DanielRicany

Hey guys, I have a 1985 Corvette, and I have advanced my base timing to 10 degrees. I'm not sure that my tuner that I use has actually set the timing in the tune, or at least not properly, so I would like to check up on that myself so I might be able to solve a few idle problems.

Where are the tables or scalars to modify in the tune for base timing? And do I need to modify like total timing advance tables or anything? What should they be set at normally, and what should they be set at for 10 degrees? I just want to make sure that it is all set up properly, because if it isn't, I can just retard the timing to 6 degrees and see if I still have the idle problems.

Thanks a lot!

cumbercr

If you are using Tuner Pro RT, go to the scalars and select Initial Spark Advance. It should be set to 6 degrees. If not, make it 6. Then adjust the distributor for 6 degrees.

Advancing base timing is really not necessary and can cause problems in other areas. If you want to make timing changes, use the Spark Advance vs. RPM vs. Load table under Tables. If idle is the problem you can adjust the timing at idle RPM.

DanielRicany

Okay thanks a lot! My tune was set at 9.84 for the Initial Spark Advance. My timing is supposed to be 10 degrees, should I change it to 10?

And I assume that the left hand side of the Spark Advance vs. RPM vs. Load table is the RPMs, and the middle area is all timing advance degrees, but I don't understand the numbers in the top line, I guess they are Loads? What are loads measured in? What do those numbers mean? Thanks a lot for your help!

cumbercr

My recommendation is set it to 6.

The numbers at the top are load. The higher the number, the more load. Its a value calculated by the computer. This is one of the weaknesses with the 85 ECM. Data logs do not record load. So there's guesswork involved in making timing changes.

It's going to be hard to help you without knowing what your tuner was doing.

DanielRicany

Will I feel a difference if I move back down to 6 degrees, or nothing at all?

When I compared the two tunes, stock tune and my current tune, there was no changes in that table. The only change was in the Initial Spark Advance scalar. I set it to 10 and it reverted back to 9.84.

If it's not going to effect my power, I would have no problem going back to 6*.

91tpiman

If you told your tuner that your base timing (distributor timing) was set to 10, then if he set the initial timing in the tune to 10 also,then that is 4 degrees advanced in the tune which actually retards timing back 4 degrees. So, it is like having 6 degrees BTDC. Raising the initial timing number in the tune really retards the timing and lowering that number will advance it. Just set your distributor timing back to 6 degrees to avoid any confusion.

91tpiman

If you move the distributor back to 6 , then you will be retarding the timing, effecting the power output. You will be 4 degrees retarded. Rememeber the 10 and 10 equals 6. That is 10 degrees at the distributor and then 10 degrees in the tune (which is 4 degrees retarded really) This is the easiest way for me to explain this to you.

cumbercr

First, 9.84 vs. 10 means nothing. That's a Tuner Pro thing.

I do not understand what your tuner was trying to accomplish. 6 degrees is the factory setting. Adding 4 degrees everywhere means you will be running over 50 degrees of total timing in some areas. But to answer your question, I don't think it will run any worse putting it back to 6.

The good thing about these changes is that you can always go back.

91tpiman

Exactly, unless the tuner already knew he had the distributor set to 10 degrees, then it all just evens out. Like having 6 degrees again. 9.84 is probably 10 in Tunerpro. It's close enough anyway.

DanielRicany

So essentially what you're saying is, if I didn't modify the Spark Advance vs. RPM vs. Load table, then I didn't get any performance improvement by setting it to 10*?

cumbercr

Correct assuming the distributor is adjusted to 10 also.

DanielRicany

Okay, fair enough. Do you think that this is the cause of my idle surge? It surges for a few seconds when I come to a stop light and then evens out.

cumbercr

No. That sounds more like the idle air control valve or maybe a TPS sticking.

DanielRicany

Okay thanks. I'll do some tests tomorrow.

91tpiman

Keep us posted , hope it works out

MrWillys

I've taken out 4 degrees globally out of the spark table for engines with big cams, and set initial to 10. Do what the tuner tells you, because he may have a reason.

Ryque

need to contac you about a chip pm me please

Cliff Harris

The parameter is known as LV8, which means 8-bit load value. It's the ratio of TPS to MAF air flow. It's calculated by the ECM and it tells the ECM how much you've mashed on the gas pedal.

Basically it's used when you hit the gas (throttle blades opened -- high TPS) but the air flow (and RPM) hasn't caught up yet. It can also be used in a situation like going up a steep hill where you mash on the gas pedal but the engine doesn't have enough power to make the car accelerate (at least not very fast).