Several posts in this thread have mentioned the "sweet spot" in engine rpm's. How do you determine that (for example in my 1988 F150, 4x2, V8/302, AOD, 3.55LS?).
Thanks for any responses.
Frank.

 

I wonder what they use to determine the 'rate of deceleration' ?



I was thinking (probably incorectly :-) that the system determined 'impending lockup' by comparing the average rear wheel speed with the front wheel speed, and thats how it senses the drop in rear wheel speed. If you put on larger rear tires, I would think the system would think impending lockup is always at hand as the rear wheels would be turning slower than the front wheels, unless there was a way to indicate to the RABS a correction factor for a different rear tire size.

 

Wow what a lot of discussion.. 1 -the speed sensor for your speedometer and pcm is at the transmission.. 2-If you change to a ratio that is offered by Ford when new, they can reflash your pcm to correct the speedo and your shift points. (You did not say what size tires you are running but if anywhere near or slightly bigger than stock.. you will do fine with 3.73s. If you are running tall tires consider 4.10s). 3-all late model trucks have overdrive transmissions..if you have the common 4 speed you are in 1 to 1 ratio in 3rd gear not 4th, so make your caluclations by that.. with that heavy of a load you will want to spend most of your time in 3rd gear, except on flat ground at highway speeds with no headwind.. Revving your engine is much better for it and the trannie than lugging it, (see specs for what rpm you get good torque levels).. and the oil and coolent flow nicely with rpms.. The torque converter locks when not overloaded in 3rd and 4th gear to avoid trannie overheating.. (an auxillary trannie cooler is also a good idea if you will be pulling..

 

Mo,

I looked through the service manual and found the speed sensor is (electronic) in the trans. Any idea how to tell which trans I have? I saw in the manual that there is a tag on it somewhere, but the numbers on the tag don't match up to the number in the manual (th emanual gives an example). Reflashing the PCM seems to be what is needed...I've been told so many different things I didn't know who to trust. I am running stock tire size. I talked to a few dealers and they all said I don't have to reflash the pcm because the VSS is in the differential...scary. The first thing I did was install a trans cooler .

 

PDQ,
I thought the RABS referenced the front tire speed too but I don't recall seeing any type of sensor or any antilock ring on the front rotor/suspension...I looked in the manual and didn't see anything in there either, unless you have front ABS. I figured the ABS got the vehicle speed from the trans sensors and compared that to the speed at the ring gear but I think everything with the antilock brakes is contained ONLY within the sensor of the differential. The sensor in the differential can tell vehicle deceleration by the number of times the antilock ring in the differential turns. If it doesn't sense a lobe on the antilock ring passing, the rear tires are locked up...etc.

howstuffworks.com says:
One-channel, one-sensor ABS - This system is commonly found on pickup trucks with rear-wheel ABS. It has one valve, which controls both rear wheels, and one speed sensor, located in the rear axle.
This system operates the same as the rear end of a three-channel system. The rear wheels are monitored together and they both have to start to lock up before the ABS kicks in. In this system it is also possible that one of the rear wheels will lock, reducing brake effectiveness.

This system is easy to identify. Usually there will be one brake line going through a T-fitting to both rear wheels. You can locate the speed sensor by looking for an electrical connection near the differential on the rear-axle housing.

If all this is the case...I should be all set with the antilock and reflashing will take care of the speedo and hopefully the shift points.

As far as thinking incorrectly goes, remember who THOUGHT they had a 3.55 rear end...I really appreciate all the help and ideas. I am getting a lot further on this thread than with the dealer!

 

Frank,
http://www.lubedev.com/articles/octane.htm says it the best. You have to test yourself. Maintain certain driving habits for a tank and calculate your mileage. When you see something that looks good, repeat those driving conditions to see if you get repeatable results. When I pulled my 4200 lb travel trailer with my F150, I got 12 mpg traveling 60-65. Traveling back I kicked it up to 70-75 and I only got 10 mpg. Trial and error.

Really want to freak? Read this: http://www.lubedev.com/articles/tips.htm

 

Thanks, Lardman, for this information and the additional references. I had never heard about adding acetone to gas--has anyone tried this?
Frank.