Slant Six Forum

Dieseling and that low of vacuum reading (vacuum is read in inches of mercury at idle, or inches for short) suggests two possible problems to me:

(1) a large vacuum leak somewhere

(2) timing that is much too far advanced or retarded

A mostly stock slant six with no vacuum leaks and proper base timing should get somewhere between 17-22 inches of vacuum at idle. 11 is way too low.

How difficult is it to start the engine? Does the engine crank slowly?

By the way, did you follow the engine break-in procedure before you began driving the truck around?

Where are you measuring the vacuum at?
On runner 6?
or below the throttle plates?
don't measure it above the plates.

You can experience dieseling when the engine is too hot. Especially on a new tight one!
Mine did that up to about 500 miles. I dropped in a lower temp stat until I got thru the break in phase then went back to the 195 degree stat.

Hopefully the timing damper has not slipped giving you an inaccurate reading on the timing.

if everything else checks out the cam must be installed retarded.

Author:	1930 [ Sun Jan 19, 2014 11:57 am ]
Post subject:	Vacuum
I know Reed and maybe some of you other guys are pretty familiar with what I am working with. I cant for the life of me figure out why 12 BTDC it will diesel and 13ish it will not. Everything that I have read and been told it should be just the opposite!! Also I cannot explain why I only have 11 pounds of vacuum manifold ( idle ) pressure, I have tested this at the base ( throttle body ) of carb and also at one of the ports that I have at the tee on the intake manifold. 11 pounds thats a fact and yet the truck runs like a champ, goes down the road, very little ( VERY minimal ) bucking/hesitation that Im going to attribute to a worn out carbie/accelerator pump/throttle shaft that is loose. I am under the understanding that I should be about 18-22. Checked compression, all cylinders are approx 150 plus pounds, ( one is 160 and another is 145/7ish but brand new engine not yet broken it I am assuming is why there is a slight fluctuation there. Not really a whole lot of vacuum lines to blame for leaking ( again Reed can attest to that ) all my emissions crap is gone. Cant figure it out. 1986 Hydraulic truck engine manual trans, no leaks at power brake unit that I am able to hear, sprayed starting either around and cant detect any surging.

Author:	Reed [ Sun Jan 19, 2014 1:01 pm ]
Post subject:
Dieseling and that low of vacuum reading (vacuum is read in inches of mercury at idle, or inches for short) suggests two possible problems to me: (1) a large vacuum leak somewhere (2) timing that is much too far advanced or retarded A mostly stock slant six with no vacuum leaks and proper base timing should get somewhere between 17-22 inches of vacuum at idle. 11 is way too low. How difficult is it to start the engine? Does the engine crank slowly? By the way, did you follow the engine break-in procedure before you began driving the truck around?

Author:	1930 [ Sun Jan 19, 2014 1:34 pm ]
Post subject:
Quote: Dieseling and that low of vacuum reading (vacuum is read in inches of mercury at idle, or inches for short) suggests two possible problems to me: (1) a large vacuum leak somewhere (2) timing that is much too far advanced or retarded A mostly stock slant six with no vacuum leaks and proper base timing should get somewhere between 17-22 inches of vacuum at idle. 11 is way too low. How difficult is it to start the engine? Does the engine crank slowly? By the way, did you follow the engine break-in procedure before you began driving the truck around? Not difficult to start at all, hit the pedal, choke closes and turn the key, if Im lucky it will start right up, unlucky means hitting the fuel pedal a couple more times and turning the key. It will start right up. Followed break in procedure the best I could with all the problems I was having with the first crappy dist. If there were still a problem with ...........(2) timing that is much too far advanced or retarded.................. Would the truck start/as easily and as well as it does? Do I need to visit with TDC deal and start from scratch? I am surprised the truck is a peppy as it is with that little six and one barrel. Ive driven much slower slugs

Author:	Aggressive Ted [ Sun Jan 19, 2014 1:59 pm ]
Post subject:
Where are you measuring the vacuum at? On runner 6? or below the throttle plates? don't measure it above the plates. You can experience dieseling when the engine is too hot. Especially on a new tight one! Mine did that up to about 500 miles. I dropped in a lower temp stat until I got thru the break in phase then went back to the 195 degree stat. Hopefully the timing damper has not slipped giving you an inaccurate reading on the timing.

Author:	1930 [ Sun Jan 19, 2014 3:28 pm ]
Post subject:
Quote: Where are you measuring the vacuum at? On runner 6? or below the throttle plates? don't measure it above the plates. You can experience dieseling when the engine is too hot. Especially on a new tight one! Mine did that up to about 500 miles. I dropped in a lower temp stat until I got thru the break in phase then went back to the 195 degree stat. Hopefully the timing damper has not slipped giving you an inaccurate reading on the timing. Measured vacuum at both places, runner six and below the throttle plates. I havent put a thermostat in it yet. Its on my too do list

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Author:	terrylittlejohn [ Sun Jan 19, 2014 4:32 pm ]
Post subject:
if everything else checks out the cam must be installed retarded.

Author:	1930 [ Sun Jan 19, 2014 5:07 pm ]
Post subject:
Quote: if everything else checks out the cam must be installed retarded. I am going to again check everything out next weekend when I have time. If everything checks out as was said than maybe I have issues that are more deeply rooted. Thanks for the replies

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