Carb manifold vacuum port problem

[Joe473]

Yes. Normally.
But for now I wouldn't rule anything out just yet. At least the steady needle is a good sign, but I would not consider it a guarantee just yet.

You said you had spark to all cylinders, even though certain ones made no difference when pulling the wires off (a bad sign in itself of course) but were they all good looking sparks? Not yellow or red, but nice and crispy blue/white with a nice snap to them?
If so, then it would seem an internal issue. Maybe...

It's just strange that all cylinders check with nice high and very even pressure numbers, if something inside them is jogging combustion. You would think it would show up with a compression test.
What about the intake design as a clue. Are all the bum cylinders on the same plane of the manifold?

And here's another oddity. If they all have such even pressures, and all have good spark, but those three don't seem to make any difference when you remove the spark, then how were they within 10 degrees of each other in the exhaust temps? Only #5 cylinder has both issues showing up during tests.
What were those temps by the way? If lower or higher than normal, maybe it will lead us to another potential issue.
Maybe they're all getting a bad mixture or the timing is farther off than you think. Could the timing marks be wonky? Did you check the timing during all this messing about? Or were you quoting numbers from a previous tune?

Good luck.

Paul

Not sure I saw the suggestion to confirm firing order but if leakdown test and compression test come back good i would double check the cam firing order with the ignition firing order.

At the same time check for a wiped cam lobe or two. Wiped Cam lobe wouldn't show on leakdown.

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[Teal68]

Not sure I saw the suggestion to confirm firing order but if leakdown test and compression test come back good i would double check the cam firing order with the ignition firing order.

At the same time check for a wiped cam lobe or two. Wiped Cam lobe wouldn't show on leakdown.

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Hard to believe but I could not sneak a minute even to dig into this more this weekend. I appreciate all the suggestions. I'll try to work an hour in here or there this week during the evenings. It's aggravating I'm not driving it during this nice weather!

Paul,
You brought up something interesting. The spark! Those 3 cylinder do have a weaker spark than the rest, but I have run engines where all the cylinders had similar spark. It's pretty easy top get those wires to jump a spark to ground, but the other 5 jump with a cracking pop! I even get shocked thru spark plug pliers if I'm not careful with the other 5.

I have swapped plugs and wires to take that out of the equation with no luck. Also tried another cap and rotor I had laying around. It has a accel under cap points eliminator much like a Pertronix. Ever seen one of those have weak spark to certain cylinders???

Thanks all!
Tyler

 

[Rustytruck]

Make sure you don't have a burned rotor or carbon tracking under the cab causing a cross fire. all else fails put the points back in and check if the spark corrects.

 

[Justafordguy]

If you have changed the cap, rotor, and wires and still have a weak spark on those 3 wires I say it has to be the Accel points eliminator.

 

[Teal68]

If you have changed the cap, rotor, and wires and still have a weak spark on those 3 wires I say it has to be the Accel points eliminator.

Well...I'm getting old. Guess I did not swap the rotor because that Accel system has a funky rotor. I did try a different cap, wires, and new plugs though. I'm sure of that! Anyhow, worked on swapping points in yesterday, and realized I don't have a regular rotor laying around. I'll pick one up tomorrow and report back.

How was your trip here? Sorry we missed each other....I should have tried to get you over to my place to help me trouble shoot the Bronco!

 

[Teal68]

Threw some points in it and put a brand new cap and rotor on it. No difference! I'm going to pull the valve covers and see if the rockers are moving on those cylinders when I turn the motor over. I'm feeling like maybe I got 3 wiped lobes. While the rockers are off I'll also check Rusty's suggestions.

Not sure how or why it happened on that small hill climb...maybe coincidence. Also, it's surprising how it still runs okay with only 5 cylinders. I can literally leave the 2,3, and 5 plug wire off and it still runs okay. Pull any of the other ones and it gets rough fast almost to the point of stalling if you don't get the wire on quick enough.

If it's the cam I have a extra motor from a Mustang sitting in the garage. It has the original 4 barrel cast iron intake too!

 

[Rustytruck]

The last thing in the ignition loop is the coil. You gotta a spare? Do you have a tach hooked up? if you have a tach temporarily remove it from the coil. Check your coil connections power of the spark starts there.

 

[Teal68]

Well, the cam is good so on to the other suggestions. Hopefully I get a chance to work on it some more this weekend.

 

[Teal68]

Finally getting somewhere....while I had the rocker covers off I loosened all the rockers, pulled one plug out at a time, and put air pressure to each one while the plug was out. 2 and 3 hissed out the exhaust, 1 hissed loudly thru the motor, and the rest barely hissed thru the motor. Sounds like exhaust valves on 2 and 3, and rings/ring on 1. 5 showed nothing out of the norm interestingly. The 2/3 leak could also be just one leaky valve with a breach between the head gasket as Rusty suggested How do I figure that out?

I'm going to tighten everything back up, see if I can steam the valves, and if I get lucky just drive it until I figure out what I want to do. I know the piston ring won't fix itself, but maybe I'll get lucky with the valves.

Very thankful to everybody on here on here for their help, and special thanks to Surfer-B for the time on the phone.

 

[Joe473]

Finally getting somewhere....while I had the rocker covers off I loosened all the rockers, pulled one plug out at a time, and put air pressure to each one while the plug was out. 2 and 3 hissed out the exhaust, 1 hissed loudly thru the motor, and the rest barely hissed thru the motor. Sounds like exhaust valves on 2 and 3, and rings/ring on 1. 5 showed nothing out of the norm interestingly. The 2/3 leak could also be just one leaky valve with a breach between the head gasket as Rusty suggested How do I figure that out?

I'm going to tighten everything back up, see if I can steam the valves, and if I get lucky just drive it until I figure out what I want to do. I know the piston ring won't fix itself, but maybe I'll get lucky with the valves.

Very thankful to everybody on here on here for their help, and special thanks to Surfer-B for the time on the phone.

Did you have the piston at TDC when you tested each cylinder? Typically the end up tapered at bottom and that could skew your results between cylinders with regards to ring seal. With the two burned valves you are pulling the the heads either way and looking at head gasket. On number 1 bring it up to TDC and see how bad it really is. Also get leakdown test set from parts store to tell you actually percent.

Was number 1 burning oil? Was the plug oil fouled? What were compression numbers on 1 vs normal and 5 vs normal? I would keep diagnosing issue with 5 before pulling it apart. If number 1 has no other signs of issues, no scoring, no Ridge at top of cylinder when you take it apart I would consider just doing heads.



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[DirtDonk]

...and special thanks to Surfer-B for the time on the phone.

Way to go, surfer-b!
Sounds like you're really getting to the bottom of things Teal. Maybe you'll get lucky and it'll just "fix itself" as some of these things do.%)
Well, we can hope anyway!;D

Paul

 

[Teal68]

Joe473,
Oil burning nor plug fouling have ever been an issue. Because of that if I can get the valves to seal I'm going to keep running it for now.

I did not think to have each piston at the top of stroke for each one.

Paul,
I know....wishful thinking. I'm just hoping it's carbon build up I can "steam" off with some drips of water down the carb while running. I did get the blue rubber valve cover gasket though just in case for re-use.

 

[gr8scott]

I'm just hoping it's carbon build up I can "steam" off with some drips of water

Here's another option. This stuff actually works. Here's my number 2 piston before and after.
Was too lazy to look at more.
http://knowhow.napaonline.com/product-test-crc-1tank-fuel-system-restore/

Edit: This was after driving 50 miles on a quarter tank.

 

[Teal68]

That's impressive! Water did not do the trick so may have to give it a try. I'm not too optimistic at this point. I'm betting I ran it too long like this and scorched the valves as result.