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Noahfreak 07-08-2013 02:06 AM

F150 MPG Blues
Hi Everyone,
I'm new to the forum and already enjoying the wealth of information I've stumbled across. A couple years ago I bought an '88 F150 2wd with the 4.9L I6, Mazda 5-speed and 3.55 rear gears thinking that I'd be able to get decent gas mileage with it. Well, I was wrong, at least so far. My best tank so far has been 15mpg and that was everything I could do that I know of to conserve fuel.
Since getting the truck, I proceeded to mechanically restore it to stock condition before making any eco-type improvements, so I've rebuilt the engine, rear-end (added a limited slip 'cause it only cost another $50 or so compared to rebuilding my original carrier) and I'm about to swap transmissions.
The truck has all brand new ignition, new injectors and as far as I know, the engine is running as it was designed to. Unfortunately, that still means that it's extremely bad on fuel and that it isn't all that powerful.
I have decided to switch from the M5R2 Mazda 5-speed to a ZF wide ratio 5-speed rather than rebuild the current transmission. The ZF has a higher numerical 1st gear for easy starts, especially loaded, and a numerically lower overdrive, hopefully getting my engine below 2000 rpm while cruising at 65 mph. It's also much heavier-duty, so hopefully it will last longer than the current one did.
I decided on all of that before discovering this forum, but man I'm glad I found you guys. My thinking was correct on the transmission mod and making sure the engine is running right, but there's so much more to the puzzle than I originally knew to maximize mpg. There's already a vacuum gauge in the mail for this truck, and I got another one for my 1994 Saturn SC2 even though that thing is already amazing on fuel. I also have a Ford-specific OBDI scan gauge for the truck on the way as well. I think some of the old sensors might be sending faulty signals to the computer. The check engine light is not on, but apparently this could still mean some sensors are out of whack.
There's no way this thing should be so bad on fuel the way I've been driving it. My father's old '77 F250 4x4 crew cab with the 4-speed non-overdrive manual behind the 351M motor would beat this by about 5 mpg, and that's with a carburetor, so there's definitely some improvement to be had.
As far as the Saturn goes, I added a less restrictive intake, hotter ignition coil packs (so I can gap the plugs a little wider), put in new injectors and generally just keep the car well maintained. When I bought it, it was averaging about 23 mpg city and about 26 mpg highway, which is terrible for such a small aerodynamic car. With the cheap mods that I did, it bumped it up to an average of 28 mpg city and a max of about 42 mpg highway. I average in the high 30s on long trips usually. I'm hoping that by adding the vacuum gauge I'll be able to get it into the 30s in the city with daily driving, and bump my best 42 mpg up into the high 40s or maybe even 50 mpg. For the truck, I'd be ecstatic if I could get into the 20s, which I'm sure with some dedicated effort, I will exceed.
I think with the help of these extremely knowledgeable forum members, I'm already well on my way to making these vehicles into the fuel sippers that I hope they can be. Thanks already to those who have provided knowledge. I can't emphasize enough how beneficial that is to the rest of us.

euromodder 07-08-2013 02:56 AM

Welcome to ecomodder - and probably a new addiction ;)

Noahfreak 07-08-2013 03:05 AM

Consider Me Addicted
Yeah, I'm obviously already addicted to cars, so this will just be a new aspect to obsess over. My nerdiness shows in how excited I am to get started on my transmission swap tomorrow or Tuesday. I hope to video it and post the job on YouTube. Will add a link here if I am able to do so.

user removed 07-08-2013 07:22 AM

I had a 92 F150 with the Mazda tranny and the 300 six. Best mileage I ever saw was 20 on a pure highway trip at 65-70 MPH. My solution was to get a 97 Ranger 2.3 5 speed and a 3.45 rear end. Best tank so far in the Ranger was over 33 MPG. For some reason the old 300 inline just is not that good on mileage and I have heard the carbed ones could do better, but I think the 5.0 has better heat distribution and may actually be the better choice. My solution was to drive my 150 very little, later I sold it.


Xist 07-08-2013 08:42 AM

Good luck. My dad brought down his F-150, which I sometimes drive instead of Bacon, but I really try to leave it parked.

lordherald 07-08-2013 10:06 AM

I had a 1978 F150 with the 300 an automatic and a bad one barrel Carb. This truck also had full running boards and I always got better than 17 MPG. Check your sensors.

mikeyjd 07-13-2013 09:16 PM

Welcome! Looking forward to seeing your work :)

Noahfreak 07-17-2013 02:19 PM

First Mod Done!
I got the ZF transmission installed! I had to make a custom-length driveshaft and a couple of things didn't exactly go smoothly, but the transmission is in and it works great. The creeper 1st gear hits 2000rpm at 7mph which is ridiculous, but just fine for me. It's a work truck, not a race car. I'd rather have the added towing capacity than acceleration capability.

The overdrive 5th gear puts me just under 2000rpm at 65mph as well, which is exactly what I was looking for. The old transmission was at about 2150, which apparently is the point at which the old 300 i6 likes to just guzzle the fuel.

I have a couple of pleasant surprises with the swap too. It has gobs more power and torque in any gear at any speed or engine rpm. I used to be able to floor the throttle and not feel any extra pull from the motor. Now, just a slight bit of throttle tip in and you get that seat-of-your-pants torque feel. I think the bearings were so bad on the R2 that the parasitic loss of power was exponentially greater than it is now. I'm sure the synthetic Dexron VI that I put in doesn't hurt either. I'm going to hold off on my vacuum gauge for a tank to see what sort of mpg the tranny swap alone yields. I'm guessing I'll get a few more mpg's even if I beat on it, considering how much peppier it feels.

There also used to be a shimmy at about 20-30mph that I thought might be tires, or even worse, the rear gears. Turns out it was the M5R2 or my old driveshaft front half, because the shimmy is gone! While testing out the driveshaft that I shortened, I took it all the way up to 70 after starting out on some slower streets, and it's smooth as glass all the way through the speed range now. Overall, I'm very happy so far with the results.

Noahfreak 07-17-2013 02:21 PM

YouTube Video of First Mod
I chronicled the whole process of the Mazda M5R2 5-speed to ZF S5-42 5-speed swap on video. I have the three video playlist up on YouTube here:

Frank Lee 07-17-2013 03:06 PM

If you want fuel economy you're going to have to slow it down to 55 and/or seriously aeromod it.

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