terrible gas mileage for a V6
 

So my gas mileage still sucks (12-13 mpg's). Replaced old vacuum lines, new brake calipers because they were cheap and the old ones were sticking, new struts, cleaned MAF sensor (may still be problem in my mind), changed 180 thermostat to 195, rebuilt the throttle body, new fuel filter, oil change, and rebuilt transmission and is now mounted down ( the mount use to be broken). The only symptom they I have left is the car stuttering when I first start it (usually just when sitting outside. Like after school after the car has been sitting outside all day is when it stutters) one time it was misfiring for like 30 sec but it has never done that again. I spent a lot replacing and fixing all the other problems and I really don't want to just throw more money into a new MAF sensor and not have it help. The orange strip is the sensor is slightly wavy which is why I have a feeling that it is starting to go bad. I checked for codes and nothing came up. Fuel pressure is good and hold when the car is off so there is no fuel leak. The timing seems to be good and the car runs much better since the throttle body rebuild but my gas mileage only had about 1 mpg improvement. What do i do next? Buy a MAF or take a look at some other cheaper options?

Re: terrible gas mileage for a V6
 

How do your plugs, wires, cap, and button look? Oxygen sensor is another item to think about replacing.

Re: terrible gas mileage for a V6
 

checking the plugs would be a good idea, the wires were recently replaced before i bought the car and what is the cap and button?

Re: terrible gas mileage for a V6
 

Distributor cap and rotor button. Check your plugs for both color and wear. Make sure to take the time and set proper gap if you replace your plugs.

Re: terrible gas mileage for a V6
 

My gas mileage sucked due to a couple of pin hole leaks in my fuel tank. the heat shield caught the drops so there wasn't any real evidence.

Re: terrible gas mileage for a V6
 

i went to go check the spark plugs when i realized i don't have a long reach socket to remove them. what size socket do i need to buy?

Re: terrible gas mileage for a V6
 

It's a 5/8" socket. And get a set of plugs and possibly wires while you're at the store (unless you go to Sears or a hardware store). Even if the wires were recently replaced, that doesn't mean their resistance is in spec. No single plug wire should have a resistance of more than 20K ohms. Yes, it does sound high, but the wires aren't exactly made of copper wire... And I second the cap and rotor... Might as well make sure as much of the ignition system is as new or plenty good as possible.

Re: terrible gas mileage for a V6
 

Word. I had pin holes in my mine as well. Found out when i went to change the fuel pump. The pin holes were covered by the tank straps. When we dropped the straps, gas started slowly dripping. :gocrazy:

Re: terrible gas mileage for a V6
 

When you say pin holes, I'm guessing that's from rust?

Re: terrible gas mileage for a V6
 

Rust from the inside, the top of my heat shield was charred from where the gas had dripped down and burned. Other than the fact that there was gas on the outside of the tank, it looked completely fine from the outside.

Re: terrible gas mileage for a V6
 

I got a spark plug out and it's white. i think that means it is getting to hot. do you think this could be a sign for what is causing my gas mileage issue?

Re: terrible gas mileage for a V6
 

it doesn't look all that bad. You may be running lean from a vacuum leak or something?

Re: terrible gas mileage for a V6
 

i checked for vacuum leaks and only found one that i already fixed. one of the vacuum hoses does need to replaced though. i put soapy water on it and it didn't bubble.

Re: terrible gas mileage for a V6
 

Now you need to pull the other 5 plugs and find out if the problem is isolated to the one cylinder or not. If that plug is white and the others are black, you possibly have an injector issue that's causing the O2S to tell the ECM to put in more fuel (O2S is sensing the oxygen content in the straight air flowing through the cylinder and telling the ECM to add fuel as a result because it thinks the engine is lean).

:edit: I didn't see the pic before I posted... That plug looks like the plugs I pulled out of my engine that was getting 30 MPG...

Re: terrible gas mileage for a V6
 

ok, i'm taking the other ones out now and i'll let you know how they turn out. thanks

Re: terrible gas mileage for a V6
 

the second spark plug on the drivers side is covered in what i think is oil and has brown going up the spark plug. i'll post a pic soon

Re: terrible gas mileage for a V6
 

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Re: terrible gas mileage for a V6
 

my problem may be fixed. i changed the three on the drivers side and then i decided to do the other three tomorrow. when moving my car out of the garage it drove so much nicer. the acceleration is alot smoother and faster. i'll replace the other three tomorrow and in a week when i check my gas mileage i'll let you know how it worked out.

Re: terrible gas mileage for a V6
 

No oil there... That's from what is probably a leaking valve cover gasket seeping oil down into the plug well and the oil coating the plug as you removed it. What you care about is the electrodes. The threads mean pretty much nothing.

:edit: You should have finished the tune-up you started in the first place before anything else. Meaning, fluids, plugs, wires, filters, PCV valve. And now that you've seen the one oil-covered plug, probably valve cover and intake gaskets (as a leaking valve cover gasket can cause a vacuum leak).

Re: terrible gas mileage for a V6
 

I had to finish up today because i have alot of school work to do for tomorrow. But i have all of next week off of school so it will be a good time to do all of that. I have replaced all the filters and fluids but the Power steering (which is fine). I replaced all the intake gaskets ans egr when i replaced my thermostat housing about a month ago. The wires, pcv valve and valve cover gaskets would be a good idea to replace. I've had to replace just about every other gasket on the car because they were all so worn. I have replaced the pcv valve and valve cover gasket on my sisters honda so at least i'll somewhat knkw what i'm doing. Thanks for the advise and somthing to do over my vacation =)

Re: terrible gas mileage for a V6
 

Don't worry I am in the same boat! Thing is I don't believe I am getting poor fuel mileage so much as a bad sending unit because I can burn a quarter tank going 150 miles, then 2 days later drive roughly 15 miles and be down to half a tank!

Though after all the problems I have had with my car, I wouldn't be surprised if more was there. Let me know how your tune up goes with her. I'm sure everyone else would like to hear good news too!

Re: terrible gas mileage for a V6
 

MPG should be calculated. Forget about what your fuel indicator shows.

Re: terrible gas mileage for a V6
 

That fuel gauge issue is partly due to the shape of the tank... It's more of a rectangle at the top and a triangle going towards the bottom with the hump in the middle for the axle pumpkin. I can get to about 100 miles on the open road before it even hits the F mark and then it goes down quicker from there. With the new sender, IDK (swapped out my sometimes not working FI sender for a carbed sender with an external pump that I haven't bought yet), but I'm hoping the same.

Re: terrible gas mileage for a V6
 

That is interesting to know. I now only want to run it with a full tank because after breaking down a few times due to improper readings (left house with quarter tank and getting to campus, 1.2 miles, I am on E). Plus it runs better with a half tank or greater!

Re: terrible gas mileage for a V6
 

Probably got a bunch of crud in the bottom of the tank that should be drained out. It happens, after 20+ years of the same tank being filled and emptied all of the time. I got lucky in that there wasn't any crud in the bottom of mine when I took the sender out (unless it's still there but is now stuck good to the inner metal of the tank due to the fact that there is NOTHING in the tank, period).

Re: terrible gas mileage for a V6
 

I'll have to mess around with that when I get more time on my hands. I currently have it parked in my shed because I ran into major problems with it. Replacing all brake lines when I get time (each one cracked :O), tie rods (inner and outer) need to be replaced, and replacing pass side manifold to fix another new leak. Aye - what do we get ourselves in to :P

Re: terrible gas mileage for a V6
 

Just for an update I have replaced the spark plugs, wires, oxygen sensor, PVC valve, and the mass airflow sensor that I got cheap from a friend. I put the Mass air flow sensor on either Friday or Saturday. I replaced everything else today. with the different mass airflow sensor my gas mileage doesn't seem any better =(. but I’m hoping the oxygen sensor may be the problem. tomorrow I am going to replace the valve cover gaskets and maybe replace a vacuum line. can you buy these vacuum lines at NAPA or can you just buy some hose at home depot?

Re: terrible gas mileage for a V6
 

You can get a package of 6 feet of vacuum hose for dirt cheap anywhere but NAPA. One package of each size will do the whole engine compartment.

Re: terrible gas mileage for a V6
 

where are some good places the buy the vacuum hoses? i see them at rock auto but the shipping is half the price. i'm just looking for some cheaper options if there are any

Re: terrible gas mileage for a V6
 

I got mine at Advance before they decided to put it behind the counter :rolleyes: . I think it was like $10-12 for both packages, both 6 feet in each. They have it in bulk, but they should also have packaged "windshield washer" hose. Take a small piece of each along to match.

:edit: It's $3 per package. Cost me more because I needed fittings as well...

I've been trying to avoid RockAuto like the plague because what they save you on the parts they hit you for on the shipping :mad: .

Re: terrible gas mileage for a V6
 

do i have to remove the lower part of the plenum to get the valve covers off? or is it possible to work around it? if i do need to take the lower part of the plenum off what is the best way to release the pressure from the fuel lines because i think you need to take them off.

Edit: i Know about the pressure release valve, but i don't have what ever it is you put on it. is there a way to use it without fuel flying in my face or on my engine block?

Re: terrible gas mileage for a V6
 

No, you can't get the valve covers off without removing parts down to the intake manifold. The only fuel line needing to be removed is the white metal tube running down to the 7th injector. If the engine hasn't been run in a while and the fuel pump hasn't been run in a while, the system is more than likely depressurized. If you're worried about it, get a rag and wrap it around a screwdriver or punch and the test port as you push in the valve stem on the fuel pressure test port to release the fuel pressure. Undo the nut holding the pipe in the fuel rail for the 7th injector (DO NOT LOSE THE O-RING INSIDE THIS FITTING!!!), swing the pipe out of the way after pulling it out of the fitting, undo the 2 bolts holding the fuel rail down, undo both ends of the injector harness, and remove the bolt holding the fuel line clip to the bracket on the engine. Lift the fuel rail up and out of the way, swinging it out towards the corner of the car and letting the fuel hoses bend (they are rubber, you know), and then take the lower plenum and the valve covers off.

Re: terrible gas mileage for a V6
 

Thank you for the information, it helped alot. i have it all off now but i didn't realize all i had to take off to get the valve covers off so i have to order more gaskets from advanced auto.
My final question is how far away am i from the head gasket? most of the gaskets in my car are in bad condition and if i'm halfway there i'm willing to go farther in to replace the head gasket. Your help is greatly appreciated Maverick :thanks:

Re: terrible gas mileage for a V6
 

You only got the valve cover gaskets, didn't you? Should have picked up the MS93020 intake gasket kit with the valve covers included. You will also want an 800-9220 injector o-ring set and HS8699PT2 head gaskets if you want to go that far. To get to the heads, pull the intake manifold and then the 8 15mm head bolts. Don't touch the rocker arm nuts. Oh, and you need to pull the nuts off of the exhaust pipe studs and replace the donuts as well. While you're at it, get a distributor o-ring (mark the rotor position relative to the base plate before removal) and base gasket to prevent the infamous 60* dizzy oil leak.

Re: terrible gas mileage for a V6
 

i skipped out on the head gasket because the process was getting rather annoying removing all of the components around them. the wiring harness that connects to all the fuel injectors is in horrible condition. there is electrical tape around the wires and there melting in some spots and some wires are just barely held together. i have a friend with a junker V6 i can keep taking parts from so i'll take his wiring harness. but how do you unplug the harness? does the clip just pull apart or is it a unusual clip? i have my hand jammed behind the engine block trying to pull the connectors apart but it doesn't seem to budge.

Re: terrible gas mileage for a V6
 

I got it off, there was a white plastic strip that basically locks it together. i got that off and i was able to un-clip it

Re: terrible gas mileage for a V6
 

i got it all back together and now it is miss firing :mad:
i would have to guess the problem is from the fuel injectors or the harness. the harness despite its condition worked before so i maybe i put the fuel injectors in wrong. i don't see any gas around the injectors so it's no leaking out.

Re: terrible gas mileage for a V6
 

i took it all apart again, then put it back together. now my car starts with no misfiring but it will now not idle, it will run as long as i hold the gas pedal down a bit. i get error code 34 "Low voltage (high vacuum) at mass air flow sensor (or MAP sensor)". i'm going to look into this and re check my vacuum lines and put my old mass airflow sensor back on.

Edit: old MAF back on and no signs of vacuum leak. the code is gone but the car still won't idle.

Re: terrible gas mileage for a V6
 

I unplugged the battery to reset the computer. When i re connected the battery and tried starting my car and i started right up with no problems. I drove it around and all seems well.

Re: terrible gas mileage for a V6
 

ok, i filled up my car today and got 17mpg! what fixed the problem was most likely the 02 sensor. I replaced the 02 sensor, spark plugs, and PCV valve first and used most of the fuel in my tank driving around from this replacement before i did the vacuum hoses and gaskets. but the new vacuum hoses, gaskets, and distributer cap definitely increased my cars torque and horse power and smoothed my idle out some more. thanks for the help everyone. i'll post a official new gas mileage report sometime next week. or maybe even longer hopefully =).

Re: terrible gas mileage for a V6
 

Well... I hate to say it, but now I am in your boat. I filled my car, drove about a total of 60 miles, and burned through 3/4's of a tank. I have already changed my plugs, wires, dizzy, no exhaust leaks as I have now replaced every exhaust component, and have new injectors (purchased in november). Sad to say I am at a loss. My friend's truck gets an easy 20 mpg and that's with a 5.7L motor towing a trailer.

What other things can i check for? I know there is carbon build up because every week I have to clean out the IAC and Throttle Body because it starts to idle erratically. Could this be a problem for some of the bad fuel mileage.

Thanks for any help guys!