[A1Fiddler]

7mpg...Help me before I have to sell it! (With bonus political rants)

Yeah, 7mpg combined city/hwy and dad is pissed. I drive with a real light foot. I think it may be the camshaft and lifters. Don't let me sell it and buy a Cherokee :cry I want to get at least 10mpg, and I think I could keep it.

Rebuilt 351M w/ 40k-50k miles since rebuild
C6 Tranny
87 Octane Gas
32" All-Terrain Tires (at 38psi)
Stock gearing (I think, I bought it used)
Edelbrock Performer 4-Barrel 600cfm Carb
Edelbrock Performer 400 Intake Manifold
Edelbrock Performer-Plus Camshaft w/ .484" Lifters
Hedman Headers
Flowmaster Single Outlet Exhaust System
B&M Racing Supercooler Tranny Cooler

Can someone help me narrow it down? Is this normal for this setup? I know there are hundreds of threads about gas mileage, but I've searched, researched, and searched some more and can't find anyone with a similar setup to me. I've changed plugs and wires, air filter (Napa Gold) is clean, tires are pumped up, maybe I could try a distributor cap/rotor kit...I should be getting at least about 10mpg, right? It will ping going up hills with a loss of power. Will 89 octane gas help my gas mileage a decent amount if I go to that to clean up the pinging?

Let the flaming begin...Figured it was worth it to try and figure this out.

Thanks guys

 

[KC200787]

I would get that timing (pinging) problem fixed.

My stock 302 was getting about 9.5mpg in city (very very short trips, about 6mi each way) and about 12.-13.5 on highway (lots of up down steap hills at about 60-65mph. I was haveing pinging problems on the long steep hills.

Regular driving wasn't a problem as long as the hill wasn't that bad, but still needed to be fixed. (New(er) wires, cap rotor and some extras, got rid of my ping)
After all of that getting fixed, I got 14.5mpg last tank with city/highway 60%city and 40% Highway. And I was gasing it pretty hard on that tank. I think I can get aobut 15-16 on the highway if I drive really nice (we will see)

Your problem is different in most ways, but I would get that ping fixed before It causes bigger problems.

I aint no expert on parts, but I would say that most of them aftermarket parts are really killing your gas milage.

 

[Hoxviii]

I'd start by making sure the rear brakes weren't dragging, the parking brakes on these trucks are famous for the cables rusting inside their sheaths.

After that check your timing and reset if necessary. When was the last time this thing had a full tuneup? air filter?

You say you have 32's, is your speedometer/odometer accurate? this will influence what your calculated MPG is.

7 mpg is abysmal for your setup, there's no reason it shouldn't be getting at least 12 if everything is in good shape since there's nothing that aggressive about that build. If anything it should probably get better economy than stock since it's a solid low RPM build.

I'd also set the idle screw on the carburetor using a vacuum gauge (after you've set the timing). Rich mix on the idles can waste alot more gas than you'd expect.


Justin

 

[A1Fiddler]

I have no idea when the last "real" tune-up was. I changed out the plugs and wires a couple weeks ago. I should check the timing. I'll have to do that today or tomorrow. The pinging is pretty bad. My speedo's not accurate, but I figure in an 8-9% increase when I calculate it (not 100% accurate, but close enough).

How would I go about checking my rear brakes?

 

[ScorpionBoy]

retime your truck. you might think of 'de-tuning' your ride like 2bbl carb and retarding your timing.

 

[TravisITGuy]

what type/brand of plugs did you install?

 

[Bronco4Life]

Problem 1: Carb'd 351M.
Problem 2: Non OD/Non lockup converter C6.
Problem 3: 32" mall terrains.

Consider EFI.
Consider an OD transmission.
Put stock 29" street tires back on.

It's yo choice. Sell it, or start changing your setup.

 

[Hoxviii]

to check the brakes block the front tires, jack the rear end up off of the ground, make sure the parking brake is released, and put your truck in neutral.

Give one of the tires a spin. it should spin freely, but with a slight "swish, swish, swish" noise. try the other side, should be the same. If a tire is hard to spin or only turns once or twice after you let go of it, something is hanging up.

And regardless of what others may say, there's no reason you can't get at least 10mpg out of that thing. Anything less than that and something definitely is not right.

Something else to look into is what timing set was put into that motor when it was rebuilt. if a stock 1980 timing set was installed with that cam you're power and economy will be in the crapper. The cam has to be installed with a "straight up" (non-emissions) timing set. Because that cam is definitely designed as an economy/torque cam and no way anyone considers 7mpg economy.



Justin

 

[james hicks]

justins right.

 

[A1Fiddler]

I'll keep my 32" mall terrains thank you. 29's would look gay on it anyway. The reason I am driving it around town is because my dad got his car stuck up at our cabin in the snow, and we use 2 vehicles quite frequently. Besides, I wouldn't be caught dead in his CR-V, and hate the '08 Outback.

I installed Bosch Platinum Plus plugs (yeah yeah, platinum plugs suck, I know).

I don't want to put a 2bbl on it, I just know that something's not right here, and want to get as good of gas mileage as I can out of my current setup.

 

[Hoxviii]

Don't even think about going back to a 2bbl. tuned right a 4bbl will get the same or better economy so long as you stay out of teh secondaries, but when you need the power the secondaries are there.

Ad to that the cost of going 2bbl and you'll just be spending money that you'd be better of using to a) track down your actual problem and b) pay for gas.

But I do have to say at least you do have an honest reason to gripe about economy at 7mpg. most people coming through here griping about economy are already getting 12-14 which is about where you should expect to be.

Justin

 

[RGJ 58]

to check the brakes block the front tires, jack the rear end up off of the ground, make sure the parking brake is released, and put your truck in neutral.

Give one of the tires a spin. it should spin freely, but with a slight "swish, swish, swish" noise. try the other side, should be the same. If a tire is hard to spin or only turns once or twice after you let go of it, something is hanging up.

And regardless of what others may say, there's no reason you can't get at least 10mpg out of that thing. Anything less than that and something definitely is not right.

Something else to look into is what timing set was put into that motor when it was rebuilt. if a stock 1980 timing set was installed with that cam you're power and economy will be in the crapper. The cam has to be installed with a "straight up" (non-emissions) timing set. Because that cam is definitely designed as an economy/torque cam and no way anyone considers 7mpg economy.



Justin

:thumbup
and hey fight the man dont get a plastic MPG car those are gay stay big and ride big if you can

 

[Hoxviii]

something else that's easy to check is if your choke is opening all the way. the choke on my 300 stuck 1/3 closed and cut my economy in half.

Justin

 

[A1Fiddler]

Haha, I would NEVER buy an econo*cough*gay*cough*car. 1: They're stupid looking. 2: They stupidly unsafe.

Cool, thanks Justin, I'll check these things tomorrow when it's light out. I would kill to get 14mpg! I'm just hoping to get it to 10-12.

 

[BroncoJo]

slow down on the highway or get some 35's, seriously.

 

[Hoxviii]

Thinking about it, also check your front wheel bearings. Jack the front of the truck up, grab a tire at 12 and 6 and wiggle. If you feel movement it's a bad/out of adjustment wheel bearing (or a balljoint that is about to die and take you with it). Also give the front wheels a spin feeling for any binding or stiffness. The front tires will be a little harder to turn than the rears, but nothing major.

If i were you i'd be praying for 14, shooting for 12, and willing to settle on 10. Most of the time your mileage just won't all of a sudden improve with one change unless something was definitely wrong (stuck e-brake, stuck choke, wheel bearing, worng timing set), but all the little things add up into a big change.

When i first got my 85 4x2 300-6 4 speed it would get about 12mpg going down the highway. A tuneup, dragging parking brake, and about to die front wheel bearing later I was getting a solid 20 out of it and managed to convince 23 out of it once. It had 3.08's and 29" tires; the 23 was flat ground, 75*, sunny, no wind, 55mph cruise, 100 miles each way the day after a complete tuneup and oil change- pretty much 100% ideal conditions.

Of course then I converted to 4x4, regeared, lifted, stuck it on 35's and was right back to getting 12mpg. (see avatar)

Justin

 

[redbeast9]

IMO, it will be in your timing and carb adjustment. Start by contacting the maker of your cam and see if it is designed to run with the factory retard or without. Then properly set your timing. Next adjust that carb properly.

I have owned several 335 blocks. These are usaly the 2 biggest issues with low MPG. Also run the Autolight plugs, you can run 1 heat range hoter if you choose. You can see my set up to the left and I run stock gears and get about 14 MPG if I keep my foot out of it. Good luck.

 

[A1Fiddler]

I drive very slow on the hwy, and 35's would kill my mileage even more.. And not fit under my truck.

Thanks for all the help guys! I was expecting to get a bunch of people yelling "SEARCH" at me, but this is awesome. I may dig into all the maintenance I have yet to do tomorrow, and start nailing things down. If it's not TOO cold and wet.

 

[The JuiceXLT]

Hey dude, dont know how much of a newb you are to 4x4s, but check and make sure your hubs arent engaged. Some asshole decided to play a prank on me one time... Couldnt fgure out why my milage was bad cuz i hadnt wheeled in months, I chek the hubs after 2 days and sure enough... by the way almost cost me a 3rd member and axel u joints. Hope Ive been a little help.

 

[A1Fiddler]

Haha, nah, the hubs aren't engaged. I pulled a friend's truck out the other day, and had to put it in 4wd, and I had to engage them, then had to disengage them after, so I've been runnin' around with them open.