Hey guys, does anyone know if the OBD I Single O2 sensor setup need the heat from a cat converter to work properly, and enter closed loop?

Reason I ask is I have a good running 351 in my 95 w/ new injectors FPR O2 sensor, tune up, all sorts of other new parts, and i can only squeeze 9mpg out of it w/ a 4r70w trans... I think i should be able to get more than that. I removed the stock cats when i did my exhaust, and im wondering if i should put a hiflow one back on there...

 

No. It's a 4-wire sensor that generates it's own heat so that it can enter closed-loop sooner than an "old style" 1-wire sensor. Technically, it might heat up a little slower without the cat', but I'm thinking less than a minute difference, if that. That's not going to have any measurable difference on fuel mileage.

How's your coolant temp looking? Might you have a thermostat that isn't fully closing, and thus keeping your engine too cold? That WILL have a measurable effect on fuel economy, especially in cold weather.

 

Have you cked for codes yet? What was your mileage before all the new parts and what promted the new parts?

 

What gearing? I'm thinking maybe 3.55 or higher...? What has the temp been lately in your neck of the woods? Other members mentioned good info.

 

OK, here goes.
Checked for codes a couple weeks ago, Came up clean.
I live in WI, Its been below freezing for weeks now, but Ive had this crap mileage since I did the engine swap a year and a half ago.
Once the truck warms up to operating temp, it runs right around the "O" in "Normal," whatever that equates to.
Truck was originally a MAF 302/4R70W/3:31s. 33"s and 6" lift. Upgraded to 4:10 gears and a 351W. I used the 302MAF controls/computer to run the 351W. When I did the swap, this is the list of new parts I put on the engine:

-Gaskets
-Valve Seals
-Oil Pump
-Water Pump
-Thermostat (195*)
-Engine Coolant Temp Sensor
-Radiator
-Fuel Injectors
-Fuel Pressure Regulator
-Plugs/Wires/Cap/Rotor
-Distributor
-Air Filter
-Shorty Headers
-O2 Sensor

Timing is set to 12* BTDC

Since I was already in there to do the swap, I took this time to do alot of other needed repairs, like replacing a leaky radiator.

And just cuz i do like to show off, heres a pic of the truck we're talking about

 

First off, given the change in gearing and tire size from stock, have you verified your odometer's accuracy?

Second, given all the fuel-efficiency strikes against you (4x4, 351, lifted, big tires, automatic, 4.1 gearing), I don't know that you should be expecting much more than about 10MPG.

It sounds like your thermostat is closing and coolant temp is where it should be - mine registers about the same as yours.

One thing to do regardless... Pull your PCM and check the capacitors for leakage. I've yet to find one that doesn't have failing components.

 

Has the speedo been recalibrated for those 33's? If not you're actually getting 12-13mpg which is normal city numbers for a 351 powered truck.

 

Nice truck and cheers on a smooth swap.

 

The speedo does actually read a little slow, I reprogrammed it when i got the truck, but the numbers must have been off. Its dead nuts accurate with 35" tires, but on 33s it reads 4-5mph fast at 60. Verified with the 2 different "your speed is" signs in our town

How would I go about doing this, and fixing it if need be?

 

See the link...
HOW TO RECALIBRATE THE SPEEDOMETER ON 92-96 FORD F-SERIES AND BRONCO .: Articles