TDC and Timing mark on 95 4.3L CPI vortec...


vballfun
08-24-2008, 02:10 AM
Just curious...

For those who have messed with their distributor (taken it out ... and 'disturbed' the engine and had to reinstall)

Is the timing mark on the crank shaft pulley supposed to line up with the indicator on the engine when the #1 cylinder is at TDC?

I haven't been able to find that info... and on my 4.3..

I can take the spark plug out of #1 and I put a long thin screwdriver into the sparkplug opening... and then slowly rotate the crankshaft pulley clockwise.. and when I can see the screwdriver end move... I stop (the piston is now touching the screwdriver) when I look at the timing mark.. it is about 30 degrees 'more clockwize' than the engine mark...

Is that 'normal'?

(trying to diagnose a cylinder 6 misfire.. and nothing electrical seems to be wrong.. have replaced spark plugs, wires, cap, rotor, distributor... checked compression on that cylinder..(180 lb) checked fuel pressure (60), vacuum..(19))

also in one of the technical 'howto's on replacing the CPI someone mentions that the 6 'poppets' actually inject in unison.. if this is the case can I 'switch' poppets with cyl #6 and #4 and see if the misfire follows????

ok.. so that was 2 questions in one post.. sorry..

-VBallFun

Gabe25
08-24-2008, 02:25 AM
Here, try taking a look at this link. Great step by step and pic.
http://www.automotiveforums.com/vbulletin/showthread.php?t=881442
Post back how your doing.

vballfun
08-24-2008, 07:37 AM
Thanks for the pointer to that post.. yes.. I had looked at it.. that's kind of why I have the question...

when my timing mark is lined up with the notch on the engine my #1 piston is still on its way 'up' and not -quite- to TDC... by the time my #1 piston hits the farthest away from the crankshaft.. my timing mark behind the crankshaft pulley is now about 30 deg past the notch on the engine clockwise.

just wanted to know if that is how it's supposed to be.. or has my timing some how become 'off' (ie timing chain slipped?)

-VBallfun

MT-2500
08-24-2008, 11:03 AM
The timing mark shoud line up at TDC of no 1 pistion.
Crank damper/pulley mark may be off or slipped pulley or wrong crank damper.
To check for slack in timing chain move crank left and right hand turn and feel for the slack in chain.
If pointer is not lining up set no 1 piston at TDC compression stroke.
And set dist as shown in picture below.
http://files.automotiveforums.com/gallery/showphoto.php?photo=51302

Start engine and if it runs good.
Timing is not adjustable but the dist rotor pointer will need to be set to line up with plug wires terminal.
You will need to get a engine capable scanner and set camshaft retard reading in scanner as close to 0 degrees - or + as you can get it.
The engine will need speeded up over 1K rpm for the reading to readjust after moving dist.

If engine runs good your timing chain is good.

To check camshaft timing and chain set no one piston TDC and on compression stroke.
The watch the rocker arms on opsite firing cylinder no 4 on V6.
The should be rocking one opening and one closing as no 1 cylinder rolls over TDC compression.
If so chain and gears are set right and are good.
Let us know how yours checks out.

Are you having a missfire problem?
If so post back and someone will help.
MT

MT-2500
08-24-2008, 11:10 AM
Older injector units have a single injector that fires all poppets at one time.
Very had to switch poppets.
Lines are brittle and break trying to switch them.
If you have the newer injector unit with 12 wires into the top of intake the injectors can be replaced one at a time or switched.
Which type do you have?
MT

vballfun
08-24-2008, 03:22 PM
The timing mark shoud line up at TDC of no 1 pistion.
Crank damper/pulley mark may be off or slipped pulley or wrong crank damper.
To check for slack in timing chain move crank left and right hand turn and feel for the slack in chain.
If pointer is not lining up set no 1 piston at TDC compression stroke.
And set dist as shown in picture below.
http://files.automotiveforums.com/gallery/showphoto.php?photo=51302

Start engine and if it runs good.
Timing is not adjustable but the dist rotor pointer will need to be set to line up with plug wires terminal.
You will need to get a engine capable scanner and set camshaft retard reading in scanner as close to 0 degrees - or + as you can get it.
The engine will need speeded up over 1K rpm for the reading to readjust after moving dist.

If engine runs good your timing chain is good.

To check camshaft timing and chain set no one piston TDC and on compression stroke.
The watch the rocker arms on opsite firing cylinder no 4 on V6.
The should be rocking one opening and one closing as no 1 cylinder rolls over TDC compression.
If so chain and gears are set right and are good.
Let us know how yours checks out.

Are you having a missfire problem?
If so post back and someone will help.
MT

Yes having a missfire in #6... I replaced my water pump 2 weeks ago.. and when I disconnected my battery and reconnected it after water pump replacement.. Ive been consistently getting a p0306.
Since then I've replaced all plugs, wires, rotor, cap, (and distributor as the base is plastic and it had become so stripped couldn't hold the cap on (275,000 miles on her) and still have #6 misfire.. good fuel pressure (60psi) good compression (~180psi) good vacuum (18psi).

Am considering replacing the coil and control module next .. thinking maybe I'm not getting a 'good' spark.. but the error code is always #6.. so I'm not sure that's it.

Id redone my heads and head gasket 2 years ago and it had been running fine for the past two years. no SES light.

I wonder if I have to 'retrain' my computer as per this post:
http://www.automotiveforums.com/vbulletin/showthread.php?t=551139
-----------

So.. you are saying that I should ignore the line and use the #1 piston position (at top on compression stroke) when inserting my dist.

As for the CPI fuel injector.. I'll have to repost that answer as the truck is at parents (I have no place here to work on it) 20 miles away. but I don't remember 12 wires.. I was thinking it only had a couple...
(mine is -exactly- like the first image in this post:
http://www.automotiveforums.com/vbulletin/showthread.php?t=473110&highlight=4.3+CPI
I'd replaced the original at 120,000.. and that one at 210,000 (when I redid the heads) so the current one has about 60,000 miles on it and doesn't seem to be leaking.. (fuel pressure held at 60 psi for more than an hour) but my thought was maybe #6 isn't 'spraying') so I could gently move the injectors and swap 4 and 6 and see if missfire follows.

MT-2500
08-24-2008, 04:03 PM
MISSFIRE CODE CAN ONLY BE CLEARED WITH A SCANNER.
If the dist cap screws are stripped out you will need to replace the dist housing.
Also a good time to repace cap and rotor.
Them set the dist and camshaft retart on a scanner and clear codes and see if no 6 missfire returns.
MT

vballfun
08-24-2008, 04:57 PM
MISSFIRE CODE CAN ONLY BE CLEARED WITH A SCANNER.
If the dist cap screws are stripped out you will need to replace the dist housing.
Also a good time to repace cap and rotor.
Them set the dist and camshaft retart on a scanner and clear codes and see if no 6 missfire returns.
MT

Yes thank you for the suggestions....

I've replaced the dist cap rotor and the distributor itself (from GM dealer it is $380 by the way) got a remanufactured one for $60.. will last me well enough.

I've done all of that already trying to keep the p0306 from coming back.. after I clear the codes.. I still throw a missfire (but ONLY after driving it, so I guess that would be call 'under a load'.. cause it will sit in the driveway idling for 10 minutes without setting the missfire code.. but it idles rough)
..

I have a lower end scanner.. (I can get codes and freeze frame data.. and clear them.. but cannot program with this one.)

so I don't know how I'll set the dist and camshaft retard.. maybe return this scanner (just got it.. ) and see if I can find one that programs..

-VBallFun

MT-2500
08-24-2008, 05:31 PM
If camshaft retard is off or fuel pressure low or maf sensor is off.
You can get a missfire.
Can you actually feel a missfir on the road?
MT

vballfun
08-24-2008, 09:27 PM
When I drive it above 30 mph.. (on highway etc) I don't even notice anything wrong with performance...

when it is idling I can feel the engine vibrating more than it did before I did the waterpump last week.

I don't get a missfire code when it is idleing.

I only get a missfire code once I take it out of the driveway for a drive.. it gets set between 25 and 30 mph at around 2300 rpm.

how do I tell if the camshaft retart is off?

Fuel pressure is good.

haven't looked at the MAF sensor.

-VBallFun

MT-2500
08-25-2008, 09:13 AM
When I drive it above 30 mph.. (on highway etc) I don't even notice anything wrong with performance...

when it is idling I can feel the engine vibrating more than it did before I did the waterpump last week.

I don't get a missfire code when it is idleing.

I only get a missfire code once I take it out of the driveway for a drive.. it gets set between 25 and 30 mph at around 2300 rpm.

how do I tell if the camshaft retart is off?

Fuel pressure is good.

haven't looked at the MAF sensor.

-VBallFun

You need to get it on a good engine capable scanner and read out camshaft retard reading.
MAF senser readings can be checked on the scanner to.
Also check fuel trim readings in the scanner.
High redings point tio lean fuel or weal fuel pump.
And always put a fuel prerssure gauge onm it to check fuel pressure.
Good luck
MT

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