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Old 06-15-2013, 10:47 AM
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98 f150 4.6 8.2 mpg!?

I've had this 98 F150 4.6 for a year now but didn't drive it much. Now that I am driving it I find it gets around 8.2 MPG, mostly city driving but it gets about the same when towing my 3200 lb race car with a u haul car trailer at 70-75 MPH. It runs good under either circumstances but the mileage sucks! It's all stock and no codes have been set. It has 247K miles on it.
Any ideas on what to start checking on this thing to improve mileage? Vacuum at idle seems to be good and throttle response is what I'd expect so I don't think the cats are stopped up. The f150 forums have been no help. Starting to wonder about those guys! LOL A lot of post on there about losing 1-3 MPG after an oil change. HUH?
Seeing a Chevy or Dodge truck with a real V8 in my furture. lol
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Old 06-15-2013, 11:04 AM
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The modular motors simply weren't designed for trucks. Most of the early 2v's make all their power between 3-4k rpm. Ford sticking with them so long says quite a few things. It's almost like if Chevy stopped making the sbc and just tried to make the best all around motor they could out of the 4.9L Caddy.

With that said, start with a basic tune-up (plugs, wires, filters, etc) and be sure to clean your IAC valve. What mileage are you trying to achieve?

Some other things to note is that the 4.6L is a bit of a mess of vacuum lines as far as modern vehicles go. Even though you said you have seemingly good vacuum, double check all the lines for cracks or breaks. They're made of a very brittle, hard plastic. On my mod motor, I cut off all the line ends with about 2" of the old line left over and used the original ends to reroute it all with standard rubber vacuum lines from the parts store.

If you still are finding yourself having issues, these motors are notorious for carbon build up. Remove the intake plenum and check the plenum, throttle body and intake for thick deposits. I would suggest cleaning them all afterwards and running a can of some of the seafoam or some kind of other alternative through the engine per the product instructions.
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Old 06-15-2013, 11:16 AM
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Quote:
Originally Posted by Valkyrie5.7 View Post
The modular motors simply weren't designed for trucks. Most of the early 2v's make all their power between 3-4k rpm. Ford sticking with them so long says quite a few things. It's almost like if Chevy stopped making the sbc and just tried to make the best all around motor they could out of the 4.9L Caddy.

With that said, start with a basic tune-up (plugs, wires, filters, etc) and be sure to clean your IAC valve. What mileage are you trying to achieve?

Some other things to note is that the 4.6L is a bit of a mess of vacuum lines as far as modern vehicles go. Even though you said you have seemingly good vacuum, double check all the lines for cracks or breaks. They're made of a very brittle, hard plastic. On my mod motor, I cut off all the line ends with about 2" of the old line left over and used the original ends to reroute it all with standard rubber vacuum lines from the parts store.

If you still are finding yourself having issues, these motors are notorious for carbon build up. Remove the intake plenum and check the plenum, throttle body and intake for thick deposits. I would suggest cleaning them all afterwards and running a can of some of the seafoam or some kind of other alternative through the engine per the product instructions.
Thanks for the info. I'll try your suggestions. As to mileage, I'm just trying to get something decent. Teens would be nice. Probably spend enough for vacuum line to pay the differance on a swap for a chevy. lol
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Old 06-15-2013, 11:32 AM
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Originally Posted by Fang16 View Post
Thanks for the info. I'll try your suggestions. As to mileage, I'm just trying to get something decent. Teens would be nice. Probably spend enough for vacuum line to pay the differance on a swap for a chevy. lol
Haha, I ended up getting rid of mine for a chevy pick up. I'm sure you could get teens out of it empty, but expect single digits when pulling anything.
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Old 06-15-2013, 12:19 PM
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A 4.6 pick up, from personal experience, and in good running/tune condition should be good for about 12-13 around town and as high as 17 open road, hauling no load to speak of, 9-10 or so with a 7000# trailer behind it. A 5.4 pickup (again, personal experience) is only about a mpg less. Both of my F150's, a '97(4x2) and an '01(4x4), were great running trucks. Even the current 6.8 F350 (4x4) runs about 10mpg city driving, 13+ open road @2000+/- rpm with cruddy 10% ethanol gas. As far as a modular engine not being a good pick up truck engine is pure unadulterated bull pucky!!!! There are just too many millions running with modular engines with many thousands of miles on them.
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Old 06-15-2013, 12:52 PM
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Originally Posted by Irelands child View Post
A 4.6 pick up, from personal experience, and in good running/tune condition should be good for about 12-13 around town and as high as 17 open road, hauling no load to speak of, 9-10 or so with a 7000# trailer behind it. A 5.4 pickup (again, personal experience) is only about a mpg less. Both of my F150's, a '97(4x2) and an '01(4x4), were great running trucks. Even the current 6.8 F350 (4x4) runs about 10mpg city driving, 13+ open road @2000+/- rpm with cruddy 10% ethanol gas. As far as a modular engine not being a good pick up truck engine is pure unadulterated bull pucky!!!! There are just too many millions running with modular engines with many thousands of miles on them.
I never said they weren't reliable. Just not a great option for doing any kind of heavy duty work. The v-10 isn't bad at all, and the 3v are okay motors but the 2v 4.6L and 5.4L (the vast majority used in light duty pickups) are absolutely anemic. The 300 I6 and windsor V8s were much better truck engines.
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Old 06-15-2013, 03:52 PM
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Quote:
Originally Posted by Valkyrie5.7 View Post
The modular motors simply weren't designed for trucks. Most of the early 2v's make all their power between 3-4k rpm. Ford sticking with them so long says quite a few things. It's almost like if Chevy stopped making the sbc and just tried to make the best all around motor they could out of the 4.9L Caddy.

With that said, start with a basic tune-up (plugs, wires, filters, etc) and be sure to clean your IAC valve. What mileage are you trying to achieve?

Some other things to note is that the 4.6L is a bit of a mess of vacuum lines as far as modern vehicles go. Even though you said you have seemingly good vacuum, double check all the lines for cracks or breaks. They're made of a very brittle, hard plastic. On my mod motor, I cut off all the line ends with about 2" of the old line left over and used the original ends to reroute it all with standard rubber vacuum lines from the parts store.

If you still are finding yourself having issues, these motors are notorious for carbon build up. Remove the intake plenum and check the plenum, throttle body and intake for thick deposits. I would suggest cleaning them all afterwards and running a can of some of the seafoam or some kind of other alternative through the engine per the product instructions.
Ran a can of seafoam through it per the instructions. Didn't see any smoky exhaust as always shows on youtube videos. Shouldn't it smoke? Put the rest in the oil and gas as can instructed. Damn fords!! lol
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Old 06-15-2013, 04:35 PM
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Check the MAF and clean it CAREFULLY.
Also how about some platinum plugs?
Even more so....02 sensors. They can be sluggish to switch and give real poor mileage. They are a maintenance item...just like a spark plug. Change the upstreams...you may be suprised.
My Nascar F 150 here in the picture gets around 17.5 on the interstate at 75 MPH with my tools in the back.
It also pulled my poncho on the trailer for several hundred miles at my last move and I thought it did pretty well for 281 cubic inches.
It is now aproaching the 200 K mileage mark.
Motorcraft parts and Mobil 1 baby
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Old 06-15-2013, 04:47 PM
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F150 8.5mpg ? Welcome to my world. I have a 76 F150 with 360, it gets about 8mpg. But at least it's consistent, it gets 8 empty, loaded, uphill,downhill,backward, forward, and sideways. But, it's never failed to carry what I load it with.
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Old 06-15-2013, 07:52 PM
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Originally Posted by LATECH View Post
Check the MAF and clean it CAREFULLY.
Also how about some platinum plugs?
Even more so....02 sensors. They can be sluggish to switch and give real poor mileage. They are a maintenance item...just like a spark plug. Change the upstreams...you may be suprised.
Thanks Tech, those are all good suggestions that I missed. Might I add that the MAF cleaning is very important if you're using (or have used) one of the K&N-style oiled reusable filters.
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Old 06-15-2013, 07:59 PM
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Plugs, filters, clean intake with Seafoam. Check your throttle body too, and clean the back of the butterfly with a little carb clean. I have full size 2000 with a 5.4 and although it seems weak pulling a trailer it gets 13 mpg all over, every day. K&N air filter, Mobil1 and Platinum plugs. I started some research for a power chip, but haven't decided which one to get, but that's next.
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Old 06-15-2013, 08:12 PM
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Originally Posted by LATECH View Post
My Nascar F 150 here in the picture gets around 17.5 on the interstate at 75 MPH with my tools in the back.
It also pulled my poncho on the trailer for several hundred miles at my last move and I thought it did pretty well for 281 cubic inches.
It is now aproaching the 200 K mileage mark.
Motorcraft parts and Mobil 1 baby
That's not bad at all. I hope you and Ireland's Child don't think I meant to offend when I said that it's not designed to be a truck motor. Truthfully it wasn't, it was designed for the Panther bodies and the MN12 Platform... Lux-o barges and personal luxury cars. I drive an 08 E-250 with a 4.6L at work, and I've owned and driven a few modulars. Every one I've ever driven doesn't make any pulling power till about 2.5-3k and after that it falls off quick.
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Old 06-15-2013, 08:24 PM
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Quote:
Originally Posted by Fang16 View Post
Ran a can of seafoam through it per the instructions. Didn't see any smoky exhaust as always shows on youtube videos. Shouldn't it smoke? Put the rest in the oil and gas as can instructed. Damn fords!! lol
Did you check the plenum for carbon before you ran the seafoam? Make sure you change the oil soon. Many may disagree but I just dont trust oil additives.
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Old 06-15-2013, 08:53 PM
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Originally Posted by LATECH View Post
Check the MAF and clean it CAREFULLY.
Also how about some platinum plugs?
Even more so....02 sensors. They can be sluggish to switch and give real poor mileage. They are a maintenance item...just like a spark plug. Change the upstreams...you may be suprised.
My Nascar F 150 here in the picture gets around 17.5 on the interstate at 75 MPH with my tools in the back.
It also pulled my poncho on the trailer for several hundred miles at my last move and I thought it did pretty well for 281 cubic inches.
It is now aproaching the 200 K mileage mark.
Motorcraft parts and Mobil 1 baby
"Change the upstreams"? Sorry, don't speak Ford. What are the upstreams? 02 sensors? Only has 1, right? Do chevy guys have to do all this "weird" stuff? Seems to me Fords are very touchy.
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Old 06-15-2013, 08:55 PM
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Originally Posted by Valkyrie5.7 View Post
Did you check the plenum for carbon before you ran the seafoam? Make sure you change the oil soon. Many may disagree but I just dont trust oil additives.
Didn't see any carbon when I had the throttle body off to clean the EGR port.
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