1978 F150 Loses Power When Driving Uphill

Forget all tests until you do the plugged exhaust test. If you can loosen the exhaust at the manifold do so and take it for a noisy run. If you cannot loosen due to rust then cut the hole. My 40 years of automotive mechanic and hot rodder points to plugged exhaust and it may not be the pipe but a converter that crumbled and passed the particles into the muffler causing the restriction. Try tapping the pipes and muffler to see if there are parts of converter inside. It should be obvious try a rubber hammer to see if a rattle occurs. One Fiesta in particular baffled many experts until I got hold of it and removed the exhaust system and dumped out all the converter pieces most no bigger than your thumb. Too many suggestions are way off base for the symptoms.

The worst case of this I ever found was a Hyundai with a cat built into the exhaust manifold itself. The car would start the cranking process at normal speed, but in 10 seconds it was turning slow like a weak battery. Jumping did not help. Charger and double jumping did not help. Only when we would stop cranking and listen immediately would we hear a hissing noise. We removed the EGR valve and plugged the vac hole, and it started immediately. With just the EGR hole open the engine felt normal till revved.

Thanks for the tip, one of the other guys mantioned a vac test also I have a friend bringing a vac guage tomorrow and we will test it.

One item I forgot to mention. If the truck is equipped with a cruise control and throttle position is governed by a vacuum operated dash pot, disconnect the vacuum line from the dash pot, plug the hose so it doesn't leak manifold vacuum and disconnect the carb linkage from the dash pot. I developed fixes for two different cruise control systems back in the 70's and if they malfunctioned, they would do the exact opposite of what they were suppose to do. Also, remove the air cleaner. Look down inside the carb while someone else floors the gas pedal with the engine off. Make sure that the throttle plate is vertical and the carb is unrestricted. Another suggestion: Put a T fitting on the outlet side of the mechanical fuel pump, Run a hose from the second port inside the cab and connect a fuel pump pressure gauge. See if you still have adequate fuel pressure when the engine looses power. L.J.

There is no cruise control and all vac lines are new. The more I work the problem the more I think that the vac lines might be connected wrong. There are so many different ways Ford hooked them up.

When you rev your engine do you notice if the distributor rotates a little?

If not, check and see if you if you can turn it by hand, it may be that it needs lubrication at the seat. loosen up the screw that keeps the distributor in place and lubricate it. Also check if your diagfram is in good shape, if it is old, then if may be torned inside. Check the fiiting at the base of the manifold or the carburetor where the hose connect to and see if it is not plugged up. Check all your vacuum hoses for leaks. Get a good air filter.

It is hard to know for sure, but it seems that the distributer is rotating about 1/2 of the speed of the engine, although by 4,000 it is hard to tell for sure.

I reclocked the dist today and plugged different vac hoses today under load and nothing changed. The fuel cap was replaced with one that vents and this made things a little better. I also did the inclined test forward and reverse and the problem was the same as when level. I will finish the other tests tomorrow. Thanks for all of your help on this everyone.

Progress is good. Now we know that it is not the jets in the carb becoming uncovered. We also now the dist is installed correctly. Is the dist vacuum hose connected to ported vacuum? (no vac at idle, only when throttle is opened)

When vac hose is disconnected from dist, there is no vac from hose or change in idle. When the throttle is increased vac is present.

BINGO. We have a winner. That is the correct set up for these vehicles.

When using a timing light does the mark hold steady or waver side to side? A wavering mark may indicate a loose timing chain or possibly worn distributor bearings.

A few times what you describe including the chirp was eventually traced to a broken cam shaft.

"possibly worn distributor bearings"

Or more likely, a breaker plate with a worn vacuum advance control "hole". In other words the vacuum advance control rod that moves the breaker plate back and fourth has worn or the hole it fits into has worn, allowing movement.

bob c can explain it better, but I don't think this is the problem.

Or more likely, a breaker plate with a worn vacuum advance control "hole".

I don't think it's the problem either though I did intend the post to indicate worn distributor bearings/bushings.

Some common ignition distributor parts, or parts related to the distributor's function, include the temperature compensator, voltage stabilizer, distributor breaker plate, distributor cap and rotor kit, distributor cap gasket (or just distributor gasket), distributor condenser wire, distributor bearing, distributor dust cover, and distributor O-ring.

The timing holds steady.

Due to the incline and grading of the lane when driving uphill the vehicle weight will shift causing greater weight to ride on the right rear wheel; bearings do chirp sometimes when they need attention.

Ok, I am tired of this. With the distributor cap off, the rotor should turn forward about 10 degrees, and spring back. The magnetic pick up should not have any significant play to it when you try to rotate in any direction. Inspect the wires that connect the magnetic pick up to the distributer housing. These are prone to failing when the wire insulation becomes brittle.

Any deviation from these findings require repair.

The only mention of noise you made is of "chirping". The only noise that I can think of that might accompany loss of power would be the noise associated with pre-ignition.

I will send you one more test. The distributor vacuum advance is the clue to distributer rotation. Rotating the distributor in the direction that would push the hose on tighter will advance the timing. For safety's sake retard the timing by 1/2" as measured at the outer rim of the distributor cap. If this stops, or reduces the noise significantly, and restores some power, your motor may be too far advanced.

A timing light is useless if your harmonic dampener has shifted on itself, or if the dampener is wrong for the application. Same results if your timing chain cover is for a different application.

Now get going and test something. If we do not get some results soon, Lynlynch, Laughing Jag and I are going to go there and put plastic bags in your gas tank. You think it runs bad now, just wait.

I once painted a brand new air filter with flat clear enamel. Is that what you want.

I've heard that if you draw lines along a spark plug insulator with a pencil..................

When I was younger, one of my favorite stunts was to replace the coil wire with a piece of wet vacuum line. As the water would heat up and evaporate, the engine would start to miss under load. If it was shut off, no restarting.

Do we need a dirty tricks thread? I have a few I would like to try.

Aw bob if the timing is to far advanced the engine would be hard starting...the chirping could be a sticky idler pulley or from a rock wedged between the cab and bed; when under load the cab shifts and the noise begins...

These maybe two different issues, does this carb have a pin hole in the base plate that may have become obstructed during assembly?

dear op, i know we have digressed, but when you figure it out..............PLEASE let us know...

thanks

A lot of people have concentrated on the distributor and its timing/advance. They, like me obviously think your problem is due to "pinging" also known as knocking, auto ignition, preignition etc. This shows up when going uphill i.e. under load. Also when towing a trailer, horse float or caravan. It can also be caused by the use of unleaded fuel in an older engine. When you had your engine rebuilt did they decrease the compression ratio to alow the use of unleaded? Did they actually increase compression ratio by shaving the heads. This would make it go like stink but cause preignition with modern fuels. It may be possible to buy higher octane fuel at the bowser in your area and that is a simple test.

No Jimrat, i dont know about the other posters, but i did not, and still don't think about pinging or any any other timing sounds. ONLY if your timing is wrong will you get pinging or any other timing related sounds. If your timing is set correctly, as i take for granted since the OP does not sound like a fool, you will not get pinging if you start calling for power, you will simply run out of power because the timing cannot be advanced correctly. ie. up to 5 deg faster than CORRECT setting. If you persist in feeding in gas and don't change gear, yes now you may get "funny" sounds.

I still believe the problem is vacuum related. You can also suck on the vac tube to the distributor. the mechnism should move readily.(Not too freely, that will bring about problems of its own)

The chirping sounds like a head gasket to me, but it could be spark knock.Did you degree the cam when installing it, and correct the pointer on the block to agree with the actual timing?Sometime the tang gets bent or moved and this will throw the timiing way off, even though it looks right with the light.

Have you tried loading the engine by putting it in top gear at low speed to reproduce the problem?

If it occurs only going uphill, then check the pick-up tube in the gas tank for integrity.

I have seen these break loose, especially on Fords.Will drive you KNUTS!

I had one that ran fine till you made a right hand turn, then it would spit, sputter, cough, wheeze, whistle,shudder, shake,shimmy,rattle,rock,tremble, hiccup,burp,gurgle,fart, and occasionally hit a tenor note.It would not do it every time, so it was hard to nail down.

Check your pickup tube in your tank.

HTRN

Check your pickup tube in your tank.

He has had the pick up tube for the tank apart about 4 times so far.

Kinda reinforces our PM, doesn't it.

Ow! my head hurts.

engine was fine through dino test and pickup tube is clean and clear.

"engine was fine through dino test."

was it Dyno'd while in the truck, or before you installed it ?

In an earlier post you said you did not know where the vacuum lines should connect to your carburator. The vacuum advance should be attached to the carburator at the port ABOVE the throttle butterfly. This will cause no vacuum at the advance at idle. When you step on the gas the port above the butterfly will then see a vacuum and advance the distributor. Sounds like it may be attached to the carb below the burtterfly. This would cause the timing advance to work backwards.

#128

I will try it on a diferent port.

From the description you told me, you have it on the correct port.

You are right. That also started to miss near the top.

The engine was dino before installation and the hill is about a 4% grade not hauling anything. The powerloss is from the engine acting as if it wants to stall and I have figured out that the chirping is from a bad trans mount. I am still in the process of the vac tests so I will get back to you on that.

Hey everyone, I have found the problem. The thick gasket under the carb has a crack through the gasket from overtightening, my fault. But thanks to you guys I discovered that I had two vac hoses switched and the fuel cap was not a venting cap also creating a vac in the tank, I also found a fuel line that was rotted and possibly sucking air and I also noticed that the rear end is very worn so I will be rebuilding it soon. Thanks to all of you for your help now it is time for a few cold ones.

Just like that. I'm done. Good by. Get out.

I feel so cheap. So used. So dirty.

Well, at least you are satisfied.

Happy motoring. Glad it was not something expensive.

But just to be sure, take out the fuel tank one more time and check that pick up. I had a friend of mine that had a bad pick up tube, so yours is also bad.

Great news, vacuum the main culprit. I think a lot of people learnt a lot from this.

Vaccuum, or lack of, has been the downfall of many a man.

Ask B Clinton

Anybody wanna buy a humidor, cheap?

congrats.............

All indications seem related to fuel delivery. Back in the 70's, sometimes the seat (seat and needle assembly) has a screen in it to prevent junk from getting into the float bowl. Check this screen very carefully. This is one of those things which often get overlooked, unless you do a complete rebuild on the carb. Good luck.

Thanks for the feedback. Now we all know a little bit more. i.e. ic engines suck.