Gas Mileage problem

[okaussie]

It is me again.

About two months ago I noticed I was having to fill up more often. Never checked the gas mileage but prior to this I was getting around 20mpg's in 2Hi. Everything is stock. 141K miles on it.

Then 3 weeks ago I replaced the fuel filter thinking it was bad. Found that the real problem was the cat was clogged. Had my repair shop diagnose and repair the problem.

Today I filled up and my gas mileage is now about 13mpg's, so I went from 20 two months ago, then the mileage dropped, then the cat went bad, replaced the fuel filter and now the mileage is at 13. What happened???

don't notice anything different in performance or anything else. Just my mileage now sucks.

Thinking I was driving my 73 IH again.

TIA

Bill

[killian96ss]

What exactly did the shop do? Have you replaced the 02 sensors? Try cleaning the MAF sensor with CRC brand MAF sensor cleaner. If you can't find any use 90 % isopropyl alcohol and q tips. The 3 tiny sensors need to be cleaned, but you have to be careful with q tips. Is your main cat ok?

Steve

[okaussie]

They replaced the entire assembly from the exhaust manifolds to the muffler. It came as one piece. I have to assume that all the associated sensors in the assembly are new too.
the receipt I have does not show any sensors being replaced so I assume they came with the assembly.

The mpg drop started prior to the cat assembly being replaced. Thought that was the problem. The cat was bad but didn't fix the mpg problem.

Guess I am going to have to buy a scanner and find out what is really going on..

Bill

[okaussie]

I took out the air filter and blew the contaminants from its enclosure and looked at the screen on the MAF. It looked clear and obstructed.

I then cleaned the Throttle Bottle out with cleaner. It already looked clean but figured it couldn't hurt.

I think the next thing is buy a scanner and see if it sets any codes.

I do have an intermittent SES light but that usually appears after refueling. Suspect a vacuum leak somewhere . That, however, does not happen alot.

Will report later if anything new develops.

Bill

[rlrnr53]

I can't see GM supplying new O2 sensors with the cat assy. They will stick you for every thing they can. If you change the O2 sensors, stick with the OE sensors, as some after market sensors don't give as good mileage. My MPG dropped recently, I checked my tire pressure, 3 of 4 tires were between 10 - 15 lbs. After inflating to about 38 lbs., mileage went back up.

[roadrunner]

Ditto the tire pressure advice. BTW, how much did the front pipe cost you? I'm looking at the same need on mine. I will however gut the pre-cat on whatever brand pipe I get as a replacement. I priced the pipe locally at a muffler shop and making one isn't an option for me as it was estimated at 300 plus bucks for a made to fit one. I agree with rlnr on the doubt of the O2 sensors being replaced. I think they certainly would have listed them separately if they had replaced them. I don't agree totally on the oem aspect though. I've been running Borg Warner sensors I got new for about 1/3=1/2 the price of oem from a supplier on e-bay. I know others will disagree but I've had good luck and no mileage detriment running them for quite a while now. As for the scanner it or perhaps a scan-gauge II would be a help but unless the light is on continuously I doubt you are having a mileage issue from that. I too get occasional light after fill-ups scan gauge says it is caused by my vent valve under the box behind the cab. Since it has always been intermittent I just clear the code and keep on driving. I'll change it if it ever becomes a constant or at least a regular problem.

[rlrnr53]

I don't know about the pipes and cats on the crew, but had one changed on an Astro van a few years ago, and it cost arounr 600.00 then.

[okaussie]

Mine was $464.89 with $120.00 labor to install it.

It says Replace Cat. Conv Assy.

I will check the tire pressures.

Will low tire pressures cause the mileage to drop that significantly???

TIA

Bill

[okaussie]

I just checked the tire pressure.

I am running 34lbs in all four tires.

Tires are Firestone Destination LE 235/70R/15.
This is the second set on this truck and did not have any flats or problems with the first set. Same with this set..

I checked the Firestone Website and the tire pressure for this tire on this vehicle is 35lbs, so I feel it is okay..

Bill

[rlrnr53]

In my case, the mpg went from about 17 to 11.5. Haven't filled up since airing up, so I don't know how it doing.

[okaussie]

I will try to purchase a scanner this week to check the O2 sensors. With the miles on my CC I am thinking it is something like that.

It changed so abruptly prior to the CAT failure that is why I am thinking that.

Maybe the loss of MPG's was precursor to the CAT failure and also caused by the O2 sensors.

Bill

[killian96ss]

The 02 sensors start losing efficiency around 80k miles and are pretty bad by 100k. I highly doubt that shop replaced them without noting it on your reciept. 3 new 02 sensors would add at least $200 to the bill. With your mileage it would be smart to replacing all 3.

Steve

[okaussie]

Just got a scanner and ran the codes:

P0452 EVAP emmision system pressure sensor/switch low

P1683 Driver 5 line 3

Now what do I do with this information???

What problems do I have and how to I repair them???

TIA

Bill

[roadrunner]

P0542 refers in the book to problems with the tank pressure switch in the pump/sender unit in the tank. Possibly a loose/bad wire connection at the tank? Others have had problems with connections there. If connection is okay then either the switch is dirty or defective or not getting power from the connector hence the low voltage warning.

P1683 refers to a PCM problem where the malfunction is most likely repaired by replacement of the PCM. Before doing that it advises to check wire connections at the PCM for integrity (corrosion etc) and for possible water contamination under and around the PCM and it's connector.

This is condensed version of what the book charts say. Sorry to bear bad news.

[okaussie]

Would any of these codes cause my fuel mileage to drop from 20mpg to 13mpg. It is just like someone flipped a switch and my mileage dropped and haven't been able to get it back.

I have noticed on other forums re: the 452 error they fixed it by replacing the gas cap due to an old, dried, cracked seal on the cap. Mine was replaced a couple of years ago.

Some have also talked about it being a sensor on the fuel pump/fuel gauge assembly in the gas tank. My fuel pump has been replaced 3 times in the last 2 years.

The mileage problem just came on all of the sudden.

As to the PCM problem, where would I find it???

TIA

Bill

[roadrunner]

P1683 does contain some references to poor fuel economy in the book. Probably due to the PCM not functioning correctly due to malfunction or poor connections. The PCM is located on the passenger side inner fender under the hood. It is retained there by two snap over bale type hold-downs and the electrical connector has a bolt retainer that must be loosened up completely to unplug it. If you are going to unplug it to check anything mentioned above make sure the ignition switch is off and preferably the battery cable is unhooked to avoid any electrical problems.

As for the 452 code I would check the pump connector first. Another possibility is your filler neck or hose connectors on it may be deteriorated. Several on here have had that problem as well. But bear in mind this code refers to low voltage hence why I feel you should check the connections first. It is possible this is also related to the PCM as well albeit unlikely.

[okaussie]

Mine is a 2002. Is the PCM you speak of on top of the radiator overflow tank that is silver in color and looks like it has fins on the top with several long connectors on the back side facing the firewall???

I will also check the connectors to the fuel pump.

I was thinking last night, are these two codes related and if so how ?? Could the PCM connector be corroded and causing all this or could a bad connector on the Fuel pump assy cause all this.

It really seems electrical since this was not a slow progressing problem.

One day I had 20mpg's and the next it was 13mpg's. Just like someone had flipped a switch to instantaneously change my mileage. I have also noticed a decrease in performance and acceleration. I think due to this my fuel is running to rich, thus loss in mileage, performance and acceleration. I do not, however, notice any black smoke from the exhaust indicating a rich fuel mixture.

It would be nice to know what the driver 5 line 3 means in the error.

More news as it becomes available.

Film at 11

Bill

[okaussie]

I went out and removed the PCM. All the connections looked good but blew them out with air anyway. Reconnected it.

To make sure there were no codes I erased with the scanner.

Then started the truck up.

Scanned. This time it came up with no errors. Shut the truck off and restarted 3 more times. Each time rescanning to see if it would come up with errors. No failure on anything detected.

I will now drive it for a while and check the gas mileage with a fresh tank.

Could not find the connections for the fuel tank assy but did check the fill hose and the evap hose to the cap. Everything looks good.

More news when it becomes available

Film at 11

Bill

[roadrunner]

It is possible for the PCM and it's connections to be related to the codes for the evap code. It would be necessary to trace down on a wiring diagram for further verification and I only have the book for a 2001 so can't guarantee it would match your 2002. An example of this would be the PCM supplying power for the evap sensor having a failure either internally or through a bad wire connection somewhere in between the two. It is not likely the evap code caused the 1683 code though.

Driver 5 line 3 refers to an internal communication error in the PCM and if I read and interpret correctly is not something that can be repaired if it persists other than reprogramming or replacement (if reprogramming is unsuccessful) of the PCM. Primarily this is a data corruption problem just like a corrupted file on a home computer.

Bear in mind also your disconnect/removal of the PCM means it will have to "relearn" and settle in to normal operation so it may take a couple or three tanks of gas before it is normalized again.

[okaussie]

Hopefully, reseating the connectors on the PCM fixes the problems.

I have had alot of problems with my truck this year and don't want to have to spend more money on it right now.
So far I have had to replace the tranny, the cat, the swaybar bushings and links, shocks.

I now also have problems with the fan clutch, the HVAC controls and the Recirculating actuator on the A/C. Just to mention a few. All of this happening since March. Not to mention three fuel pumps in the last two years.

TIA

Bill

[F9K9]

...............Bear in mind also your disconnect/removal of the PCM means it will have to "relearn" and settle in to normal operation so it may take a couple or three tanks of gas before it is normalized again.

It may take 10 or more "driving cycles" to make the PCM aware of a problem and set off a SES or MIL. Chasing these codes are a just plain fun. What is really irritating is to have a code clear by itself, let you feel all warm and fuzzy and then, BAM, it's back!

[roadrunner]

[/quote]Chasing these codes are a just plain fun. What is really irritating is to have a code clear by itself, let you feel all warm and fuzzy and then, BAM, it's back![/quote]
Sounds like a mallard strafing run on your CC to me Reed. Just make sure ya keep em down there by you. I can get in enough trouble without waterfowl aid.

[okaussie]

During this particular problem, I never experienced the SES light coming on. The only thing I noticed is that my mileage dropped around 40 percent at once. Not gradual. That is what leads me to believe this is something electrical has failed.
Just put the first tank of fuel in it last night since I scanned it and reseated the connectors on the PCM.

Will Scan it on my next day off which is Friday. To see if it has learned anything.

Right now the truck still runs the same as before.

Bill

BTW Roadrunner, what part of Kansas are you from????

[roadrunner]

Oakley. Northwest corner. Much further West and you're in Colorado. Further North you're in Nebraska (which is where I was born and raised only a bit farther north and east). Find where I-70, highway 40, and highway 83 all cross and you are there. We await your results.

[okaussie]

Just curious.

Have family in Jennings and Logan.

I used to live in Olathe before being transferred to the OKC area.
TIA

Bill

[okaussie]

The SES light came on today.

Ran the scanner. The only error was the P0452 again. Also states that the same code is pending. The PCM error code referenced earlier did not show up.

Maybe reseating the PCM connectors fixed that problem and now I am left with this error code.

Now the fun begins trying to find the cable layout and location of this error.

Bill

[roadrunner]

I'd still start by checking the integrity of the electrical connectors at the tank sender unit. I know it's not very accessible or fun but I think this is likely where your problem lies with that pesky 452 code.