Bucking issue under load?

[FuzzFace2]

81 F100 flare side 4x2, 300 six,NP435, Advance Adapter over drive, 2.75 gear and 235/75/15 tires.

Well I have had this bucking issue unloaded in 4th gear & over drive at about 45 to 50 MPH going up a little hill when taking the trash to the dump every week. It was not really bad so I never looked into it.

Yesterday I pulled a 20' enclosed trailer for our car club for our yearly show.
The bucking was so bad I really could not get above 45 MPH.
I pulled the vacuum line to the dist. thinking maybe a break in the wires to the pickup coil was the cause, did not help.
Both unloaded and loaded I did not see the factory tach "bounc" but it dosemove kind of slow, and the air fuel ratio gauge is about 12.5 to 13.5 a little on the rich side but is normal for this truck when under load.

It seams the more load on the motor (pulling the trailer) the worst it was. If I backed off the throttle it stopped but lost speed and when back on it bucked again.

Today I started looking in to it and so far have not found the cause., what was done.(I did 1 thing and took for a test drive, then the next ....)
1- De-greased the motor after tighten up valve cover bolts. Used shop air to blow dry.

2- Pulled the coil horse shoe connector and plug wire from coil and checked, both ok.

3- pulled cap & rotor, found a little water in side but think from the de-grease. Blew out with shop air.
Cleaned up posts in cap and rotor, they were not that bad.

4- plugged in old Motor Craft DSII box. It leaked potting when hot out and why it was changed.
The 2 plugs looked good to the box.

5- with the motor running after all the above I moved wires to the coil & DSII box and it did not skip a beat. I dont see a way to really check the pick up coil at this time.

I guess the next thing is to pull the carb and either pull it apart, I have rebuilt this when I first got it on the road, or find the Ebay carb I bought and install it.
Back to the garage to plan the attack!
Dave ----

[Gary Lewis]

In my experience a miss under load is ignition.  So I'd be looking at plugs and plug wires since the cap and rotor look good.

Look for a track or even a crack down the insulation of the plug that might indicate that it has been arcing over.  Or maybe throw a set of plugs at it to know that's not the problem.  Then plug wires.

[85lebaront2]

One quick way to look for plug wire issues is check at night in the dark, a glow around the wires indicates weak insulation. One other item, check voltage at the coil + terminal running, I believe it should be around 6-7 volts DC due to the resistance wire in the harness. If it is low then that will cause misfiring (bucking).

On the older Fords it was made as a plug in wire built into the dash harness and was available as a service part. You bought the service wire, unplugged the bad one and plugged the new one in and secured it to the harness.

[FuzzFace2]

I can tell you the Ebay carb did not make a change on the bucking but it feels like it has more get up and go.
It also idles smother and leaner from a 13 something to 14.5. If I tried to adjust it to that it would run ruff.

Also on the test drive it is running leaner across the board. Before was 13's to maybe 14's now 14's to 15's even saw a 16 once so the MPG should go up too (I hope).

On the test drive it was bucking but get the RPM up to 3K+ and you could still feel it up that high.
I stopped for new plugs and picked up a coil as I feel it is not a fuel issue, not running out of gas more like shutting off and on really really fast.
It did not feel like it was bucking as bad after the test so wonder if the plugs are fouled from running to rich from the old carb and now running leaner they are cleaning off?

Taking the wife out to dinner for 25 years married and tomorrow taking her for a medical procedure so cant work on the truck for a few days.
​​​​​​​Dave ----

[FuzzFace2]

Both have good information thanks.
I should point out the wires and plugs were replaced with the cap & rotor when I first got the truck.
The motor had a miss, a compression check showed all good there so I replaced the cap, rotor, plugs and wires and no more miss.
I then took the whole truck apart for the 4 year rebuild.

I will check the coil in put volts just to make sure it is good. Garbage in garbage out right LOL
As you can see from the post above got plugs and coil not that I have ever seen a coil go bad.

Also for leaking plug wires in the dark spray water from a squirt bottle on them and if they arc they are bad.
BTW after the de-greasing the motor started right up and ran smooth as I had to get it back to my garage & tools.
Dave ----

[85lebaront2]

16:1 is quite lean, the old 2 barrel 390s would run that lean with no problems and that was with breaker points. Have you taken any of the plugs out and examined them for carbon build up on the insulator and for burned electrodes?

On coil failure, I have seen a few, I have also seen carbon tracking on the coil tower leading to arcing to the can or one of the primary wires.

[FuzzFace2]

85lebaront2 wrote

16:1 is quite lean, the old 2 barrel 390s would run that lean with no problems and that was with breaker points. Have you taken any of the plugs out and examined them for carbon build up on the insulator and for burned electrodes?

On coil failure, I have seen a few, I have also seen carbon tracking on the coil tower leading to arcing to the can or one of the primary wires.

No I have not pulled the plugs yet and have a new set I just picked up and coil at same time.

I should say I have seen a coil go bad like you said, arcing from tower to 1 of the wire leads as spark was looking for the easy path to ground.
This was caused by bad plug wires where the spark did not want to go to the plugs.
This happened when I was just starting out to repair cars so it kind of stuck with me LOLO.
When the coil went bad it stayed bad.

Again this only happens under load, heavier the load the worst the bucking.
I got a feeling the new plugs will not fix it because it would have to be ALL THE PLUGS as it kills the power / bucks.
If 1 or 2 plugs failed you could feel that as a miss not shut off like is happening.

As for the 16 on the AFR I only seen it pop up.
Once I can get it to run with out bucking I will look at the AFR closer and adjust as needed.
I also remembered the old carb was missing a part for the needle / jet and think why that carb ran rich.
I also seen fine rust in the bowl of the old carb.
The new fuel filter on the carb did not have rust come out before I put it on the new carb.
Thanks for the help
Dave ----

[Gary Lewis]

When running the carb I saw 16:1 on Big Blue under light loads with no problems.  Tip into it and the metering rods popped up and the AFR came down.

As for the bucking, the way you are describing it makes me rethink things.  If it is as if the engine shuts off and then comes back instead of just one or two cylinders dropping out then I don't think it is plugs or wires.  That sounds like something in common with all cylinders, such as the cap, rotor, coil, coil wire, ignition module, or power supply to the coil.  But you've inspected the cap and rotor and replaced the ignition module.  So that leaves the coil, coil wire, or the power supply to the coil.

If replacing the coil doesn't help then I'd consider getting a Chrysler ballast resistor and bypassing the resistance wire in the harness to see if voltage is a problem.  Start the engine and then jumper from the battery to the coil with a wire that includes the ballast resistor.

But what if it is fuel?  Like too little fuel volume or pressure?  I'd think you'd see the AFR go wonky in that case when the bucking starts, and since you aren't I still think it is ignition.

[FuzzFace2]

I also think it is something common to the ignition system and why I got the coil.
I got plugs as I want to pull them to see what they look like so might throw plugs at it.

The coil wire looked good at both ends but did not measure it. But being it started right after the water bath I ruled it out. Same on the other plug wires.

I will check volt to coil and hot wire and or replace it to see if that helps.

But gut feeling is pickup coil in the distributor is starting to go bad under load.
More testing needed.
Dave  ----

[AmericanSavage]

Hey Dave,

Are you SURE this is ignition related?  I only ask because once I had this problem--in a 1973 chevy.  Turned out the splines between the engine and trans were almost completely chewed through.  Anyway, FWIW.

I am interested if this is a coil issue though.  

[FuzzFace2]

AmericanSavage wrote

Hey Dave,

Are you SURE this is ignition related?  I only ask because once I had this problem--in a 1973 chevy.  Turned out the splines between the engine and trans were almost completely chewed through.  Anyway, FWIW.

I am interested if this is a coil issue though.

I am almost 100% sure it is a spark issue as it feels like the motor shuts off & on really fast.
If it was a fuel issue it would spit & spudder as it ran out of gas in the carb.
If the tach moved faster when not getting power I then would know for sure it was a spark issue.

Bill & Gary gave me some things to check and I have a new coil to try but my gut is telling me pick up coil in the dist.
There is only 1 store around that has one in stock, Standard Product.
So after I do more checking I may go get it.
Dave ----

[FuzzFace2]

Well I am on the right path
#1 thru #6 left to right or top to bottom.
Changed the plugs, first 3 did not look bad and was thinking this is not it then got to #4 and WTH!
The motor never showed any signs of a miss up to this bucking but looking at #4 I dont know how that could be?

Took it for a test drive and the bucking is pretty much gone under load (empty but it did buck before the plug change).
Thing is I can feel a miss at steady throttle and trying to speed up in the higher gears, 4th and 4th OD.
I will let the motor cool down some and see if I can swap the plug wires from that plug to another and keep and eye on the 2 plugs to see if they show any signs of an issue.
I will also recheck the cap closer for spark tracing. But it is strange if it was cross firing I am not getting any back firing anywhere as you would think you would?
Dave ----

[AmericanSavage]

Dave,

That looks white and ash like—oil droplets?  

[FuzzFace2]

AmericanSavage wrote

Dave,

That looks white and ash like—oil droplets?

I hope not
I dont think it uses and oil between changes that I can think of.

Now when I first got it back on the road I had a lot of "milk shake" in the breather cap * hose to the air filter and the dip stick tube from condensation that I dont have now.

I also have not see any oil smoke out the tail pipe on start up or driving.

I know before I bought the truck it was only used around the small yard as it it did not have plates while he had it. Bought for his son as a project but son did not like it.
Before they told it was a farm truck so may not of been driven much then also?
So it could be with me putting miles on it it has "sealed it" by seating the rings better and getting it up to temp and staying there longer?

I am going to try and swap the plug wire with another plug if I can and see if it is a plug wire issue by checking the 2 plugs over time.
If the other plug dose the same I know it is a wire and not the hole.

Maybe I should try and find them plug adapters that we used back in the day when the motor burned oil and fouled the plugs
Dave ----

[Gary Lewis]

Are you losing any coolant?

[FuzzFace2]

Gary Lewis wrote

Are you losing any coolant?

It dose go low over time but I think it leaks from the NG vacuum valve for the no water flow when the HVAC is in vent.

The hose is too large for the valve and I am for ever tightening up the clamps.
I hope it is not what you are hinting to other wise
Also not getting any white / sweet smoke out the tail pipe or it has not gotten that bad yet?

I also dont remember or did not test that far, what hole had the miss when I first got the truck?
Also dont remember any of the plugs looking as bad as that one I pulled out.

Just a thought  I am running coolant to heat the intake for cool / cold weather. I did use a freeze plug in the EGR port with sealer but wonder if the intake had a crack or bad casting and leaking coolant to that hole?
It is right at the area where the coolant is.

More to keep an eye on now
Dave ----

[Gary Lewis]

How many miles do you have on those plugs?  If it is 5K or so then maybe it isn't a big issue?

[FuzzFace2]

Gary Lewis wrote

How many miles do you have on those plugs?  If it is 5K or so then maybe it isn't a big issue?

I would say 10K no more than 15K, 2 or 3 oil changes since the truck has been on the road.
Figure a little over 3K for each change so guess closer to 10K.

I swapped the plug wires with another hole so will keep eye on the 2 plugs.
I also pulled the plug end metal part  out of the "good" wire so I forced it back in and fingers crossed it holds till I check plugs.

I also swapped out the coil, cleaned the connections, not that they were bad and that did not help.
You can feel it miss just cruising along and under even light load like pulling away from a light or stop sign.

I have rechecked the wires and plugs for the DSII system and they all look good.
I have even moved the wiring around with the motor idling and nothing.
Only thing that it can be now is the pick up coil. (maybe, see about the lean carb below)

All IGN tune up parts have been checked over as they only have maybe 10K on them.
Plugs have been changed and that was the biggest change. No more bucking but you can feel a miss when driving.

Carb has been swapped out with a new Ebay one.
It starts as fast as the old carb but may need to adjust the choke a little.
What I dont like is it runs vary lean based on my AFR gauge. Just normal driving holding speed it runs in the high 15's to mid 16's.
When I first started it after a cool down, motor still a little warm, fast idle came on but the AFR went so lean it blanked out when I first started driving it and you could feel it "lay down" lack power.
It was a little better after it got up to temp but it just dose not feel right.

I did readjust the idle speed & mix and will see if I can adjust the needle / jet richer as what I am feeling could be a lean miss fire now?

The fight goes on!
Dave ----

[Gary Lewis]

So even after all of this, including replacing the plugs and swapping carbs, it is still missing?  

If I remember correctly you have swapped the DS-II module.  But you haven't replaced the pickup module.  I think that would be my next step as it is the last of the common items.

As for "laying down", I do understand that when things go quite lean.  But in my experience you don't get the bucking that you are experiencing.

[FuzzFace2]

Gary Lewis wrote

So even after all of this, including replacing the plugs and swapping carbs, it is still missing?  

If I remember correctly you have swapped the DS-II module.  But you haven't replaced the pickup module.  I think that would be my next step as it is the last of the common items.

As for "laying down", I do understand that when things go quite lean.  But in my experience you don't get the bucking that you are experiencing.

I think I fixed 1 thing but caused another in trying to fix the bucking.
Here is my take:

Yes I did try a used DSII box, no change, everything else is in good shape.
Changed out the coil, no change. Swapped plug wires from bad plug with another plug and will keep an eye on the 2 plugs to see if the wire was the cause or ????
FYI I pulled the metal plug end out of the good wire when I did the swap so the wires will be replaced at some point.

In trying to fix the bucking I installed a Ebay carb I have had for a year or so.
It runs a lot leaner than the old carb and this may be the cause I have now that is more of a miss than bucking like before.

When I changed the plugs this stopped the bucking but now feel a miss just about all the time when driving.
Being the AFR is running in the mid 15's to mid 16.s and some times I have seen 17's I think I am feeling a lean miss. I want to richen up the needle and jet to see if that helps the miss.

If not I will pick up a pick up coil and change it out.
I had seen it posted some where a bed coil was causing a PITA and once out of the dist. he found a crack in the unit.
Still trying to fix this.
Dave ----