Hi, I'm new to this forum after recently buying a 1983 F150. Any advice or help you could offer would be most welcome. I have searched the forums and tried a few things but am still having problems. So I will start at the beginning.

The truck is a F150 XLT Super Cab with a 5.8L V8 engine. The engine was replaced at some time, so im not sure what version it is.


Everything started off fine, but since first cold day, I have had problems with a rough idle when cold even though it starts first time. The idle speed starts off about 1500 then when i put it into drive, it drops to under 1000 and runs rough. I checked the automatic choke and it snaps shut as it should. When it warms up slightly it runs a lot better although the idle remains at 1500 in park and 1000 in drive.

Then i noticed a few days later, that when running after the engine is warm, If I gave it some gas say when climbing a hill, it started to misfire cough and splutter. Again I went to the forums and found some suggestions, changed the fuel filter (cylinder attached to the carb) and the air filter, also tried running on different tanks but nothing improved. If anything it now worse. Now when warm, the engine runs very rough, there is a lack of power when accelerating and a vibration around 2000 rpm. Through all these problems though it idles very smoothly all be it a bit fast.

There appears to be a number of things i could now try, but as to which is the first thing, any advice would be appreciated. There is one other thing I replaced but don't think it is connected and that was the starting solenoid.


I would appreciate if you could explain any abbreviations used in any reply as I am not familiar with some of the terms used.

Thanks in advance

Erl

 

I would try new spark plugs & wires

 

Check the distributor cap for corrosion inside, if so, replace, along with the rotor.
Then with the plugs, wires, cap, and rotor replaced, you'll know that side of things is A-OK for at least 50,000 miles. It's called baselining.

 

Yeah, I agree with the other guys. I would definetely start by replacing the plugs, wires and most likely the rotor. That will make a night and day difference in a lot of situations. Good luck....

 

How are you guys equating idle speed issues and poor Hill performance with Spark?

While I agree that If the truck is new to you Spark plugs and wires are a definite must, Im very hesitant to say thats your problem, All the issues you are describing to me point to the carb, if the filter screws into the carb itself, then you have a stock motorcraft Im assuming, Pull it off the intake and take it somewhere you trust for a rebuild.

 

There is a good chance he is not hitting on all cylinders (No punn intended) Really it sounds like a spark problem to me. If not, I would say work on the carb. New plugs, wires, cap & rotor can't hurt and it's a lot easier than pulling the carb.

 

Check/replace vacuum hoses and tighten carburetor mounting nuts. Also check EGR valve and ports for excess carbon buildup. Try a can of Seafoam Engine Cleaner poured through carburetor per instructions on can.

 

Many thanks for all the replys.

I will start off replacing the plugs, wires, rotor and cap and I will also try the Seafoam engine cleaner. I should be able to get this done this weekend, so I will let you know how i get on

Could you tell me where the EGR valve is and I will have a look at that also.

Thanks again

Erl

 

I agree with Icicle for the most part. The idle problems you have are definitely carb related. Probably your choke pull-off and someone set the base idle too high.

As for your misfire under load, I would still suspect secondary ignition. Cap, rotor, plug wires and plugs. When you are under a load cylinder pressure rises and increases the amount of voltage required to jump the gap of the plug. Electricity will always take the path of least resistance and jump to ground through a bad plug wire or boot. I'm sure alot of us here have seen a spark jump an inch or more. It will sometimes find it easier to jump a 1 or 2 inch gap than jump a .045" gap in a hot cylinder!
You could also have a weak coil. It may not be able to produce a hot enough spark to jump the gap.

Let us know what you find!

 

EGR (Exhaust Gas Recirculation) Valve assy. sits directly behind carburetor and mounts to a spacer located between carburetor base and intake manifold. Adds a small amount of exhaust back to the intake manifold to reduce combustion temperature thereby lowering the amounts of Oxides of Nitrogen (NOx) emissions. Many folks remove them when "de-smoging an engine".

 

Missing under load is clearly indicitive of a high voltage problem. I agree that you should replace the plugs, cap, rotor and plug wires.

It also sounds like the fast idle cam is not returning properly, which would account for the fast idle.

 

Missing under load is a symptom of at least a few different things, not just a "high voltage" problem, and FWIW Voltage is the same throughout the RPM band, the spark is no hotter at 4,000 RPM than it is at idle, just more frequent

Missing under load could also be a fuel related issue..... but he never mentions anything about missing under load, he said misfiring, coughing and sputtering, which could (probably is) be timing, or fuel also.

Tune it up, spark plugs, wires, rotor and cap, change the oil and all that good stuff, time it with either a timing light or vacuum gauge, and have the carb rebuilt, and your problems should disappear.

Speaking of vacuum gauges, buy one (cheap) and check vacuum at idle too, it should be about 19 cm/hg at idle, and steady, but steady is the important part, eliminate vacuum leaks too, because an old truck thats been sitting or poorly maintained probably has some, vacuum line is cheap too.

Im willing to bet that if you pull a spark plug and look at it, it will be black and sooty, a dead giveaway of a rich condition, which I bet among other things, you have.

Sounds like you got a decent truck that needs a little TLC, Im not trying to argue with these guys, because I think what they are suggesting needs to be done anytime you purchase a "new to you" vehicle, and those parts probably arent in great shape, but I really dont think its your major gremlin right now.....

Good luck and keep us posted

 

Timing may cause pinging and/or power loss but it does not by itself cause the engine to miss. It's true there may be other issues such as a lean or rich condition involved with his truck but it sounds like he is describing a misfire. But that's the English language for you.

 

The original poster should be thoroughly confused by now!

I think the choke is adjusted too rich. When its cold, it closes too much and acts like the truck is misfiring. It could be something as simple as gummed choke linkage.

When you start it up and let it warm up a little, before you put it in drive, bump the gas pedal and see if the idle drops to more normal. If it stays high, the choke is still on full. At any rate, its not good for your truck to shift into a gear with the idle up high. Puts a strain on your drive train.

Good luck.

My '83 has the 351W engine too. Its a powerhouse. It runs great.

 

That is not entirely correct. The voltage to fire a plug at idle is roughly 5,000 volts. The voltage required to fire a plug under a load can be as much as 50,000 volts.
The coil is not a generator producing a set current at a set voltage. It has to respond to the demands of the engine at all RPM's.

I'm certainly not suggesting that this is the only possible cause of a misfire under load however, the description of the problem leads me to that conclusion.