Unbelievably bad gas mileage

[laserfish]

As someone else mentioned and I have experienced, a blown power valve allows a lot of gas to pour down the carb throat. Black soot is a big giveaway. Good luck, gas is too expensive to pour out the tailpipe unburned.

 

[JAFO]

Funny stuff - I'm here in a hoity-toity guard-gated community in Kalifornia - my wife owns an AMG63 and I own 3 gas-hog SUV's - our BEST mileage is ~15mpg! I wake up WEEKLY to a burning cross in our front yard, LOL. We're not too popular with our Prius-owning neighbors, doncha know...

FYI, I have a friend that drives a Prius. They touted their great gas mileage. Then his front driver's side headlight went out. In most cars you are talking a maybe $20 bulb at the most. Not the Prius. It was a $600 circuit board plus labor. I mentioned that a repair like that really chews into that gas mileage savings doesn't it? And a prius, what are they going to do with those polluting batteries when they die? And the cost of replacement batteries? And the resources required to manufacture such a vehicle. Those 'green' cars are just there to give someone a warm fuzzy feeling. I don't really see them as so green.

FROM A FORUM-
The problem with intermittent HID headlight operation appears to be common with the Prius, but is also occurring with other models. I own a Sienna with the same problem. The dealer first replaced the HID computer $1,100, then the bulb $400, and now tells me I need a whole new headlight assembly for another $1,100. This is all in three months.

 

[Timmy390]

Funny stuff - I'm here in a hoity-toity guard-gated community in Kalifornia - my wife owns an AMG63 and I own 3 gas-hog SUV's - our BEST mileage is ~15mpg! I wake up WEEKLY to a burning cross in our front yard, LOL. We're not too popular with our Prius-owning neighbors, doncha know...

What would they do to me....driving my big 2500HD Duramax 4 door 4x4 around...LOL

Tim

 

[jckkys]

I've reading some the derogatory posts that referring to the FE engine series, in generalized terms such as " they're old technology POS". The reality is far different. They were actually excellent power sources for everything from Mustangs to F500s. The gas price in the early '60s was about 25 cents/gal. but drivers were still looking for economy. My dad kept track of the MPGs on the 5000lb. '63 Country Squire with a 2bbl 390, and tuned it up when it got below 15 around town. My '66 428PI with nearly 400 HP got nearly that with 17 MPGs doing 75 and I was lead foot kid on the edge of loosing my license. The emission laws were the death of FEs, not out dated design. The 351-400M engines that replaced the FEs were never an improvement. To get 5.6 MPGs in a 2500 lb. CJ5, something besides the engine choice, is going on.

 

[66BlueGoose]

One of the reasons my other car is an M3 and not a Prius... http://www.bbcamerica.com/top-gear/videos/thirsty-prius/

Another reason, no one has accidentally walked behind my Bronco ('66 no reverse lights) or my M3 when backing up. I have almost been hit multiple times by the silent deadly reversing Prius owner...

 

[Chowbird]

You guys are cracking me up. I am also the anti Prius household, but I live on a farm so I'm in with cool crowd....the under 15 mpg crowd. If I told them I was getting 5.6, they'd probably elect me mayor.

Agreed, the CJ has substance abuse issues.

Here's the plan. Starting on Monday with a buddy:

Rebuild the Holley and check for Vac leaks
If that doesn't help maybe replace the intake manifold with the one supplied when I bought the jeep and put a better 4 barrel on it which I think was OE. I picked the 4 barrel intake manifold up and moved it into the on deck circle and I nearly dropped both testicles to the ground. It weighs about as much as a Prius. Maybe aluminum might help my cause. But then I again I have this one, it's rareing to go. It fits in with the overall excess everything theme. Hmmmmm


Let's see what this 352FE is capable of.

Thx!! Tim

 

[Timmy390]

FE = boat anchor I'm Kidding.........but seriously they are heavy.

As I type this I'm wearing my "Fear begins with FE" shirt from the FordFE.com site. Had my Stang out today and I never drive it without my FE shirt.

When I built the 390 that's in my Stang, I ditched the 80 pound cast iron intake and went E-brock RPM performer. Also went with E-brock heads. Prob lost 150 pounds or more....lol

FE's are a different kind of animal for sure. FE's in general were low RPM torque monsters. Might be a combination of the cam and the 4.11's that's killing you.

Tim

 

[jckkys]

What those unfamiliar with building FEs don't know, is the fact that they breath very well with no special heads or manifolds. The 352 and 390 have the same heads and exhaust manifolds as the 428 PI. The cam and crank are the main difference. The 428 PI also had a beautiful aluminum intake that looked just like the cast iron CJ intake but 50 lbs. lighter. 390 GTs had only the CJ cam to thank for respectable performance. I built a 460 with 429 CJ cam and top end that never came close to the 428 PI. The huge valves and ports just didn't work. No surprise that the 427 FEs were the best stock engines Ford made in the muscle car era.

 

[nail_it_95]

My dad had a 1974 chevrolet 1 ton with a 454 4 speed 4.56 gears and it didn't matter how you drove it would get 4 mpg all of the time. It was all stock.

Have you checked the tach to see if it is accurate. Check and see what tags are on the axles to see what gears.

 

[cekautsky]

i didn't read thru all of the post but if your sure of the math than i would definitely say there is something wrong. Holley sometimes can pop the power valve which will basically opens a nice size hole at the bottom of the float bowl directly to the venturi. Its an easy check and experience always says to start with the simple things first. I had a 73 ford f250 4wd with a 390 and a holly 2bbl and it got bad milage but never below 8mpg when driving conservative.

 

[CA650]

Carb got a big bog when you accelerate hard? How about pops and backfires?
.

You mean that's not normal?
I run a holley 2Brl on a 302 and this is how it runs.

I've never looked into the carb since i was going to swap the top end of the motor and add MPFI. But maybe its worth doing some tuning on this before I get to the other mods. The throttle response is terrible. I notice it more now since I swapped the exhaust and I punch WOT a lot more because I love the sound. ;D

If I have these symptoms and my gas milage is also crazy bad.. maybe like 7mpg I'm guessing.. whats the quickest fix?

 

[jckkys]

Holleys are not the best off road carbs but they're good for almost any application including 4x4s. They are also the most tunable of all carbs. There are plenty of Holley books that walk you through the tuning process. Previously owned Holleys are can be FUBARed to a point where it may be a good idea to call Holley with the list# on the air horn and get the original specs.

 

[CA650]

Well I dropped mine off at my shop based on this thread this week. I'll let you guys know what they say. I wrote 2br, but it's actually a Holley 4 barrel.

I asked this afternoon what my guy thought and he said it was running lean/starved. I think he's wrong but he was just getting into it. I burn gas so damn fast it's a joke.
My throttle response is really slow.. But the carb looks great like the previous owner might have recently added it. Not sure... Anyway. I will sort it out and let everyone know.

While there my mechanic showed me his 442.. I want one of those now too.

 

[Chowbird]

So I'm the OP that was getting 5.6 MPG in my CJ5. You guys had some great suggestions on how to remedy the all time leader in bad gas mileage. Soooooo here's what I did:

Got a mileage counter that was correct to a gnat's ass. Compared that to my odometer. The odometer was off because of the 33s, but not by much. Somebody somewhere had tinkered with it trying to get it right. It was off by a factor of .084. (For example if I went 7 miles on the odometer the trip counter read 7.5) Tested my calculations with stock car driving the same distance. They all matched. So got that part of the equation pretty exact for counting miles. (Turns out that my 5.6 MPG that I have gotten since the dawn of time every f-ing time I calculated the mpgs was actually 5.7. I was kinda bummed...that number had been with me for so long it was like losing an old friend.)

Next, took the CJ to a buddy's shop that specializes in high performance crap. Pretty active in the local racing scene. Let him loose on the carb. He changed the accelerator pump from a .05 to a 3.5 and the jets from 76s to 68s. I'm repeating the numbers here so if I'm off a bit on the lingo don't laugh.

The results.....10.8!!!!!!! Now I know that number sucks, but when you've been stuck with the Melissa McCarthy of MPGS, its nice to take out Cindy Crawford for a spin....no wait Cindy would be like 40mpgs...how about Jessica Biel.

Thanks to everyone for the tips and advice.

 

[Rustytruck]

Thanks for the update. I still think you can do better. Did the shop mess with the timing? I'll bet due to the light weight CJ you could advance that quite a bit. Are you using a distributor with a vacuum advance and ported vacuum? I would also look at adjusting the timing curve inside the distributor. The out of balance weight of the motors torque to the super light CJ you should be able to run up the timing advance getting more power down low so you don't have to use as much peddle to get going thus saving more gas.

Might try driving with a vacuum guage and changing your driving style and shift points.

Right now should be starting to get fun to drive instead of feeling like a pig running up hill.

 

[DirtDonk]

Yes, great news Chowbird! Thanks for the update. Sounds like a pretty big score to me!

That's actually quite a large jet change, so those that said it was running rich were right on track. Jessica is a win-win in the mileage department.

Paul

 

[bknbronco]

without reading through all the above posts....let me throw this out in case it hasn't been discussed...swap out the speedometer gear....I netted 10mpg instantly!

 

[76Broncofromhell]

The only real way to get good mileage in an Early Bronco is to lie about it.

 

[bknbronco]

The only real way to get good mileage in an Early Bronco is to lie about it.

Smiles per gallon right? I don't even worry about it some days it only cost a 20 spot to drive it around some days its 2- 20 spots.

 

[76Broncofromhell]

Smiles per gallon right? I don't even worry about it some days it only cost a 20 spot to drive it around some days its 2- 20 spots.

I've contemplated kicking a guy in the nuts at the gas station after he asked me what kind of mileage my rock crawler gets.

Then I looked at his Jabba the Hutt wife eeking out every last pound of the weight rating of that poor minivan, devouring that box of gas station donuts and realized: God had already kicked this man in the nuts.

If you're worried about gas mileage, a Bronco is not for you.