Gas mileage - 351 [Archive] - FSB Forums

: Gas mileage - 351


j. r. Nice
11-08-2004, 10:21 AM
This is probably pretty common complaint but I couldnt find anything applicable in the search.

I've got an uncut '89 XLT with 351, C4. Stock gears and tires.
I put a set of Summit headers on it and the mileage went up a bit (12-13 mpg). It had gradually gone down to 11-2.
I recently installed an FIPK and expected better mileage. Now it's down to 9-11 with same driving style. It seems to idle and run smooth. I recently replaced the plugs, wires, cap /rotor.

I'm just wondering if something could be up with the brain or the EFI causing it to give worse mileage. I know these things love gas anyway, but this is crazy. I'm not much on EFI so talk to me like a junior.

EDIT: ooops - your right - C6 - didnt engage brain. Thanks!



J. R.

kemicalburns
11-08-2004, 10:30 AM
well curious did you swap the C4 in there cuz that tranny wasnt offered. a C6 was though.

now to your question. once you have done these mods you might replace your O2 sensor then disconnect the battery and let the ecu reset itself . then reconnect and drive in various conditions for 30 -45 mins. this will help the ecu relearn the changes that have been made. Might also get the codes pulled before you reset the ecu to see what it thinks is going on.

late

jermil01
11-08-2004, 10:31 AM
You have a c-4 in an '89?? Are you sure it's not a c-6?? Either way, the lack of OD is hurting your MPG's. I don't get much better than 10 out of my '92 with a 302 EFI. Like you stated, they're heavy rigs and just like gas. What type of RPM's are you turning while you're cruising?

j. r. Nice
11-08-2004, 11:31 AM
You have a c-4 in an '89?? Are you sure it's not a c-6?? Either way, the lack of OD is hurting your MPG's. I don't get much better than 10 out of my '92 with a 302 EFI. Like you stated, they're heavy rigs and just like gas. What type of RPM's are you turning while you're cruising?

Yes, C6, (hadda brain fart!). If I rmember correctly 70 is about 2600 or 2800?
Doesnt seem to be laboring. I actually dont do much freeway with it and it doesnt seem to matter.

j. r. Nice
11-08-2004, 11:34 AM
well curious did you swap the C4 in there cuz that tranny wasnt offered. a C6 was though.

now to your question. once you have done these mods you might replace your O2 sensor then disconnect the battery and let the ecu reset itself . then reconnect and drive in various conditions for 30 -45 mins. this will help the ecu relearn the changes that have been made. Might also get the codes pulled before you reset the ecu to see what it thinks is going on.

late

Youre right, thanks for catching that. Would the o2 sensor be a stock one?
Where is he o2 on this. I thought it was on the exhaust but I havenet looked.
Thanks, I'll try that. Anything has got to be better than this!!

J. R.

Gacknar
11-08-2004, 11:35 AM
Do a tune up.

Check for codes, here is how.
http://fordfuelinjection.com/index.php?p=13

j. r. Nice
11-08-2004, 08:58 PM
Thanks - I'll give that a try......

j. r. Nice
07-03-2005, 03:20 PM
Well 7 months later and still having crappy mileage. Since the original post I have done all the suggested......here's a recap;

Summit shorty headers
K&N FIPK kit
Tune up w/ new wires/plugs/cap/rotor
New O2 sensor
Checked/fixed/cleared the ECC codes
new fuel pump
replaced damaged upper intake (plenum) gasket - helped a little
new fuel pressure regulator (today -results unchecked yet

It idles smoothly and doesnt seem to starve for gas, so I have eliminated fuel flow issues like a clogged filter or dirty injectors.

any other ideas or suggestions......I am not opposed to taking it to the dealership to "put it on a machine" if I thought it would net me more than what I already have.

FYI ...I checked the upper intake at the suggestion of a friend who has a similar problem and the FORD dealership couldnt find it.

chucktastic
07-03-2005, 03:38 PM
Be happy with your gas miliage. No body buys a FSB for the high gas miliage! Im lucky if I get 8-10pmg on average and I have a 90 with a 351 and E4OD tranny.....

Could always try one of those tornados! Ive heard those work wonders. lol Either that or just park it and dont drive it. Get a honda or diesel jetta (wifes new car?) 45+ mpg cant beat that...

magnumpi
07-03-2005, 05:31 PM
Is your catalytic converter plugged up and is your EGR system operating properly. Both of those can cause a loos in MPG when messed up. You should be able to get about 12mpg out of it. I can with my Carb 351

BoatDude
07-04-2005, 12:04 PM
I'm getting about 14 with my STOCK 1996 302. I just installed the K&N drop-in style filter, I'm wondering what results I'll be getting! Strangely, my mileage has been slowly going up, and I'm not quite sure why. About a tenth of a MPG at every fillup. No complaints on that though! I just thought I'd share my nice mileage :thumbup

:beer

Tony

MuddyBronco13
07-04-2005, 12:28 PM
yeah, i get about 11-13 on my 96 w/ 351/E4OD, but i also have 33's w/ stock gears, so i know that throws of the calculations a little, meaning i have really gone further than what i calculate, anyone know a way to know for sure?

BoatDude
07-04-2005, 03:55 PM
There's a way to reset the speedometer constant on the newer trucks like yours, MuddyBronco13. I just don't know how offhand, try searching for "speedo constant" or something. I'd look for you, but i'm too lazy :goodfinge.

:beer

Tony

montanaman81
07-04-2005, 05:30 PM
well, if you're looking for better mileage you could get a focus or maybe one of those escape hybrids. otherwise there just isn't much sense in complainin' about it

j. r. Nice
07-04-2005, 05:44 PM
well, if you're looking for better mileage you could get a focus or maybe one of those escape hybrids. otherwise there just isn't much sense in complainin' about it

well, I didnt buy it for the mileage, I pretty much knew it wouldnt be good. They are heavy and have the aerodynamics of a crackerbox :thumbup
but I'd do it all over again.

But I know it got decent mileage (12) at one point, and much like my youth, I'd like to figure out where it went.

Probably just a tired 351. Compression readings on the first (left) bank are about 135......which seems a little low.

kemicalburns
07-05-2005, 09:59 AM
135 isnt bad
what size tires are you running again?

j. r. Nice
07-05-2005, 12:24 PM
135 isnt bad
what size tires are you running again?

after doing both sides, they range about 132 - 142. And I think I would allow a few points for possible leakage of the compression gauge fittings (quick disconnects). So I think they're at least consistent. Not sure what kind of readings to expect. I thought I saw someone posted in the 160 range.


tires are std. 31 x 10.5 x 15 Michellins.

about the only thing left I can think of is cats, but it idles/runs well enough that I dont think theyre clogged. It needs a new exhaust so I may end up replacing them anyway.

I bought this truck in 2000 with 124k on it. Cosmetically, it looked like Ma & Pa Kettle owned it. I bought it from a wholesaler who knew nothing about it. But I do know it got better mileage.

j. r. Nice
07-05-2005, 12:29 PM
Is your catalytic converter plugged up and is your EGR system operating properly. Both of those can cause a loos in MPG when messed up. You should be able to get about 12mpg out of it. I can with my Carb 351

Dont think it (EGR) is, checked all the lines and there are no codes. I replaced the EGR and sensor about 2-3 years ago.

The cats I cant swear to. It runs good and doesnt seem to be doing anything unusual.

j. r. Nice
11-13-2005, 12:48 AM
Well at long last......I added a Bassani exhaust from the headers back. I had also installed an FIPK earlier. Didnt seem to help much on in-town driving but on the road I got 15 mpg! I am happy with that and will keep it for my interstate cruiser.