Need help with a 1227747 TPI issue

[JF in MI]

After replacing everything electronic I still had the same problem. The issue still seemed to be not enough fuel between 1200-1500 rpm but only at manifold vacuum below 10"Hg (65kPa and up). I started thinking about the injectors. Was thinking that maybe the low number of pulses (due to the low rpm) has the injectors maxed out as to flow and they are incapable of meeting the fuel demand of my custom throttle body even if I increase it in the program (fuel tables 1 and 2 maxed out and thinking this could explain why massive changes had no effect). I didn’t want to increase the fuel pressure because I’m near the maximum recommended. I went through my spare parts bin and found a pair of 61 lbs/hr injectors to replace the 54 lbs/hr ones I had installed. I figured this is an approximate 10% increase in flow so I had to reduce the program flow (BPW) by 10% everywhere else except in the 1200-1500 range and things seem to be working. Will try a few more test drives in the coming days (weather permitting) to see if nothing changes.

I stand corrected on this. In subsequent tests it was just as bad (seemed too sensitive to air temperature or something). I thought my first design was bad and tried something different and that was worse. Went back to my original with some minor changes; The original design has two injectors feeding side draft through a large single 2 and 3/8 inch vertical pivot throttle plate into an open plenum manifold. My thought was that too much of the mixture was being deflected by the plate to the forward cylinders and not enough to the rear ones and only at the low air flow at this low RPM. Moreover possible/probable mixture separation. I angled (possible in my setup) the injectors about 10 degrees to spray more fuel to the "back side" of the throttle plate so as not to allow the plate to deflect as much. I also re-installed a previous small internal manifold baffle however this time highly perforated to hopefully disperse the fuel more evenly. Talk about a complete 180! Now no matter what I did with the programming I couldn't get it to stumble, flat spot or run bad at ANY rpm. I dropped the BPW over 25 points and the fuel table 1 fuel in the 1200-1600 rpm high manifold pressure range about 30% and the 2000-3000 rpm low manifold (cruise) pressure range 10% with no ill effects and, if anything, more power. Been running smooth as silk with great cold starts and did a mileage test yielding 17mpg on this 5.4L upper performance V8 with 3.70 rear end at 55mph.

[1project2many]

The original design has two injectors feeding side draft through a large single 2 and 3/8 inch vertical pivot throttle plate into an open plenum manifold.

Hmm... Are you running something that is similar to the original Rochester mechanical injection manifold?

I angled (possible in my setup) the injectors about 10 degrees to spray more fuel to the "back side" of the throttle plate so as not to allow the plate to deflect as much. I also re-installed a previous small internal manifold baffle however this time highly perforated to hopefully disperse the fuel more evenly.

Crossfire manifolds use a small plate under each throttle body that's cut similar to a fan. It causes fuel and air to swirl and mix in the intake. Removing these plates introduces new and exciting driveability issues.

[JF in MI]

Hmm... Are you running something that is similar to the original Rochester mechanical injection manifold?

Crossfire manifolds use a small plate under each throttle body that's cut similar to a fan. It causes fuel and air to swirl and mix in the intake. Removing these plates introduces new and exciting driveability issues.

You may be right in that it was a similar issue.