Stumble on Deceleration
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Post Fiend
Joined: Mar 2011
Posts: 8,501
Likes: 4
From: Lynchburg, VA
Stumble on Deceleration
Ive been having this problem for a few weeks. The truck is a '79 F150 w/ 351m and C6. Ive tried adjusting the dashpot, idle speed, and idle mixture to no avail. Im reading around 20-21hg in neutral and 16-18 in drive-not really sure how good those are. Timing is set to spec, emissions components are intact; although I did pull the cat off, take the insides out, and put it back on. On a possibly related note, Ive been experiencing hard downshifts on occasion. I pulled the vacuum line off the vacuum mod and theres no sign on trans fluid. Any help?
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Post Fiend
Joined: Mar 2011
Posts: 8,501
Likes: 4
From: Lynchburg, VA
It seems a bit unusual that its just started doing this recently. I double checked the float level in June when I rebuilt the carb, it should be good.
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Post Fiend
Joined: Mar 2011
Posts: 8,501
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From: Lynchburg, VA
Upon letting my foot off the gas, the engine rpm drops and the vacuum drops down close to 10hg. It sounds like its gonna die but then starts back running good again. It only does it at lower speeds, maybe only in first gear, although Im not 100% sure.
Senior User
Joined: Oct 2010
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I had the same type of thing with my 351w. Lettin off the gas it would stumble and shake. Turns out the air/fuel mixture screw on one side wasn't working. Replaced the carb and it all went away
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Post Fiend
Joined: Mar 2011
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From: Lynchburg, VA
Oh joy, partial carb rebuild this weekend then.
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Post Fiend
Joined: Mar 2011
Posts: 8,501
Likes: 4
From: Lynchburg, VA
Hmm, so I went to Advance Auto to get some Sea Foam and talked to the parts guy while I was there. He suggested replacing the trans. modulator and maybe finding a new dashpot. I just orderd a new modulator so Ill put that in tomorrow and see what it does.
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Post Fiend
Joined: Mar 2011
Posts: 8,501
Likes: 4
From: Lynchburg, VA
Replaced the trans mod, started driving down the street, had to turn around. Took the carb off a blew out all the passages. Runs better now but still stumbling. Adjusted the dashpot almost all the way out a while ago; ill see what that does in the morning. If that doesnt change anything, its probably gone and Rockauto has them for $10.
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Post Fiend
Joined: Mar 2011
Posts: 8,501
Likes: 4
From: Lynchburg, VA
I just checked it yesterday, was 16/32. I just noticed something that I hadnt noticed before, a ticking noise coming from the right valve cover
could these two things be related? Sticky lifter? Bent pushrod? Burned valve??
could these two things be related? Sticky lifter? Bent pushrod? Burned valve??
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Post Fiend
Joined: Mar 2011
Posts: 8,501
Likes: 4
From: Lynchburg, VA
Checked the compression on the 1-4 cylinders:
1-135
2-155
3-140
4-145
Not sure if thats good or bad, but that would rule out a sticky lifter or bent pushrod, right?
Maybe Ill check my wet float height later and see what that is...
1-135
2-155
3-140
4-145
Not sure if thats good or bad, but that would rule out a sticky lifter or bent pushrod, right?
Maybe Ill check my wet float height later and see what that is...
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