Timing on a 95 4.3l vortec (vin w)

I've recently replaced the head gaskets on my 4.3 l... and pulled the distributor to do this..

Since the engine was 'disturbed' I had to follow chiltons instructions on putting it back in .. which basically is
1) put engine at TDC for cylinder 1 on compression strok...
2) on distributor align the dimple on the bottom end of shaft (with gear teeth) to the arrow on the top part of the distributor housing base.
3) drop the distributor in to it's position.. and the rotor should turn clockwise just enough to point to the '6' that is molded into the housing base.

...
ok.. so I did this..
now... when I take a timing light to my crankshaft pulley... at idle it is about 5-10 degrees 'late' ( the tick on the pulley is 5-10 degrees counter clockwise of the engine block mark.. when facing the engine from the radiator towards the rear of truck)

when I pull on the accelerator cable to give it some gas it to about 2000-2500 rpm .. it goes to about 30-35 degrees away from the engine block mark.

...

when I first put the distributor in .. I didn't have it quite at TDC (I thought I did but didn't) and it gave me a check engine light that was basically saying the camshaft sensor missalignment.. (1345) so I redid the distributor at TDC this time..

...

so.. I guess my question is.. is this the normal timing for that engine? or am I still a tooth off and for some reason the computer isn't telling me?

ps. before everyone tells me to turn the distributor.. this is one that is totally comp. controlled.

thanks,
vballfun

If your not getting any SES light, and the engine is running good, then you have done it properly. What your talking about is the advance that is controlled by the computer, and the more you rev the engine, the more advance the computer will produce. The advance is set by the computer, based on engine parameters. So if your engine is running good, it looks like all is good.

If memory serves me right this system has to be set up with a scan tool.

With your engine warm, disconnect the shunt plug. That will lock the system in open loop so that the timing won't move around. The SES light will be on while the wire is unplugged. Set the timming to TDC useing a timming light. You may need to move the distributor one tooth. The SES light will go out when you plug the connector together and restart your engine. Your Chilton Manual must explin this procedure?

With your engine warm, disconnect the shunt plug. That will lock the system in open loop so that the timing won't move around. The SES light will be on while the wire is unplugged. Set the timming to TDC useing a timming light. You may need to move the distributor one tooth. The SES light will go out when you plug the connector together and restart your engine. Your Chilton Manual must explin this procedure?

This procedure will work if you have a PCM equipped truck (under dashboard), it will not work if you have a VCM equipped truck(computer under the hood). The VCM system the distributor goes in one way, and that is it, as long as its not 180 degrees off, your pretty much (generally)good to go.

Correct. The "cam position sensor" in this case has a resolution of about 180º of cam rotation. It's basically there to tell the PCM which half of the cycle the crankshaft is in. The finer positioning detailed by the instructions is chiefly to assure that the spark terminals are aligned correctly so the rotor and cap terminals are not miles apart when the spark occurs.

FWIW, 35º at 2,500 RPM sounds O.K. to maybe a little light. I like to program them with a bit more advance at low load values and higher RPMS for best mileage and thorough burn. The factory programming tends to be a bit more conservative like that.

Correct. The "cam position sensor" in this case has a resolution of about 180º of cam rotation. It's basically there to tell the PCM which half of the cycle the crankshaft is in. The finer positioning detailed by the instructions is chiefly to assure that the spark terminals are aligned correctly so the rotor and cap terminals are not miles apart when the spark occurs.

FWIW, 35º at 2,500 RPM sounds O.K. to maybe a little light. I like to program them with a bit more advance at low load values and higher RPMS for best mileage and thorough burn. The factory programming tends to be a bit more conservative like that.

So 35º after TDC is 'normal'? and I didn't mis insert the Dist. by 1 tooth? I just thought spark was supposed to happen a few degrees before TDC.. and if it happens after TDC the gas mix has already expanded and the combustion is less efficient... so I guess I just confused by it sparking at 30-35º after it's passed TDC.

they almost never set timing to atdc its useally btdc at full throttle it can go as far as 35* before

they almost never set timing to atdc its useally btdc at full throttle it can go as far as 35* before

that's what I was thinking.. I'm gonna have to check again and figure out which way my motor is 'rotating'.. I thought it was always clockwize viewed from the drivers seat.. thus counterclockwize from the radiator.. and I'm seeing the tick mark about 25-30º after the pully rotates past tdc (counter clock wize) :-(

:banghead:

Can the distributor body be turned slightly on the vcm equipped?

My distributor I think has nothing inside it and by the lloks of it with a flash lite the body looks pinned with a roll pin. It's kinda hard to see whether it moves (like an old chevy) Does it?

If you have the distributor with the spark plug wires coming out the side of the cap, as opposed to coming out the top, with the computer located under the hood, (VCM) this is the enhanced ignition system and turning the distributor will have No affect on the timing of the engine. The timing is done by the VCM, with info supplied by the crankshaft sensor and the camshaft sensor. With this engine, a timing light means nothing.

Rather than asking about a timing change, I am trying to find out whether or not the body of the distributor physically can be rotated?

Can the body be turned (like the old ones losen clamp and rotate) or is it keyed, fixed, pinned? so that one cannot turn it?

It cannot be turned... however I believe I have resolved my concerns over the timing.. I just took the distributor out again.. set engine at TDC one more time.. and put the distributor back in, following Chiltons instructions again.. I guess th first time I did it, it was just a tooth off.. (cause I did have to wrangle it quite a bit the first time.. and may have wrangled a little bit too much and placed it one tooth off.)

Anyway I believe the timing is looking correct now. thanks all.

now I have heating issues... but that's another thread..

-vballfun

Ok, thanks. I am clear that the body of the dist. cannot be rotated.

What Blue and Del are saying is that moving the dist will not affect the timing at all.

Looking at fronts of engines turn clockwise.