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Well the test results are in. The New TPS, Trottle Position Sensor, solved most, the rest of my low MPG problems and my low power, low torque problem.
It is the 87 renix 4.0, AW4 automatic, 4X4 Wagoneer. My old TPS tested good on the ECU side, but lacked the proper span on the TCU side. Both sides tested good at idle! The TCU side tested bad at WOT, not enough span. For more blow by blow details see the old thread titled "RenX Files" (or ReniX Files?).
Anyway my old 8 mpg local, 12 to 13 mpg highway gas mileage for the last 2 years, recently tested as high as 17.7 mpg, 119.8 miles, 6.77 gallons of 87 octane gas, with 10% 0-35 mph local travel, 20% 0-45 mph semi local travel, and 70% 55 - 65 mph highway travel all in the city. Other tests got 15.4 MPG mixed city stop and go with 70% city freeway travel, some in heavy traffic, and 14.68 mpg in 232.6 miles, 15.85 gallons of mixed city with some heavy stop and go traffic on the freeways at rush hour. Based on the test results I must be near 20 mpg for pure non stop 65 mph freeway runs. I have yet to get a pure 65 mph long miles run from a fresh fill up to confirm the best highway mileage, but based on the overall data it looks like I am at 20 mpg +/- 0.5 mpg for the 65 mph highway mileage now.
The best I got before replacing the TPS was about 14 mpg highway and about 12 mpg average city. So I got a good 4 to 6 mpg increase out of the new TPS.
The reason for the huge difference is the way the TPS signal handles the transmission operation via the TCU. The bad TPS was causing the Tranny to shift too early at too low of an engine RPM, like 2000 rpm at WOT, and I believe it was reducing the tranny fluid pump pressure to the torque converter thus reducing the power transfer to the rear end from the engine.
Anyway, the verdict is in, A bad TPS on the TCU side only can have drastic negative effects on gas mileage and power.
Oh, and for those hot heads here on (I say hot heads jokingly!, meaning those who think a 4.0 needs to run real hot to get good mileage), I am still running my 165 F thermostat!!!!!! and I have reached about 20 MPG highway mileage, and already measured a 17.7 MPG mixed city /traffic / mileage for a 119.8 mile test run. The worst mileage I got before replacing the bad TPS was all local neigborhood stuff, 0-35 mph , last winter with it parked for 10 minutes warming up each morning, got about 6.5 mpgs on one tank.
It is the 87 renix 4.0, AW4 automatic, 4X4 Wagoneer. My old TPS tested good on the ECU side, but lacked the proper span on the TCU side. Both sides tested good at idle! The TCU side tested bad at WOT, not enough span. For more blow by blow details see the old thread titled "RenX Files" (or ReniX Files?).
Anyway my old 8 mpg local, 12 to 13 mpg highway gas mileage for the last 2 years, recently tested as high as 17.7 mpg, 119.8 miles, 6.77 gallons of 87 octane gas, with 10% 0-35 mph local travel, 20% 0-45 mph semi local travel, and 70% 55 - 65 mph highway travel all in the city. Other tests got 15.4 MPG mixed city stop and go with 70% city freeway travel, some in heavy traffic, and 14.68 mpg in 232.6 miles, 15.85 gallons of mixed city with some heavy stop and go traffic on the freeways at rush hour. Based on the test results I must be near 20 mpg for pure non stop 65 mph freeway runs. I have yet to get a pure 65 mph long miles run from a fresh fill up to confirm the best highway mileage, but based on the overall data it looks like I am at 20 mpg +/- 0.5 mpg for the 65 mph highway mileage now.
The best I got before replacing the TPS was about 14 mpg highway and about 12 mpg average city. So I got a good 4 to 6 mpg increase out of the new TPS.
The reason for the huge difference is the way the TPS signal handles the transmission operation via the TCU. The bad TPS was causing the Tranny to shift too early at too low of an engine RPM, like 2000 rpm at WOT, and I believe it was reducing the tranny fluid pump pressure to the torque converter thus reducing the power transfer to the rear end from the engine.
Anyway, the verdict is in, A bad TPS on the TCU side only can have drastic negative effects on gas mileage and power.
Oh, and for those hot heads here on (I say hot heads jokingly!, meaning those who think a 4.0 needs to run real hot to get good mileage), I am still running my 165 F thermostat!!!!!! and I have reached about 20 MPG highway mileage, and already measured a 17.7 MPG mixed city /traffic / mileage for a 119.8 mile test run. The worst mileage I got before replacing the bad TPS was all local neigborhood stuff, 0-35 mph , last winter with it parked for 10 minutes warming up each morning, got about 6.5 mpgs on one tank.
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