Frustrating problem with timing advance

[Laid GP]

I recently replaced the distributor on my 95 350TBI truck, and I can't get the timing quite right. When the timing advance is unplugged, it consistently hits the zero mark on the timing indicator when I put a timing light on it. It runs and drives fine like this with the timing advance unplugged, albeit with a high idle (around 1200 rpm) and sometimes dies when going in to reverse. I plug the timing advance in with the truck running and let it run for a bit to adjust to the change, and it feels fine but will just die out of nowhere and will not restart with the advance wire plugged in.

I think I may have a small vacuum leak at the line that runs from the TBI to the valve cover. Other than that what could be the problem here? I have been tinkering with this thing for months and just want a truck that runs and drives dependably again!

 

[marsmann]

If mechanical timing with EST bypassed and basically no computer advance is fine then your distributor/install is ok. What you are dealing with is all within the computerized advance timing. A vacuum could cause some funny loping or surging of the idle which would move the mark when putting a timing light to it but I would be looking to test the coolant temp sensor or TPS. Both play a critical role in adjusting the computerized timing.

 

[Laid GP]

Thanks for the advice marsmann. I'm going to replace the cracked vacuum hose and go from there.

 

[magimerlin]

At work we had an issue like this... finally hooked the computer up to it.. coolant temp was telling the computer in was -40 degrees...it was about 90 degrees that day... dead sensor.. replaced sensor and fired right up and had no issues..