88 burb with problems
 

Cool new board, I believe I will be spending a lot of time here now.
My burb has a massive exhaust leak from the right manifold. Cracked all the way around. I plan to replace it tomorrow, but here's the deal.
Most mornings after startup, When I take off from a stop light the engine all of a sudden runs rough as if the timing has jumped. The SES light comes on and all performance is lost. I check the code, its a 43 (ESC). I turn off the truck, to reset the code and continue off to work. I checked the code again and all I get is 12. My book tells me it may be the spark knock sensor but to test it, they recommend tapping the block near the sensor. Would the exhaust leak trip the sensor and cause it to retard the timing? Why would I not have the code stored in the ECM until 50 restarts?
How do I check the static timing on this engine, I know I have to disconnect something and check it at around 500-600 rpm.
Any ideas?

the exhaust leak could trip the ESC circuit if it is bad enough. That is also the reason you really cannot run a gear drive on a newer engine with ESC.

If you are pulling the code out (reading it) it will clear all codes. If it does not come back, you will get the code 12 (all clear).

I replaced the manifold this weekend and it stopped the code 43. While I was under there, I replaced the engine mounts, trans mount, and shocks. Truck rides much smoother.
I still have the hesitation from idle to about half throttle. I'm going to replace the map sensor this weekend and see if it helps with the MPG and hesitation.

you might check the EGR while you are there as well.

I found the problem with throttle response. Timing was waaaay too far retarded. Once the throttle was approx half way, the weights in the distributor would advance the timing annd make it seem to run correct.
The PO assured me the timing had not been changed since the engine had been installed.
I checked the timing, found it off, pulled the timing cover and found the chain to be tight. The distributor was tight so I can only assume someone changed the timing along the way.
I appreciate the help and suggestions from this forum and the truck threads as well. If I can help out, I'll try my best.