est bypass
 

Where is the est bypass connector on 87 z28 305

Look for a single brown or brown/white wire close to the PCM/ECM.
Unplug the connector, set timing, reconnect, remove battery cable or ECM fuse removing DTC, reconnect all.

I think he's asking because in his other thread he has an error code 42 (EST issue), and code 33.
The est plug is on the drivers side near the firewall and brake booster.
Whenever you set the timing, that harness gets unplugged. In doing so, that trips a code 42.
After the timing is set, you reconnect the plug, and clear the error code from the ECM either by disconnecting the positive battery cable, or unplugging/replugging the ECM harness connector. When you do this though, you will clear all codes (lose the 33). But if it is still a present issue, the code will return.
It's quite possibly someone else may have set the timing this way without resetting the ECM, unless this is a new development that appeared out of the blue.
Code 33 btw has to do with your MAF sensor: bad connection, short or break in a wire, bad sensor, or bad ECM.

Agree with the statement, but if the timing was set without bypassing, would not the ECM make up the difference?
I'm just asking for my own education.

Yes it would, and you'd be chasing your tail because the ECM would be readjusting the advance.

yes code is new both 33 and 42 wanted to know what wiring to inspect for a short, thats one thing i hate, shorts. my car loses power when applying a high level of throttle or when coming to a stop have replaced iac valve, fuel pump fuel filter, and cleaned throttle body

Simular problem to a friend's '89 GMC 1500 in 1995. Die on decel, no upper power.
Unplug EST and ran good, but not great, but better than plugged in.
Changed ECM and transferred chip, but to no avail.
Dealer changed out the dist assembly including cap, no plug wires, problem cured.
Still haven't figured this one out.

so where is the est plugged in to? and if i unplug will it still throw the code and so changing the distributor,plugs,and wires fixed the issue??

Look for a single brown wire with a connector.
Could be anywhere, pass kick panel next to the ECM, firewall next to the dist, some easy accessible place for a technician to get to.
Yes, it will give a DTC, CEL will be on, but engine should at least run.
Yes, dealer changed just dist aseembly and cap, no wires or spark plugs.
JMT's

Go back and reread my first post, the answers to those questions are in there.