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1981 B-150 short Van, stock 225, California emissions package, Electronic Spark Advance (digital Lean Burn), Non-feedback Holley 1945, AT
Driven for economy, not for speed.

It almost looks to me like the carb is going could be the fault here.

Which carb do you presently have?

When was the last time the carb was taken apart and rebuilt/cleaned?

If it is the Carter BBD or Holley 1920, I would suspect something along the lines of the rear most (or left from the fuel inlet) bore is putting out too much fuel... Normally, a cylinder running too lean will have a bone white look to the tip, dry black soot indicates a rich A/F mixture.

I am sure Dan can chime in and direct you to the best BBD/1920 rebuild kit to get, but if the van was sitting that long, you definitely have some varnish buildup inside the carburetor. Get it cleaned out and put back together clean, and to factory specifications.

If it is the 1945 Holley, then I think we have somewhere else to look. With only 1 venturi, it doesn't really have the ability to run only 1 cylidner way too rich, another slightly rich, and the other 4 perfect.

~THOR~

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1984 D100 Shorty Custom
Certified Auto Appraiser - RevItUp Classic Appraisals
President - Cherry City Bombers CC
Part of Tyrde-Browne Racing

Holley 1945, R-9132-A, correct for this vehicle and assumed to be original.
Rebuilt: a few years ago.
Cleaned: last month. It was already pretty clean, yet there was a little gumming and the needle was stuck in the seat.
That’s what it is, and that’s what i thought, hence my puzzlement!

Thanks for your thoughts, Thor (on this and the PCV)… awaiting more.

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1981 B-150 short Van, stock 225, California emissions package, Electronic Spark Advance (digital Lean Burn), Non-feedback Holley 1945, AT
Driven for economy, not for speed.

With the problem apparently confined to one cylinder I wouldn't expect the carb to be at fault. Since the #6 plug is the worst I would examine vacuum line routing to the vacuum "tree" on the #6 intake runner and make sure there isn't something amiss. I would also perform a compression test to see if there are mechanical issues.

The pinging and surging can be either fuel or ignition related, but I would first examine the ignition system. It's entirely possible the computer is receiving bad inputs or the computer is defective.

Does this engine have hydraulic valve lifters or are there adjusting screws on the rocker arms?

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Joshua

I'm gonna watch this thread, finally someone with a similar problem to me. Your spark plugs look very much like mine, except my plugs 1 through 5 are good and just number 6 is rich. I've had this problem for a few years now, even before and after an engine rebuild. I have eliminated everything I can think of and still no solution. But I managed to do a few things to alleviate the problem.
My main issue originally was number 6 plug would soot up at even the smell of fuel, and until I had the engine up to running temp it would missfire at anything over 1/3 throttle. Then even once warmed up it would miss at full throttle under heavy load eg. top gear up a steep hill. I tried a few carby things which won't relate to you because I have a different carby but these small changes did little. I also tried a hotter spark plug in the 6 spot which helped a bit but not enough.
My engine, as per usual, had the brake booster hooked up to the number 6 intake runner and the pcv to the carby. I got rid of the missfire totally by switching these two hoses ie. pcv to number 6 runner and brake boost to carby. Although getting rid of the missfire the number 6 plug would still soot up but not foul enough to missfire.
I then changed from a 2BBL carb to a 4BBL carb........welcome back missfire. It wasn't as bad as it was originally, I had no missfire once up to running temp. I got sick and tired of the missfire when cold so I installed a Crane Hi-6 ignition, which again cured the missfire problem completely. The Hi-6 can fire that 6 plug no matter how fouled it is. The spark it produces is quite frightening.
So now I'm at the point where my engine runs perfectly but number 6 still soots up. I can clear it by going for a very long drive, 45 mins or longer, but other than that it's sooty all the time.
Good luck and I hope we can both get to the bottom of this problem.

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62 Valiant, 225cid Slant 6/PB 904 with lots of good bits

http://www.moparmarket.com/readersrides ... user=SV162

I would do as Joshie225 perscribed and do a compression check. Then I would do a cylinder leakdown test. If say the number 6 intake valve were slightly open, it *might* be dragging in extra fuel. That's a long shot, but you never know. This would also be evident on a vacuum gauge, the needle would bounce around alot.

Do you have a vacuum gauge to hook up? If not, then they aren't all that expensive, and can be a great help in diagnosis. Get us some numbers for cold idle, cold in gear, and then the same for when it is warm. That way we can tell if the issue gets better or worse as the engine warms... assuming that it is a mechanical issue we have here.



~THOR~

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1984 D100 Shorty Custom
Certified Auto Appraiser - RevItUp Classic Appraisals
President - Cherry City Bombers CC
Part of Tyrde-Browne Racing

The #6 plug will be the lowest cylinder since engines have a slight slope to them.

If there's a slight dribble to the carb (float level to high, perculation after shutdown, or whatever), excess fuel may just travel down and/or puddle in the #6 intake runner.

So the #6 cylinder may just be getting a really rich mixture every once in awhile.....

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Thanks for asking your question with such detailed background info and pictures. You're getting advice ranging all over the map from "minor adjustment" to "engine overhaul". One thing we can rule right out is an intake valve being stuck slightly open and "dragging in extra fuel". That might happen in other universes or in the Twilight Zone, but not in this dimension. Here in this universe, a stuck-open intake valve causes very conspicuous and repeated spitback through the carburetor ("backfire"), since there's no longer a barrier between the combustion chamber and the intake tract when the spark plug fires.

More diagnosis is needed before we can help you narrow in on what's wrong. The 1981 California-spec Slant-6 had a lot of failure-prone emisison control devices and systems which worsened driveability and increased the tendency to ping even when new and working according to specifications. There are lots of reasons, from vacuum leaks to (very likely) faulty Lean Burn to a clogged catalytic converter why your van might be pinging so easily.

But before we get into any of that, let's look more closely at the EGR. You say the EGR valve's diaphragm is leaking. That's certainly likely to cause pinging and driveability faults, especially on such a delicately-balanced emission control system as your '81 has. It's almost academic given that you'll be installing a new valve, but testing it is pretty easy: With the engine at a normal curb (hot) idle and the air cleaner removed, attach a good strong source of vacuum to the EGR valve itself. You can use a vacuum pump or just use a length of hose to duct manifold vacuum directly to the EGR valve. If the EGR valve stem moves visibly when vacuum is applied, and springs back when vacuum is removed, then the valve isn't stuck. If the engine "gags" (idle drops and roughens or engine stalls) when vacuum is applied, then the valve and passages aren't fully clogged. If no substantial change in idle speed or quality is noted, then the EGR valve and/or manifold passages are clogged. Clogged valve requires replacement, clogged passages require manifold removal and physical cleanout.

If the valve passes this test, that still doesn't necessarily mean it's working correctly; the EGR control system in '81 is quite complex with thermal vacuum switches, a vacuum "amplifier", and other components. If everything's not hooked up correctly, and/or if there are missing or failed components, the EGR won't work when it's supposed to (under light load and steady throttle) and you'll get pinging.
If needle/seat is sticking, carb is in need of thorough clean-out and rebuild, and probably new float — especially given other driveability faults noted.
Mmmm…those switches aren't considered rebuildable. What did you do, exactly?
A throttle shaft air leak isn't causing your problem, but what makes you call it unlikely? It's a good bit more likely than a choke shaft air leak, which is of no consequence whatever.
Mmm...I disagree. The first four actually don't look quite fine, they look too hot and/or too lean, which goes hand-in-hand with pinging. #5 looks almost perfect; that's just about what you want all the plugs to look like. #6 is definitely carbon-fouled, which makes me wonder what-all exactly is hooked up to your vacuum tree on the rearmost intake manifold runner. Also, while you're answering that, check if your intake is aluminum or iron. Because of the way the engine and manifold are mounted, #6 tends to be the first to run rich with a borderline mixture-distribution problem. If there's liquid fuel in your intake manifold, it's going to tend to run rearward to the last cylinder. Your #6 plug looks more fuel-fouled than oil-fouled, so we can probably hold off on worrying about internal engine problems for now.

Get NGK plugs next time; Autolite is another once-good brand that has gone to crap. Also, today's gasoline is a great deal cleaner burning than the stuff available at the pump when your '81 was new, so you can step down a heat range or two for reduced ping tendency while still keeping the plugs clean. Try an NGK UR6GP (that's a Platinum plug; if you want to cost-reduce the experimentation, use UR6 plain plug). Of course, unless/until whatever's fouling the rear plug is solved, they'll carry on fouling.
That's possible, but one doesn't necessarily follow from the other.
That's your only option other than pulling the head.
The cat is likely already plugged, but if it is not, you're not likely to clog it with any out-the-tailpipe cleanout method. What would exit the engine would be carbon powder, not chunks big enough to stop up the cat. See here.
Yeah, might as well. None of the blowout methods will clean out clogged EGR passages, but you might be sending a fair amount of carbon powder through the valve.
The PCV valve has no way of knowing what's going through the exhaust tract, so leave it be or replace it, at your option.
A bowl of soup. A meal in itself!

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

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1981 B-150 short Van, stock 225, California emissions package, Electronic Spark Advance (digital Lean Burn), Non-feedback Holley 1945, AT
Driven for economy, not for speed.

Ah. Yeah, every time the carb comes apart, it's going to need readjustment. Sort of like every time you replace a burned out headlight, it needs re-aiming even if you didn't touch the aim screws during the R&R.
Well, a variant of the olde-tyme method can be pressed into service to get you within the same ZIP code as the ballpark, but it may or may not result in a passed emission test: with the engine at full operating temperature, set the timing and idle speed to spec, turn the idle mixture screw one full turn counterclockwise, then turn the mixture screw clockwise ¼-turn at a time, slowly, until the engine just begins to drop RPM (use your ears together with a tachometer to detect this). Then, open the screw back counterclockwise ¼-turn, then clockwise 1/8-turn so the engine is just on the very edge of lean idle. You want the final adjustment to be in the clockwise direction so the screw won't move under spring tension.
...choke fully open, too?
I would say definitely a new float. They're made out of Nitrophyll, and the fuel formulations, especially in California, starting in the early '90s have been *very* different to what was available when the vehicle was built. Soft materials (gaskets, seals, floats, flex lines) designed for older fuel formulations often aren't fully compatible with the newer recipes. "Clean inside" is good, but "sticking needle and seat" suggests it isn't as clean as it might appear.
Try for a Walker kit.
Ah. When I read your word "rebuild", I visualised replacing the contacts and such. You thoroughly cleaned the switch. That makes better sense to me. (for curiosity: do you keep Stabilant-22?)
Mmmmm...which topmost Holley 1945 port? At the front or at the rear of the carb? What size is this line? Trying to determine if you're talking about an idle enrichment line or a bowl vent line.
My interpretation is that either you're running lean in general but you've got an internal fuel leak issue flooding #6, or (maybe more likely) the overall mixture's about right but you've got an internal fuel leak issue flooding #6 and your spark plug heat range is too hot.
The firing status of adjacent cylinders won't affect a cylinder's spark plug.

H'mmm. I think I'd probably do the "Italian Tuneup" (blowout), then change the plugs to the recommended NGKs and see what happens.

Got any Kreen?
Yup.
Yep, usually not hard to find.
Can't recommend it. You're going to be sending potentially a large amount of trash through the system; you want a filter that's not going to go into bypass prematurely.
Easy: one chooses the 10w30, because 10w40 and (now difficult to find) 10w50 are far, far more sludge-prone. See this article.
Blow out carbon
Replace EGR valve and spark plugs
Adjust carburetor, timing, and idle speed

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一期一会
Too many people who were born on third base actually believe they've hit a triple.