1994 TBI 350 Stretched Timing Chain

[Schurkey]

My father suggested giving more timing than whats specified and that seemed to mask the issue, making the truck drivable.

Once again these issues rear their ugly head at random, with the exception of the back firing through throttle body (that goes away with additional timing).

Have you found TRUE TDC, and compared that to the damper/timing pointer?

 

[megafan0258]

After all you've changed / inspected, I thought for sure you'd see it on a vacuum gauge.

How sure are you it's not transmission related? When's the last time it's been serviced?

I was able to get the vacuum up to 21inches with additional timing. It will fluctuate when the idle gets unstable, whish seems the occur at random.

As for the trans, it supposedly has a shift kit that was put in prior to my ownership. Approximately 40k ago. Most of the fluid has been changed due to a mishap with cooler lines but I am waiting to drop the pan. I have a filter and oil but would like to resolve the running issue before doing that because I have other parts I'd like to do at the same time (rear main, carrier bearing, trans mount, etc...)

I don't believe it's a tranny issue.

 

[megafan0258]

Have you found TRUE TDC, and compared that to the damper/timing pointer?

I did that to the best of my abilities when I changed the timing chain. Everything lined up as it should. I also replaced the damper, old one was still okish but the timing cover seal wore a groove into the snout.

I finally got TunerPro working. After about 2 hours of clicking around I figured out I needed TunerPro RT to have the Data Acq tab in Tools/Preferences.

Live Data is eminent!

 

[termite]

I did that to the best of my abilities when I changed the timing chain. Everything lined up as it should. I also replaced the damper, old one was still okish but the timing cover seal wore a groove into the snout.

I finally got TunerPro working. After about 2 hours of clicking around I figured out I needed TunerPro RT to have the Data Acq tab in Tools/Preferences.

Live Data is eminent!

What Schurkey is getting at is bringing number one piston to top dead center, Compression stroke, and comparing timing mark on cover to damper. You can then confirm your distributor is set correctly and subsequently base timing (bypass unplugged).

 

[megafan0258]

What Schurkey is getting at is bringing number one piston to top dead center, Compression stroke, and comparing timing mark on cover to damper. You can then confirm your distributor is set correctly and subsequently base timing (bypass unplugged).

I did all of that and it checked out.

I currently have it set to 7 degrees to prevent it from back firing through the TBI and to allow me to drive it without dying from a stop. I believe the computer is pulling timing, I just don't know why.

 

[megafan0258]

Small update...

I just realized I didn't have a gasket on my distributor when I replaced it with a billet unit from Jegs.

Could that be causing some issues?

 

[n2xlr8n]

Small update...

I just realized I didn't have a gasket on my distributor when I replaced it with a billet unit from Jegs.

Could that be causing some issues?

Sure. Oil leaking past it....but not a timing issue. If you can, put the original distributor back in it. Heck, put all the original parts back in if possible. This is not rocket science.

I can understand why you think it "feels" like it's pulling timing (and it may be), but again, if the (4L60e?) transmission hasn't been checked out, do it.

 

[megafan0258]

Sure. Oil leaking past it....but not a timing issue. If you can, put the original distributor back in it. Heck, put all the original parts back in if possible. This is not rocket science.

I can understand why you think it "feels" like it's pulling timing (and it may be), but again, if the (4L60e?) transmission hasn't been checked out, do it.

No oil that I can see, I was thinking more vacuum.

Anyhow, I've swapped parts in and out with no success. Original distributor was roached. I've had 2 different distributors since then, no change. I did keep the ICM and that's what currently in there (I swapped it in hoping for the best, I was wrong)

As for the transmission, yes it's a 4L60E.
It isn't slipping and I'm certain it's an engine related issue. I don't believe my trans would cause back firing through the TBI out of gear.

 

[rebelyell]

AFAIK, the ONLY way to verify True TDC is roll motor thru until #1 piston Itself is verified Truly at TDC ... then Verify the Zero Groove on damper is aligned Exactly with Zero on timing tab. If it's Not so aligned, you can be certain the damper's rubber bond has failed, and damper's outer inertia ring has slipped (Go Buy a New Replacement Damper ... they're not very expensive).

 

[scott2093]

I don't believe my trans would cause back firing through the TBI out of gear.

Could a goofy preload cause this?