I have a 88 5.0 w/100,000 on it. Has a new fuel pump new filter,pressure regulator,plugs, plugwires,K&N filter. I have gutted the cats and put a singleflow turbomuffler on it. It only gets 10 in town on the highway whatever it's just sucking the gas! Any idea's?????

 

First step... pull the codes. You may have some stored even without seeing the CEL.

 

Is the CEL even wired out on the 88?

 

You think that's bad, drive an F350 crewcab with 15,000lbs hitched .

While you've gotten good advice so far... let me ask the obvious - did you get better mileage before, and suddenly it went down, or was it a gradual decline over many miles, or did the mileage suck all along?

I ask because mileage on pickups of that vintage vary from 10-15, sometimes a hair more (17ish) but usually 12-13 seems to be about average.

My 81 crewcab, going downhill with the clutch in, engine off, and a strong tail wind still got only single digits. In fact, I think it used gas sitting dormant over night!

 

Nope not a code one. And as long as i have had this truck it's only got 10 mpg but my dad swears up and down that he got 18 out of it! He owned it for 3yrs. before I inherited it. i Have tried Lucas FI cleaner in it and that did'nt even help.

 

18 is on the high end of the scale, and I would assume your father was mistaken. However unlikely, it is possible, especially if it's a stick and he dogged the truck most of the time (like, shifted below 1800 rpm most of the time).

Because of the radical difference, have your father drive the truck with you as a passenger, and say nothing, just observe. Maybe there is a radical driving style difference... I typically get 15-16ish on the highway with my 93 crewcab, and if my wife drives it she averages 9-10. She shifts higher than I do, and accelerates like it's a car. Trucks are heavier than cars, and not very aerodynamic so.

Without codes, I'd suggest maybe your catalytic converter is about to go (i.e. stuffed up) or there is a small vaccum leak that's not big enough to annoy the EFI system but enough to "adjust" the map sensor whereas the truck is fueling itself incorrectly. It's difficult to troubleshoot the really small leaks but if they're there that can confuse the EFI computer.

Ideally, a smoke machine (make friends with your service station) is the best way to find them, it pumps harmless white puffy smoke into one of the vaccum ports and if you see smoke coming out of anywhere other than the butterfly valve on the throttle body, you have a leak.

I did this on my crewcab last summer because of a sudden poor driveability issue, and discovered the brake hose, three vaccum hoses, one of the hoses that feed vaccum to the heater/dash assembly, several of the emissions lines, AND the gap in the upper/lower intake was leaking.

All very small, barely visible leaks, but summed together was probably the equivilant of a huge gaping hole.

If you don't have access to such a machine, and don't want to pay your service station for such a service, you can make a simple fitting to the vaccum port using a section of fuel hose and a brass fitting, which you attach to a $15 regulator with hose clamps, and attach the regulator to your air compressor, and set the regulator for 3psi tops. Apply air pressure, then shut off the compressor and listen. If you still don't hear any leaks, spray the vaccum hoses and seam of the upper and lower intakes with water in a windex bottle, and look for bubbles. Takes longer than the smoke method, but of course your cost is a foot of fuel line hose, two small clamps, and a $5 brass fitting, assuming you have an air compressor and a regulator.

Don't set the regulator higher than 3-5psi though... you don't want to pop the hoses... just find leaks.

 

Ok that sounds like a good start. My catalytic converter is no more and I have replaced almost every vac hose when I got the truck. The Map sensor though does raise a flag in my mind though. No codes for it but would it still work without codes and push gas to the engine?

 

Also I forgot to mention it's a automatic C-6 tranny. And one thing i've noticed is at 65 mph the moter is definatly singing around 3grand! I know it's a 3 speed but is my gas consumption just from the engine rev?

 

3000 RPM is not uncommon at 65mph with a C6 in a truck. You have any idea what the dif ratio is? I had an old '71 E-350 with a 302, C5, and 4.11 dif. At 60 mph, it sounded more like an airplane than a van. And yes, it drank fuel like a dragster.

 

I'm at 13 to 14 city maybe 16 if I'm lucky on the highway.

 

Before plenum leaks, crossfiring 7&8, and generally a lot of other Ford 100K blues, my 4x2 M5OD consistently got 18-22 highway, depending on where I set the cruise control. If I ran 80 MPH, I could count on 18. Drop to 75, I'd get 20. Drop to 72, I could squeeze out 22. 16 is excellent for the 4x4. You're totin around a lot more weight in the front end. Needless to say, when it dropped to 12 highway, I wasn't a happy camper. I've got it back up to about 17 or so now, but haven't given up. Still gonna do some tricks with the wires on the right bank and see if that cleans it up a little more.

Oh yea, a couple more notes about the old E-350. No fan clutch. If you think the aerodynamics are bad on the F-150s, try driving an old pug nosed box with a curb weight of around 6000 pounds. It was a stretchy too, formerly a church bus before someone did a custom conversion on it. It had the 2bbl Motorcraft 2150 carb, mechanical/vacuum dizzy with points/condenser, so nothin fancy there, not even TFI. Dual pipes with very burnt out glass packs on it, so kinda sounded like it meant business. Didn't have much trouble with folks crowding me in traffic. Wasn't very fast, but would pull the gates off Hell. On a good day, it got 8 highway on a long trip. City was about 6. But, alas, gasoline was only about $0.68/gallon then too.

 

I have a '93 with a 5.0 and an E4OD, and I probably get 16 tops (largely due to that added weight of my box, and the way I leave a stop sign). With a 3-speed, I would probably get about the same as you. By the way, 65mph (105Km/H for me) without an overdrive would definitely suck the fuel on the long haul. I would suggest either going lighter on the pedal, or get an AOD.

 

Well it just so happens this laborday weekend that I decided to tear into the old ford and fix those pesky oil leaks coming from the valvecovers. And when you had mentioned plenium leaks this flew a red flag! Everbody knows you've got to take apart the whole freekin top of the moter apart to take the valve coversoff. When to my surprise as i lifted off the plenium i noticed a carbon trail from one port to another! Could this be part of my problem? I hate to beat this subject to death but any tips on saving moola on gas would be much appriciated! And yes part of my problem is putting my foot to the firewall but Heh it's a Ford!

 

Was the carbon on the machined surfaces? If so, yeah, you're getting a little crossover flow between ports. Just make sure there's no corrosion or wear on the machined surfaces if the plenum's been loose for a while. The new gasket is very thin, so be very careful putting it on that you don't slide the plenum around on it and break the webbing in the gasket. Best way to do this is to put some 'headless' bolts in as studs to hold the gasket in place and guide the plenum down on it. I used some Permatex Indian Head Gasket former to enhance the seal of the gasket. Have used the stuff on VW's for years, and it won't get brittle.

There's normally going to be some carbon and oily build up in the plenum and risers strictly because you're pulling oily vapors out of the crankcase, and dumping exhaust in there through the EGR. What kind of shape was the gasket in? I had chunks missing out of mine. What I've found, is that fixing the plenum leaks cleaned up the low-end missing and hesitation. My high end miss turned out to be cross-fire between #7 and #8 cylinders. Clean 'er up best ya can, put it back together, tweek it, tune it, and play with it till ya get the best mileage you can from it.

 

Thanks for the help guys!!! I'm currently getting about 16 w/ac on so that is a big plus