Has anyone fiddled with the individual cylinder trims using tunercat ?

I was taking a closer look at the values in my bin file for my 94 LT1 and noticed that one cylinder idle trim value is set to 0.90 in the idle trim table. The off idle ones are pretty close to +/- 6% but the idle value for #7 is almost 10%. I have compared my bin values to the stock ones and they appear to be the same.

Here are the values for idle -

1 - 1.016
8 - 0.977
4 - 1.000
3 - 1.000
6 - 1.031
5 - 1.000
7 - 0.906
2 - 1.023

Notice the #7 value is .906 which is almost 10%. This seems a bit large to me unless the LT1 intake is really screwed up for that cylinder or the tunercat translation is wrong.

The off idle is:

1 - 1.063
8 - 0.961
4 - 1.023
3 - 1.023
6 - 0.953
5 - 0.977
7 - 0.984
2 - 1.047

The off idle values are closer and #7 is much closer to 1.000 than the #7 idle value.

I am wondering if the idle can be smoothed out a bit by adjusting the trim values.

Any suggestions comments etc....

Thanks in Advance.

 

I don't think you'll get very far if your using the stock manifold, other then correcting for maybe slight variances in wear.
10% of what?. It might be 10% of 1% of the pulse width, or an adder rather then a multiplier. I doubt if it's 10% of the overall fueling computation.

 

Ahhhhhhhh. To have SEFI.

Tim

------------------
TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's with bigger cam, bigger stall, and bigger exhaust.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

 

FWIW, I think I read somewhere (Lingenfelter?) that the LT-1 intake airflow distribution is uneven from the front of the block to the back. If GM trimmed the fuel this way, it would seem to support that thought. HTH

DrJ

 

This is just a guess but on a short runner one plenum (single plane) intake design the #5 cylinder will steal some of the intake air charge from #7. Especially at idle when the intake isn't working at its potential. I think GM did a great job with the LT1 and that this method of tuning was very intentional for the manifold used.

 

Using software to cover for poor design, is a great cover, but that's all.
To really get the trim right means data logging 8 WB O2s.
Batch to batch, and good design will get you more HP.

 

Really shouldn't be a problem with SEFI.
With the injectors working at a 2% duty cycle at idle, there is lots of time for the fuel to sit around waiting for the valve to open. Remember these are very slight corrections.

The 8051 PCM is just flat inna league of it's own. The LT1 is not a bad design, but linked with the 4L6E tranny is just awsome. I been putting a few hours in on the 8051 and have really come to like it. Some talk was that it was because it uses a MAF/MAP system. Well we went to MAP only and it's great.