Holley 2d Projection Manual
I have a NOS Holley pro jection system which I have put on a 71 International school bus. 345 engine, 5 speed manual trans. DUI distributor, Intake manifold machined to match TBI.
Dual exhaust.I have installed several of these systems over the years and had great success with them. However this one has been a bit of trouble.The problem as it is now,1.
A part throttle stumble, not speed sensitive.I have checked the throttle position sensor per Holley's instructions for voltage and do not find dropped or uneven voltage through it's range of motion. It is much worse without the O2 sensor connected.
These systems should be tuned without O2 as best as possible then connect O2.2. The high speed fuel adjustment on the ECU does nothing, no change no matter where it is turned.3. Fuel mileage is really poor and exhaust smells rich. I have converted International trucks of the same engine and overall weight of the bus, so do have an idea of what to expect. 6-8 mpg typically, and am only getting 4-5 mpg on the busI am thinking the ECU may be bad and new ones are not available.
How could I check my ECU, or could a GM ECU be used since this is at least based on the GM TBI system. I realize some wiring may need to be changed, what else needs to be done? Had not thought of pulling some plugs, but good idea. Can do that tomorrow.I have ordered an air/fuel meter with it's own o2 sensor, so I can better monitor what it happening.The O2 sensor in it now( for the holley system) is about a month old, and the previous one did bench test as bad. I did not bench test the new one, so am assuming it is good.
Of course assuming at this point does not get answers.as to the other truck getting better fuel mileage it was a 1600 Loadstar, with a 345 set up with the same pro jection system, and a 4 speed, with two speed rear, and in high, ratio of 5.8, the bus is 5.14 in high on the rear.The 1600 was grossing 26,000 lbs, and the bus is 18,000lbs normal running weight. By the way the the bus is converted to an RV, so other then water and fuel the weight does not change much. Put the air fuel meter on with it own O2 sensor.
It shows,First 1/3 throttle movement very rich about 11:1Mid range throttle 13:1Last third 12:1So rich across all. I disconnect the O2 sensor for the projection system, and started re tuning it to get at least close to 14.7. Then plugged the O2 sensor back in. Works much better now.A few notes, getting the light throttle to 14.7 is not happening best there is 13. That is with the dial turned as far as it will go to the minimum. I am running it in small block mode, and did verify the throttle position sensor is set correctly.Mid range does dial in to 14.7, however any change in throttle and it looses track and then takes a second to readjust to 14.7.
Holley 2d Projection Kit
Holley Projection Kit
Must be a rather slow processor. Have the top end set about 13 now.
Holley 2d Projection Manual 2016
So clearly only on mid range does the computer read thr O2 sensor on this system. I did not remember that from others of these I have used, but it has been some time since I have used pro jection.Fuel mileage has improved, and the part throttle stumble has mostly gone away.
Might try setting the throttle position sensor a little different to see if I can can bring light throttle in a bit closer.
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