6mpg from a 3fe!!! What gives!!!! (1 Viewer)

[yodanut91]

Hello, having a issue with my rig, it is using ALOT of fuel. I was expecting 11-13mpg with 33's. But I got 6mpg. Constantly.
Specs are
33x12.5r15 tires
4" lift
arb bull bar

No engine light or rough running.

I have done
new spark plugs
new plug wires
new cap and rotor
new air filter
egr and smog delete
valve adjustment
Seized caliper(replaced)
new oil in everything
re built a440f trans with new torque converter.

What do I do next!? It has a little power but nothing above or below average. I am running 87 octane in the tank. I have run 3 cans of injector cleaner though it over the past 5 months. Could the cat converters be pooched? I have a lot of suit on the tail pipe too. Could leaning out the afm help? I don't know much about the 3fe so what advice you have is helpful

A lot of people have made threads on bad mileage but they are getting 8-9mpg, mine is at 6 and the engine seems to run great with no stumble or hickup.

HELP ME! I am spending a fortune on gas! A tank only lasts 200km/120mi!!!!!!!!!!!!! I am not hard on it either I cruze at 100km/h -60mph no hard starts or hard acceleration.

 

[jwilber]

Mine is about the same. Its probably a combination of many things. Are you adjusting for tire size when you figure your mileage

 

[SUMMIT CRUISERS]

A couple of things come to mind: Have you reset your ECU after the tune-ups? Did you advance your timing per FSM with the jumper wire in the diagnostic box? As I recall your truck can take up to about 12 degrees of advance. If you hear pinging under a load, retard your timing a bit until you get to the sweet spot. Depending on your climate and elevation , if it is very cold and you are running E-10 gas, there is a good chance that you will be seeing about 7 to 8 mpg.

 

[yodanut91]

Reset ecm? No idea how..... yes i did check and adjust timing according to the fsm. I am at about 12 of advance. Not pinging and it is just past the mark, I had it set to 14 but it was pinging so I pulled it back to 12, hard to see in there. haha! Yes that is with tire size adjustment. I had a look underneath and found the exhaust is pusing out of the union pre cat on both cats. Possibly plugged, I am going to rip them out on friday amd inspect them. If they are plugged it could be the cause of my issues. For now I am driving it really really light. I am interested in this ecm reset, I will try that tomorrow.

 

[cruisercommando]

My wife's '93 was having crappy gas mileage issues. Turns out the O2 sensors were bad. No engine light, but codes were stored in the ECU. Two new sensors, and her mileage has gone from crappy (9-11MPG) to sucky (13-14MPG).

 

[LS1FJ40]

A couple of things come to mind: Have you reset your ECU after the tune-ups? Did you advance your timing per FSM with the jumper wire in the diagnostic box? As I recall your truck can take up to about 12 degrees of advance. If you hear pinging under a load, retard your timing a bit until you get to the sweet spot. Depending on your climate and elevation , if it is very cold and you are running E-10 gas, there is a good chance that you will be seeing about 7 to 8 mpg.

This. I am getting about 7-8 mpg on 87 octane with 10% ethanol fuel. When I switched to 93 octane and no ethanol I get about 10-11 mpg. The past few weeks it has been very cold -5 to +5 degrees and I'm seeing barely 7 mpg.

Also, winter gas sucks here in the Midwest. All the crap they put in it to keep it from freezing doesn't help fuel mileage. On the plus side I've run some pretty sketchy fuel in my 3FE over the years (here in the US and Mexico) and it always runs and never throws the CEL.

Be glad Obama has fuel prices low.

 

[thedoughboy]

Reset ECU = Disconnect ground at the battery...for a bit.

Restart and drive your car as normal. After about 5-8 times your ECU will be "reset".

At least, that's what they tell me. The first initial cycles your engine may run a little rough.

 

[yodanut91]

Hmm ok. I am going to reset my ecm, check cats/gut them and put a tank of 91 in it. See if it makes a difference.

 

[yodanut91]

i have a hard starting issue too. beginning to suspect the fuel pressure regulator and the fuel pulsation dampener.

 

[Alleycats]

Maybe check your timing?

 

[Tenzig Norgay]

It doesn't matter the octane, just no ethane bro.

 

[yodanut91]

timing is good and i am using 87 octane

 

[jonheld]

Most likely your cats are plugged and your O2 sensors are shot. These are wear items and have a lifespan and can dramatically effect efficiency. The O2 sensors can be out of spec and there may or may not be a code flagged by the ECU.

After ANY work is done under the hood or to anything related to any electronics or any sensor, I like to pull the 15 amp EFI fuse as a first step. Even for a basic tune up, pulling the fuse should always be a first step. This does 2 things. It clears any stored codes so you're not being fooled by multiple codes if you're troubleshooting, and it allows the ECU to relearn the basemap of all the sensors in the EFI system.

http://www.sdsysdesign.com/tlc/images/OBA/Fusebox.jpg

 

[jonheld]

Another thought regarding poor MPG is the cooling system. If the thermostat is stuck open or the fan clutch is seized, then the motor will not maintain proper temperature and will cause poor economy.

 

[fantic]

i was fighting a high idle problem and replaced the coolant temp sensor. The idle came down and get close to 2mpg better milage. But i didn't start out at 6mpg.

 

[yodanut91]

The thermostat is new and fan clutch is working great. i was thinking the cats are plugged but i am going to replace the FPD and the FPR first and re check my mileage. i reset the ecm already too!

thanks !

 

[Eicca]

O2 sensors, plugged cats, fuel regulator and damper would definitely be the next things to do.

With my 33s, 2" lift and roof rack I could do 13mpg averaging 70mph.

Also see the "EGR disabled" mod link in my sig to put the cherry on top when all else is done.

 

[yodanut91]

Hmmm okay. I will have a look at them next. I found my FPR was not connected at all. Along with a s*** load of wiring mistakes. Slowly making my way through it. Egr delete is done I used the same link to do it. Thanks

 

[jcarter]

Cooling - I assume it's warming up properly. New thermostat doesn't mean "not stuck". When I was down to 8 mpg, I couldn't figure it out either, until I took a long, cold highway trip and the temp guage barely moved off cold. When I replaced the thermostat, I put both old and new in pan on stove and watched them open and close simultaneously (odd). Kept the old for back-up, installed the new, back up to a wopping 11 mpg.

 

[yodanut91]

Nah mine runs warm on the hiway, gets to half and stays there. Don't think it is a cooling issue. I found my FPR not hooked up. I re connected it but I think it blew the FPD being unhooked for god knows how long.