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Discussion Starter #1
Recently I bought an 87 F250HD, it's a non cat 460, 4v Holley 4180, and 4 spd and has 116,000 miles. I bought the truck cheap because it wasn't running well and the p.o. was disgusted with it. When I looked at it, the p.o. had the carb rebuilt, and put new wires on it. The truck ran like it had 2 wires crossed and had a strong smell of gas under the hood along with a rich smelling exhaust. When you stepped on the throttle it would back fire through the carb, note this is while the truck was parked and not driven.

When I got the truck home, I found the wires to be correct ( 15426378 firing order ).When I tried to run the engine, I found the condition had digressed to the point were the engine was running on 1 cylinder. I moved on to the carb because it appears to have been a spray paint rebuild. It appeared to have been partially dis assembled and painted gold! When I took it off I found a massive internal fuel leak in the carb. the inside of the manifold was wet with gas and 7 of the 8 plugs were wet with gas, all were black with soot.

I found the carb to be butchered a bit and bought a good core from a fellow VFM'er and rebuilt it, I used the base plate from the original carb because of some differences on the throttle lever, everything else on it appeared to be the same.

After I installed the carb, I did a quicky compression test, I found #2 to be at 180 psi, #3 to be at 130 psi and all the rest to be 150 psi. I wasn't expecting to find great results because the walls had been washed down with raw fuel. I didn't think this was too bad, I figuired the 180 psi was do to pooling of fuel in that cylinder, ( I had drained the oil and would say that there was about about 1 1/2 gallons os gas in with it! ).

I put in new plugs and started it, now at least it was running. I still had it popping through the carb though. I replaced the cheapy wires with a good set and it ran a little better. I started spraying WD40 on the vacuum lines looking for vacuum leaks because idle quality wasn't great, running a little rough, not firing evenly. Didn't really find anything.

I replaced the gasket under the carb and the one between the intake manifold and egr spacer along with the egr gasket. I checked out the egr valve with some WD40 to see if it's seat was leaking and didn't really find anything. The engine ran pretty much the same.

Next, I moved on to the vacuum lines. I disconnected the p.b. booster line and put a rubber cap on it, no difference. After that, I started to unplug the vacuum lines from the vacuum trees with caps. This helped greatly and the engine run much, much, better but still have some popping through the carb when the throttle is opened quickly and still a little roughness at idle.

With the timing set, and the vacuum line off the dist. I'm getting about 19-20 inches of vacuum with the needle fluctuating slightly.

In summing things up, at a fast idle, it seems that I have some what of a steady mis. Also I've notice that the vacuum pull off of the choke isn't really working, I need to hold the choke open with something untill the electric choke holds it open, I'm getting about 7.35 volts to the choke. I don't think I missed something when I rebuilt the carb, but it's possible, I'm not going to assume anything. I've also have taken all the plug wires off one at a time to see if it was anyone cylinder is causing the problem, but it didn't go away ( back firing through the carb ). And yes the timing chain is a little worn.

I'm getting a little frustrated because I'm missing something but can't quite figuire out what. I think I still have a vacuum leak causing the back firing and also forgot to mention the egr plate looked in very good shape. Any clues, ideas, HELP!!!!!!!!! please, thanks.

Tom
You can do anything you want to......ONCE!
aka "my 66 coupe"
 

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Good chance that homebrew carb caused more problems than you've seen so far...

Since you mentioned EGR plate, I'll assume the truck has smog equipment....

Yuk....

You should be able to find a factory service manual for your truck....I have the complete manual set for my '85 F250HD and I believe it has sections on the gas engines although I have the diesel...

Those manuals outline many test procedures and repair instructions for things I didn't even know existed....they were 50.00 well spent when I bought the truck new...

If no one has come to your rescue, when I have some time this evening I'll drag them out and see if I can find your problem in there....the differences between the model years at that time should be minor...

Pat
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Since the car is still backfiring through the carburetor, it would make me consider a couple of things. Maybe the valves have been incorrectly adjusted. But then the compression test might discount that cause. Does it look like the valve covers have been off before? It wouldn't take too much trouble to give them a re-adjust to make sure. It could also be that the timing chain has slipped just a cog or too. Enough to make it run like poop but still start and run. Of course I'd go ahead and get a new choke pull off diaphram(cheap) and maybe check the distibutors advance diaphram.

Hey, the easiest thing to do would be take to a shop you trust and get it on a Sun diagnostics machine. That might answer some questions without as much wrenching.

66 C-code convertible
66 C-code coupe
65 GTO hardtop
76 Nova hatchback
 
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Tom, here are a few common problems related to rough running 460. Intake manifold gasket leak,often on lower edge of gasket under manifold, will usually suck oil and smoke on cornering. If your carb has vacuum actuated bowl vents, test them for leaks with a vacuum pump, should hold vac. if not the vac. is applied to fuel in the bowls , this really screws up fuel flow.Also remember several old TSBs from Ford regarding worn distributor drive gears and sheared pins.Hope this helps.

Chris.
 

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Discussion Starter #5
Yeah, a lot of the stuff is going to fall off soon. One of the two smog pumps is frozen, a lot of the plastic vacuum lines are very brittle and cracked, yes, they have been circumvented. I'm leaning toward the carb too, I'm going to try the Edlebrock off of my 66, soon as I can find a ball stud to mount on it to connect the throttle linkage. I was pretty carefull doing the rebuild on the carb, I don't think I omitted something, but in all my years of trouble shooting has taught me NEVER ASSUME anything. I was wondering if there was some cronic problem that they may have had as far as the engine goes, such as intake manifold gaskets failing ect..

What's neat about this truck is that it didn't have a catalytic converter on it from the factory. It has dual, 2 1/2 pipes going to the muffler. The muffler has one outlet on it but is shot. I'm going to look for a pair of Flowmaster at the spring swapmeet at Raceway Park in Old Bridge/English Town N.J. next month. The track is about 60 miles from my house.

I've forgotten about going to the Summer Nationals there because it's such a zoo trying to get there on the 2 lane local roads!

Tom
You can do anything you want to......ONCE!
aka "my 66 coupe"
 

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Discussion Starter #6
No the valve covers have never been off. Mechanically, the engine is very quiet, very little blow by and basically appears to be in good condition. I've thought about the chain also, but I don't think I'd be pulling that much vacuum. Basically I don't want to randomly replace parts. I was looking more towards some cronic problems with this combo that may be known to someone who works on these things.

Tom
You can do anything you want to......ONCE!
aka "my 66 coupe"
 

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Discussion Starter #7
Thanks Chris, this is more what I was looking for. I haven't noticed smoking, mechanically the engine is very quiet with very little blow by. The v.c.'s have never been off, but looking in the filler cap, everthing looks very clean. Right now, I have all the vacuum lines by passed with rubber caps wich helped a lot. I'll have to try and remove the vent hoses from the bowls. Thanks very much.

Tom
You can do anything you want to......ONCE!
aka "my 66 coupe"
 

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In the meantime, you might post your problem here and see what the truck experts have to say....

Also, you can view recalls and tsbs from AllData here

Have fun!

Pat
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Look more closely at the EGR valve:
EGR valves fail in one of two ways: 1) The rubber diaphragm used to open and close the valve has failed. 2) The valve gets clogged from carbon build up.
The symptoms of a bad EGR valve are:
Rough idle, A "miss" or slight "popping" in the exhaust at all RPM's, Large amount of backfiring, The car runs rich, and the spark plugs are black when you pull them out.
Use a vacuum pump to test the valve.apply vacuum to the valve. The motor should run rough and want to stall, that would be a good valve.If it would not hold vacuum or did not want to stall that is a bad diaphragm.
If the valve holds vacuum and you saw no change in the idle the valve is stuck open or partially clogged

Greg B
 

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Discussion Starter #11
When I had everything apart, The egr had a home made gasket that blocked everthing off, I did put some WD40 on the seat to see if it was leaking, but didn't appear to leak.

Tom
You can do anything you want to......ONCE!
aka "my 66 coupe"
 
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