Ok guys in case you forgot, here is the rundown of what I have, mods, and what has been done, and now my latest trip to the shop to have my truck diagnosed by professionals -

I have a 99' 2x Ranger Sport with a 3.0 and an auto tranny. It has a 3" body lift, with 8" wheels and 31x10.50 BFG All terrains. To accomodte the larger tires I re-geared from 3.73's to a 4.10 gears with a locker. The only mod I have done to this truck performance wise is I have opened up the air box, if I could get the milage back right I would start working on a new exhaust, but I have not gotten to that point yet.

Over the last several months I noticed a dramatic milage loss. Before the addition of the 4.10 gears I was getting close to 21mpg on the highway, I never really checked closely after the gear swap, but I was still getting decent milage (just by looking at the milage traveled per tank on my odometer), but the last few months I had noticed I was only traveling about 160 to 180 miles per tank in town and maybe 200 to 220 on the highway. I started crunching numbers and my milage had dropped to 12 to 14 mpg in town and 14 to 16 mpg on the highway.

I have done a complete tune up, plugs, wires, fuel filter, ran injector cleaner through the system twice with a tank of gas. I have replaced all three o2 sensors. None of this has made any change in my gas milage. While I realize the mods I did would have a negative effect on gas milage, the milage I am presently getting just does not add up, especially when you consider that I am still slightly over driven with my present gear and tire set-up. I have noticed a slight bog when standing on the gas from a dead stop, the truck takes off, but it's like it doesnt really take off hard until you hit 3000 rpms.
Maybe that is due to the tire set-up, maybe not. My truck has been set up this way, with the tires and gears for close to two years now, so it's not like I just did this and the milage just dropped, it's been set up this way for a while, and then the milage started to drop.

Yesterday I took my truck to a local shop that I have used in the past and that I completely trust. They spent about two hours with my truck hooked up to their computers and since there was no check engine light they went through all of the sensors, checking to see if they were all within the proper paramaters. None of the sensors were off at all. They were all within the normal working paramaters. The only wierd thing they noticed was that during their test drive with one of their scanners hooked in the signal the VSS Sensor is sending to the computer, the speed it was telling the computer was slower than the speed shown on my speedo? I really don't understand this because my speedo actually shows a slightly slower speed than am actually driving (it's 4mph slow at 55mph, in other words when my speedo shows 51mph I am really doing 55), but when my speedo was showing 50mph the VSS Sensor was telling the computer diagnostic system that it was doing 43 to 45mph. My VSS Sensor was replaced about a year ago, it went bad like many of us have had happen on this board, but I don't know if that is the culprit to my problem or not? I am really at wits end here guys, this is not my first ranger set up like this, and the really bad gas milage I am getting is not right. Like I said I understand and expected some sort of milage drop for the bigger tires and lift, but the drop I am seeing does not add up right, especially when you consider that I am still slightly over driven. I am now considering having ford reprogram my computer for the proper gear set and tire heigth, but I do now know if that will make a difrence or not. Please any help at this point would be great - sorry for such a long post but I want to make sure I give a complete and proper description of the problem and everything I have done to correct it -

Waves

 

Waves, this is interesting.
I am going to suggest some things that may have been gone over before, so don’t think I am trying to be a S/A. First I don’t understand the vss numbers they gave you. The typical values I have show 65 Hz @ 30 MPH, and 125 Hz @ 55 MPH. So it is a frequency reading not a voltage value or direct MPH reading. It is also not quite linear so it would be hard to convert the reading into a mph speed reading. It may be that their test device does this and they gave you good numbers, but I would question their statement. However, if true, it would give you a much lower number of the miles traveled and would give you lower mileage figures if you used the indicated mileage to figure your gas mileage. Example (indicates 43 at 50) you go 300 miles and the mileage indicator would only show 258 miles to a tank. You have indicated you think the speedometer is about 4 miles per hour slow. I am not sure how you came to that number, but the vss number is about twice that number.
I think your idea of getting ford to reprogram the rear end and tire size is a very good one. It won’t change you mileage, but it may explain the mileage numbers you are getting off of the speedometer.

The other thing I don’t understand is it would also effect the speedometer and your really going much slower then you think you are.????

Dave

 

Dave - I got my milage numbers through checking with side by side driving with a new vehicle with factory sized tires and talking on a cell phone and by also using a hand held GPS with seven satelites tracking. I did the gear swap using a simple mathmatic formula, in order to bring my truck back to as close to stock gear ratio as possible. When my speedo shows 43 mph I am actualy going 45 when showing 51mph I am doing 55, the number off increases a little the faster you go, at 61 on the speedo I am doing 70mph. Now as far as the computer the shop had, they had two, one was a large hand held unit, the other was a larger unit on wheels. The smaller unit was the one they took on the road test, I went with the mechanic the second road test he took, he wanted to show me what he was talking about, it showed the VSS sensor and the MPH it was reading off my rear diff sensor (thats the only vss on mine, I don't have the system with two vss sensors that I have heard about), like you I really found that strange, but I saw it with my own eyes, the guy was not bs-ing me. In any case this system they had also showed the Hz readings on that sensor and the others, that is one of the things he checked on all of my sensors, he checked to see if they were all in the normal operating range.

As for what you were saying about my odometer being off, it accounts for about 2 tenths maybe 3 in my gallons per mile equation, but not the 5 or 6 mpg off that I am getting. I also started to notice the milage being off when I went on a regular road trip I take, it's right at 200 miles, I would normaly be able to make this trip, following the speed limits, using about 3/4 of a tank of fuel, presently I can barely make this trip on a full tank.

I feel like I have covered all of my bases on this with no luck at all. Also I forgot to mention in my first post the shop also checked my fuel pressure and everything checked out there as well. I am going to have the computer re-programmed for the correct rear diff and tire size in a couple of weeks (need more $$$$$ for this), the only other thing I can think of is to have my catalitic converter and resonator checked by a mufler shop, maybe they are becoming clogged or there is an issue there, I noticed during the replacing of the o2 sensors that the two before the cat had lots of black build-up on them, indicating the truck has been running rich, while the one after the cat was clean, indicating the cat is doing it's job, I just assumed it was ok..but????? I am really lost with this one guys, this just is not right my truck is sucking down gas like a full size with a V8 -

 

Waves, wish I knew what to tell you. If it is running rich It could be a leakly fuel injector. Not being able to stop fuel flow to one cly, but that would show up on one plug and the Air/fuel ratio would be off. One last thing what rpm are you running at say 60 mph. If i can think of anything else I'll post it.
Dave

 

Dave - I am with you on not being able to think of anything else, am about to run accross town to visit a friend, (I'm in Houston so accross town is a looooonnnnggggg treck on the freeway, I will post exact numbers when I return, but off hand I think at 60mph my rpms are close to 2100 or 2200, I know that 65mph is close to or at 2500, to clarify I would be meaning around 59 on my speedo, 65mph being my real speed, but I will post some exact numbers later this evening or in the morning tomorow. Thanks for reading and replying, and trying to help-

 

Come on guys. Lets help Waves out. This has been a long standing issue, any ideas out there??
Dave

 

Dave - while traveling at 60mph I am turning 2100rpm's, 65mph - 2400rpm's, 70mph - 2600rpms.
Thanks for trying to get more input on this -

Waves

 

I don't have an answer but a suggestion. Where you still getting good gas milage prior to the summer heat. I only bring this up because I notice that heat seems to make a big difference on my ranger.

During my recent vacation my worst tank was 16 or so and my best 25. 16 was across the Nevada desert and it was 106. My best was from Big Sky, mt to Cody, wy. and it was in the low 70's. Today I made a 350 mile trip, temp in the low 70's and got 22.

I think getting you computer reprogramed is a good idea but I really wonder if most of this is not being caused by air temp. For a comparision I'm running a Volant intake and have a 2.5 single cat back, 4:10 gears and factory tires.

 

Waves, I just checked my 02 ranger. 4.0l, auto, stone stock. (@ 60mph 2100 rpm.) I think your gearing checked out ok. (as you said) It looks like you your not off by anymore then maybe couple hundered rpm. Nothing that should affect your mileage. You may want to reconsider having your cpu reprogrammed for the rear change and tire size. I don't think you need it.
Dave

 

tmyers - I live in Houston, Tx - it's almost always summer here. In fact we have had two, don't laugh, very rare summer time canadian cold fronts in the last couple of weeks, it brought our temperatures down to high 80's low 90's from the normal high 90's low 100's we normally have here in the month of August - if your not used to it, it can be like hell here until late september. It's in the 90's here for about six months of the year, then 70's to 80's for three to four months, after that we have a couple of months of very mild winter. I don't think that this is a weather related issue since I have gotten good gas milage previously in our hotter summer months. I think we can rule the climate out due to the almost constant summer conditions I live in, thanks for the idea though. The milage numbers I have given are with the A/C on (you can't live without it here, they don't even sell cars here without it), the almost 21mpg I have gotten on the highway was with A/C on as well. Anyway thanks once again for the idea though -

 

Does anyone think this could be a cadlitic converter or resinator issue? Someone has suggested to me that I might have those two items checked, that they might possibly be clogged? Is there really a way for an exhaust shop to check them, or is there something I should be listening for or some sort of indication for a problem here? Or am I just grasping at straws?

 

Possible but have you also notice a drop in power also?

 

The only noticable performance issue I am seeing is a slight bog when you stand on it from a dead stop, but once you hit 3000rpms - the truck really begins to take off. Other than that I haven't really noticed anything -

 

I'm doubting then its a clogged exhaust then. If it was the more you stand on it the worse it gets.

 

have you checked the distributor yet? also how hot is the truck runnin? you can check your cat by gettin the truck heated up, that means about 30 min, and look under to see if it is glowing. also check to see how much pressure is coming out your exhaust. your truck is way newer than mine, but similar problems, so maybe there is a similar solution.