Mileage

[Fish&Fowl]

Here's the deal. I have a '96 Chevy half ton with the 305 Vortec. I have been averaging 17-18 hwy. and 14 city since I've had it, and I lose a mile or 2 mpg in the winter.

Within the last 250 miles, I got just under 10 hwy, then 11.5, then about 9 again. I have never gotten anywhere near this bad of mileage with it in the 2 years I've had it. I don't know if I can chalk it up to some bad gas or what Anyways I can't afford to be driving this thing getting that kinda mileage. Anybody had this happen or got any suggestions?

[DTro]

It could be a number of things.

I know one of the big culprits are bad Catalytic Converters.

We had the MPG go south on one of our cars and it turned out to be a bad injector. It was dumping raw fuel into the exhaust

Others here are more qualified than myself to answer but just tossing that out.

Are there any drivability issues?

[Fish&Fowl]

That's the problem. The truck runs fine and has had all new plugs and wires, a fuel pump, a fuel filter, one new injector all since I've owned it. These are also the first replacements on the truck, and with 140some thousand on it all that stuff is to be expected.

Could you smell gas or see where it had been dripping with the converter??

The only other catch is for all of the 250 miles, I have been pulling my trailer with a sled and portable on it. I have been driving it in 3rd to keep it from downshifting all the time, but only went 60. I pull everything using 3rd for the most part and have never seen anything that bad for mileage. Thanks for the suggestion though I will look into it, along with anything else I can possibly look at.

[LwnmwnMan2]

Quote:

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That's the problem. The truck runs fine and has had all new plugs and wires, a fuel pump, a fuel filter, one new injector all since I've owned it. These are also the first replacements on the truck, and with 140some thousand on it all that stuff is to be expected.

Could you smell gas or see where it had been dripping with the converter??

The only other catch is for all of the 250 miles, I have been pulling my trailer with a sled and portable on it. I have been driving it in 3rd to keep it from downshifting all the time, but only went 60. I pull everything using 3rd for the most part and have never seen anything that bad for mileage. Thanks for the suggestion though I will look into it, along with anything else I can possibly look at.

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Get back to us when you drive it like you normally do.

At least it gives an idea against what probably 90% of your "normal" driving is like.

At least you eliminate the pulling the trailer part.

[Finns]

Might also take in to consideration the time it sets idling. My mileage goes down in winter because of the time I let it warm up.

Finns.

[Fish&Fowl]

That's the plan for tomorrow. Take a road trip after trout fishing with NO trailer and see what happens.

Finns,

I have filled up when the truck is warm and drove it strictly on the highway non-stop for each mileage check, that is why I can't believe how bad it is.

Thanks for the replies, I'll get back at ya tomorrow after fishing.

[jltimm]

I thought I heard somewhere that the PCV valve could be the cause to this problem? Airjer where are you?

[Capt. Don*]

Your change in fuel economy is directly related to your change in driving habits. Driving in 3rd gear even at 60 mph is going to make a noticable difference, you are not in overdrive, the torque converter will not lock, throttle position will be higher causing fuel injector pulse width to stay on longer and rpm will be higher. Your truck has the lateset generation of on board monitoring systems,if it had a true driveability problem and fuel was dumping and causing it to run too rich, especially making a noticeable change in mileage you would have a check engine light on, power loss and at the very least idle concerns if not stalling at idle. I don't feel you have any component related problems. I don't know that you are doing yourself any favors driving in 3rd gear. Modern overdrive transmissions are capable of pulling a trailer in overdrive provided your trailer isn't a 53' semi trailer. It doesn't sound like you've got anything overloaded, I'd try pulling it in overdrive and compare your results.

[gunflint]

Bingo!

[Jeremy airjer W]

Bingo for the most part capt. don!!

[Fish&Fowl]

When I pull in OD it downshifts every minute up to the the rpm I'm running when it's in 3rd. I realize driving the 3rd drinks a little more gas, but it has never been that much of a difference before. I'm guessing that's what it has to be...there is no other problem with the truck that I can tell. Thanks for the replies.

[PierBridge]

Sounds like a leaky injector.....you have lost 40-50 percent of your hwy mileage I don't think all of that can be attributed to the trailer and 3RD gear towing. Just because you don't have code set doesn't mean you don't have a problem somewhere.

[Fish&Fowl]

Well the service engine light finally came on. It was the EGR vaccum that needs replacing. I knew something had to be wrong to lose that much mileage, not just driving in 3rd. It has never been that bad before and it shouldn't just change like that.

Also pulling in OD is not recommended with any transmission if it's downshifting all the time.

[Jeremy airjer W]

Quote:

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Well the service engine light finally came on. It was the EGR vaccum that needs replacing.

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The What? The EGR system has two functions. One is to reduce combustion temperatures which helps reduce "ping" under heavy acceleration and two, helps reduce NOX. If the EGR is not working it is not going to affect fuel economy. The egr is commanded on under acceleration, at idle or cruise it will rarely be on. If the EGR is stuck open you would imediately notice a ruff idle and possible a stiff brake pedal. (we see this all the time with the 4.3 liters)

Are you sure it wasn't something else? Fuel pressure regulator? MAF (mass air flow)?

[Fish&Fowl]

Now that is the question. Almost everything I've read up on now has said that an EGR would also mean some rough idling/stalling. Hooking it up to the computer said it was the EGR, but something still isn't adding up. Mileage did go up to near 15 last time I checked it too (not pulling a trailer.)

I got a buddy going to Eveleth for auto tech. and he has been looking into this for me and talking to his teachers. I will mention the FPR and MAF to him as well and see what he says. Thanks alot. I will let ya know the verdict.

[Jeremy airjer W]

Do you remember what the code was?

The "scan tool" is nothing more than a tool. It is not a magic box that tells you everything that is wrong with your vehicle. It is also not sophisticated enough to pinpoint a problem nor is it sophisticated enough (yet) to tell the difference between a mechanical problem, fuel problem, or spark problem. It can however tell you that a cylinder is not firing!

We get fords in all the time (I realize we are talking Chevy’s, but this is a good example) with codes for insufficient EGR flow. Many do it yourselfers would interpret this as a bad EGR valve which is rarely if ever the case. Quite a few times it is the DPFE sensor (the sensor that monitors EGR flow codes). Sometimes it is carboned up EGR ports behind the throttle body (very common in crown vics, marquis, town cars and contours. rarely but sometimes there is an issue with the vacuum supply to the EGR valve.

The scan tool says one thing but three different but quick tests need to be done to see exactly what is going on. The first is to see what the voltage is for the DPFE sensor using the scan tool. Should be under a volt KOEO. If it’s any higher, which it usually is, then I unplug it and check the scan tool. If it reads 5 volts than I can be reasonably confident that the ECM is working and the sensor has failed. If I see the correct value for the DPFE then I start the car and apply vacuum to the EGR valve if the engine stalls than I know the EGR is working and the ports are open and the problem is with the vacuum supply to the EGR. If it doesn't stall than I make sure the valve is actually moving and then remove the throttle body to confirm that carbon has blocked the erg ports preventing any flow.