Only getting 160 miles on 25gal tank

[pcharm129]

Hello gentleman. I'm having a seriously confusing and costly problem with my truck, and NOBODY seems to be able to figure out what's going on. I have a 25gal tank and for some unexplainable reason i'm only getting 160 miles on it. Basically 6mpg! AND i don't have any codes! I have a pcm4less tune and i removed the resonator. Got a straight pipe from the muffler. My exhaust drips water and my mechanic is no help. It also stalls from time to time. I've addressed everything i can think of except a faulty pcm. Which i will address soon because i have another one i bought from pcm4less some time ago. I don't think anyone knows these trucks better than you guys on this forum. If you can help me solve this mystery i would GREATLY appreciate it...Thanks

 

[signalnc]

what temperature is it running at ?

 

[SnowBlazer]

There you go, it's probably a broken T-Stat. I was only getting maybe 200 miles tops highway on my 18 gallon tank. Replace mine Wednesday then sat in an hours worth of traffic in the hailstorm yesterday and only used maybe 2 gallons max.

 

[Robbabob]

what temperature is it running at ?

If you don't have a scan gauge, is the needle near vertical or just 1 tick to the left? Need this reading after 10 minutes or so of the engine running.

 

[Mounce]

If you don't have a scan gauge, is the needle near vertical or just 1 tick to the left? Need this reading after 10 minutes or so of the engine running.

If it's really bad it won't make it to one tick from 210..

Other than that, how many miles are on it? Throttle body clean? Ever changed the plugs?

 

[Robbabob]

Correct, if our theory is correct, it's only going up about a 1/4 to 3/8. Just giving the OP a reference.

 

[Blckshdw]

How long have you had this condition? How does the power feel when you hit the accelerator? Thinking plugged cat possibly.

 

[djthumper]

To better answer you question we need the mileage and some maintenance history. When was the last time that you cleaned the throttle body? Have you replaced the plugs?

 

[Sparky]

What everyone else said. History is pretty darn important, as you could be having a snowball effect. 1 thing starts going, which impacts another thing, which together causes another thing, and boom you have a mess.

 

[Tiggerr]

Definitely check t-stat, and cat/O2 sensors. Something's making it run ridiculously rich or worse. Does it smoke at all? Like black running too rich smoke? Is your tailpipe excessively black/sooty? Doubt it would be the pcm itself. Anythings possible though. Same with TB and plugs. They wouldn't cause that alone. Although you could be fouling plugs running that rich. If not t-stat or exhaust issue or pcm, might be time to do compression leak down test.

Not trying to be an a$$ but I assume you've checked for fuel leaks too? Man that's a lot of fuel to go through! My semi gets better mileage lol

 

[pcharm129]

Thanx for all the replies fellas. This issue started like 2 or 3 years ago. I can't say exactly when things went bad because i wasn't really paying attention to gas mileage. I just happened to notice it one day. So, as of now she has 144,419 miles on her. I bought her in 2010 with 118,000+ for $3k.... My temp is 210. Changed the T-stat about 2 years ago with the fan clutch. I've cleaned the TB about 3 times in the last 3 years. I dont have ANY power off the line. Never have. I believe its a power management thing with this model though. Even with the pcm4less tune it didnt show much improvement. But she does much better when your already in motion. There is a delayed response though when you mash the gas. She revs hard then catches. Like she had to think about the question before she answers...lol. I've gone thru about 3 coil packs so far, and have changed the plugs about 3 times. About to change them again next week. She does get better hwy mileage. Around 275. But thats still ridiculous. There is no smoke issue and i changed the cat sensor and the right side O2 sensor. It improved a TAD bit with the right side sensor cause i was getting something like 140mpg at one time! There are no apparant fuel leaks. Although i have not had the tank dropped to check above it. I also changed the fuel filter. Here is another thing. I went away for 3 weeks, came back, then saw that fuel gauge read about 7/8's, when i could SWEAR i filled it up before i left. But honestly i'm not sure. But i figured i'd give you all the details i have. I asked the mechanic to check my fuel injectors and he said they're fine. But i really don't think he checked. Also, the other day there was a random knocking in the engine. Kind of like if you threw a rock in a dryer. But after a restart or 2 it went away and hasnt yet returned. Well, thats all i have for now. I hope it helps...

Oh. I also changed the power steering pump, the water pump, and the tensioner...

 

[littleblazer]

No power off the line and slow response when moving kind of sounds like a plugged cat to me. When's the last time you checked the air filter? Also, was the knock when it was cold, as in not to temp? If so it is probably just piston slap and I wouldn't worry about it too much....

 

[BlazingTrails]

Everything you are experiencing are symptoms of a clogged catalytic converter. Mine was doing the same thing when I bought it and it was the worst looking catalytic converter i have ever seen.

 

[pcharm129]

Yes, the engine was just started. And i never had power off the line. Even when the mileage was ok. I've seen numerous complaints about it online. Slow and partial opening butterfly on the TB. I guess because the. EXT is more of a. "family" vehicle. I had been thinkin CAT also, but my mechanic said its unlikely because its getting good exhaust pressure. I can confirm that the exhaust seems to be breathing well. But i do keep thinking CAT also for some reason. Just didnt want to spend all that money to change it then find out that it wasnt the problem. It IS the original CAT though. So if i must, then so be it...

 

[littleblazer]

Pull out the o2 sensor in the manifold and see if you get more power, that will tell you if it's the cat or not.

 

[signalnc]

You said you filled it up, went away, came home and the gauge was reading 7/8ths.....could someone be stealing your gas?.......also just thinking out loud ---if you had a leak in your gas tank you should get a P0440 code......unless the previous owner had some issue and somehow rigged it so the PCM is not throwing a code. Never heard of someone doing that but I wouldn't be surprised if someone couldn't figure out how.

 

[Sparky]

Pull out the o2 sensor in the manifold and see if you get more power, that will tell you if it's the cat or not.

Yep, while without the O2 sensor plugged in it will run in an open loop constantly and throw a SES light, it will at least put another exhaust escape in and help find out if your exhaust is getting plugged up.

 

[bobdec]

You said " I had been thinkin CAT also, but my mechanic said its unlikely because its getting good exhaust pressure. " have you confirmed he measured pressure between the exhaust manifold and the cat. AKA: Removed the upstream O2 and tested with a guage. Can he tell you the pressure at idle and at high RPM ?.

 

[Mounce]

By "I changed the right size o2 sensor" what do you mean? The I6 only has o2 sensors on the right side. You do have the I6, right?

 

[Mooseman]

EXT's are not known for their mileage. Bigger, heavier and tall gearing does not make it a good city vehicle. I usually get 13MPG city with my EXT and I was able to get 21MPG when driving strictly highway. But 6MPG is bad. Sounds like mine when the cat was plugged.

 

[Mounce]

I've got a bad thermostat in mine and still get around 15mpg with normal lead-footed driving. On our interstate trips to Kentucky, we can fill up and drive all 400 miles to there and have a quarter tank left... So I guess my EXT gets good mileage. Yeah, 160 is really bad.

 

[Wooluf1952]

Just wondering here: How many gallons do you put in at a fill-up?

 

[Mounce]

Who, me? I think the most I've ever put in was 22-23 or so gallons, we try not to let it get real low.

 

[Wooluf1952]

Who, me? I think the most I've ever put in was 22-23 or so gallons, we try not to let it get real low.

Nope. I was wondering how many gallons the OP was putting in his truck at fill-up. Just looking to see how he was coming up with the range and MPG's.

 

[pcharm129]

I thought the I6 had 2 upstream O2 sensors, bank 1 and bank 2, and one down stream. Mite be thinking of the Explorer i hhad before this. No the mechanic didnt measure anything. It was an observance. When i fill up i reset the odometer. I get approx 40 miles per 1/4 tank. Like clockwork...!

 

[Mounce]

Nah, it only has two. Should be something like

Bank 1: sensor 1; sensor 2

 

[Mooseman]

We have larger tanks. 25 gallons IIRC. Shorties just have 20.

 

[Sparky]

I thought the I6 had 2 upstream O2 sensors, bank 1 and bank 2, and one down stream. Mite be thinking of the Explorer i hhad before this. No the mechanic didnt measure anything. It was an observance. When i fill up i reset the odometer. I get approx 40 miles per 1/4 tank. Like clockwork...!

V engines have two upstream sensors, but since we have only one row of cylinders we only have 1 upstream sensor

 

[pcharm129]

Ahhh... Gotcha. Thanx for the clarification.

 

[littleblazer]

I thought the I6 had 2 upstream O2 sensors, bank 1 and bank 2, and one down stream. Mite be thinking of the Explorer i hhad before this. No the mechanic didnt measure anything. It was an observance. When i fill up i reset the odometer. I get approx 40 miles per 1/4 tank. Like clockwork...!

I get 40 miles before it comes below the full tick.... Somethings up without a doubt.

We have larger tanks. 25 gallons IIRC. Shorties just have 20.

Thought it was 22 for most and 18ish on the early models?

 

[Mounce]

EXT's have a bigger tank. It's either 25 or 26. I couldn't remember yesterday and I still can't remember lol. It's easily found in a google search though.

 

[djthumper]

SWB have 22 gal tanks except for the 2002 which has 18. The Ext have a 25 gal tank.

 

[swede]

I get 40 miles before it comes below the full tick.... Somethings up without a doubt.
Thought it was 22 for most and 18ish on the early models?

Me too, take some driving to make the needle move down from full tank mark

 

[littleblazer]

Sorry, I knew the ext had the larger tank, just confirming that the swb had 18 and 22. I haven't had the pleasure of thermostat replacement, the place we bought it from replaced it for us. I'm a little sled off the line, but it hauls everywhere else. One day I'll line up the envoy and trailblazer and see just which is faster. I was going to test back pressure since the dealer said the thermostat was bad for like 10k miles.... so my cat probably does not have optimal flow.... but it works. [emoji2] I still get 12.5ish around town.

 

[pcharm129]

I'm a little sled off the line, but it hauls everywhere else.

Yup...

There's a rev and delay before it responds though. It"s not immediate. Sucks! Thought the pcm4less tune would take care of it but no luck...

At this point i would KILL for 12.5!

 

[littleblazer]

There's a rev and delay before it responds though. It"s not immediate. Sucks! Thought the pcm4less tune would take care of it but no luck...

Mine revs and takes off, but it's a dog till about 20mph. The down shifts on the highway and around town are stupid powerful though. But trying from a stop it feels like it can't get out of its own way for a little bit. It's not that bad and I thought it was normal but the envoy has no tune and taller gears and pulls much harder from a stop. My guess would be I would lose off the line, but I would quickly overtake because it accelerates faster. The early models had plugged cat issues, check the back pressure, it isn't that hard if you just did the o2 sensor.

 

[BlazingTrails]

Dang I was getting 12.5 mpg pulling the 2,375 lb trailer 75 mph up the interstate. 4.2, 4.10 gear, Hella tuning.

 

[Tiggerr]

There's a rev and delay before it responds though. It"s not immediate. Sucks! Thought the pcm4less tune would take care of it but no luck...

That has the sound of trans slippage. Nothing a tune can do about that.

 

[BlazingTrails]

New servo will take care of the slipping. It's about $20

 

[littleblazer]

New servo will take care of the slipping. It's about $20

Hmm....