Inefficient Fuel Consumption

(1992 W Series, 4x4)

I do very little driving in my truck... typically just back and forth to work to the tune of around six miles a day... so it's taken me a while to determine that yes, in fact, my gas mileage is terrible.

At first, I thought perhaps it was all the treatment my other half had decided to pour down the tank--not only did it get filled with Premium, but he took it upon himself to add octane boost AND fuel injector cleaner to the mix. And at only 120 miles to the tank I said, "Damn, I hope it was just all that crap he put in there and that'll be the end of that."

But no. I just refilled the tank, and with a grand total of 15 miles on it, it's already used far too much fuel.

The vehicle smells as if it's burning rich. It used to have terrible idle problems, and after replacing fuel filter, plugs, wires, rotor button, cap, PCV, TPS, and cleaning the AIC (and the self-contaned EGR module as best as possible), it was determined that someone somewhere had fuxxed with the timing and once set properly, my idle problems are under control.

Vehicle still idles slightly roughly, and occassionally lags when I hit the gas, instead of taking off the way it should.

Any suggestions would be highly appreciated, as I do not like paying 45 bucks a tank for only 120 miles of moving.

Your CPI is more than likely leaking and dumping fuel. This can be confirmed by pulling the upper plenum and looking for washing. (Where one side is cleaner than the other) If the passenger side is washed, the CPI is bad, if the driver's side is washed, it's your nut kit. If you do replace your CPI, replace the nut kit as a matter of course.

It is not the CPI or nut kit. The kit was replaced 2 years ago according to the former owner, and during the course of searching for my idling problem six weeks ago, the plenum was pulled and it was plenty dirty all around, just like it is supposed to be.

I'm averaging what appears to be only 5-7 miles a gallon at this point. :eek7:

Just because it was replaced 2 years ago doesn't mean they can't go bad...(a lot of people go through 2 or 3 before getting one that last more than 6 mos). That said... Check your fuel pressure and bleed down rate with a pressure tester at the shrader valve on the back of the plenum. Might give you a lead there.. In order to to have to refill your tank with only 15 miles on it you're dumping fuel somewhere... That means the following

CPI/Nut kit is bad (check pressure)
Fuel pump is bad (check pressure)
You have a tank leak (stay away from matched)
You have a line leak


Have you checked your oil for gas?

No, I haven't checked my oil for gas, but, I just had the oil changed two different times in two months (because the first one was a bad change) and everything was kosher... and the truck has never been right.

One of the crappy mechanics I took the truck to mentioned that there appeared to be a problem with my fuel pressure. I didn't think that a fuel pump could cause excessive fuel burn though?

No, I haven't checked my oil for gas, but, I just had the oil changed two different times in two months (because the first one was a bad change) and everything was kosher... and the truck has never been right.

One of the crappy mechanics I took the truck to mentioned that there appeared to be a problem with my fuel pressure. I didn't think that a fuel pump could cause excessive fuel burn though?

With short trips like that, your engine is never really warming up at all.

You probably have some carbon build up and you will be in need of a tuneup soon.

I had a tuneup not 200 miles ago. Plugs, wires, rotor button, dist. cap, fuel filter, air filter, the works.

Just because my truck doesn't warm up fully doesn't mean that i should be getting 5 mpg. That's ridiculous. >.>

I had a tuneup not 200 miles ago. Plugs, wires, rotor button, dist. cap, fuel filter, air filter, the works.

Just because my truck doesn't warm up fully doesn't mean that i should be getting 5 mpg. That's ridiculous. >.>

Did you ever check the fuel pressure or for gas in your oil?

I don't have gas in my oil, I did check.

I haven't been able to have the fuel pressure checked since I don't have the tool to do it. As I said, though, one of the mechanics it's been to pointed out that it seemed to be giving off some low pressure readings... although I'm not sure how LOW pressure would result in all the problems I'm having. <.<

I don't have gas in my oil, I did check.

I haven't been able to have the fuel pressure checked since I don't have the tool to do it. As I said, though, one of the mechanics it's been to pointed out that it seemed to be giving off some low pressure readings... although I'm not sure how LOW pressure would result in all the problems I'm having. <.<

If your pressure is low you're more than likely dumping fuel (hence running too rich) and causing your bad miledge.

I had a tuneup not 200 miles ago. Plugs, wires, rotor button, dist. cap, fuel filter, air filter, the works.

Just because my truck doesn't warm up fully doesn't mean that i should be getting 5 mpg. That's ridiculous. >.>

Yes it will mean your fuel economy wil be horrible.

You will be barely getting into closed loop.

You will be in rich open loop mode until the engine warms up.

Pardon my ignorance, as well as my diversion from my dilemma, but would you care to explain to me exactly what it means to 'dump fuel'? Curious minds want to know.

Pardon my ignorance, as well as my diversion from my dilemma, but would you care to explain to me exactly what it means to 'dump fuel'? Curious minds want to know.


Too much fuel entering the combustion chamber.

Ok, now I'm going to look like a fool.

There is gas in my oil.

I swear I checked it last time, and I did not detect gas in it.. perhaps it was because it had been sitting for a day or so. But I checked it today and it has an obvious odor of gasoline.

Needless to say, the vehicle has been parked and will not be moved from the spot... I don't want everything fouled more than it likely is already.

So what is the likliest culprit then, if the gas is getting into the oil? I'm assuming something complex and highly expensive, since that tends to be my run of luck lately. >.>

Low fuel pressure & fuel in the oil?

Dollars to donuts, it is going to be what was stated before. CPI injector/Fuel Regulator/Nut kit. If you still have the work you have had in the past under warranty, take it back to that butcher until he/she gets it right. Only sure way to check if the problem is inside the plenum without taking it apart is to go and rent a fuel pressure gague and hook it up, take a few readings. Your culprit in all probability is going to be in your fuel injection system. I am curious however, are you seeing black puffs of smoke out of the exhaust at startup? Does the truck smell rich, loping/stumbling idle and or diesels when you take the key out of the ignition too?

The truck smells like it's running rich. No smoking that I can see, but it's hard to see from teh driver's seat. >.> It doesn't idle perfectly, but since the timing was fixed it's much better. Sometimes it hesitates a bit at acceleration, and it feels like I'm not getting the power I should.

Can't tell you how thrilled I am that it's going to be fairly expensive to fix..

Ever done a tuneup?

I had a tuneup not 200 miles ago. Plugs, wires, rotor button, dist. cap, fuel filter, air filter, the works.


>_>

<_<

Get the timing rest with the timing wire disconnected from the PCM under the dash.

Also, do you have the vortec nameplate on top of your motor?

Yes, I have the lovely Vortec engine. It's going into the mechanic right now for official confirmation that the CPI and/or nut kit needs replaced.

Bleh. -.-