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Video of engine stumbling - ideas?

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dr johnny fever
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Video of engine stumbling - ideas?

Post #1 by dr johnny fever » Mon Oct 29, 2018 6:54 pm

I just finished swapping out my stock 86 F150 intake, carb, and exhausted (well, the carb wasn’t stock, I got rid of the Feedback monster and put in a manual choke 1bbl YF about a year ago).

I put in a Clifford intake, EFI exhaust manifolds and y-pipe, and a manual choke Edelbrock 500 4bbl.

It was missing and stumbling before, but it’s worse now. Here is a video I shot under the hood and then at the exhaust you can hear it. Any suggestions of what you guys think the problem is?

https://youtu.be/ADWIlnaZZ_I
1986 F150 4X4

pmuller9
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Re: Video of engine stumbling - ideas?

Post #2 by pmuller9 » Mon Oct 29, 2018 9:14 pm

What did each cylinder show for compression when you did a compression test?

sdiesel
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Re: Video of engine stumbling - ideas?

Post #3 by sdiesel » Mon Oct 29, 2018 11:35 pm

always always start with ignition .
be sure all is perfect order.
many times u will need look no further.
a long love affair with the 300 six.
my lastest and final fling is a fresh 300 in an 88 ford f350 dually 4X flatbed

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dr johnny fever
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Re: Video of engine stumbling - ideas?

Post #4 by dr johnny fever » Tue Oct 30, 2018 3:24 pm

My buddy borrowed my compression tester so I’m not sure, but I’m going to check it as soon as I get back, probably this weekend. The ignition is aftermarket GM style HEI. The stock computer controlled ignition and feedback carbs system was completely shot and there was nothing in the junkyards for 100 miles, so that’s how I ended up with this set up. I’ll go through it again make sure everything looks good and report back.
1986 F150 4X4

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Shorty
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Re: Video of engine stumbling - ideas?

Post #5 by Shorty » Tue Oct 30, 2018 9:20 pm

When you swapped out the feedback carb did you change the distributor too?
85 F150 on 78 bronco frame C6 np205 welded dana44 front, trussed posi nine inch rear. EFI exhaust manifolds into one 2 1/2" rolls on 35x12.5x15 Maxxis Trepador.

pmuller9
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Re: Video of engine stumbling - ideas?

Post #6 by pmuller9 » Tue Oct 30, 2018 10:01 pm

Shorty wrote:When you swapped out the feedback carb did you change the distributor too?

dr johnny fever wrote:The ignition is aftermarket GM style HEI.

1986F150six
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Re: Video of engine stumbling - ideas?

Post #7 by 1986F150six » Wed Oct 31, 2018 10:55 am

Dr. Fever,

You stated that it was missing before replacing intake manifold, carburetor and exhaust manifold. If installed correctly [I bet they were!], the missing [before and after] is most likely caused by something other than these items.

Maybe pull each spark plug wire [1 @ a time] while idling to see if the missing cylinder(s) can be found. Then, swap spark plug wires to see if the miss follows a particular wire.

Check the distributor cap and rotor for signs of arcing.

Pull the spark plugs and examine. Maybe put in a new set just in case.

Verify there are no vacuum leaks.

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Re: Video of engine stumbling - ideas?

Post #8 by Max_Effort » Wed Oct 31, 2018 5:43 pm

I hear popping and misfiring. I’d start with ignition.
How is the inside of the distributor cap? Any carbon between the post that could cause more than one cylinder to fire at the same time?
Pull one wire at a time with the engine running and see if the popping stops with a cylinder “de-activated
Then move to the air intake, vacuum leaks. It would have to be very lean to pop.
Then valve train and rockers, broken valve spring, worn exhaust lobe..look to see if all the rockers are moving the same amount.
Perform a compression or leak down test to see if you have a leaking intake valve.
Another source of popping in the intake is a head gasket blown in between two cylinders.
Last edited by Max_Effort on Wed Oct 31, 2018 6:23 pm, edited 1 time in total.

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THE FRENCHTOWN FLYER
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Re: Video of engine stumbling - ideas?

Post #9 by THE FRENCHTOWN FLYER » Wed Oct 31, 2018 5:59 pm

A friend had a truck - Chevy V8 - that had a misfire. He asked me to help him find the cause.
I told him to start it up.
After about a minute I licked my finger and briefly tapped it on each exhaust port.
On seven of the cylinders when I did that there was a "TSSSsss" sound accompanied by a hot finger.
On one cylinder I left a spot of wet saliva.
"There's your dead cylinder" I explained. (It turned out to be a wiped cam.)
simple
FORD 300 INLINE SIX - THE BEST KEPT SECRET IN DRAG RACING

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woodbutcher
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Re: Video of engine stumbling - ideas?

Post #10 by woodbutcher » Thu Nov 01, 2018 3:53 pm

:hmmm: Hi FTF.Something that would be a little easier on your finger would be to use an eye dropper with some water in it :lol: .
Good luck.Have fun.Be safe.
Leo
"People never lie so much as after a hunt,during a war,or before an election".
Otto von Bismarck

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THE FRENCHTOWN FLYER
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Re: Video of engine stumbling - ideas?

Post #11 by THE FRENCHTOWN FLYER » Thu Nov 01, 2018 9:57 pm

True dat.
But I always have my finger with me and the spit is a renewable resource.

BTW Dr johnny fever, I loved you on WKRP in Cincinnati.
FORD 300 INLINE SIX - THE BEST KEPT SECRET IN DRAG RACING

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dr johnny fever
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Re: Video of engine stumbling - ideas?

Post #12 by dr johnny fever » Sun Nov 11, 2018 10:49 am

Sorry took so long to reply, been out of town for work ( Frenchtown Flyer - you know, town to town up and down the dial LOL).

Here’s what I got when I did the compression test:

C1 = 107
C2 = 110
C3 = 110
C4 = 112
C5 = 110
C6 = 116

My brother told me I was supposed to take all six spark plugs out before I did the test, but he didn’t tell me this until after I did the test. So in case it makes any difference these compression numbers are all with the other 5 plugs in.

I have pictures of the spark plugs I can post as soon as I get figure out how to do it now without photo bucket. Will do the other checks today as well.
1986 F150 4X4

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THE FRENCHTOWN FLYER
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Re: Video of engine stumbling - ideas?

Post #13 by THE FRENCHTOWN FLYER » Sun Nov 11, 2018 1:19 pm

Those numbers look good to me. Nothing to indicate that your misfire is due to low compression. It would have to be below about 70 psi before misfires will occur.
More important than "plugs in" or "plugs out" is the cranking speed for the compression test. Like dyno numbers, its good not to compare one test location/weather/gage/cranking speed with another one. Closeness to each other cylinder is more important.
FORD 300 INLINE SIX - THE BEST KEPT SECRET IN DRAG RACING

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