Only getting 160 miles on 25gal tank
- Thread starter pcharm129
- Start date
Mounce
Member
- Aug 15, 2012
- 191
Update time... Went to see littleblazer today.
Filled up before leaving, drove 46 miles, topped off on arrival. Burned 4.6 gallons (AC off). Littleblazer calculated about 9.8mpg (hwy).
I drove 40 miles on the return trip and topped off again. Burned 3.127 gallons. I calculated 12.8mpg (no AC, about 85% hwy). Improvement, but still far from good.
@littleblazer...Thanx for the help homie! I really appreciate you taking the time out to look at the truck...
And thank you EVERYBODY here on this thread trying to help me thru this headache...!!!
Filled up before leaving, drove 46 miles, topped off on arrival. Burned 4.6 gallons (AC off). Littleblazer calculated about 9.8mpg (hwy).
Littleblazer checked the vacuum pressure and said its good. Checked the manifold and tightened a loose bolt. No other issues were noticeable. We are now both suspecting PCM or Injector issues...gmcman said:
I drove 40 miles on the return trip and topped off again. Burned 3.127 gallons. I calculated 12.8mpg (no AC, about 85% hwy). Improvement, but still far from good.
Around 2000 RPM @ 75MPH...Sparky said:
Confirmed. RPM jumped a few hundred when done at 75MPH...gmcman said:
@littleblazer...Thanx for the help homie! I really appreciate you taking the time out to look at the truck...
And thank you EVERYBODY here on this thread trying to help me thru this headache...!!!
Mooseman
Moderator
I tried searching through your thread, didn't see anything about it but, did you check or replace your CPAS? Got reminded of this in another thread.
Tiggerr
Member
Camshaft position actuator solenoid. On the pass side of engine kinda behind the ps reservoir. Goes into the head.pcharm129 said:
littleblazer
Member
- Jul 6, 2014
- 9,266
I can confirm that it is plugged in and wires weren't frayed to where the tape starts. Sound wise, I don't know what a bad one sounds like. It seemed fine.
Tiggerr
Member
- Aug 15, 2012
- 191
Success on the security relearn for the PCM. Truck started and drove a bit. Now, im hoping its not just wishful thinking but i think there's a little more bite on the take off. Just filled up, so i'll let the thread kno if anything changes with the mpg.
Mooseman
Moderator
I think we're all interested in finding this as it may help a lot with their mileage issues or at least prevent them.
We are standing by...
We are standing by...
- Aug 15, 2012
- 191
No good fellas. Calculated 7.8 mpg. Its actually an IMPROVEMENT of about 1 point something mpg from before. I think the improvement came from littleblazer tightening up that manifold bolt though. And to be honest, i was driving REALLY hard for the test. So im sure the numbers would be a tiny bit better had i gone a little easier. Nothing drastic though. So...still up the creek with no paddle...smh
- Aug 15, 2012
- 191
No actual meter was used. More of a knowledae and expertise thing. And I'll do another test...and take it a bit easier this time...gmcman said:What was the vacuum reading when you all did the test? You can't go out and hammer it and look for decent MPG's.
Fill it up, take it on a road trip, then top it off and then calculate MPG's....and drive easy.
gmcman
Member
- Dec 12, 2011
- 4,656
I'm not doubting anyone's knowledge, but you can't really guess a vacuum reading....14 inches and 17 inches will sound almost identical, let alone any fluctuations.pcharm129 said:
If you had a loose manifold bolt, chances are there could be another vacuum issue elsewhere.
This is basically to check for any sticking valves or unmetered air.
littleblazer
Member
- Jul 6, 2014
- 9,266
Well, the sticking valves should've been ruled out during the compression test. IIRC the vaccum reading on torque was a little low. But I don't remember...
gmcman
Member
- Dec 12, 2011
- 4,656
Best way to check vacuum is a separate gauge, also you can check for needle fluctuations.
You want a rock steady needle, any vibrations or fluctuations will tell if you have a valve issue based on severity of the fluctuations.
These engines tend to pull on average 19 inches or more in a healthy state.
You want a rock steady needle, any vibrations or fluctuations will tell if you have a valve issue based on severity of the fluctuations.
These engines tend to pull on average 19 inches or more in a healthy state.
gmcman
Member
- Dec 12, 2011
- 4,656
Is that a reliable gauge? Looks like almost 23" and that's kinda high but not that it's a bad thing. Is that gauge on a Mityvac? If the needle vibrates back and forth that would likely indicate intake valves not fully seating.pcharm129 said:
- Aug 15, 2012
- 191
Yes guage is reliable. Dont know the brand. It belonged to the garage. The needle vibrations were VERY minimal. Thought twice about even mentioning it. Like isaid, slight jitter...gmcman said:
Update: Upgraded to Corvette servo today. I think it may have DECREASED the acceleration, since i swapped the PCM. Not sure yet. TBD...
Mooseman
Moderator
Another direction to possibly look at. One member replaced his fuel pressure regulator and seems to have improved power and MPG.
http://gmtnation.com/forums/topic/13868-replaced-fuel-pressure-regulator/#entry447241
You didn't mention if you replaced yours and if you checked the pressure, it would just be at idle, not easy while driving. May be worth a look.
http://gmtnation.com/forums/topic/13868-replaced-fuel-pressure-regulator/#entry447241
You didn't mention if you replaced yours and if you checked the pressure, it would just be at idle, not easy while driving. May be worth a look.
- Aug 15, 2012
- 191
I didnt replace my FPR, just the filter (during the early stages of this problem). The old one was actually fine, but did it anyway. I did check the pressure from the filter line and it was great. 60 if i recall correctly. It was text book whatever it was. I remember THAT. Do i have to do another pressure test from under the hood? At the regulator?Mooseman said:
gmcman
Member
- Dec 12, 2011
- 4,656
Before you throw down $$$ on a FPR, I would first go get a can of BG 44K, it's about 20 to 25 bucks, fill up, and I can't remember but if you haven't changed your fuel filter yet, do so.
Double check the manifold bolts, the one in front is a slight pain to get to but be sure to check all of them....I think there's 10 bolts.....1 then 2, then 1, then 2 etc...this is real important.
The fact your needle is anything other than rock steady, except minute movement when the TB controls idle, tells me the intake valves are gunked up...the 44K will help this real quick. Even though you used Techron, get some 44K.
Then after that tank let's reevaluate but you have to drive easy, you can't lead foot it....driving like a grandma should get you about 15 mpg in the city/hwy.
Double check the manifold bolts, the one in front is a slight pain to get to but be sure to check all of them....I think there's 10 bolts.....1 then 2, then 1, then 2 etc...this is real important.
The fact your needle is anything other than rock steady, except minute movement when the TB controls idle, tells me the intake valves are gunked up...the 44K will help this real quick. Even though you used Techron, get some 44K.
Then after that tank let's reevaluate but you have to drive easy, you can't lead foot it....driving like a grandma should get you about 15 mpg in the city/hwy.
Wooluf1952
Member
- Aug 15, 2012
- 191
I fully understand that. Well, im planning to head out to PA this week and hit up a few U-Pull-It yards. Maybe i can find a FPR. If not. I saw some on Ebay for around $55.gmcman said:
Tranny Servo Update: Don't like it. Truck seems to accelerate slower than before the swop. Think im gonna put the old servo back in...
gmcman
Member
- Dec 12, 2011
- 4,656
Before you take the drive, stop by a dealer or shop that you know sells it, and put a can of 44K in there.
As far as the trans kit, that should have no bearing on your acceleration...I don't see how it would unless you're starting off in 2nd.
Put selector in 2nd from a stop and see if it changes.
As far as the trans kit, that should have no bearing on your acceleration...I don't see how it would unless you're starting off in 2nd.
Put selector in 2nd from a stop and see if it changes.
Tiggerr
Member
- Aug 15, 2012
- 191
I dont want the Mods to stab me in the knee with a spork (ðŸ˜), so i wont belabor this servo issue. Just wanted to make my results known since it was a proferred solution to a possible symptom, mentioned earlier in this thread. It did shift. But after i changed the PCM, but before the Servo change, it felt like she got a little quicker on the low end. After the Servo change it feels like the zip has disappeared.gmcman said:
gmcman
Member
- Dec 12, 2011
- 4,656
The corvette servo adds more surface area to the apply piston resulting in more force on the clutch, quicker and firmer shift, this should not affect your acceleration.
What did you do when you replaced the servo? Did you reuse the old pin? If not, did you make sure the length was the same on the new pin? Did you get all the seals installed correctly?
Could be coincidence with the PCM change. Did you get a CASE relearn? If not, does anyone know if not having a CASE relearn would affect performance?
What did you do when you replaced the servo? Did you reuse the old pin? If not, did you make sure the length was the same on the new pin? Did you get all the seals installed correctly?
Could be coincidence with the PCM change. Did you get a CASE relearn? If not, does anyone know if not having a CASE relearn would affect performance?
Mooseman
Moderator
We are kinder, gentler Mods. We use a spoonpcharm129 said:
https://www.youtube.com/watch?v=9VDvgL58h_Y
gmcman
Member
- Dec 12, 2011
- 4,656
Do you have any codes present?
If that were my truck, I would want to know the combustion chamber is clean....that's what the 44K is for.
After that, we can further diagnose. Just the fact you said the vacuum needle was vibrating, even just ablittle, tells me that there's a good chance the CC's are gunked up, so bad that it's getting under the valves.
Maybe not, but there's really not much else to try aside of a seafoam/ top engine cleaning or water injection but that's not the best choice if you're not careful.
Of there's alot of carbon built up, your timing could be getting retarded alot, could also be the reason for poor acceleration.
BG 44K has the strongest chemicals you can get over the counter....I'm 99% sure on that.
If that were my truck, I would want to know the combustion chamber is clean....that's what the 44K is for.
After that, we can further diagnose. Just the fact you said the vacuum needle was vibrating, even just ablittle, tells me that there's a good chance the CC's are gunked up, so bad that it's getting under the valves.
Maybe not, but there's really not much else to try aside of a seafoam/ top engine cleaning or water injection but that's not the best choice if you're not careful.
Of there's alot of carbon built up, your timing could be getting retarded alot, could also be the reason for poor acceleration.
BG 44K has the strongest chemicals you can get over the counter....I'm 99% sure on that.
- Aug 15, 2012
- 191
Professional install at tranny shop. No case relearn. 1 code for rear ABS sensor. Used Seafoam through Brake Booster hose already (No Smoke).gmcman said:
Update: This past Friday, refilled after lit fuel light. Odometer was 201.7; fill up took 22.947 gal; approx 8.8mpg (mixed driving. City/Hwy.). Left CT today with a fresh fill up. Drove 71.4 miles (Hwy), topped off, burned 5.103 gal; approx 14mpg at an almost consistant leisurely cruise controlled 65mph (No AC)...