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New Timing
01-13-2014, 09:36 AM
Post: #1
New Timing
1995 GMC Jimmy 4.3 L 4wd
New Long Block Install
Still in the Engine Break In Phase and Cleaning Up /
Finishing Minor Detail Items.

Engine has been started only about 11 times.
Longest idle 50 minutes last night.
Can't run it too long because I am going with a new
Electric Fab which isn't fully installed yet

Question :
Timing # 1 spark plug is reading approximately. 5 degress BTDC
. Why. ?
I have not found the Gray black stripe wire anywhere which is suppose to dusabkuthe timing adjust.
Has cimputer
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01-13-2014, 11:59 AM
Post: #2
RE: New Timing
Recalling two different locations for that wire over the years. One is on the fire wall near the master cylinder booster and the other is near the ECM along the harness. Both are outside the wire loom.
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01-13-2014, 12:30 PM (This post was last modified: 01-13-2014 12:36 PM by cferry7.)
Post: #3
RE: New Timing
Rupe. -
Will this wire disable and set timing to 0. ?
Suppose to. ?
Do I have to wait certain amount of time or mileage before the ECM or Computler reseor back to exact. Timing. 0 degrees. ?
It is starting first time every time now with the 5 degree difference which is nice.
just takes alot of CCA from battery guess because it's new engine.
Thank you
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01-13-2014, 08:36 PM
Post: #4
RE: New Timing
That vintage has adjustable timing so pulling the plug is what you do to set the base timing with a light by turning the distributor. When done you tighten the dist then plug it back in and the ECM does the rest.
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01-14-2014, 08:48 AM (This post was last modified: 01-14-2014 09:42 AM by cferry7.)
Post: #5
Rolleyes RE: New Timing Tip
Hi Rupe. -

A shortcut / tip which I found ( after much trial snd error ) on the 4.3 L vortek is
THAT YOU CAN locate TDC of # 1 cylinder by removing the Oil Filler tube in right valve cover, place a mini mag pickup tool on the # 1 intake valve rocker - which is viewable and accessable thru this filler hole. ROTATE Engine clockwise with Crank pulley center bolt. Watch for this rocker to open then start to close all while watching the timing mark on the harmonic balancer.
I found thus much easier than removal of valve cover or piston position thru spark plug hole.
I imagine some pros simply can use a compression guage on number 1 spark plug hole and determine when compression stroke is happening and the timing mark on harmonic balancer.
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01-14-2014, 10:19 AM
Post: #6
RE: New Timing
Good tip, I like it!

BTW, there's usually 2 timing marks on that engine so your tip will work for many people. The reason for the second mark is for that same engine in a van. Since in that case you are turning the engine from below (it's way easier on a van with all of that stuff in the way) there's another mark on the cover down there. IOW, one mark will show on top at about the 2 o'clock position and the other shows up around 5 o'clock. The lower mark on the cover is just a line without any degrees. Basically it's for finding TDC and that's it. When both marks are in place (and with your trick) you are there.

BTW, Recalling your timing spec is a few degrees retarded for that year. (after TDC) If you go too far advanced obviously it may be hard starting but it may also fail a tail pipe test with high HC / NOX readings. Just a heads up here.
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02-04-2014, 06:29 AM
Post: #7
RE: New Timing
I have not run engine much since last post.
Been working on other minor cleanup tid bits.

I am still searching for the mysterious Timing Disable wire . . .

I quote another source I received last night : : :
"1995 used 2 different computer control systems so yours may or may not have the EST ( electronic Spartk Timing ) wire.
IF yours has vertical attached wires on distributor, the EST wire is located behind top edge of the passenger foot well floor carpet, under the dash. It's a tan wire with a black stripe with black plastic connector. IF the spark plug wires attach horizontally, yours does not have the EST wire."
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02-04-2014, 10:31 AM
Post: #8
RE: New Timing
if the computer is located on the rh fender wall in the engine compartment.....it is called a vcm vehicle control module and truck has the enhenced ignition system and Ignition timing is preset and cannot be adjusted. The distributor cannot be rotated and will not affect engine timing.if it has a pcm....it is located rh passenger side under ip and then equipped with a distributor(DI)system and The location of the "set timing" connector with a Powertrain Control Module (PCM) controller is near the PCM connectors in the passenger compartment.
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02-04-2014, 10:44 AM
Post: #9
RE: New Timing
Never gave it much thought but that sounds about right. The "flat top" dist cap is the newer version and usually the timing is not adjustable because the hold-down clamp rests on a pair of flats machined in the dist housing. IOW, you can't turn the body at all to set timing the old fashion way. Basically you find TDC, drop the dist into place, (there's a mark on the rim of the body for the rotor) and if the CEL stays off you are set. If it's in the wrong place (off a tooth) you will get a code.

If you have the earlier style that wire breaks out of the ECM harness so all you have to do is locate the ECM and follow the harness. Some were located behind the glove box and others were in the right side kick panel. As I recall, disconnecting that wire will turn on the CEL but incorrect timing will not.
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06-14-2014, 12:53 PM (This post was last modified: 06-14-2014 12:57 PM by cferry7.)
Post: #10
RE: New Timing
Since my last post.
A local mechanic has told me that GM for my odd year make 1995- 1/2
that the computer does all timing variables; no wire to find and dist is tab locked in one position. While @ idle it is not abnormal for computer to advance/ timing by 5 -10 degrees. Their is no need for the special timing scan tool adjustment. These informative pieces of info I have been told. This is the way the Engine is at idle, presently

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