Chevy timing issue tbi 350 help

customjeepyj

customjeepyj

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Feb 12, 2011
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Trinity
78 chevy 350 converted to tbi custom chip no knock sensor egr or tranny sensors, all been deleted. Ran fine for year. Carb intake adapted to tbi holly 670 cfm tbi unit. New dist, new module, new pick up, timing chain new and dots line up. New coil and at idle timing still jumps around about 20 degrees. Runs hot idles at 1200 sometimes then 700 depends on how it feels. Fuel pressure good. Spare computer still no fix. Can't figure out help please!!! Thanks. Ohh runs exellent with carb and hei dist.
 
wonder if you have a vacuum leak...
 
Try swapping the E.S.C. in the dist?
 
Temp sensor. (If your not sure how old it is, change it, its cheap)
TPS (Trottle Position Sensor) can have dead/worn spots that send strange signals.

also check the gray common sensor wire for 5v.

Unplug DST timing wire and check ignition advance, stock is usually 0 but most aftermarket chip advance it some. The jumping around your seeing is the ECM doing its thing.
 
Thanks I give it a shot temp sensor less than 6 months. Tps who knows? But why would the ECM let it jump around so much at idle. And it runs like crap anything above 2500 under load
 
Actually went to his house he thinks the brand new pickup is faulty so trying ac delco pickup today! Hope it works. He said the cheap pickups sometimes u have to go through 3 to get a good one. Who knows. Thanks!
 
You didn't mention the ECM/binary models, but it makes a difference (actual control vary between generation/binaries).

  1. Have you checked the base timing w/ bypass disconnected? The ECM will only adjust it so far...
  2. I know this ain't gonna be a popular request, but have you checked for codes? (unpopular because most folks going the TBI route skip installing a SES lamp :rolleyes:)
  3. Lastly, I'd suggest you start with the basic stuff (Key On-Engine Running voltage checks, & Initial setup procedures) before continuing to throw parts at it hoping for resolution (always an expensive venture!)

:beer:
 
Yes very expensive and gotta guy coming monday with a computer and he's gonna try to read what's going on with it. I disconnected the wire still jumps around from about 10 to -10 degrees.
 
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