Only getting 160 miles on 25gal tank

[pcharm129]

I can tell from a quarter tank whether mpg has changed because its been averaging 40mpg for well over a year now. I have zero back pressure so the CAT is golden. No, i didnt disconnect the battery. I guess thats why i initially got the misfires. But that has corrected itself. And no, there are no codes present. I'm telling you guys...there are GREMLINS at play!

 

[Mooseman]

You're not driving a Prius here. It's impossible to get 40 MPG with these trucks. I averaged 14 MPG with my EXT (which is coincidentally the same as my V8 9-7x) with a best of 21 MPG all highway, fully loaded with A/C. Off the showroom floor, they were spec'd at 15/21 MPG.

I would still disconnect the battery.

 

[signalnc]

my ext with the i6 gets 14 around town and right around 20mpg on the highway.....the instant/average mpg in the computer is going to be very close to what you actually get by filling the tank and doing the math manually.....and sorry but I agree with moose, putting in x gallons to get it to a quarter tank is not going to be as accurate as filling it all the way up to full, running x amount of miles, then fill it up again and do the math.

 

[littleblazer]

My full tank average is around 12.3 right now. Doesn't like the heat. Hop on the highway and i'm almost 22. There is something wrong. But you need to do a fill from when the light turns on. that should leave around 5 gallons in the tank. Reset trip, drive till the light comes on, Fill and report the mileage, it should be very accurate.

 

[kjkim93]

These cars weren't made for mileage. Everything on my car checks out with no codes or problems. Max of 11-14 city. 21-22 highway.

 

[pcharm129]

You're not driving a Prius here. It's impossible to get 40 MPG with these trucks. I averaged 14 MPG with my EXT (which is coincidentally the same as my V8 9-7x) with a best of 21 MPG all highway, fully loaded with A/C. Off the showroom floor, they were spec'd at 15/21 MPG.

I would still disconnect the battery.

Sorry, misprint. I meant 40 miles on a quarter tank.

And yes. I can pretty accurately tell you what im getting in mileage from a quarter tank. I've been dealing with this issue for around 2 years...

 

[Mooseman]

I would still recommend that you do a full tank to empty calculated MPG's so we have a better idea of what we're dealing with here.

Another thing you should also do is a compression test.

 

[littleblazer]

I would still recommend that you do a full tank to empty calculated MPG's so we have a better idea of what we're dealing with here.

Another thing you should also do is a compression test.

I believe that was done. Below?

My compression test was positive...

Screenshot_2015-06-09-02-22-45.png

And just 2 days after the plug change, plug well 1 was again filled with oil... I think i see intake manifold gasket change is in my near future...smh.

20150608_161328.jpg

 

[Mooseman]

D'oh! Missed that. The oil leak wouldn't affect fuel consumption though. The engine looks to be mechanically healthy.

Going for a long shot here. Is the fan clutch operating normally? If it's locked up, it will sound like a jet engine and kill your mileage.

 

[bcchevy]

Fan clutch

 

[pcharm129]

Going for a long shot here. Is the fan clutch operating normally? If it's locked up, it will sound like a jet engine and kill your mileage.

Yes its working properly. Roars when it first starts for about a minute then settles down. Im thinking fuel injector ports may have enlarged or maybe gas leak somewhere along the fuel line. Going to try changing the pcm soon.

 

[Mooseman]

If you have a Bluetooth interface like the ELM327, and Torque on an Android device, you could read your fuel trims. I'm not totally versed with those but they do give a good idea of what's going on.

 

[pcharm129]

If you have a Bluetooth interface like the ELM327, and Torque on an Android device, you could read your fuel trims. I'm totally versed with those but they do give a good idea of what's going on.

I already posted that on page 2, and another on page 3. Should i post again?

Im also supprised The Roadie hasnt chimed in. I sent him a pm when i started the thread and asked for his input. Remembered him from Trailvoy. *Shrug*

 

[Blckshdw]

Im also supprised The Roadie hasnt chimed in. I sent him a pm when i started the thread and asked for his input. Remembered him from Trailvoy. *Shrug*

This is generally frowned upon. We like to have all troubleshooting and solutions posted publicly on the site to assist other members and future searches. Obviously anything discussed via PM is only visible between those participants. Also, real life and other interests divide people's time, so they may not participate on the forum as much as they used to.

 

[pcharm129]

This is generally frowned upon. We like to have all troubleshooting and solutions posted publicly on the site to assist other members and future searches. Obviously anything discussed via PM is only visible between those participants. Also, real life and other interests divide people's time, so they may not participate on the forum as much as they used to.

You misunderstand me. I INVITED The Roadie to participate IN the thread...

 

[djthumper]

In case you have not noticed... the_roadie is not able to be around much these days. Those of us that have participated in assisting you in this thread have hit about everything that it could be. IIRC you also stated that you have been fighting this issue for a couple of years. The longer that you deal with little issues, the bigger those issues become and spread. If you aren't willing to try what we have said... Do you really think the roadie would chime in to be not listened to?

 

[pcharm129]

In case you have not noticed... the_roadie is not able to be around much these days. Those of us that have participated in assisting you in this thread have hit about everything that it could be. IIRC you also stated that you have been fighting this issue for a couple of years. The longer that you deal with little issues, the bigger those issues become and spread. If you aren't willing to try what we have said... Do you really think the roadie would chime in to be not listened to?

What are you talking about??? I've done pretty much EVERYYTHING that i've been asked to try. And i've posted pics and tried to keep the thread abreast of everything thats going on. Your comment is unfounded.

As for The Roadie. I was simply stating an observance. I invited The Roadie to this thread the same day I STARTED it. I know he has a wealth of knowledge so i sent him a pm to come take a look and add his 2 cents if he was so inclined. Thats all... I appreciate EVERYONE here's input, and everyone taking the time to try and help me figure out this issue...

 

[littleblazer]

Okay. Since there is way too much going on right now, let's make a flow chart to help cover what was done and not. We'll start at where it starts.
1. Fuel is pressurized by the pump then goes through the filter to the regulator.
2. Fuel is regulated to the injectors.
3. Fuel enters the combustion chamber. Plugs, compression, exhaust.
4. Exhaust Gasses leave the chamber and enter the manifold and flow to the cat. (Checked) then run out and exit the tail pipe.
5. Things attached to the motor, fan, alt., evap system.

Failing injector leaking excess fuel into the chamber, possible.
Don't think a failing fuel pressure regulator would cause bad fuel economy, but measure pressure while running.
No exhaust restriction
Compression is good.
Fan clutch check out iirc.
Plugged evap? I don't know.

What else is on that line that could cause issues?

Edit:I know I missed a lot.

 

[Mooseman]

All I asked was to get a calculated MPG to at least see if anything that was done so far (plugs, TB cleaning, etc) has improved things.

Was the CAT replaced before or after the plugs were changed? When was the backpressure test done? Was it done above idle too?

Although I have read back through most of this long thread, I imagine that you checked for any external fuel leaks? Top of the tank at the pump lines is common.

Anybody able to read the fuel trims posted earlier? That would give an indication if it's something with the air/fuel being burned or something else.

I think we're all just as frustrated as you are. It has been a challenge.

 

[littleblazer]

Fuel trim 4.6% doesn't seem too out of wack.

 

[coolasice]

How was the back pressure measured? Was a proper 0-10psi gauge used and what was the pressure at 2500rpm?

 

[coolasice]

Just throwing this out there, but the phone photo shows you idling at 900rpm... Is this normal for you? If so I bet you have a vacuum leak at your fuel pressure reg vac line... Which would account for excessive fuel consumption both at idle and driving... Just a thought.

 

[pcharm129]

All I asked was to get a calculated MPG to at least see if anything that was done so far (plugs, TB cleaning, etc) has improved things.

Was the CAT replaced before or after the plugs were changed? When was the backpressure test done? Was it done above idle too?

Although I have read back through most of this long thread, I imagine that you checked for any external fuel leaks? Top of the tank at the pump lines is common.

Anybody able to read the fuel trims posted earlier? That would give an indication if it's something with the air/fuel being burned or something else.

I think we're all just as frustrated as you are. It has been a challenge.

I understand Mooseman. At present i can say its behaving the same as before the plug changes and throttle body cleaning.

To my knowledge the CAT has never been changed. And the back pressure was tested at idle and at 1500 rpms, before the plug change. Revved it myself. And tested with proper gauge by a mechanic.

The fuel pressure was tested last summer and it was prefect. Changed the fuel filter anyway since i was down there. But, the top of the top of the tank has NOT yet been inspected for leaks.

As for the fuel trims, the mechanic said that they were off. I believe he said they showed that the pcm was over compensating for a lean condition. Dont quote me though. Thats when he pulled a p0171 code. But that code has not returned since the plug change. Also changed the oil 2.5 weeks ago.

Just throwing this out there, but the phone photo shows you idling at 900rpm... Is this normal for you? If so I bet you have a vacuum leak at your fuel pressure reg vac line... Which would account for excessive fuel consumption both at idle and driving... Just a thought.

I idle in the 600's. I'm sure i hit the gas and the screenshot happened to get caught at that moment. Thanx for the input!

 

[signalnc]

my LT has a computer read out for MPG's--does the LS have that too?

 

[coolasice]

my LT has a computer read out for MPG's--does the LS have that too?

Not unless it has the dic option.

 

[SnowBlazer]

I can tell from a quarter tank whether mpg has changed because its been averaging 40mpg for well over a year now. I have zero back pressure so the CAT is golden. No, i didnt disconnect the battery. I guess thats why i initially got the misfires. But that has corrected itself. And no, there are no codes present. I'm telling you guys...there are GREMLINS at play!

I average MAYBE 300 miles to the tank....if I'm not dicking around and revving at people...which is a common occurrence. Also, I barely do any highway driving as I don't have a highway going from east to west....so all city driving.

 

[pcharm129]

my LT has a computer read out for MPG's--does the LS have that too?

No bro. I believe that option is for LT and beyond. LS is base model.

I average MAYBE 300 miles to the tank....if I'm not dicking around and revving at people...which is a common occurrence. Also, I barely do any highway driving as I don't have a highway going from east to west....so all city driving.

Your getting about TWICE what i am...TRADE YOU!!! Lol!!!

I just tried swapping out my PCM. But i cant get passed the security relearn. Tried for 2+ hours. I just CAN'T get a break...smh.

I also forgot to mention. She's running through gas heavily at idle too. I went through about a quarter tank in like 6 or 7 hrs idling. Heat or AC on though. Dont know if that's normal or not. And someone told me that there may be a place under the hood to test fuel pressure. Don't know if that is something i need to do. When i did it i was under the truck by the fuel filter...

 

[Tiggerr]

Have you checked your intake? Bolts tight? Gasket good? No cracks? Throttle body gasket? Something is seriously off for you to have good compression, good ignition, etc. and be running that rich. If this was a carbureted engine I'd think your choke was stuck. Can't remember, did you change o2 sensors? I know you had cat checked but I'm dubious of the results at that RPM. Don't see how it could be any good, after dumping that much fuel for that long. I think id pull it/replace it and see. Even just rig up a straight pipe temporarily. Piece of flex pipe even, if they still make it in automotive sizes. Thinking your PCM wouldn't be it. Anything's possible at this point I guess though.

Some fuel rails have a test port in them. Idk if ours do or not. Never messed with mine.

BTW my heavy footed better half, in probably 60/40% city/hwy managed to avg 15.3 MPG since we bought the Rainier. She drove it for about 2 1/2 yrs. According to DIC. Something is really out of whack here

 

[pcharm129]

Have you checked your intake? Bolts tight? Gasket good? No cracks? Throttle body gasket? Something is seriously off for you to have good compression, good ignition, etc. and be running that rich. If this was a carbureted engine I'd think your choke was stuck. Can't remember, did you change o2 sensors? I know you had cat checked but I'm dubious of the results at that RPM. Don't see how it could be any good, after dumping that much fuel for that long. I think id pull it/replace it and see. Even just rig up a straight pipe temporarily. Piece of flex pipe even, if they still make it in automotive sizes. Thinking your PCM wouldn't be it. Anything's possible at this point I guess though.

I haven't gotten to the vacuum leak test yet. Not finished building my smoker. But will be donw soon.

I changed the o2 sensors less than 2 years ago. Around when i noticed the mpg issue.

Once the mechanic checked the back pressure. He had me come over and see it for myself. One of his assistants did the revving at that point so i couldnt tell you what the rpms were. But i do trust the results, as my personal mechanic and the muffler guys both said the exhaust was fine. And I myself can attest to it seeming fine. The exhaust pressure will blow your sweatpants against your leg at about 3 feet away when revving. The actual test was just a formality so i could officially rule it out for the forum.

The PCM had a bad pcm code during the early stages of this issue, which disappeared at some point. So I'm thinking that maybe it STILL has a problem and just can't diagnose itself. And that maybe its seeing phantoms. Meaning its trying to compensate for an issue that doesn't really exist...*shrug*. One thing's for sure. It couldnt hurt. And it would be one less thing to consider in this process of elimination...

 

[Mooseman]

The relearn should be the easy. Maybe you got a dud or it's the wrong one?

 

[Wooluf1952]

I may have missed it.
Did you use an AC Delco O2 sensor? These truck often have problems with Bosch O2 sensors, although that might have set a CEL.

 

[pcharm129]

The relearn should be the easy. Maybe you got a dud or it's the wrong one?

Don't say that Mooseman!! The way my luck is going with this truck it wouldn't supprise me...smh. I bought it from PCM4LESS a couple years ago when i had the faulty pcm code...

So just to confirm the process...
1. Turn key to the crank position and hold for a few seconds
2. Let the key return to the run position for no less than 11 minutes
3. Then turn key to off position for no less than 30 seconds
4. Repeat steps 2 & 3, approx 3 times and try to start...

I may have missed it.
Did you use an AC Delco O2 sensor? These truck often have problems with Bosch O2 sensors, although that might have set a CEL.

I believe they were Delco. For sure they werent Bosch. I know they don't like Bosch.

 

[coolasice]

No bro. I believe that option is for LT and beyond. LS is base model.

Your getting about TWICE what i am...TRADE YOU!!! Lol!!!

I just tried swapping out my PCM. But i cant get passed the security relearn. Tried for 2+ hours. I just CAN'T get a break...smh.

I also forgot to mention. She's running through gas heavily at idle too. I went through about a quarter tank in like 6 or 7 hrs idling. Heat or AC on though. Dont know if that's normal or not. And someone told me that there may be a place under the hood to test fuel pressure. Don't know if that is something i need to do. When i did it i was under the truck by the fuel filter...

Have you checked vacuum at idle to the fpr? Like I mentioned earlier, if there is no vacuum to the fpr at idle it is pushing fuel at full pressure to the injectors which would mean excessive consumption and with a vac leak it would make the engine compensate by increasing injector duration...

 

[Mooseman]

That is the correct procedure for the relearn but I wouldn't wait too long at the off position, just a second or two. And when it's time to repeat at the end of the 10-11 minutes, the security light goes off.

Maybe it's not connected properly or there's a bent pin? Check for communication with a code reader and check for codes.


BTW, I merged your last posts. Please use the multiquote.

 

[pcharm129]

Have you checked vacuum at idle to the fpr? Like I mentioned earlier, if there is no vacuum to the fpr at idle it is pushing fuel at full pressure to the injectors which would mean excessive consumption and with a vac leak it would make the engine compensate by increasing injector duration...

Sorry for the delay. Been in a whirlwind lately. Soooo, how do i check the vacuum to the fpr?

 

[coolasice]

Got a vacuum gauge? First check the for to see if it is leaking by disconnecting the vacuum line to it and plugging the line with something. Start the truck andnlet it idle and watch the fpr to see if gas leaks from the vacuum port(it shouldn't)

 

[pcharm129]

Got a vacuum gauge? First check the for to see if it is leaking by disconnecting the vacuum line to it and plugging the line with something. Start the truck andnlet it idle and watch the fpr to see if gas leaks from the vacuum port(it shouldn't)

I guess i'll have to look up a "how to" on that. Fpr = fuel pressure regulator, correct?

 

[Sparky]

Yes sir.

 

[pcharm129]

Cool. I'll put that on the list.

 

[pcharm129]

First check the for to see if it is leaking by disconnecting the vacuum line to it and plugging the line with something. Start the truck andnlet it idle and watch the fpr to see if gas leaks from the vacuum port(it shouldn't)

Done. No leakage.

Have you checked vacuum at idle to the fpr? Like I mentioned earlier, if there is no vacuum to the fpr at idle it is pushing fuel at full pressure to the injectors which would mean excessive consumption and with a vac leak it would make the engine compensate by increasing injector duration...

I'm not sure that our trucks have vacuum at thr FPR. I found this on Trailvoy:

http://forums.trailvoy.com/showthread.php?t=36752#/forumsite/20572/topics/36752?page=2

tblazed said:
The only way there would be vacuum at that port on the resonator would be if the filter is clogged, or you have your hand over the air inlet and you are choking off the air! Manifold vacuum may run 18-22 in-hg at idle, but there won't be any significant vacuum on the atmosphere-side of the throttle plate. Just whatever drop across the filter element there is, which should be close to none. I doubt you could measure the pressure drop across a filter with a typical vacuum gauge.

Then PROSPHOTO said:
-I stand corrected (sorry tblazed )...Our trucks use a fuel pressure regulator that is more commonly used in a return-less fuel system (as opposed to our return systems that work off of manifold vacuum)

So, should there be vacuum or no? Because i absolutely do not have any...