mt01

I recently did an L31 swap into my '86. Re-used the stock aluminum Corvette heads and the entire TPI setup.

The car has a very slight miss under load, more noticeable when cold than hot.

I have an ALDL cable and TunerProRT. When I connect the cable and start datalogging, the car runs great and does not miss.

Knowing what's different about "diagnostic mode" might give me a hint on how to troubleshoot the misfire.

What changes in the ECM's programming when a 10k resistor is across pins A and B ?

Cliff Harris

From the FSM:

Closed loop timers are bypassed
EST (spark) is advanced
IAC will control engine idle to 1000 RPM
On some engines canister purge solenoid will be enabled
Park/Neutral restrict functions will be disabled

If your cable/software allows you to remove the 10K resistor, then try that and see how it affects your results.

MrWillys

What injectors are in this vehicle?

mt01

It has Bosch EV1 style injectors, I assume they're original unless a previous owner changed them.

MrWillys

Observe your BLM counts in closed loop and report the average finding.

JackDidley

It probably adds timing advance when you hook up the ALDL cable. Pretty sure its in the bin.

Cliff Harris

It only does that if there is a 10K resistor in the cable. You should NOT use the 10K resistor because it affects the settings. See post #2.