gear is off by one tooth when set in place the necessary advance may not properly occur.

Incidentally what form of gasket was used when attaching the carb?

I made sure that I geared the dist in properly and rechecked it 3 times.

Just an idea, but is the transmission fluid level checked and OK some time after you replaced the transmission?

Going uphill with low level transmission fluid could cause dry running of the gears and cause the chirping sound.

Another cause could be the plain bearings in the engine.

I will recheck fluid level.

I've read all responses to your question. All good suggestions,but I have not seen

any mention of the egr valve. I'm not positive all 78's had one, or in all states.

I can tell you - having owned a couple 78 F-250's that some of your symptoms

are similar to egr problems. The egr is opened with vacuum(usually via thermo

switch). The chirping may be the introduction of exhuast gas to intake at the wrong

time. The egr may also not be seating properly. If you have one of these don't

disregard - as they are famous for burning valves, overheating, cracked/warped

heads.

There is an egr and seems to work ok but can I plug it or is it better to keep it in use.

EGR systems allow exhaust gasses to flow back into the intake manifold at engine speeds above idle. This has the effect of lowering the amount of air getting into the cylinder. It will hurt engine mileage and performance if too much is allowed in too early. Try removing and blocking the vacuum line to the EGR valve and retest.

I tried it and it made no difference.

Good. That is one item eliminated.

You say you replaced the engine and transmission. Are all the fasteners in place?Going uphill could shift the engine backwards and causes some friction if moving parts are pressed together, for instance the driving train against some bearing. This could make that chirping sound?

I made sure every bolt was installed.

A loose spark plug will cause this too...

When #1 flashes TDC on compression pull dist. cap and check the position, and condition of the rotor, and location of the timing marks, if within limits then proceed with trouble shooting.

Proper routing of ignition wiring is critical (#5 & #6) on ford 351 engines and use motorcraft wires.
Another possibility is vacuum leaks. Open the throttle, less vacuum in the intake, less leaking from the sides or hoses, less problem with missing. Higher vacuum or less throttle, gonna pull in more "stray" air and cause lean misfire. The easy way to find a vacuum leak, check with an unlit propane torch by passing it along those vacuum lines and around the connections. One of the least suspected, but possibly more common places is a failed diaphragm in the brake booster. A vacuum gauge is perhaps the best investment made when troubleshooting drive ability issues on Fords. If any pulsing in the vacuum, the next test needs a compression gauge. You probably have a burnt valve or blown head gasket then or a distributor off by a tooth can produce same.

Don't overlook testing the EVAP cannister

Have you checked if the vacuum hose from the intake to the distributor is connected correctly or it is not liking? This is advance for the distributor. If you have one. I imagine you have an electronic ignition? You may not have one. Check your timing by rotating the distributor a few degrees left or right.

Just about every engine that lost power on uphill situations that I have had the chance to diagnose was caused by restricted exhaust. On vehicles like yours if it still has some OEM pipes cause may be inner pipe collapsing since some pipes were made in two layers for noise suppression. This was quite common. Test by cutting a hole about size of quarter or larger near engine and try the hill. If problem goes away start replacing pipes. Sometimes you can tell if the pipe collapsed by tapping and notice the difference in sound from one point to the other. Cheers.

"On vehicles like yours if it still has some OEM pipes cause may be inner pipe collapsing"

this happened on my dad's 72 buick.........back in the day..what was wierd was that it happened right after we changed the plugs, air filter, oil & filter, etc ,,,,so we spent a bunch of time thinking that we did something wrong, before taking it to a mechanic, who finally found out what the problem was.....

or maybe someone shoved a potato in your tailpipe.....

to the OP, please post the solution when you find it.... we are all now vested in this project :)

Over axle tail pipes were common to de-laminate and restrict on the late 60s and early 70s big GM cars.

Rather than cutting a hole, it is less expensive to just loosen the exhaust manifold from the cylinder head, or the exhaust pipe. No need to re-weld the hole then.

Per chance, is the fuel filter on correctly? Some filters will let fuel flow backwards, albeit with more restriction, so an engine will run until put under load. It doesn't really explain the chirping sound, but it's a simple thing to check.

please remove the exhuast near the y pipe and try it a lose baffle in the muffler or a collapsed double wall pipe will chirp and cause a great reduction in power as the engine can not flow good air in if the bad cant leave

I replaced all of the exhaust pipe.

If your vacuum advance has a strong spring in it to allow vacuum advance only at high vacuum conditions, the hill may kill off sufficient vacuum to allow the vacuum advance to return to the non-advanced position. That COULD be the condition you are describing. If the vacuum advance unit on the distributer has a hex like appearance to the hose end, you can stick an allen wrench into the vacuum port, and turn the adjuster counter clockwise to lower the vacuum required to pull the advance in. While you are in that area, please check the distributer rotor to see if it is able to advance by centrifugal weight movement. If the weight mechanism is frozen, you will be lacking some of the advance needed for that hill.

I replaced the exhaust pipes when I changed the motor and I will troubleshoot all of these possibillities until I find the problem. I will update you all later and hopefully with the solution. Thanks.

Sounds like your power loss is related to ignition timing. What type of distributor did you put in the engine and if you have disconnected the vaccum hose to the ignition advance did it change anything if the system has an after market weight system you may need to change them out in order to get the proper power curve.

It is an oe replacement and it is new also, I will look in to it further.

If it is also new, that should eliminate the chance of vacuum advance, ignition pick up and it's wires, and the centrifugal advance systems. This also eliminates some things. At least we are narrowing it down. This is progress.

As most of you know my realm is nominally electrical engineering and not mechanical engineering, so I do not speak with any kind of authority here. I really am surprised at all of the shade tree mechanic solutions proposed here. I'm predominantly not seeing anything that I would call engineering. I see very little testing procedures or instrumentation mentioned here to identify the root of the problem. Now in all fairness there have been a few clever non-instrument tests suggested here, but most have been just declarations of what might be the problem.

I would consider doing an engine vacuum test to try to identify what is failing. With the addition of just a longer vacuum hose this test can be done while even trying to climb the hill.

The readings going up the hill are going to be progressively less vacuum as power is lost. The addition of the variable load on the engine (hill) will only cause additional changes to the readings. BUT, there is some very good information that can be gathered with a vacuum gauge. For example, if the exhaust is too restrictive, manifold vacuum can actually become pressure.

Also, the point on the vacuum gauge where the power falls off would be handy to know, It could be a combination of high setting on vacuum advance, and low setting on the power valve.

Good point, I will let you know the results of the vac test tomorrow.