Poor gas mileage and Poor power

[scottrgeorge]

I need some help. I have been through several forums and have not yet had a solution. I have a 2005 Chevy Trailblazer with 76,000 miles on it. Ever since I bought it 3 years ago I knew something was wrong. We bought this one to replace the 05 trailblazer that was totaled. It saved my wife and kids lives and never spent a day in the shop with 98,000 on it so we figured it would be great to get another one. Well long story short we first took it in last year for plug 4 misfiring on idle. They diagnosed it and told me the head needed to be replaced. So lucky for me we had an extended warranty and so we got that done. Our engine power and MPG's dropped significantly after the head was replaced. I took it back in several times and they stated nothing is wrong with it and it works just fine.

I finally ended up taking it to another GMC dealership and they saw problems with it right away. With their troubleshooting they determined the engine needed to be swapped because the leakdown test failed on all 6 cylinders. So the warranty company bought one with 20,000 miles on it. I thought all would be well at this point. However driving away I felt the same issues and saw the MPG's at the same 10 to 11 MPG in the city.

I mentioned the catalytic converter to the dealership and they said there was no code for it so it couldn't be the problem. So I bought an OEM cat anyways from the dealership and installed it, and took it to a muffler shop to have them replace the muffler. Still the same problems. It has a horrible time getting up the smallest of hills and just bad gas mileage. So I took it to an independent mechanic and as they test drove it they told me the engine load(according to their computer) was at 100 percent on the highway going 65 on a flat surface. That didn't seem right to them or me. So at this point I decided to come to the experts on these forums and see what you all might think it could be. Below is a list of everything I have replaced or had done to it. Thanks in advance for your advice.

1. Head Replaced
2. Engine Swapped with used one with 20,000 miles on it
3. OEM Catalytic Converter with Aftermarket muffler
4. Downstream(post cat) O2 sensor
5. Upstream O2 sensor
6. Camshaft Position Sensor(Distributor)
7. Cleaned throttle body with throttle body specific cleaner
8. K and N air filter
9. New AC Delco Plugs installed at dealer after engine swap
10. New Fan Clutch
11. New Water Pump
12. 4x4 module(4x4 was broke and there were a couple parts they replaced)
13. New Fuel gauge sender unit(in tank I believe its the filter and pump as well)

 

[KNBlazer]

was your computer flashed to the latest update?

also, just because there's no code for the CAT, can't mean there's a problem elsewhere in the exhaust....

 

[scottrgeorge]

According to both dealerships yes it was. Funny thing is I have no codes or check engine lights or engine reduced power lights or anything. Its driving me crazy.

 

[KNBlazer]

does it accelerate (rev up) just fine at idle? if it's a 2wd, Lift rearend on car stands pop it in neutral and see if wheels are easy to spin... check all four brakes, you could check the rearend as well....

lol, you have a 4x4, missed that...

 

[scottrgeorge]

Its a 4x4. I was also wondering about the brakes maybe rubbing. What would I look for in the rear end? I am mechanical to a point, engine parts mostly however frame and axles and stuff I am not too familiar with

 

[KNBlazer]

Its a 4x4. I was also wondering about the brakes maybe rubbing. What would I look for in the rear end? I am mechanical to a point, engine parts mostly however frame and axles and stuff I am not too familiar with

Probably a lot of metal shavings in the fluid...

 

[scottrgeorge]

Ok I will check that out. Also it does rev up fine in idle.

 

[gmcman]

I want to speculate the first shop who swapped the head either didn't need to swap heads or didn't fully diagnose the problem. Not to start off on a bad note but why did it fail a leakdown test after the head swap? Why wasn't that checked after the swap?

Engine load (Calc Load) will register 100% if you just lightly step on the gas pedal, that's not an issue.

Cyl #4 is a very common issue with misfires since the cowl drain is right above that coil pack...slight notch in sheet metal. Water or moisture will contaminate the plug well and cause misfires. Hate to say it but it likely just needed a coil pack to begin with.

What aftermarket muffler did you get? The stock is about the best you can get if you don't mind quiet...very freeflowing. I had an issue with a Walker Quiet Flow and the inside dropped to about 1 1/4" ID...dropped 3 MPG right off the bat...stock ID is about 2.5-2.7" so food for thought.

I think someone had good luck with the FX series but not sure. I went back to stock and reclaimed my lost MPG's. The exhaust on these vehicles are well thought out in terms of flow and sound supression...albeit unattractive at the exit.

Really is a bummer you have gone through all this, hopefully we can make it right.

 

[KNBlazer]

fan clutch an acdelco/gm unit?

you could, first thing in the morning drive fo a very short distance without the serp belt on, and see if the problem is still there....

 

[gmcman]

now that I think about it, I wonder if the timing could be off 1 tooth....?

 

[Sparky]

Could well be enough to make it run bad but wouldn't that throw a position code?

 

[gmcman]

The code that gets thrown is from the sensor that is beyond its range.

Why it's beyond its range is what we need to find out, most times it's obvious like a misfire or crank sensor but a crank angle code could be bad timing...etc.

I would think it would pop through intake if timing is off, or have an odd exhaust note though.

 

[scottrgeorge]

I want to speculate the first shop who swapped the head either didn't need to swap heads or didn't fully diagnose the problem. Not to start off on a bad note but why did it fail a leakdown test after the head swap? Why wasn't that checked after the swap?

My thoughts exactly. They swore up and down it was fine. I took it to them 7 times. Before the head swap we were getting better gas mileage than after the head swap.

Engine load (Calc Load) will register 100% if you just lightly step on the gas pedal, that's not an issue.

Ok, good to know, the mechanic was an independent and I didn't have a clue.

What aftermarket muffler did you get? The stock is about the best you can get if you don't mind quiet...very freeflowing. I had an issue with a Walker Quiet Flow and the inside dropped to about 1 1/4" ID...dropped 3 MPG right off the bat...stock ID is about 2.5-2.7" so food for thought.

I may have to look into that, however the gas mileage stayed the same after the muffler swap, my wife and I do like it quieter so I may get that anyways to make her happy.

 

[scottrgeorge]

The fan Clutch is an OEM part it was bought and replaced at a Chevy Dealership

 

[scottrgeorge]

That's what my independent mechanic thought, but he checked the timing and it was good to go, as far as the chain is concerned.

 

[Sparky]

I'm really curious... jack up the vehicle, put it on jack stands so you can spin each wheel freely, and make sure nothing is overly stiff to spin.

Usually the fan clutch doesn't fail in a way to drag the engine down, especially not that much. Even if it did, you'd hear it constantly roaring.

 

[scottrgeorge]

Well, I finally heard from the brake repair shop. All 4 wheels spin freely, pads have 50 percent or more on each and are wearing evenly. So that gets rid of the brake issue and the wheels locking up. Not sure what to do next.

 

[gmcman]

Compression test, dry then wet.

Vacuum test.

 

[gmcman]

If they put a motor in there's no idea on condition of injectors if it was a long block. Injectors could have sat for a year.....who knows.

What is the fuel pressure?

Need to get some fuel trim numbers.

If it were mine, 1 can of bg44k and drive a tank, see what happens. I would do that first and then start checking things.

 

[Royalwapiti]

Does the 4x4 work as it should? Is there anyway the transfer case could be dragging down the performance?

 

[gmcman]

You really need to perform a dry then wet compression test. Post results.

 

[gmcman]

What year did they change the cylinder heads, was it 2005 or 2006? If they changed the heads in 2005, make sure you don't have a pre-05 head. I doubt this happened but doesn't hurt to check.

 

[HARDTRAILZ]

06

 

[scottrgeorge]

Sorry I have been gone so long. So it kept bugging me that even though the fan clutch had been replaced by the dealer with OEM parts it still seemed too loud. I have pulled the harness and been driving to and from work about 6 miles each way. Well my power seems to be back and my gas mileage is now at 50 miles for 1/8th tank instead of 1/4 tank. So my question would be is it the clutch which is new OEM, the harness, or the relay? I know it's got something to do with one of those things. I hesitate to take it back to the dealer because they tell me the fan is running as it has been commanded to run(as far as speed goes). What do you all think. Mileage is at its worst in low speed in city or even continuous back roads driving 25mph. Back road driving not at all a 4 wheel road but just standard road I got 176 miles on my 22 gallon tank.

 

[scottrgeorge]

4x4 was serviced and some parts replaced by the dealer. I tested it and works as it should.

 

[KNBlazer]

a couple of weeks ago, I drove almost 100 miles, prior to hitting the highway, I filled up, the next day I filled up again to see what my mpg was... I calculated 18.4 mpg with A/C on and 100 degree ambient temp... about 93-95 miles were highway, the other 5-7 were street.... my mixed mileage is anywhere between 14.7 to 15.6

 

[gmcman]

Well,18.4 isn't too bad...higher than alot of people.

Someone here had a clogged resonator recently and pulled the hair-like packing media from it. Check yours to see if anything is trying to exit the tailpipe. You should hear a normal exhaust note and not a whishing noise.

 

[scottrgeorge]

It's a brand new cat back. Nothing coming out.

 

[scottrgeorge]

I'm getting more like 10mpg if I am lucky. My thing is the whimpy hills. Unless I downshit or push the pedal it drops speed. My 01altima 5 speed clears the same hills without downshifting. It just feels like a rope is tied to a cement block and I drag it every where I go.

 

[Sparky]

Can't see it being fan clutch dragging you down that much, especially without it constantly at 100% and roaring like a jet at all times.

 

[scottrgeorge]

Unplugged it runs with more power and feels normal as well as double the mpg.

 

[gmcman]

When the motor is cold, let it idle for about 30 sec, then carefully, you should be able to stop the fan using a rag pressing against the smooth side of the fan.

 

[scottrgeorge]

I found the fix. I drove it to a dealership and traded it in on a Nissan Xterra. Too many problems for a truck with only 76000 miles on it. Thanks to all for you help and input. I just don't have enough money to keep messing with it.

 

[gmcman]

Man.....sucks you had to part with it but Xterras are cool.

How many miles?

Make sure you get something in writing on maintenance, especially on those O2 sensors. Nissan is proud of them...lol.