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loss of gas milage

1K views 18 replies 9 participants last post by  Power Ram 
#1 ·
well after getting my car back, ive filled it up twice in a week and a half. seemed odd to me so i watched my trip odometer and my gas gage, did a lil math, and discovered my gas milage has droped from around 23mpg to 15.5mpg. thats a pretty big drop. i was wondering what might casue this, i havent checked the usuals yet(gas and air filters, spark plugs and wires). there is no gas leaking anywhere, fuel rail is clean and no leaks. i was wondering if there is anything else i should check. also, i keep my speed around 60mph, same as before i took it to the shop. any help is appriciated
 
#2 ·
23 mpg??? my otis tells me i'm averaging (sp?) around 17.3 i have the 3.3L, not sure if the 3.5 gets better gas mileage, bu ti wouldn't think it does

-bob
 
#4 ·
krypt said:
well after getting my car back, ive filled it up twice in a week and a half. seemed odd to me so i watched my trip odometer and my gas gage, did a lil math, and discovered my gas milage has droped from around 23mpg to 15.5mpg. thats a pretty big drop. i was wondering what might casue this, i havent checked the usuals yet(gas and air filters, spark plugs and wires). there is no gas leaking anywhere, fuel rail is clean and no leaks. i was wondering if there is anything else i should check. also, i keep my speed around 60mph, same as before i took it to the shop. any help is appriciated
How's it running, krypt? Maybe the timing belt slipped a notch on the crank or something.... I can't imagine you're running on all 6 cylinders if you lost that much mpg. I remeber reading somewhere that each notch your timing belt slips it retards your timing 9 degrees or so. One notch off and car runs like poop--two or more notches and good luck keeping it running. Btw, any codes?
 
#5 ·
it probably wont make much difference, but check your tire pressure - i just checked mine yesterday and all my tires were about 7lbs underinflated
 
#7 ·
krypt said:
my car runs great, no misses or anything. my car was in the shop to have the crankshaft replaced. and my car has the 3.3l engine.
My bad--no timing belt then as you know. I guess it still could be a timing related issue, especially if the crank was just replaced.
 
#9 ·
after hacking away at that airbox(one of the bolts wouldnt lossoin up) i discovered a fairly clean air filter, a few bugs caught in it, but nothing major. i did find out that my throtel body was pretty dirty, almost a dark dark grey color, shot some carb cleaner in , let it run for a bit killed the engine and wiped the insde as best i could, but you can see a big difference where i couldnt reach with my rag. a dirty throtle body wouldnt cause my gas milage to go down like that would it?? i dont know where the fuel filet is, im used to them being inside the carb or right in front , one of those inline kind. where is tho one on the intrepids?
 
#10 ·
Dude, if your 'Trep has about 90-110K miles on it, it might be a coincidence that your O2 sensors just gave up. Ours gave up overnight, or seemingly. Like you, MPG has gone from 23-26 to about 17, and I'm trying to be ultra-gentle with it, until I get the sensors replaced. They just seem to last about 100K, period.

Unlike every other car I've had with 'modern' emmissions stuff, I'd swear I can *feel* the O2 sensors *not* working while under full-throttle, between about 3K nad 5K RPM. The engine kinda hesitates a little, like it's getting too much fuel, which is probably is, as it's going to run "open loop" with bad O2 sensors, which means full-on rich...all...the...freakin'...time....

Kelly B
'95 ES, 3.5, needs O2 sensors, and I need *another* week off from work just to catch up on stuff....
 
#11 ·
im worried because my car only has 63400 miles on it. and 209 are on a fresh rebuilt engine. i cleaned out the throtle body and cleaned the air filter and took out the air restricter. i didnt think it would make that much difference, i went from 15.5mpg to 17.7mpg. not back to where it should be. ill give the o2 sensors a check when i can
 
#12 ·
Eeeek! A rebuild at only 63K?!?!?!? Oh, a toasted crank...what a drag. Sorry, dude.

My uncle, a bona-fide car nut (he's still working on trying to put the 3.5L, w/the 4-speed tranny, into a *K*-car (can't quite figure out how to shorten the axles)...) claims the 3.5 is one of the best built engines he's ever seen, and he's built more than a few rail dragster motors. I mean, he was taken aback by how solid it looked, the first time he saw one. Claimed ours would last as long as I wanted it to.

Hmmm, a 'dirty' TB, eh? Interesting. Make sure the EGR valve isn't 'stuck', as that can introduce all kinds of nasty, oily stuff into the intake. I've not had the intake apart on this car, but is the TB before or after the injectors? If after, you may be seeing it running rich. Also, given this is a rebuild with low miles on it, are you sure it's "right"? Hard to explain, but if it's "wrong", you should be able to feel it. I wonder if the shop who did the rebuild got all the computer connections back, correctly....

Yeah, check for codes. Might not be any, but it can't hurt. If they did a full-on rebuild, it might be 'tight' for the first thousand miles, but still, 17 MPG ain't right.

Kelly B
 
#14 ·
the throtle body is before the injectors. i havent had time to check anything else out yet, i still need to check my fuel filter. anyone know where it is located?? plus what is the procedure for checking for codeds? is it key on/off 3 times?
 
#15 ·
Fuel filter is under the car, towards the back (cant remeber specificly).

To check for codes, turn the key from off to on (not all the way to start) 3 times, and then leave it in the on possition. The check engine light will flash after a couple of seconds. Count the flashs, and stop counting when there is a pause (means new number).
 
#17 ·
Last Saturday I changed the oil, put new plugs in, replaced the air filter, and removed the air restrictor(pretty easy to remove actually). In the last 2 tanks of gas since then my mileage suddenly dropped from an average of 23 combined city/highway driving(we live 20 miles from town and I work in town) to 16 consistent on both tankfulls!! For some odd reason removing that silencer killed my mileage, even though it resulted in a nice roar at WOT:D. I put it back in today before heading in and filling up again. I only got about 240-250 miles on each of the last tanks before the gas light came on compared to the well over 300 miles I was getting before. We'll see in a couple days how it doing. I need to put some injector cleaner in the tank too, hopefully that will give few more mpg.
 
#18 ·
Power Ram said:
Last Saturday I changed the oil, put new plugs in, replaced the air filter, and removed the air restrictor(pretty easy to remove actually). In the last 2 tanks of gas since then my mileage suddenly dropped from an average of 23 combined city/highway driving(we live 20 miles from town and I work in town) to 16 consistent on both tankfulls!! For some odd reason removing that silencer killed my mileage, even though it resulted in a nice roar at WOT:D. I put it back in today before heading in and filling up again. I only got about 240-250 miles on each of the last tanks before the gas light came on compared to the well over 300 miles I was getting before. We'll see in a couple days how it doing. I need to put some injector cleaner in the tank too, hopefully that will give few more mpg.
Ease up off the gas pedal, bro. :p

Seriously though... When I did my exhaust mod and changed my filter to a K&N last summer I was hoping for an increase in mpg. On the city/hwy loop I drive to and from work, I would get about 20mpg before the mods, and about 16-18mpg after the mods!. Ack! What happened? I was embarrassed to post my mpg results, and actually haven't to this date.

Well, it turns out that the 3.5L can drink a LOT of gas and get poor mileage when you get on the gas pedal. I was romping on my car a good bit and enjoying the new sounds that it made. Now that I'm back to my "normal" driving habits, I do get better mpg with my mods. I consistently get 21-22mpg on my work drive loop now.
 
#19 ·
argus said:

Ease up off the gas pedal, bro. :p

Seriously though... When I did my exhaust mod and changed my filter to a K&N last summer I was hoping for an increase in mpg. On the city/hwy loop I drive to and from work, I would get about 20mpg before the mods, and about 16-18mpg after the mods!. Ack! What happened? I was embarrassed to post my mpg results, and actually haven't to this date.

Well, it turns out that the 3.5L can drink a LOT of gas and get poor mileage when you get on the gas pedal. I was romping on my car a good bit and enjoying the new sounds that it made. Now that I'm back to my "normal" driving habits, I do get better mpg with my mods. I consistently get 21-22mpg on my work drive loop now.
Well OK, I spose that has a litt to do with it:blush: I'll probably just wait till next spring to take the restrictor back out so I can fully utilize all of it's power band while burning rice;):D
 
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