Timing confussion?

[para driver]

here's the background, I had the 95 TBI replaced with a Vortec crate motor and tbi/vortec intake. I think the shop that did it used the tbi balancer. I suspect the timing marks are NOT correct for this combination. This was done many years ago, and that mechanic has since moved on. I had to replace the head gaskets, and it hasn't run quite right since.

(yes I disconnect the beige timing wire from the computer)..

IF I time it at Zero degrees Indicated, it runs like CARP, won't take the throttle, bogs and coughs like crazy.

IF I time it at 8 degrees Indicate, it runs better but still hesitates, won't pull strong, but the idle RPM increases.

IF I run it at 12 degrees Indicated, it runs pretty decent, but the idle stalls once in a while. No noticeable knock under hard acceration and it pulls solid up to the rev limiter before shifting.

So.. and maybe the only answer is to TDC the engine with a degree wheel, but is there a way to tune the initial timing by vacuum or rpm??

[drumer919]

You know there is an easier way to verify the timing mark that with a degree wheel right? Just need to use an old spark plug to make your self a piston stop and put it in the #1 cylinder, then turn the crank backwards till it hits the stop, mark where the timing pointer is on the balancer then rotate the engine forwards till it hits the stop and mark it again then find 1/2 way between the 2 marks and you have your true TDC mark.

[para driver]

I have a tool for that (extended threaded like a plug).. can a timing chain stretch THAT much over 140k miles??

[drumer919]

What do you mean can a timing chain stretch? That question just seems a little odd, not being related to the OT. But yes its possible, to check for a stretched timing chain pull the disty cap and check for rotational play.

[para driver]

I know they stretch, but was just trying to quantify how much? 12 degrees seems like a huge amount. I just threw a vacuum gauge on it, and it likes 10 degrees btdc, and pulls 19 In/Hg at idle.

[Fierobsessed]

I hope you've tuned it, or had it tuned. I have the same setup. When I first put it together with the OE EPROM, It ran like horrid garbage. It started, and idled fine. But, any throttle input at all (when in gear) resulted in backfiring, sputtering and stalling. From there I did a LOT of tuning. First I hammered the fueling pretty good till I got it reasonably close. I turned off EGR and CCP function for tuning. This eliminated the throttle tip in stall I had. It was a bit of a dog, quite disappointing.

Then I Imported a "Vortec" timing table. This table is FAR more aggressive then the TBI's old one, and it seriously woke the engine up. My timing is still set to zero degrees. I think you might be just putting a bandaid on a tuning problem by adding timing with the dizzy, assuming you haven't had a tune.

Chain stretch is a bad thing, you shouldn't have more then a couple crank degrees in either direction. And at 140k, its almost time anyway. Iv'e dropped a chain at 180k once.

Oh, and I'd be very conscious of your intake gaskets and intake manifold bolt torque. I thought I did a good job the first time. But I always had a shudder (weak cyl's) in cold weather till the engine warmed up. Which is usually a sign of a leaky intake gasket. Im in the process of replacing those crap felpro gaskets with GM ones. And this time I was extremely careful about the torquing of the bolts and the position of the intake manifold itself. The top part of the seal is right on the edge of the gasket, and there is enough play in the mounting bolts on the manifold that it can completely miss the seal.

[para driver]

the question is, I don't trust the damper to give me a true TDC.

[def1]

why wouldn't the damper work? both engines are gen1 sbc truck motors. I assume both are 350's.

[webcat]

Originally Posted by def1

why wouldn't the damper work? both engines are gen1 sbc truck motors. I assume both are 350's.

Thats what i was thinking too !

Originally Posted by para driver

I had to replace the head gaskets, and it hasn't run quite right since.

So if the mechanic had it tuned at one time at least you know its tunable (meaning decent tuned prom chip)

[webcat]

Originally Posted by Fierobsessed

Oh, and I'd be very conscious of your intake gaskets and intake manifold bolt torque.

X2 on those crappy felpro gaskets
I used them FELPRO 1255 the first time , needless to say they leaked , i have the GM intake gaskets now and also used the GM sealer instead of the black rtv silicone , so far no problems !

[webcat]

Originally Posted by para driver

IF I time it at Zero degrees Indicated, it runs like CARP, won't take the throttle, bogs and coughs like crazy.

What do you get for a manifold vacuum reading when you have it set at zero degrees?

[webcat]

Originally Posted by para driver

(yes I disconnect the beige timing wire from the computer)..

Here's a link to a guy that was having problems with his timing connecter , he put a multimeter on the advance signal wire to verify it was working
http://www.fullsizechevy.com/forums/...at-expect.html

[para driver]

Originally Posted by webcat

What do you get for a manifold vacuum reading when you have it set at zero degrees?

The best vacuum I got was at an indicated 14 BTDC, at indicated zero btdc I was pulling 7-8. At zero it wouldn't take any throttle even after it warmed up. At 14 btdc it runs pretty well, that's what makes me suspect the balancer and timing mark do not represent true TDC. I want to change the timing chain pretty soon, so I will have to degree the motor anyway.

[whitelightnin92]

Originally Posted by para driver

The best vacuum I got was at an indicated 14 BTDC, at indicated zero btdc I was pulling 7-8. At zero it wouldn't take any throttle even after it warmed up. At 14 btdc it runs pretty well, that's what makes me suspect the balancer and timing mark do not represent true TDC. I want to change the timing chain pretty soon, so I will have to degree the motor anyway.

you dont have to degree it, but it wouldnt hurt

[drumer919]

Yea why not just do what I originally suggested to check the mark on the dampener, you said you have the tool.

[webcat]

Originally Posted by drumer919

Yea why not just do what I originally suggested to check the mark on the dampener, you said you have the tool.

X2

I take it you have no codes?

Do you have a vacuum leak or intake leak?


.

[para driver]

I'll have to check for leaks, but I don't think so..