89 TBI 350 problems

[Gamikatsu]

Engine runs....very rough.

getting code 42. timing light on, you can see it go from 16 deg to zero, back to 16... surging. PUT it in gear, timing drops permanently to zero. Brown wire with black stripe is plugged in. engine has new TOP end, Holley TBI, TBICHIPS.com stage 2 chip. Was running Great for a few weeks after top end rebuild. suddenly looks like ESC just stopped working. have replaced Ignition control module, Electronic spark module, PROM chip to stock chip, ECU has been replaced with a reman'd from parts store, STILL nothing fixes the problem. I have a Distributor from the junk yard, i'm about to put the bottom end in to see if its that. has new cap/rotor/plugs/wires. i can think of two probable causes at this point. Wiring fault somewhere, or POSSIBLY the knock sensor is hearing my Rocker arms clicking because i have one or 16 still clicking a bit, and its dropping my timing to zero.... not sure. Where should i start? does ANYONE have any ideas at this point? I'm at the breaking point with this truck and am about to do a Carb swap....


Ed

 

[Tempted]

The timing numbers are correct. The reason it is jumping around is because of the surge, not the other way around. Check your IAC, TPS and look for vacuum leaks.

 

[Gamikatsu]

Thats what we thought. but the IAC is brand new, and functioning as best we can tell, and TPS is at .65 v. we've searched for vaccuum leaks all day. it is Surging, and Brian from TBI chips thought it was because the stage 2 chip with no cam. so i put hte original prom back in. still surging/stalling.

 

[Gamikatsu]

oh IAC is brand new on the 3 week old holley TBI. i know many don't like it but it was GIVEN to me for free, BNIB, for doing a fuel pump, tune up, and a freshly rebuilt factory TBI that used to be on my jimmy. Ran great for 3 weeks until i ran into this electrical problem. TPS reads .65 v at Key on engine off, and 4.8v at WOT. so its functioning. no vaccum leaks that are detectable using Ether, Carb cleaner, etc. I even jumpered the ESC wire (brown with black) from the ECU in the dash, to the distributor connector itself with NO luck...

 

[Tempted]

Try unplugging the MAP.

 

[Gamikatsu]

will try that. what would it do?

 

[GMCTRUCKS]

Vacuum leak.

 

[Gamikatsu]

Any help please.... still getting a code 42. No idea what could be the problem. Still running like absolute garbage.

 

[Chris]

Most likely a vacuum leak. Unplug your EGR valve to verify it isn't stuck open, also spray carb cleaner around the base of the throttle body to see if the gasket is damaged. Holley TBI units are notoriously junk, FWIW.

 

[Gamikatsu]

FIXED!!! WIRE LOOM had rubbed against the body on a pinch rail of sorts, and chaffed through the wire loom into the insulation of a few wires. Found it by realizing we had a couple of blown fuses. Figured it was a grounded wire somewhere and started following wiring harness. Runs like a bat out of Heck.