390 pulsing problem- RE-HASH

blackagatha · Post by **blackagatha** » April 18, 2007, 3:04 pm

I think firing order is correct... I'll check it though. Coil is an Accel, advertised as 12v. Anyway, I had a 6v coil in there that ran great for all this time on 12v. Actually, come to think of it, I don't think there was anything wrong with it when I pulled it. Nothing wrong with almost everything I've replaced.

Plug wires have nice plastic separators, don't touch eachother or truck/ engine. I've rubbed my hands all over the wires when it's running and I don't get electrocuted.

I replaced a couple of vac caps. Checked hoses. Not too many hoses/ places to go wrong. I remembered a problem that drove my dad up the wall with his 390- His plastic carb spacer shrunk slightly, and made a massive vacuum leak- so I took a wrench to mine and found it to be slightly loosened, but not the problem.

Ford4jack · Post by **Ford4jack** » April 18, 2007, 5:48 pm

Have you checked your spark plugs. I have had some that looked fine and fired great when tested but then not fire under compression.

You can pull your plug wires off one at a time to locate a missing cyl then swap that plug with another hole to see if the problem moves.

good luck with your truck.

blackagatha · Post by **blackagatha** » April 18, 2007, 7:05 pm

I pulled plug wires, none of them were totally dead cylinders. Every cylinder fires, as all of the wires affected the run quality. It just seems that they may not be firing hard enough, due to leaky valves. I do not suspect rings, because there is no oil residue in the plugs, and it is not smoking.

Uncle Skip · Post by **Uncle Skip** » April 18, 2007, 7:10 pm

When you have the valve job done, be sure to have hardened seats put in.
If you have low compression that is the giveaway but quit driving the truck until you get your new valves or you'll pound the seat completely out (new heads?) :oops:

Let us know.
U@ss

DocDave · Post by **DocDave** » April 18, 2007, 9:28 pm

This must be drivin you nuts! :shock:

Old vacuum leak test
Get a propane torch. Do NOT light it.
Start engine
Pass torch turned on full (NOT LIT) around areas of suspected leak (carb, intake)
If the engine starts to run better suddenly, you've found your leak
Do NOT try this on an old flathead. Mine used to light the torch every time I went near the head (Bad headgasket) :oops:

I've found many a leak using this. Not sure about using it on the booster though
Really hope you find the problem.
eliminate one system or part of a system at a time and work in a logical sequence.
Dave

Ford4jack · Post by **Ford4jack** » April 18, 2007, 10:59 pm

If you think you have valve issues you could try pressurizing your cyls and listening for in/ex leakage?
If you try this be careful. If the test cyl is not all the way down it will be when you put the air to it.

blackagatha · Post by **blackagatha** » April 18, 2007, 11:36 pm

tonight was the worst she has ever ran. She is not moving any more until I figure this damned thing out..... And YES. it is driving me up the wall.

Tonight, I had to limp her home at about 25 mph/1000 rpm. If I even pushed the gas more than a gentle caress, the engine shuddered HARD and was a constant pop out the carb.

I have no air compressor. No torch, no compression tester, no measuring caliper. not even a freaking timing light. Nothing I need. It's all at home and I'm 200 freaking miles away... I'm gonna have to get my dad to drive up here, drag aggie home on a towbar, tear her apart, drag engine to P.O. Machine in Tucson, to get whatever the hell it is fixed. The semester of school is about a week and a half from over. Then I get like 1 week break, then Summer School starts. I'm beginning to fear that I may have to cancel the damned summer school in order to fix truck.

P.O. Machine is where I got the machine work done the last time. He's the most reputable guy in Tucson, always swamped with work, because people "know". He put in hardened valve seats. And as far as I am aware, "he does stuff right". Maybe something was a bit wrong... who the hell knows... Everything was supposed to be good as new.

Bills 66 · Post by **Bills 66** » April 19, 2007, 12:48 am

Did you ever check your fuel filter? Also there is a flexible hose from the tank outlet that deteriorates down between the cab corner and frame. If it is plugged or collapsing it will run as described. Just a thought.
Bill

blackagatha · Post by **blackagatha** » April 19, 2007, 1:35 am

the only fuel filter is integral to the fuel pump. It is brand new. Hose from cab to line is basically brand new. Hard line is less than 2 years old. No kinks. Nothing makes sense.

jakdad · Post by **jakdad** » April 19, 2007, 5:51 am

Before you pull the engine and go through all that, why not take it to a competent shop and have them diagnoss it. Might save a lot of money and work. It almost sounds like a timing chain gone bad, but I don't remember if you had the occasional backfire through the carb. Anyway, just another long distance thought. Take it to a shop. Good luck.

Slick Fan · Post by **Slick Fan** » April 19, 2007, 12:18 pm

I'm taking bets on a flat cam...with possible timing chain problems thrown in.

ELpolacko · Post by **ELpolacko** » April 19, 2007, 1:40 pm

Sounds like classic vacuum leak symptoms. You don't have a carburetor adapter on this do you?

The propane torch works really well, but so does WD-40, Carb Cleaner, Brake Cleaner, Electrical Cleaner or just about any other aresol that burns. Spray around the base of the carb taking care not to spray into the air horn of the carb and just little squirts around the base of the carb.

Most of the 390's I have dealt with love to cook the crap out of the carb base gaskets. A quick test and a 2 dollar gasket fixes it.

When you're broke and desparate, everything goes to hell. That's Murphy's Law for you.

shawns fords · Post by **shawns fords** » April 19, 2007, 6:59 pm

I will put 5 bucks on Slicks bet its a flat cam I just went through all of this with my FE last summer, exact same symptoms first it was a few bent pushrods then the stumbles and missing and everything else was fine, I have the cam in my storage unit for safekeeps all lobes worn flat and I still could light up the rears and pass E test :lol:

I cant even imagine what its going to run like with a stroked 428 in her :twisted:

blackagatha · Post by **blackagatha** » April 19, 2007, 7:53 pm

I determined that my truck IS NOT DEAD!!! YEEay.

It's still making a soft pulse/ slight miss I think, but my realization of the doomsday was false. Turns out when I put the points back in the distributor, I left the 12 volt connection on, like a dumbass even though everybody tried to remind me that it should have been 6 volt. The points were all burned to hell. Got thinkin about it late last night, realized that what it was doing was exactly like what happened when the points went shut.

So in a couple days I'll quit being all happy and go back to trying to figure out what the hell the pulse is. But for now, I'm okay about it. (relief)

I need to talk to my pa. Something kinda like this pulse was going on last year. I don't remember what it was though.

eliminator46 · Post by **eliminator46** » April 24, 2007, 10:04 am

It sounds like you have a little relief going now. I haven't read the recent posts until today. I was actually feeling the stress!!!!!!!!!! Wow, like a dramatic plateau. Hope it works out dude.
Adam

blackagatha · Post by **blackagatha** » April 24, 2007, 11:09 pm

haha yeah. I'm really glad she's not (DEAD).... but I'm still pissed because she's still missing a little. Think it's on the right bank of cylinders, as it makes popping sounds in the right exhaust pipe. It seems though, to be more pronounced right now than before she started going to hell absolute.

She's been doing this thing for a (LONG) time now, where if I really romp on it and get it into the higher rpm range (My C6 likes to hammer 3rd at 80 if I keep the pedal all the way down), it goes POP POP POP in the right pipe right before it shifts, like one of my exhaust valves is floating. I wonder if this float could have caused the valve/seat to erode/burn??? I hope not, but that could explain it why she has developed the miss... anybody concur?

eliminator46 · Post by **eliminator46** » April 25, 2007, 6:53 am

I concur Scotty.
That popping noise is normally associated with a stuck valve, some refer to it as a floating valve. This is caused by a couple of things.
1. Bent valve
2. Weak valve spring, causing slow to close. If bent and stuck, would pop all the time.
3. Pre ignition, where the plug is firing too soon from "Bad timing" where as the result will be a hole in the top of the piston eventually.
4. Flat cam, where as the valve does not open enough to exhaust and will result in the popping back through the carb too.
5. IN-efficient fuel supply from one side of the Carburator, caused by plugged jets in the carb, or bad floats. I remember the old "power valve" in some carbs burning up from excessive backfiring in the carb, not knowing what kind of gas pump you have on the top.
6. Burnt valve, where as poor fuel, preignition, flat cam all play a role in depositing excessive carbon deposits to the seat side of the valve or head resulting in non closure and allowing internal expansion to leak back either through the intake or exhaust.
7. Intermittent "Dead" cylinder, whereas the result will be excessive fuel build up in the exhaust and upon detonation will be popping in the exhaust, eventually Blevying of the muffler, so to say.
We used to take and shut the motor off at 40-50MPH in neutral, pump the gas a few times and turn the key back on, sounding like a M105 Howitzer going off and resulting in "Blowing up the muffler".
You definitly have issues, but it is running. Concentrate on the school work, and fix it when you can.
Drive it like you bought it, and not like you stole it. haha :wink:

eliminator46 · Post by **eliminator46** » April 25, 2007, 7:22 am

Oh yeah, a couple of other variables to consider are,
8. Bad lifter
9. Bent push rod
and Number 10.
10. Rocker arm bent.

If it were mine, and it's always easier to armchair quarterback the game, I would start with verifying the Tchain slack. (moving the crank back and forth while looking at the rotor to see how much movement of crank before the rotor moves)
Buy a cheap timing light and verify the timing. With it being an intermittent problem, the diagnosis always gets tougher. Then a compression check on the "east" bank of cylinders, if not all. Delta "P" is the difference in pressure accross cylinders. A considerable Delta "P" between any two will narrow down the cylinder.
Another thing I do is use a test light to kill cylinders for determining Dead cylinders. Only good for an all time dead cylinder unless you can figure out how to do at 80MPH. I connect the ground and poke it through the boot at the distributor for each plug wire, a change in enging performance indicates a good one. The bad think is it does put a little hole in the boot and will shock you next time you touch it with bare hands, but a good quick check. I used it all the time on customers cars, knowing I would not be touching it again after determining the problem.
I think we all have been here before if you are over 30.
Just baby it.
Also curious if the Ethynal fuel is a player in the game?

blackagatha · Post by **blackagatha** » September 13, 2007, 2:22 am

MMMKay people.... It's been quite a while, and I'm sure this page has fallen into forgotten ideas by now...

I recently tore the heads off and took them to the machine shop- just about the best guy in Tucson.

He told me I had 2 bent intake valves, replaced them, shimmed the springs to stiffen them up, checked everything out to specs. I put it all back together, she still thumps, and now she does a little popping in the left pipe at idle, when hot, when in park. I think it's a carb issue, but I have no idea.

Still going a slight degree of apeshit about the thumping though. One of these days I'm gonna tear the lid off the carburetor and see if there's anything in it. I'm gonna hurt myself if I find out that all this trouble was a carb problem.

Paul Merrell · Post by **Paul Merrell** » September 13, 2007, 7:27 pm

What caused the bent valve? Did you see any bent push tubes they are aslo easy to bend? I found four bent tubes in my truck. When I had it tore down.