Why eratic bouncing, line from balancer and timing tab??

[Nasty-LSX]

I just bought a 87 GMC with TBI. I tried to set it at 0 TDC, but the line on balancer just bounces from 0 to8 degrees. Like a half inch movement. New timing chain, all rebuilt top end. Runs good after 1500 RPM, but seems to not be smooth running. First TBI for me to have. Dont know Jack on where to start.

 

[chengny]

To set initial timing on EST applications, the system must be in by-pass mode. The following is from the 1987 Fuel, Emissions and Driveabilty Manual:

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[Nasty-LSX]

Thanks that help big time!!

 

[chengny]

Just to confirm (for others who may be searching for a solution to this issue);

Did the mark steady out with EST in by-pass as described above?

 

[Nasty-LSX]

Just to confirm (for others who may be searching for a solution to this issue);

Did the mark steady out with EST in by-pass as described above?

Yes sir, it stayed solid on the timing tab 0 line.

Still runs rough at idle. Not sure where to start.

 

[Georgeb]

Yes sir, it stayed solid on the timing tab 0 line.

Still runs rough at idle. Not sure where to start.

Try setting it around 8 deg. Mine runs better there.

 

[Nasty-LSX]

will do! Will repost tommow

But wait. Wont my idle go up on RPM?

 

[chengny]

The ECM will adapt and bring the revs back down - to a certain degree. You might have to make slight adjustments until you find a sweet spot.

But before you deviate from the factory specs, make sure you have all the basics covered. A few areas you might want to check:

No air leaks (under the throttle plate and in any associated hoses)

Secondary side of the ignition system in good order (i.e. plugs, wires, distributor cap, rotor, etc.). A good check for bad plug wires is to crawl under the front end when it's dark. With the engine running, take a minute and look up on both sides of the block. If you see any flashes, your wires are bad...change them.

IAC valve is clean and is able to move freely. Be sure the wiring connections to it are clean & tight. Also check TPS connections. The IAC & TPS work together (via the ECM) to maintain a smooth idle.

 

[Georgeb]

I should have asked if you idle is rough as in random mifires or suring up and down?