ok here it is, i have a 88 ford bronco II. i have asked this question before but never found the problem. 2.9 with a4ld trans, it gets real crappy mileage. when i first got the truck about 6 years ago it had a blown head gasket and no oil pressure, so i picked up an engine out of a 91 ranger (2.9) this motor runs like a champ but just no mileage. its been in the truck for 5 years now, no leaks, no smoke, passes emissions like a new car. i have checked the fuel pressure, its fine. new o2 sensor, all new injectors, changed out aic and map just cause i had them laying around, still no difference. new exhauast and catolytic converter. the engine is running warm enough so the computer should be working fine, there are no codes. 195 t-stat. checked timing with spout removed, stock is 10 dbtdc, well my truck pings pretty bad there so i recently kicked it back to 6 dbtdc. this helps quite a bit, pinging is almost gone. just a little in overdrive. tire pressure is good, brakes are not hanging up, fresh tune up with properly gapped plugs cap & rotor. new air filter. you name it, i have probally done it. so.... why am i getting 12 mpg in the city and 15 on the freeway if im lucky?????? and no its not leaking fuel, also after 3 years of running autolite platinums the plugs still looked really good, no vacuum leaks either that i could find, engine vacuum is around 19-20 inches at idle. help me! gas is $235 a gallon here!!!!

 

That's a tough one. Based on what you've stated, it sounds like you might be leaking fuel from somewhere.. Maybe only a little leaks when you take off and it's just hard to see. I can't imagine what else it could be..

Pete

 

well its not leaking fuel from anywhere, i have gone over everything multiple times. everyone says that the bronco II/ 2.9 gets about 17-23 mpg. not mine! i just cant figure it out. what about the pinging? the engine does have around 160,000 on it now, but has always received a 3,000 mile oil change and all other maintenance. i had to turn the timming back to 6 dbtdc to get rid of the pinging. any other sugestions on the fuel mileage?

 

when you got the new 2.9L did you also get that trucks computer.
when you say no codes you didn't even get a code 11 check the computer.
what size tires are you using? any body lifts or suspension lift center of gravity changes more is needed to make the truck move. any axle mods or changes
any gears changed?

 

no i didnt use the other trucks computer, i used the stock computer that came with my 88 bronco II. would i need the 91 ranger computer? since they are both had a 2.9 and an automatic? as far as the computer codes i meant no problem codes, yes it shows the 11 code which means everything is ok. tires are 235/75/15. same size i have always had. i know they are a little bigger than stock, i have the same size on my 89 bronco II and the fuel mileage is fine on it. no body or suspenion lifts, no gear changes, still the stock 3.73 gears. do you think that i need to get a 91 ranger 2.9 computer?

 

Have you done a compression check? You may be blowing gas out poorly seating valves from carbon build up. If that is the case, you have two options. Physicaly cleaning them in undiluted Purple Cleaner, or having the motor cleaned with a Motor-Vac. http://motorvac.com/
And how did you check for vacuum leaks. When I was getting that bad of gas mileage, I replaced all my vacuum lines, and it still didn't give me beter gas mileage. What finally fixed it was two things....along with the Motor-Vac.
I tested the MAF sensor (it is located on the firewall,upper left side). To test it, you disconnect the vacuum line from the plenum,put about 5cm of preasure into the sensor...it should not leak down....if it leaks down...put a new sensor on.
The second thing I did was replace the distributor and TFI module.
I hated getting 12-13 mpg! Now getting 19 with mixed city/hwy driving.
About the computer..call this company and ask them if it maters.
Micro-Tech Automotive Industries. 1-800-688-1588, or talk to Mike Avery directly at ext 124 (same #). They also have a web page: http://www.micro-tech-auto.com/contact.htm
Hope this helps.

 

thanks a lot, i will call. well as to how i checked for vacuum leaks, first visual, then used a vacuum gauge, i also checked map, fuel press reg, brake booster, etc. with a vacuum pump. i also sprayed carb cleaner around all sealing surfaces, i am positive there is no vacuum leak, i checked the trans modulator too. as far as the distributor, it is the origional one off the 91 ranger engine that i used, the tfi and coil have been replaced. i am really wondering about the computer now? even though there are no codes, maybe its the cause. ive been running it for 5 years now. i just cant see how i can get such crappy mileage and pass emissions so good??? and just incase anyone is wondering, i fill up drive a couple hundred miles (wont go much furter LOL) then fill back up and do the math. gallons into miles. thanks for the info.

 

maf's weren't on rangers or bronco2's until 91-on some rangers and b2 had maf but they were from california.

we have MAP sensors

 

Bad move, unless you spend a little time verifing the wiring between the 2. Took me about 3 hours to compare the diagrams from a 1990 MAF California ECU against my 88 Ranger ECU. I also tripple checked it. Most of the wiring is going to be the same, but they variated things like transsmission shift solenoids and some have 2 fuel pumps, while some only have 1. The newer ECU will also have a wire for a fuel pump monitor, if you do not hook it up, the computer will throw code 96. Not sure if that perticular computer has that or not.

The thing that gets me is that you have bad fuel mileage AND pining. What kind of gas are you running, and how is it driven? If you have a lead foot like I do, you're going to use a ton of extra fuel. Have you been keeping an active log of the fuel mileage recently? You might try a different gas station...

Pete

Edit:
Also, is that an 88 2x4 XLT A4LD? PM me if you're thinking about changing the ECU. Mines still good, I went with a non-computer friendly cam and had to swap to the 90 MAF ECC. The reason for the rebuild was low oil pressure and cracked head. ECC worked perfect when I took it out.

 

as far as the fuel i use cheveron 87 octane. ive been thinking about it, everything on my 88 bII engine was the same as the 91 ranger engine. all of the sensors, all of the plug ends, i used a lot of the 88 parts on the new engine or replaced them. i currently have the timming set back to 6 dbtdc and the pinging is gone. thats where im going to leave it. you cant tell any difference in the power, so im not worried about that. i remember before i installed the 91 engine i pulled the pan to replace the gasket, the pan was spotless, no sludge at all. i was told that the engine always had a 3,000 oil change and it showed. so the engine had been cared for before i got it. i just replaced the plugs, cap & rotor, the plugs on the drivers side looked great, the plugs on the passengers side were not real bad but did show a whitish ash look (too hot or too much timming advance) i then changed the plugs in my 89 bII, same thing, except that one doesnt get bad mileage. ?????? maybe that head just runs a little hotter? anyways the 88 is running really nice now. i will have to see if the new plugs and timming did anything for the mileage. i doubt it though. as for my driving i drive like a grandpa. i dont accellerate hard, i do make sure to drive it on the hiway though to keep it clean. i always check my fuel mileage. it always sucks. the trans is the a4ld 4x4 trans. it was rebuilt 5 months ago also. my truck is a 88 bII xlt, auto, 4x4. looking for a mustang svo now, anyone have a nice one 4 sale near nevada?

 

What gear ratio do you have? What are your RPMs cruising at 65? I have an '89 Ranger with the 2.9, and while my mileage isn't great, it's a little better than yours. My A4ld lost the O/D before I ever got the truck, and it had 4:10 rear in it. I swapped in a 3:45 and I turn about 3200 at 65. Most of my driving is highway, with a little city and the best I've ever gotten is 17, and that was all highway. -TD

 

i have the stock 3.73 gears, at 65 mph it about 2,000-2,100 rpms in overdrive.

 

And there was no change after the tranny was rebuilt? There is a fair amount of slip in those things, it's supposed to account for SOME mileage decrease over a 5 speed, but not like you're experiencing. Oversize wheels/tires, lift kit maybe? Check wind direction and always try to drive with a tailwind? Heck, you got me stumped. It sounds like you've done or checked durn near everything. -TD

 

The 2.9 had a lot of issues with one head getting hotter then the other, the fix for this can be as simple as adding an H-pipe to the system just before the cat… I did it to mine and the Bronco2 I had got better gas mileage and also quit being a “Hot Head”. lol

 

well everyone will tell you the pinging is normal for a 2.9 ands they are prone to it. but this does't mean we should like it. honestly my 2.9 87 ranger pings of and on. What i have learned is that when my engin is doing this i get roughly 16mpg (plus i am a lil heavy foot around town). when the pinging stops i am making almost 21 mpg. so i don't know in your case. i do recomend checking the vacume tube boots they can crack and lose seal over time. if they don't feel snug there isn' t nothing wrong with spending a few bucks to replace them sicne they are onl y what 2 bucks a piece