Help me troubleshoot my TBI Issue

[Rust Buster]

Hi guys,
First a little background on the truck
1988 V30 (1 Ton 4x4 Dump Truck, manual tranny, TBI 350)
This is the mountain neighborhood plow truck and never goes off our private roads. I did a complete rebuild of this truck this fall, all major systems and sensors are new, to include:
Rebuilt stock TBI
Long tube headers with heated O2 sensor
Coolant temp sensor
IAC
Oil pressure sensor
MAP
TPS
EGR Valve
EGR Solenoid
Speedway Motors TBI wiring harness
Distributor (stock replacement)
Ignition Coil
Plugs/wires
Fuel pump

Here's the problem. Truck starts and runs/idles pretty well. It does have a delay/say when you open the throttle. I have all the vacuum lines capped at the TBI except for the PCV port and MAP port. The only sensor I have not changed is the ESC module, but one is on the way.

When I check the timing (using the correct method by unplugging the timing wire), it runs very very rough and will cut out at 0 degrees. It only idles smooth at a ridiculous amount of advance, that is off the indicator plate. It will run decent at about 8 degrees advanced, but anything close to 0 gets a rough idle.

If I unplug the ESC module, there is no noticeable difference in anything. Is that normal? Also, the EGR valve doesn't seem to be doing anything. Normal? When I run a scan, I get about 6 codes, relating to EST, Coolant temp sensor, inlet air temp, etc...but I'm not sure how accurate this is. There is a TON of vacuum at idle on the PCV port.

It runs pretty good at that advanced timing, but with all the codes and the sag/hesitation when you open throttle, I am assuming there is an issue and better performance to be had.
Any ideas?
Thanks in advance!

 

[89Suburban]

I personally have no idea what affect headers have on a TBI system, but I know these systems rely on some sort of exhaust back pressure. There are different EGR types on these and they are controlled by that EGR relay. There are tests for all of this. They are on the site here if you search. If in find the time I will post them here for your reference.

 

[shortboxchevy77]

Sounds like a bad ECM to me, especially with it throwing an inlet air temp code since that system has no such sensor. They do really weird things when the ECM starts to go south. One test to try is to hold the ECM in your hand while its running and give the case a few good raps with your knuckles like you are knocking on a door. If it changes the way the engine runs at all you have a bad computer.

 

[89Suburban]

See if this helps:

http://www.gmsquarebody.com/forum/showthread.php?t=8719

 

[Rust Buster]

Sounds like a bad ECM to me, especially with it throwing an inlet air temp code since that system has no such sensor. They do really weird things when the ECM starts to go south. One test to try is to hold the ECM in your hand while its running and give the case a few good raps with your knuckles like you are knocking on a door. If it changes the way the engine runs at all you have a bad computer.

Well at this point, the only parts of the whole system that are not brand new are the ECM and injectors. What makes the ECM go bad and will I need a manual tranny specific one, or does it not matter?

 

[shortboxchevy77]

The circuits go bad in them, they just go bad. You will need an ECM with a matching number, the number will be on a sticker on the outside of the ECM. If the ECM has the right number but came out of an auto just pull the chip access cover and install the chip from your ECM.