BWilcox

Hi Guys, Been tuning on my 355 TPI. The part throttle BLM adjustment was successful with just Injector Constant updates. The base MAF tables looked ok. The idle BLM is in the 140 range? Idle timing is around 28 degrees BTDC. Idle RPM is 975. WBO2 reports 16:1 to 17:1 idle AFR. NBO2 reports 50 mVdc. Cam overlap (50 degrees @ 0.006", lift ~ 0.580"). Idle MAF reading is ~ 7.8 grms/sec. Idle vac ~ 14 mm Hg. I have not been able to find any vac leaks. The idle grms/sec seems ok for a 355. The engine runs great at idle. In order to bring down the BLM, I have to raise the MAF Table 1 greatly. Just does not make sense. What is the best way to provide the equivalent amount of idle fueling? i would like to mantain the present actual AFR without the 140 BLM help. I noticed two tables in the $32B hack. Inj Offset Bias vs. Batt Volts Low Pulse Width Injector Offset vs. Base Pulse Width Under what tuning conditions should these tables be tweaked? Am I missing something? Help is really appreciated. Best Regards, Bruce

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95 4x4

Read the sticky it helped me out alot (The Prom Tuning Guide Book and FAQ: Common Questions and Answers)The Prom Tuning Guide Book and FAQ: Common Questions and Answers .The WB won't help you out at idle the cam over lap is hurting you giving you a false reading . Read the cam section explains it very nice .

tequilaboy

Do you really want to add additional fuel, or just bring the blm down?

Increasing the MAF table in the idle region, or increasing the low pulse width offset in the vicinity of the idle bpw will provide additional fueling and should bring the blm down. The end result however, may be too rich at idle.

To help bring the blm down without extra enrichment, you may want to offset (reduce) the slow O2 error and fast rich/lean thresholds for the idle airflow region so that it appears to be rich at a lower O2 voltage than the present value(s).

Another option would be to tune the rest of the cells to run on the rich side (blm < 128) and also limit the maximum blm to something like 136-140 to minimize overfueling.

95 4x4

I'am SD and in my case i don't have as much overlap as you . I had a chance to use a five gas analyzer during one of my emissions run and i adjusted my Idle 02 Voltage Thresholds down by 100 mV all three values and it brought me right in to 14.7 stoich . By doing this i accounted for the extra oxygen getting by (overlap) and the 02 sensor would read correctly at idle only.

BWilcox

Hi Guys,

Thank you for the help.

Great comments and questions!

Do I want to add extra fuel or just fix the BLM?

I am still debating the issue.

Today, the weather in NC is warm (around 90 F).

The idle BLM approached 145 and the NBO2 sensor was switching and the WBO2 average was in the mid 14 to mid 15 range.

The car ran great and there was very little idle smell.

Does this result mean I should add fuel to center the BLM?

or

Should I add a little bit more fuel (Inj PW Offset table) and offset the O2 constants?

When the weather is cooler, the car also runs great with the higher than normal Idle BLM values.

Given the sniff test, the car does not seem rich at all.

I have read many of the posts and it seems like folks experience true phantom lean issues and then the ECU over-compensates and the result is really rich running.

In my case, the car does not smell rich. It smells clean.

I am running the Ford/Bosch 24 lb / hr injectors. I am wondering if these guys open a little slower with respect to the GM injectors?

Best Regards,

Bruce

95 4x4

My results where the same as you and i had the phantom lean issue . The WB and the NB02 won't help you at idle if they are reading to much oxygen . Why not try a test and lower the offset O2 constants at idle and see what it does i have a seperate table just for idle . Not sure if you have the same with your definition .