Off-Road Forums & Discussion Groups - View Single Post - misfire diagnosis w/ vacuum gauge
View Single Post
post #9 of (permalink) Old 07-10-2009, 09:16 PM Thread Starter
Tim-E
Journeyman
 
Tim-E's Avatar
 
Join Date: May 2007
Location: HHI SC
Posts: 117
Thanks: 0
Thanked 0 Times in 0 Posts
 
back on this subject(AARRRGH!!!!! i'm so sick of this misfire!)
I got a hold of a new vac. gauge.

some background:

1983 258
Timing set around 8*
hei/mc2100
plugs with 1k miles on them
wires about a year old
fuel press: 3psi(plenty right?)
NO EGR valve

here goes:
At the intake manifold plenum, i get a vacuum reading of 17 in hg @ 800 rpm. The needle stays pretty steady, maybe fluctuating .25-.5 in hg. Is this a reasonable vacuum reading for this engine?
I'm still getting a slight misfire at all RPM.
for example, it at its worst @1100 the engine will shake and shudder, and will not stay steady, fluctuating 25-75rpm. But it doesn't sound as bad as plug wire being unplugged, it just sounds like a cylinder isn't firing as strong as it could.
At higher RPM the miss is still there...

I'm leaning toward leaky intake manifold gasket maybe? it was loose when i bought the rig 7 years ago, i tightened it, but maybe it doesn't seal up the same as in the initial install?( I hear a very, very slight whistling sound for a few seconds somewhere in that area when i shut the engine off after it is warm)
Ive sprayed carb cleaner around there and found no leaks. However, i never sprayed from the bottom up...i'm gonna try that tomorrow.
Tim-E is offline  
 
 
For the best viewing experience please update your browser to Google Chrome