Only getting 160 miles on 25gal tank

[pcharm129]

Hey all! Sorry for the delay. I lost my phone the other day. SUKS!!! Thanx gmcman for taking the time to take a gander at my truck and helping me out. SO...on my journey to Atlantic City, I filled up in Fort Lee, NJ. I drove 138 miles to AC, averaging between 80 and 90. Drove to see gmcman about an hour away doing about the same. And did very minor driving in AC itself. When I filled up to head back to NY, I had 311 miles on the odometer, and gas light was on. My fill up took 24.376 gallons. So basically I was almost completely empty. So the truck averaged 12.7 hwy mpg. On the return trip, I gritted my teeth as I agreed to drive back at 65 to 70 mph for gmcman (longest drive of my LIFE...lol!), to see what the results would be. So, I did a consistent hwy cruise of 70 mph for about 128 of the 138 miles I drove before topping off. The fill up took 9.415 gallons. So the truck got about 14.6 hwy mpg. Better, but I'm still not quite there yet...

 

[Sparky]

What spark plugs are you using and how old are they? It was probably covered already (I did skim the thread but didn't see it), but I just replaced the spark plugs in my TB and it regained both power and a good 1-2mpg. They were only just due technically (100k miles on them, 212k on the truck) but from how it had been acting and how it acts now I should have changed them 25k miles ago.

 

[pcharm129]

What spark plugs are you using and how old are they? It was probably covered already (I did skim the thread but didn't see it), but I just replaced the spark plugs in my TB and it regained both power and a good 1-2mpg. They were only just due technically (100k miles on them, 212k on the truck) but from how it had been acting and how it acts now I should have changed them 25k miles ago.

Got ACDelco irids in there. Not even 3000 miles on them...

 

[Blckshdw]

I drove 138 miles to AC, averaging between 80 and 90.

I did a consistent hwy cruise of 70 mph

Our EXTs are pigs in mud at those speeds. I've found the sweet spot, as far as instant MPGs on the highway, is around 50-55. According to my Scangauge, I usually sit around 18-19mpgs. Between 65-70 it drops down to about 16mpg, and if I cruise 80+, it slumps down to about 14 and below.

Best I've ever seen on the screen, for a few minutes at a time, was 20-21mpg. Weather was a bit cooler, I was in cruise control behind a semi doing about 55, and there was probably a tail wind.

FYI - I've got just under 102K on the clock, and a PCMofNC tune for 87 octane, but I run 89 in it. Same year engine and gearing as yours.

 

[Mounce]

Yeah, 80+ and ours drinks gas too. Almost ran out of gas one time after driving around 80 for 100 or so miles, gas gauge stepper motor was shot and very inaccurate until I pulled the fuse to reset it.

Going 70-75 on the interstate we get around 20mpg and will have a quarter tank left after a 400 mile drive.

 

[Mike w]

@Mounce what fuse does that...gas gauge stepper motor was shot and very inaccurate until I pulled the fuse to reset it.

 

[Sparky]

Got ACDelco irids in there. Not even 3000 miles on them...

I figured as much but just wanted to double check given my recent experience with my truck.

 

[Mounce]

Not sure on number but it's labeled (ipc) in the under hood fuse box on the chart.

10a fuse

 

[littleblazer]

Fuse 24? I believe.

 

[Mike w]

indeed it was 24 thanks.

 

[Mounce]

If your gauge isn't going back to 0 when key is off then it's definitely the stepper motor. You any good at soldering?

http://pages.ebay.com/motors/link/?nav=item.view&id=121201075148&alt=web

(not meaning to derail your thread)

 

[pcharm129]

If your gauge isn't going back to 0 when key is off then it's definitely the stepper motor. You any good at soldering?

http://pages.ebay.com/motors/link/?nav=item.view&id=121201075148&alt=web

(not meaning to derail your thread)

Yes. But mine zeros out. And I'm sorry, but I just can't accept the fact that it could be acceptable to get less than 400 miles on a 25gal tank, even if I cruised at 100mph until the truck choked off from running out of gas... This is a I6, not a V8 or above. If I'm not mistaken, I'm getting worse mileage than a Hummer. Maybe I'm in denial, but I just can't comprehend it...

 

[budwich]

Having not gone thru the 10 pages, pcharm129... have you changed out the cam position / variable timing solenoid? Even though it may not throw codes, a poster on the general forum reported replacing it "popped" his mileage from low teens to twenties.

 

[Daniel644]

Having not gone thru the 10 pages, pcharm129... have you changed out the cam position / variable timing solenoid? Even though it may not throw codes, a poster on the general forum reported replacing it "popped" his mileage from low teens to twenties.

I believe the CPAS was mentioned, but that may have been the other bad gas mileage thread, don't know if it was ever tried, I'm working on trying to get better MPG and have done the standard stuff and haven't seen any improvement so I've moved on and my new CPAS just arrived today, will probably install this weekend and can report back any improvements after that, I've also gone ahead and just ordered a FPR as some have said they have seen improvements in MPG swapping it out, that should get here next week, maybe then I can top this 14.8 MPG cap I have, truck has 210k miles so it couldn't hurt to replace these parts either way.

 

[Daniel417]

Just read over your entire post.
Things to check are
fpr hose
Rubber intake cap
then on level ground put in neutral and Jack up one wheel at a time and spin to check for friction.
What I suggest is..
First replacing valve cover gasket. ~$15
Second replacing intake gaskets. ~$15
Third exhaust gaskets. ~$10
At this point you know everything is sealed up tight.
Also you might wanna redo a new back pressure test for cat.
These engines are made to run forever. The engines variables are determined by iat (intake air temp) map (manifold absolute pressure) and upstream o2 (downstream is strictly for logging emissions).
After replacing the gaskets if you are still having issues replace iat ~$20 then MAP ~$80
I noticed your temp is running a little low.
I'd replace coolant temp sensor.
And possibly thermostat.
The variable Timing exhaust cam is controlled by knock sensors which retard the timing based upon engine noise. With corvettes you can put a ls6 knock sensor into a ls1 or lt1, as a performance mod. I don't know if that's possible with our platform but would be interesting to find out. I would replace the actuator and both sensors.
@ this point you should be enjoying new car fuel economy.
If not go ahead and get a fpr and new injectors.
Your almost there.
Also you didn't mention if you put modded computer back in. I would if you haven't already.

 

[pcharm129]

Sorry for the long delay fellas. I've been trying to get ready for my trip to see my family in Trinidad. Actually at the airport now. I'll be gone for 3 week, but i'll try to keep an eye on the thread so that i can respond to any questions or whatnot.

Having not gone thru the 10 pages, pcharm129... have you changed out the cam position / variable timing solenoid? Even though it may not throw codes, a poster on the general forum reported replacing it "popped" his mileage from low teens to twenties.

Yes, i changed the Cam Actuator Solenoid some time ago. Had oil in it so i knew it needed changing.

Just read over your entire post.
Things to check are
fpr hose
Rubber intake cap
then on level ground put in neutral and Jack up one wheel at a time and spin to check for friction.
What I suggest is..
First replacing valve cover gasket. ~$15
Second replacing intake gaskets. ~$15
Third exhaust gaskets. ~$10
At this point you know everything is sealed up tight.
Also you might wanna redo a new back pressure test for cat.
These engines are made to run forever. The engines variables are determined by iat (intake air temp) map (manifold absolute pressure) and upstream o2 (downstream is strictly for logging emissions).
After replacing the gaskets if you are still having issues replace iat ~$20 then MAP ~$80
I noticed your temp is running a little low.
I'd replace coolant temp sensor.
And possibly thermostat.
The variable Timing exhaust cam is controlled by knock sensors which retard the timing based upon engine noise. With corvettes you can put a ls6 knock sensor into a ls1 or lt1, as a performance mod. I don't know if that's possible with our platform but would be interesting to find out. I would replace the actuator and both sensors.
@ this point you should be enjoying new car fuel economy.
If not go ahead and get a fpr and new injectors.
Your almost there.
Also you didn't mention if you put modded computer back in. I would if you haven't already.

Thanx for the in depth post. I already replaced the FPR. And gmcman took a temp reading on the CAT and said it was ok. l'll try to get started on some of those gaskets when i get back. But it might be a little too cold by then. I may have to put things on hold til it starts to warm up again. We'll see what happens. I also changed the Thermostat a while back too.

 

[pcharm129]

Im back fellas! Hope all is well with everybody. Im going to buy the valve cover gasket, intake gasket, and IAT sensor, so that i wil have them when time and temperature permits. Think i may say screw it and just change out the injectors too, since the manifold has to come out to change the gasket.

 

[Sparky]

Really hope that takes care of it. I think I've said before you have more patience than I do I think!

 

[pcharm129]

Really hope that takes care of it. I think I've said before you have more patience than I do I think!

Believe me Sparky, if I had the money to move on from this, I probably would. But not the other hand, I REALLY don't want to let this situation beat me!

 

[Ziggy]

Hey PCharm, quick question. I see in your profile pic that you've got some big chrome wheels on your truck. I had a set of 20s on an Explorer Sport a couple of years ago that I bought, and when I swapped them out for the factory wheels and tires, I couldn't believe how HEAVY they were. Swapping them in favor of the factory wheels and tires netted me better fuel economy and ride quality. Since it's getting colder now, if you've got the factory set, maybe try running them for a couple of months and see if there is any improvement by reducing the amount of unsprung weight?

 

[Daniel417]

Unscrew the oil cap and smell it. If it smells like gas then you have a leaking injector.

 

[HARDTRAILZ]

I can agree that heavy wheels and tires make a HUGE difference in MPG.

 

[pcharm129]

Hey PCharm, quick question. I see in your profile pic that you've got some big chrome wheels on your truck. I had a set of 20s on an Explorer Sport a couple of years ago that I bought, and when I swapped them out for the factory wheels and tires, I couldn't believe how HEAVY they were. Swapping them in favor of the factory wheels and tires netted me better fuel economy and ride quality. Since it's getting colder now, if you've got the factory set, maybe try running them for a couple of months and see if there is any improvement by reducing the amount of unsprung weight?

I do have the factory wheels. And i thought about the exact same thing. But i dont think i can stomach putting them back on. I put WAAAYYYY too much effort into making her look like she does, to put those flip flops back on her. My heart just cant take it....

Unscrew the oil cap and smell it. If it smells like gas then you have a leaking injector.

I havent gotten to her since ive been back. She is still parked up. But i will definitely give that a sniff when i get to her. Def by next week...

I can agree that heavy wheels and tires make a HUGE difference in MPG.

I agree with that too. But not at the rate of mpgs that im experiencing. We're talking about a 50% loss...

 

[Sparky]

I know it would be hard to stomach, but even if you did it just for a short time (1 full tank worth) just to see where that lands you so you know what the approximate difference is. At least lets you know where you should be expecting to be with the aftermarket vs stock.

 

[pcharm129]

I know it would be hard to stomach, but even if you did it just for a short time (1 full tank worth) just to see where that lands you so you know what the approximate difference is. At least lets you know where you should be expecting to be with the aftermarket vs stock.

Gotcha... I'll make that happen at some point...

 

[pcharm129]

Hey fellas. Happy holidays to you all. I haven't yet done anything else to the truck. I did smell the oil cap as suggested. No gas smell. And im niw loosing coolant, but i think i see where its slow leaking from. Gonna check that out before the New Year. I'm also shopping for winter/snow tires for the stock wheels, so they will be going back on shortly. I've been looking at the Blizzak dm line, but they are pricey. I want 265/65-17. I really dont want to spend more than $100 per, but i do want to get something decent. Especially the way i drive . I'd welcome any tire suggestions anyone might have that i can check out. I have a quick question. If/when i replace my injectors should i go with Delco or Delphi?

 

[gmcman]

Happy holidays to you as well. Just to briefly go over what we have discussed....yes, big wheels and tires will eat MPG's. Also, at the speeds you drive it just becomes exponential.

As far as snow tires.....you are just gonna have so take it easy, or you will burn them up. I have the Blizzards DM and they are the most amazing tire I have ever used...in winter...by a WIDE margin.

Find some spare steelies, get them mounted and swap them for winter use. You will save a ton on mounting and balancing and you can take them off for the extended dry spells.

 

[coolasice]

If you have a swb and have not done the ext rotor swap you can fit 16s on it... the cost of 16 vs 17 is fairly significant

 

[Mooseman]

His is an EXT so he has to go with 17's.

I'm gonna have to read through this thread myself. Although not as bad as you, I'm getting 12MPG on my EXT, worse than my 9-7x V8. Check the MPG's in my sig. I got a back pressure tester and I will be replacing the O2 sensor since, as far as I know, it's original with 285K Km.

Fuelly is also a good way to track mileage. Enter mileage and gallons at each fill up.

 

[smt 59]

His is an EXT so he has to go with 17's.

I'm gonna have to read through this thread myself. Although not as bad as you, I'm getting 12MPG on my EXT, worse than my 9-7x V8. Check the MPG's in my sig. I got a back pressure tester and I will be replacing the O2 sensor since, as far as I know, it's original with 285K Km.

Fuelly is also a good way to track mileage. Enter mileage and gallons at each fill up.

I changed my O2 sensor and the mileage got worse, dealer says the computer has to adjust, just by 2L/100 but I thought is was to get better.

 

[Mooseman]

Maybe resetting the PCM would hasten that relearn.

 

[pcharm129]

Thanx for the replies guys. But i didnt get an answer about the fuel injectors. ACDelco or Delphi?

 

[Blckshdw]

Both are OEM suppliers for GM vehicles.

 

[Mooseman]

Maybe Delphi makes them for ACDelco. either is a good choice. I don't even know that ACDelco makes their own parts at all. I'm pretty sure Raybestos supplies their brakes, NGK does their plugs, Behr makes their electro-viscous fan clutches and they sure don't have their own refineries to make their lubes.

 

[pcharm129]

Thanx guys!

 

[pcharm129]

Hello Gentlemen! Hope all is well with everybody. Its been cold here in NYC so I havent touched the truck (except to put on the stock rims and snow tires [Blizzacks]) since my last post. Its warming up now, so im going to jump back into this gas mileage issue. I saw some fuel injectors w/fuel rail on ebay for $85. So i think im going to start there. Maybe there's a leak in my fuel rail? My muffler is also leaking near the edge, so im going to change that too. Still cant bring myself to touch the catalytic converter though, since the backpressure test came out so well, and an exhaust place said that the exhaust pressure was fine (they didnt test though). Changing the wheels didnt really affect anything. I may get 170 miles on a full 25 gal tank instead of 160, but the affects were negligible. As usual, I'll keep you guys posted...

 

[jsheahawk]

I just read that whole thread for the first time. You really are a patient guy. Props, bro. Props.

 

[Mooseman]

I know you probably did this already but I recently replaced the O2 sensor on my 4.2 and gained 2mpg. It was not throwing any codes or anything else to make me believe it was an issue. I also reset my fuel trims after the replacement with my Tech 2. Might do the same by disconnecting the battery for 30 minutes.

 

[pcharm129]

Hey Mooseman! Yeah i covered that early out. I think i remember it making an ever so slight improvement, because i think at that time i may have been getting "150" miles on a tank...lol.

 

[pcharm129]

So, are you guys ready to hear about this NIGHTMARE??? I believe this journey has come to an end by default...SMH. Ok, so last Thursday I began to work on changing the fuel rail and fuel injectors, and the bad coil-pack-well gasket that was allowing oil to fill the spark-plug well. As im sure most of you know, the intake manifold job is a major pain! I started at 4pm. By the time i finished the job and got the valve cover and manifold and everything back together it was after 2am Friday morning... The old fuel rail and injectors did not come out easily. Had to pry them out. Even harder to put back in. Took quite a bit of effort. As for the manifold, it took me about "6 hours" to get the back bolt out! Once i finished i was excited. However...Murphy's Law was in full effect. And my excitement went up in smoke when, as i'm screwing in coil pack #3, the friggin bolt snaps off in the engine. Sooo, i dont panic. I just know a broken-screw remover set is in my immediate future. So i just continue to put everything back together. I replaced the relay and went to start my baby up and...no joy. She wouldn't start. The one moment she did start for a second, ended with what sounded like a mechanical clank. Tried again and same thing happened, with more mechanical clanking. After that, i decided that i would have to do this job ALL OVER AGAIN, to see if by chance a socket or something fell into the valve area without me knowing. I postpone the inevitable because i have to get up at "6:30am" for work! Got about 2 hrs sleep. After work, got to get another 2hr nap, before i had to go to a Wake. After the Wake, i got another 2hr nap, before i had to go back to WORK! Yeah, life was great...smh. Now...Saturday rolls around, and i decide to tackle this headache again. Went out and bought a bunch of new tools to make the situation easier, now that i know the difficulties of the job. Im sore everywhere, with multiple cuts, bruises, and welts. But before i jump into it, i decide to try and start her one more time with the remote start to see if i can pin point where the sound is coming from. Figured maybe a screw or something got caught up somewhere in the drive belt and/or pulleys. This time, the clank seemed FINAL. Like nothing in the engine is going to move at this point. I removed the drive belt and turned all the pulleys by hand. All turned, except the engine pulley. Wouldn't BUDGE. So, i start the tear down again. Things went much faster now that i upgraded my toolbox for the job and know what's what. I get to the point where its time to remove the broken coil-pack bolt and WHAM! Murphy's Law. My drill burns out (it was a cheapo set i bought from craigslist just to leave at my girlfriend's house for small household stuff). Now, my girlfriend calls her sister's husband to find out if he has a drill to lend me. Long story short, he did. She walked about 10 blocks over to get it for me, and the drill he has...is a 12 volt Black N Decker...Jesus Christmas. SO, i have little choice at the moment, so i load up the broken-screw remover and get back to work, then...YUP MURPHY'S LAW! The broken-screw remover bit BREAKS inside the broken bolt. Now, all my Dewalt power tools and good drill bits are at home, in NY. But i'm doing the work in NJ. So of course im not equipped to drill out hardened steel. So i just skip that part of the job. I ultimately get back into the valve compartment and...CRAP! There was no socket of foreign items left in the compartment. But, what there WAS, is a displaced valve spring, 2 spring caps, 2 rocker components that depress the cap and spring under the camshaft, and a hole where, im sure, a rod is supposed to be, that the spring slides over. ALSO, what i forgot to add, is that in the process of removing the valve cover, i dropped the ratchet, which fell straight through to the floor. When i went to retrieve it, i saw that there was oil pooling out onto the floor. So, it seems that the spring rod fell through into the engine itself, and is jamming some gears. I have absolutely NO CLUE what could have cause this to happen. Didn't touch ANY of that stuff. Simply changed the gaskets in the valve cover and fuel injectors. Maybe one of the bolts in the valve cover snagged and dislodged them when i was reassembling it??? I just dont know what could have happened... Now, im sure my mechanic is going to tell me im going to have to change the engine. I just can't believe this mess...