Real lean at idle with a D1SC..

[Redline Motorsports]

Customer just dropped off a freshly built F-body project for tuning. It is a 408 with a D1SC. AFR heads, LSX/90/90 and 750cc R/C injectors. I just wanted to get the car to idle so I started with a stock file and scaled the injectors as noted. I have never used the RC injectors before so I took the 750 cc and divided it by 10.5 to converter to lbs/hr. This equated to 71.428 in which I dumped into the spreadsheet to come up with the IFR slope based on the pressure being used.

I also set the timing to 25 degrees at idle to provide some stability, set the fans to come on earlier and loaded the tune. The car was VERY hard starting and once running was idling with a AFR between 18-25:1 !

Once the car went into CL the LTRIMS where buried in the 12-18 % range. The motor has a decent size cam, especially for a blower motor so some lean idling is expected due to overlap. It was even that lean while holding the rpms at 2500-3500 rpms so it seemed that it was globally lean. What I wanted to try was to fudge the IFR to increase the fueling globally just to get the car to run. I couldn't remember if raising or lower the IFR increased or decreased fueling.....Seem to remember that decreasing the values increased the fuel.....need confirming...

I was also wondering that since the blower is moving more air at idle (under vacuum) that the increase was leaning the stock VE table.....but wouldn't the MAF at least jump in a makeup some of the error?

Just finished a 04' GTO 377 with a D1SC and it ran decent on stock values and needed very little tweaking to get it perfect. I have never seen a car run so damn lean like this. It is definately lean as it has a nasty popping lean mis and throttle response has holes in it. Its lean.

Anyone use these RC 750cc injectors? I am assuming that the math is done right and I am not off as it seems.

Looking for some insight!

Thanks

Howard

[caver]

I strongly suspect airleaks. If you have a 4 gas stick it in the tailpipe and observe the oxygen readings.

All the blown cars I have done (most non GM)with a maf have needed mucho leaning out at idle and light throttle because of the increased airflow over the maf.

Why donty you just increase the VE table by 15% or so and observe what happens.

[Redline Motorsports]

Yeah I agree that most need leaning out. The guy that put the car together for this kid was not a EFI type guy so there are many areas I need to check. I already found that the drivers side valve cover pcv was fillling the intake with raw oil and making the motor smoke like crazy. I suspected a possible leak but will try loading the VE table as a test. I'll go back and scale the IFR back to what I started with and add the 15 % and see what happens. My point to the post was to see what others have experienced with the ProCharger with respect to idle fueling to use as a check point. Thanks for the feedback and I hope a couple others will chime in.

Maybe some carb spray and expose an intake leak.....

[caver]

I like to use water to test for vacuum leaks as it is very easy to pick up where it is being sucked in.

[Blacky]

I couldn't remember if raising or lower the IFR increased or decreased fueling.....Seem to remember that decreasing the values increased the fuel.....need confirming...

Given no other changes....

Increasing the IFR will tell the PCM that the injectors flow more fuel, so the PCM will reduce the pulse width in an attempt to deliver the "same" fuel mass (i.e. it gets leaner).

Decreasing the IFR will tell the PCM that the injectors flow less fuel, so the PCM will increase the pulse width in an attempt to deliver the "same" fuel mass (i.e. it gets richer).

Regards
Paul

[Redline Motorsports]

Ditching the RC injectors and going to 60lb Motrons for starters. At least its a predictable injector. I have a feeling that some of the problem is the injectors.

[Redline Motorsports]

Installed the 60 lb Motrons and the car fires up and idle like a champ! Another example of having unknown injectors vs. known injectors. I guess its always better to know your enemy!

Now I can get tuning!