<TABLE cellSpacing=1 cellPadding=4 width="100%" border=0><TBODY><TR><TD class=msg vAlign=top width="100%" bgColor=#ffffff>I have an '86 F150 with the in-line 6 cylinder (4.9) and factory air.



It ran at high idle, backfired and ran-on after shut-down for almost a year until I finally figured out that the carburator throttle-body had separated and was allowing air in, so I disassembled the carb, tightened it back up and adjusted the idle to run at @ 750 RPM. It ran beautiful for about a week, and then all at once it started running very, rough. Low power, I have to floor the thing to get it to go and/or start. It smells of raw gas at the exhaust (very strong). I pulled the plugs and they were all completely (and evenly) carbon fouled. I replaced the plugs, wires, distributor cap, rotor and air filter. The running improved slightly for a while, but not by much. It's been 2 days and I think the new plugs are carbon fouled again already.

My Haynes Manual says that carbon fouled spark plugs are either caused by too rich fuel mixture or weak spark.

I found a valve on the left side of the carburator which I assumed adjusts the fuel/air and I closed it completely. This had absolutely no effect on the problem at all. Also the when I removed the distributor rotor, the end where it passes around was blacked and carboned, but it was at least 2 years old and so I don't know if this is normal.

I replaced the Voltage Control Module about 3 years ago, and I don't know if this could be the problem. Also, there is a small metal cylinder attached to the side of the engine and is very exposed and looks very old. I think this is the condensor.

So my suspects are:

Bad Voltage Control Module
Bad Condensor
Bad/Broken Fuel/Air mixture Valve (could this happen ?)
Something inside the carburator closing off the airway (I had been running without an air filter for a while....)
Timing Belt slipped (if the spark is firing too late, wouldn't that cause this ?)

Or something else.

Any help would be greatly appreciated. It's Sunday and I have a job tomorrow and would like to get this thing fixed sometime today.

Thanks in advance,

Billy


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I spent the hottest part of the day troubleshooting, and I think the problem is the fuel/air solenoid. I moved it around, inspected it & the wiring first thing today, and when I started the truck it ran fine. But only for a short while, and then back to the same old.

I read a consistant and constant 9.75 VDC on both blades of the connectors. I assume this is normal, but even with this voltage the truck just reeks of gasoline. So I am thinking the solenoid is bad.

It was said a "computer" sends the data (voltage) to the solenoid, and I don't know about any computer. Is it a sensor ? Could that be the problem ?

Where does the voltage to the fuel/air solenoid come from ?

 

Have you tried pulling any codes yet?

 

No, and I don't know how to. I assume you need a special code reading tool. My Haynes manual lists the error codes and what they mean.

Is this something you can get Auto Zone to do ?

 

A reader for OBD1 is fairly cheap and can probably be had at autozone.

 

Have you tried putting a vacuum gauge on it?

 

The valve you found to adjust fuel air mix. and turned all the way in would have a mate if it's a 2 barrel carb. Is it? I'm not a carb guy but I would be that your fuel air was rich to compensate for the vacuum leak and fixing the leak made it richer which fouled your plugs. A dirty rotor would just compound that issue. As was suggested previously, eliminating vacuum leaks is in order. If your rotor was 3 years old then your wires are probably at least just as old. New plugs, wires, rotor and cap followed up by a proper carb adjustment are a good start to ruling out the most common problems. Fuel filter too. Let us know what you come up with.

 

First, thanks for all the help. The problem is still ongoing, and I still need help as I don't have the money to pay a professional mechanic, nor can I afford to have the truck down for repairs, as it is my only work vehicle.

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Quote:

The valve you found to adjust fuel air mix. and turned all the way in would have a mate if it's a 2 barrel carb. Is it? I'm not a carb guy but I would be that your fuel air was rich to compensate for the vacuum leak and fixing the leak made it richer which fouled your plugs. A dirty rotor would just compound that issue. As was suggested previously, eliminating vacuum leaks is in order. If your rotor was 3 years old then your wires are probably at least just as old. New plugs, wires, rotor and cap followed up by a proper carb adjustment are a good start to ruling out the most common problems. Fuel filter too. Let us know what you come up with.

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I do not think the unknown valve (at the bottom of the carburator on the passenger side) controls the fuel mixture, as everything I have read indicates that the fuel/air mixture is done by the fuel/air mixture control solenoid (mounted on the carburator), which I have replaced (see below). However, if I am wrong, please correct me. I really would like to know what this needle valve is for.

And even though the fuel is very rich, I intend to replace the fuel filter tomorrow, although I cannot understand how a clogged fuel filter will cause the engine to run too rich. It's been about 2 years since it was replaced, I frequently run out of gas and have to add gas from the dirty can I keep in the back of the truck so it's very possible the filter needs changing anyways.

The carburator is a single-barrel, if that is relevant.

Quote:

Also, there is a small metal cylinder attached to the side of the engine and is very exposed and looks very old. I think this is the condensor.

The Counterperson at AutoZone informed me that this cylinder is a noise-suppresion device designed to keep the whine of the engine from disrupting the radio.

Thus far I have replaced:

The Fuel/Air Mixture Control Solenoid ($85.00)
Ignition Control Module ($40.00)
Oxygen Sensor ($25.00)
Ignition Coil ($12.00)
EGR Valve Gasket (5.00)
Distributor Cap & Rotor and Spark Plug Wires

I found a vacuum-hose "tree" (behind the carb) that had a broken rubber boot (to plug the nipple) which I replaced.

Overall, the performance of the truck has improved, but I still am getting only @ 6 mpg, it blows a light, grey-white smoke and the exhaust smells both of raw and incompletely burned gasoline.

It idles a bit rough, but better than it did before. Acceration from a stop is bad; I have to open the carb wide-open to get any power.

The primary symptom I have noticed over the last few days is that the "bad running condition" is intermittant. Sometimes this thing just purrs along better than it ever has before, and sometimes it's horrible and embarrassing, particularly at long and hot intersections.

One avenue I am looking into is I read somewhere that an exhaust manifold that has come loose from the engine will allow air (oxygen) into the exhaust and cause the O2 sensor to send a "rich" signal to the Fuel/Air solenoid.

HOW it gets there is the critical question for me still, as I cannot find out what device/source of voltage signal is the solenoid recieving from. I believe the solenoid is the cause of the rich fuel/air mixture, but cannot figure out why or how to fix it.

I also read that the exhaust manifold for the '85 F150 (the model from the previous year as mine) is known to be of poor quality, and will warp away from the engine if it gets wet or overheats. I frequently spray my (hot) engine with a pressure washer, so this may be what has happened.

I tried to tighten the first bolt on the manifold and it immediately sheared off. 2/3 of the metal on the bolt had been gone for years; I could tell by the rust. I went to the Ford Dealership yesterday and the Counterman there could not find the specific replacement hardware for the exhaust manifold on the computer, and suggested that I remove them all and then try to match them piece by piece.

I'm going to dedicate an entire day to this. I need to borrow a car, and purchase an extractor kit first, as I suspect there may be more sheared bolts in the future.

So these are my current "suspects" now.

1. Separated Exhaust Manifold
2. Faulty (unknown) Device that sends voltage to the Fuel/Air Mixture Solenoid.
3. Vacuum leak somewhere, but I have looked EVERYWHERE numerous times.

These are my ONLY ideas on what the problem might be. If anyone could give me any other avenues I would be very appreciative.

Also,

Quote:

A reader for OBD1 is fairly cheap and can probably be had at autozone.

What is "OBD1" ? Where/how are these codes read ? There is a hanging, bright red connector in the Engine Compartment. Is there where the codes are read from ?

Quote:

Have you tried putting a vacuum gauge on it?

No, and this is a new suggestion to me. Is this to measure manifold pressure ? (MAP? - or something like that . . .)

Could low MAP be the cause ? What creates MAP ? How do I measure it ?

Thanks again for all the help. Please remind me if I missed anything, I am very serious and very determined and intend to be very meticulous about this until it is fixed. Thanks again.

Billy

 

OBD1 is the first generation of On Board Diagonstics for computer controlled cars. And yes, that red connector is where you check. There are loads of articles on OBD1 and relateed EEC-IV informtion. Google for just those two items and you will be reading for days.
The is one article in one of the Mustang articles about how to use a volt-ohm meter and your OBD connector to check for codes and can be found at:
http://www.corral.net/tech/maintenance/eecivtest.html

Scroll down the page a bit, well actually I'd suggest reading the whole article, and you will see the setup.

Chuck

 

Here is the least expensive reader I found doing a quick search for OBD1 readers:

http://www.oneautoshop.com/B000EW0KH...de_Reader.html

Chuck

 

MAP is manifold absolute pressure. I can't see how an exhaust leak would make the O2 sensor read lean. That needle valve sure sounds like fuel/air to me. Once again I'm not a carb guy but that screw gets tuned in until the rpm's decrease and then it get's turned out aprox. 1 full turn. Stick with the tune up parts, vacuum leaks and carb adjustment. Does your CEL (check engine light) come on? Even durring start up to indicate that the bulb is good? The CEL can also be used to read codes once you install a jumper wire in just the right place. Keep us posted. Good luck.

 

This is if you have a Carter YFA 1-V, feedback single barrel carb, which it probably is since they were used on the "under 8500 GVW F150's with the 4.9L engine":

The Ford manual shows the the idle/air adjusment screw in two different views; 1) looking at the carb and with the choke on the left, the screw will be on the bottom right and may have a tamper proof cap on it. Although a PO may have removed that cap. Or 2) with the choke on the right the screw is on the right side bottom on the inside of the fast idle adjusting screw. A tamper proof cap may or may not be on it. Clear as mud?

The nomal way of adjusting the idle/air screw(s) on a four barrel, is to adjust to the highest vacuum reading, starting by turning the screw out about 1 -1/2 turns from bottom and then adjusting from there, going in about 1/4 turn. The 1 barrel probably works the same way.

Chuck

 

I would say time for a carb kit.
Are you still running it without a air filter? Trash can get sucked in and mess up the carb.

 

Thanks again for the help. Before I respond to the latest posts, I have some new information that might be useful.

I have noticed over the last several days that the problem seems to be heat related, as the engine runs fairly well when I start it up first thing in the morning. Performance degrades steadily after that, until it is barely running and blowing smoke by the end of the day.

One of the things I have been trying to do is ID the specfic carburator for my truck. Is there a way I can confirm if this in fact is what I have ?

Yes it's clear, unfortunately neither of these describes my carburator. It has an electric choke which is not positioned either right or left; rather it is at the back (toward the back of the vehicle) of the carburator. I've connnected it and disconected it, adjusted it per the intructions from my Haynes manual, and spun it to the extreme in either direction; nothing I have done has changed the performance of the truck one way or the other.

The "fast idle adjustment screw" is on the right (driver side) as you face the engine compartment, as well as an adjustment "plate" of sorts. Here is a link to some photos of the carb.

http://s57.photobucket.com/albums/g2...Ford%20Photos/

I have spun this needle valve anywhere from all the way closed to about 4 or 5 turns open and it seems to have no effect whatsoever. This morning I pulled the needle valve completely out in order to inspect. I thought perhaps there might be a missing/damaged "o"-ring or something that might be allowing air to enter through the valve. I found no "o"-ring or any other means of sealing this valve; all that came out was the needle itself and the spring. The tip of the needle was very dry, did not smell of gasoline and had a light carbon build-up. This valve does not seem to meter fuel; rather it seems to be metering exhaust gases. Perhaps it is connected in some way to the EGR valve, as it is near the very bottom of the throttle body and only about 3 inches from the EGR valve.

Tomorrow is my big "manifold disassembly day". I intend to remove all the bolts, etc... for the exhaust manifold, then clean the threads in the block, replace the bolts with new hardware and replace the exhaust manifold gasket. This is all operating under the theory that the exhaust manifold is allowing air to get into the exhaust and causing the O2 sensor to send a "rich" signal to the fuel air solenoid.

I still have some pending and important questions.

First, how is voltage sent to the fuel/air solenoid ? Could this component be bad ? If so what is it called and can I replace it ?

Second, I am still unsure how I can have a "fuel/air mixture valve" (needle type, as has been suggested) when I know for a fact I have a fuel/air mixture solenoid that ought to be doing the job of adjusting the fuel & air ratio. It seems unlikely that both would exist on the same carburator.

Third, my latest "theory" is if perhaps the intake manifold bolts have worked loose. I'm not real sure how the vacuum system works, but if I remember my High School Auto Shop class, it has something to do with the intake manifold.

If the Intake Manifold is physically loose from the engine block (and leaking air) would that cause the symptoms I have ? Tomorrow I will check to see if those Intake Manifold bolts are all present and tight.

I have a new Air Filter in now. I am also wondering if "trash" may be involved, and if the exhaust manifold repair does not fix the problem, the next step is to tear-down the carburator. I have most of the kit I purchased left over, as I only used the two flange gaskets for the throttle-body.

 

The thing about blowing smoke after it heats up coud be a head gasket issue. How many miles are on it?

To find a vacuum leak I take a can of starting fluid and spray it in suspect areas. Having a tach hooked up while you do this will enable you to see as well as hear the rpm's go up when you do find the leak. Just be careful because if your spark plug wires or cap are letting the spark go anywhere except the spark plugs, the starting fluid will definately go BOOM!!!!

Running a compression test on a hot motor will give you an indication of the health of the head gasket.

Lastly, jam those vacuum lines on all the way.