Need help with a 1227747 TPI issue

[JF in MI]

I am stumped by this one. Background; This is a custom made throttle body approximately 30% larger area than a standard two butterfly TBI for a Chevy 350. Everything else is pretty standard; 1227747 using $42, only sensors are coolant temp, MAP and TPS. Small distributor HEI, 55lb injectors (IIRC) and 12.5 lbs steady pressure. Due to too many drivability issues in closed loop (too much to list) I now only run it in open loop only. It now runs like a dream in all conditions except between 1200 to about 1500 rpm where it falls flat (and stays there) at any manifold vacuum under 10” HG but above that is fine. No matter what I’ve tried nothing changes. I don’t think the throttle plate should make a difference because at that low RPM even a standard plate would easily drop to zero vacuum. Here is what I’ve tried (in increments) with no changes;
Going maximum rich to below stock 5.7L lean on fuel table 1 @1200 at all MAP above 50kpa.
Going maximum rich to below stock 5.7L lean on fuel table 2 @1200.
Going down some and way up on main spark table @ 1200-1400RPM at all MAP above 50kpa.
Power Enrich vs RPM from 3%TPS up to 99% @ 1200.
Power Enrich vs MAP close to stock 5.7.
Accel Enrich from stock 5.7 to 10x more.
Swap MAP sensor.
Swap ign module, coil, and 3 ECMs.
Verify TPS and coolant sensor via data readout.
Several types of spark plugs.

It feels like half the cylinders drop out and as soon as I let off to over 10” vacuum they instantly jump back. Any ideas, suggestions.

[Fast355]

I am stumped by this one. Background; This is a custom made throttle body approximately 30% larger area than a standard two butterfly TBI for a Chevy 350. Everything else is pretty standard; 1227747 using $42, only sensors are coolant temp, MAP and TPS. Small distributor HEI, 55lb injectors (IIRC) and 12.5 lbs steady pressure. Due to too many drivability issues in closed loop (too much to list) I now only run it in open loop only. It now runs like a dream in all conditions except between 1200 to about 1500 rpm where it falls flat (and stays there) at any manifold vacuum under 10” HG but above that is fine. No matter what I’ve tried nothing changes. I don’t think the throttle plate should make a difference because at that low RPM even a standard plate would easily drop to zero vacuum. Here is what I’ve tried (in increments) with no changes;
Going maximum rich to below stock 5.7L lean on fuel table 1 @1200 at all MAP above 50kpa.
Going maximum rich to below stock 5.7L lean on fuel table 2 @1200.
Going down some and way up on main spark table @ 1200-1400RPM at all MAP above 50kpa.
Power Enrich vs RPM from 3%TPS up to 99% @ 1200.
Power Enrich vs MAP close to stock 5.7.
Accel Enrich from stock 5.7 to 10x more.
Swap MAP sensor.
Swap ign module, coil, and 3 ECMs.
Verify TPS and coolant sensor via data readout.
Several types of spark plugs.

It feels like half the cylinders drop out and as soon as I let off to over 10” vacuum they instantly jump back. Any ideas, suggestions.

What is the engine combination?

[JF in MI]

>What is the engine combination?<

336 CID (1962 327, 250HP bored .060 over) with stock cam, flat top pistons with an open plenum straight runner manifold. Very smooth stable idle at a stable 15-16" vacuum.

[dave w]

Possibly post a TunerPro RT data log and .bin file?

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[JF in MI]

Possibly post a TunerPro RT data log and .bin file?

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I don't have TunerPro nor any data logs. But here is "the thing"; If I did then which one would be relevent? I've done literally dozens and dozens of files with settings ALL over the spectrum with NO change in results. Somewhere along the line I should have seen "something" of a change. Also with it never going closed loop (and not even having a O2 sensor) what would BLM mean? That said, here's a question; in this setup does the stoichiometric AFR number in the ECM constants table have any meaning?

[dave w]

I don't have TunerPro nor any data logs. But here is "the thing"; If I did then which one would be relevent? I've done literally dozens and dozens of files with settings ALL over the spectrum with NO change in results. Somewhere along the line I should have seen "something" of a change. Also with it never going closed loop (and not even having a O2 sensor) what would BLM mean? That said, here's a question; in this setup does the stoichiometric AFR number in the ECM constants table have any meaning?

Often there are clues about what to change within a data log.

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[JF in MI]

Often there are clues about what to change within a data log.

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Dave;
I certainly appreciate your efforts but I am at a loss as to where this data is (I only have winALDL and it is finicky as to when it works) and what/where these parameters are to change. Are we both talking about TC $42 for changes? Also, I have no knock sensor.

[dave w]

https://ls1tech.com/forums/lt1-lt4-modifications/1298009-tunerpro-rt-v5-tutorial.html

Most of the information in the link applies to the 1227747, with different .adx and .bin files

[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.

[greasegrenade]

You can really chase your tail using auto parts store brand sensors.Stick with ac delco (gold professional if available) or delphi .

[JF in MI]

You can really chase your tail using auto parts store brand sensors.Stick with ac delco (gold professional if available) or delphi .

In this case, even though the data stream showed all measurable parts working correctly, I had run out of ideas so just started throwing parts at it. Fortunately I had almost everything on hand as spares including injectors. When I built my throttle body (it has a single large plate instead of the normal factory twin plate but still uses twin injectors) it appears the part throttle air flow was far greater than I anticipated and added to that it looks like I initially mixed up and installed the wrong injectors.

[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.