1971 300 EFI. VERY bad economy & disc conversion??

gp · #1 (**permalink**) 11-03-2009, 04:19 AM

I have a 1971 F100 I've owned for 31 years. In 1998 I transplanted a 4.9L EFI 6 cyl engine and C6 into the old girl. The initial fuel economy was sensational - 23 mpg and needless to say I was thrilled. After a short period of time the milage became much worse and now has deteriorated to less than 9 mpg!!!
The input resistances are all within range and I've kept the ECT sensor clean. I don't drive this old thing much [certainly much less than 2000 miles per year], but I plan to use it more often in the new year. Any suggestions apart from changing the computer [which may be my next move]??

On another matter - I fitted a brake booster and the improvement to the old drum brakes is wonderful. However; I'd like to convert to a disc brake front end. What's the most straight forward swap over?
G.P.

bmuhlbach · #2 (**permalink**) 11-03-2009, 10:09 AM

Get the front end and the proportioning valve from a newer truck 79 is the last year that will bolt in.Could go Power steering also if you don't have it now.

Conanski · #3 (**permalink**) 11-03-2009, 10:14 AM

With EFI pulling the codes should always be the first step.

DLP Performance · #4 (**permalink**) 11-03-2009, 09:05 PM

Make sure your new brake booster isn't leaking.

jhooch · #5 (**permalink**) 11-04-2009, 02:11 AM

Make sure you use the proper disc/drum master cylinder also. Just take I-beams, lines and all from a 73-79 F100/150.

DLP Performance · #6 (**permalink**) 11-04-2009, 02:40 PM

As far as a disc- swap, the easiest way is to find a truck at the junkyard around the same year as yours. The tierod ends are a little different on the later models. You can take the kingpins out & swap the whole spindle assembly to your truck. Of course you'll need the afore-mentioned proportioning valve & master cylinder for disc brakes. The brake hoses are different, too. I would replace the calipers, hoses, master cylinder w/ new parts to be safe.

Danger_Dave · #7 (**permalink**) 11-04-2009, 07:24 PM

lol i like how u put 1954 wife under all the vehicles in your sig.

DLP Performance · #8 (**permalink**) 11-04-2009, 09:44 PM

Holy crap, your steering wheel's on the wrong side!!! That's an interesting grille. Is that Aussie original?

jhooch · #9 (**permalink**) 11-04-2009, 10:56 PM

If you take the whole thing, I beams and all, you can simply take the steering linkage out of the later truck too. Heck, the last one I did, 77 into a 71, I didn't even have to align it, I set it up and it was perfect.

gp · #10 (**permalink**) 11-07-2009, 02:49 AM

Yeah, the steering wheel will look odd to you but I cope. I made the grille in a rush one day because a very inconsiderate bird kamakazied into me and smashed one insert. I'm looking for a replacement, but they are as scarse as hens teeth. Do you know where I can find a good grille insert? (I'll need to find the remaining piece to determine which one is missing). I need to put some time into this poor old truck but I've been spending all my spare time restoring my '77 Kawasaki. I really need to rectify the poor fuel consumption so I can afford to leave town without a huge credit card or filling up the back with gold bullion!.

orich · #11 (**permalink**) 11-07-2009, 11:05 AM

I see a lot of trucks with these motors in the junk yards with the head pulled off that have valve troubles. So I would first Read the spark plugs then check the compression.Do a good tuneup. Plug wires may look good and may6be bad so Check wires with an ohm meter is thte best way..
orich

orich · #12 (**permalink**) 11-07-2009, 11:10 AM

I see a lot of trucks with these motors in the junk yards with the head pulled off that have valve troubles. So I would first Read the spark plugs then check the compression.Do a good tuneup. Plug wires may look good and may6be bad so Check wires with an ohm meter is the best way..
orich