DRP delay to injector pulse

[95GMC_sierra]

Hello all

95 gmc big block, edelbrock MPFI, edelbrock heads, flat top pistons, roller cam at 264, new build. 7427 PCM, $31 bin, innovate WBO, moates APU1, tunerpro S/W, jumpered memcal mods made and MPFI mode selected as per the write ups on this board...

Having a hard time getting the idle smooth, mild misfires perverting the wbo and blm corrections. Wbo dances around +/- 0.8 afr, timing jittery+/- 2 degrees, kpa also +/- 2

pretty sure the ignition is solid, wiring solid, and am in the fine tune stage but that damn misfire, more pronounced while in drive with the brake on under 1500 rpm's.

I played with with the injector delay from the DRP today, bin came from edelbrock at 0 degrees delay, I added 5 degrees, might have gotten better, added another five, pretty sure it got better, added five more and I felt like I was on something, added five more for a total of 20 degrees delay from DRP for injector firing and it seems like it's working. Wbo afr seems to get richer as I delay the injector timing more. Then I did a data log in the driveway in closed loop and corrected the blm's. And the corrections seemed to move in the right direction accept for the two lowest idle speeds... 700 to 1000 rpm's

as you can see I am in the trial and error mode here trying to find this misfire and finish the tune...

question: how far is to far on the injector delay from DRP? What is an except able range I should expect?
any ideas on the misfire are appreciated also... I'm so close I can taste it...

in addition, the bin has a master timing bias and this was set to 3.9 degrees, which is what the timing is set for at idle, warmed up, and the connector disconnected. I moved that 3 degrees above and 3 degrees below the 3.9 degree starting point and the tuner pro gauges changed as expected degree for degree but the misfire persists... Is this an acceptable place to make diagnostic timing changes while observing kpa's? Timing at idle went from 24 +/- 2 when at o degrees master timing bias and to 29 +/-2 when at 7 degrees master bias... No noticeable improvement

any ideas?

john

[Roadknee]

Hi John.

Are you using the WB to view/datalog AFR only, or are you also using the simulated narrowband in place of a standard narrowband?

Can you describe the misfire? Does it coincide with the O2 switching the AFR lean?

I don't think there is a magic number for the delay from DRP to injector firing . Trial and error and give it what it wants.

By "master timing bias" do you mean main spark bias or initial timing advance? Both can be used as a tuning aid as you are doing.

[95GMC_sierra]

Hi John.


Are you using the WB to view/datalog AFR only, or are you also using the simulated narrowband in place of a standard narrowband?


Can you describe the misfire? Does it coincide with the O2 switching the AFR lean?


I don't think there is a magic number for the delay from DRP to injector firing . Trial and error and give it what it wants.


By "master timing bias" do you mean main spark bias or initial timing advance? Both can be used as a tuning aid as you are doing.

Wideband and narrowband side by side in the tri wye header collector and I use both wideband corrections and blm narrowband corrections and watch both for validity and cross checks. Using blm for fine tuning now


the misfires and wbo/timing/kpa instabilities are occurring frequent and are related, which comes first... The chicken or the egg... I don't know what is a symptom and what is a cause... But yes, they are coincident


the initial spark advance flag is what I am talking about, sorry. So many terms and so few brain cells left. The original bin came with 3.9 degrees and changing this did change the gauges on The tunerpro dash but was it an actual timing change or just a numbers change in the display? Main spark bias flag is set to 0 and I have the same question for that flag..... Does it alter timing or just the dash gauge math?


thank you


john

[Roadknee]

The ECM subtracts the initial advance and main bias from the spark tables. If you reduce these the ECM subtracts less and increases advance the engine sees.

[95GMC_sierra]

The ECM subtracts the initial advance and main bias from the spark tables. If you reduce these the ECM subtracts less and increases advance the engine sees.

Thank you road knee that will be a useful quick tool to use. I can multiply the entire table and subtract by adding timing in those flags.

John