Timing Light vs Data

[eutu1960]

The data I am reading is different than the reading I am getting with a timing light, base timing is set at 6 degrees with EST wire disconnected,
All following readings are with EST wire connected.


Idle: 7 degrees
2000 rpm:14 degrees
3000 rpm:15.5 degrees.




That is way off from what the my data logs shows.
Data Log at Idle is 24.61 degrees
Data Log at 2000 rpm is 52.73
Data Log at 3000 rpm is 49.57


I also have a code 42, so far test are pointing to the ECM, I replaced the Ignition Control Module with a known good one.
Here Is A Link to my Data. https://drive.google.com/file/d/0B5d...ew?usp=sharing

[jim_in_dorris]

First, what ECM are you using.
Second, code 42 is EST wire disconnected, connect the wire, pull the negative terminal at the battery and reconnect to clear code 42
Third, unless you have patched the bin, the data stream does not contain timing data
Forth, with base timing set at 6 degrees, the ECM will correct for it. To change the base timing that much, you should patch the bin.

[eutu1960]

This Is a Stock L98 in 90 corvette the timing I listed is with the EST wire connected and I am getting a code 42 with that same wire connected
this has the factory tune, Timing is set at 6 degrees with EST wire disconnected as per the FSM, the code 42 comes back after being cleared
as soon as the car is started. My question is do you think the a bad ECM is causing the difference in the data and the actuel timing.

[1project2many]

If the ecm is unable to control timing you will see disparity. Code 42 indicates that the ecm is unable to put the module in "EST" mode where it will accept timing signals from the ecm. A faulty ecm is one possible cause of code 42.

You could confirm the engine is running on module timing by watching for relatively fixed timing at the balancer from idle to 1600-2000 rpm with a rapid increase in advance above that.

[JP86SS]

That is mask $8D, timing info is shown in data.
Is this a new build?
What is the BCC you are using? (ANHT ?)
If so, you may have a V6 memcal in there, not the V8.

[eutu1960]

I have come to the conclusion that the problem is the harness between the ECM and the ignition module
the car has over 186K on it and the harness is showing its age, to answer JP86SS question this is not a new build
I plan on doing a new build this winter and I want to solve any engine management problems before then,
the car still has its OEM Memcal that came from the factory no changes there yet.
Since data logging is showing advance taking place but not showing the same at the spark plug I feel this must be the problem
I will have to do some probing of the wiring harness.

[eutu1960]

Fixed, there was a short in the distributor just where the wires come in through the distributor one of the wires was pinched.
Now I have to decide if I should get a tune to correct for the blm's for the new injectors or wait until winter when I do my tune.
At idle my blm's are around 108, at highway speed they seem to be pretty good.