I have a 92 Eddie Bauer Aero with a 4.0L Engine and Digital Dash but my average fuel economy is 11.6 MPG which to me is really poor because I have the car in good shape and engine runs smoothly.
I read in another post of someone disconnecting the MAF and getting great gas mileage.
I tried that, disconnected sensor, My check engine display lights on at digital dash, but the MPG went up from 11.6 MPG to 15.4 on the Average Economy Display.
Power was increased significantly, but at stoplights engine dies and I have to restart. As long as I'm moving the beast engine runs great.

It shouldn't make sense, if I reconnect MAF, Information display reads NORMAL mode and power goes down significantly.

Is my MAF defective?
Or is the ECM compensating for something else?
Appreciate the advise.

 

even 15 mpg on the PCM controlled LIE-O-Meter MPG gauge? is poor mpg for the 4.0L on the highway. mine gets 22 mph calculated by the human brain and real math on the freeway driven at 60 mph.

the PCM with the MAF disconnected goes into a default limp home mode with no adaptive air/fuel control only default factory limp home tables. the PCM has no way of knowing changing air intake mass with the MAF disconnected.

what PCM codes do you get after driving with the MAF connected and then with the MAF disconnected? clear codes before each test and drive for 20 miles each test. most auto parts stores will read the codes for free, call ahead

only guesses at this time but the normal suspects are a failed MAF, failed O2 sensor, failed ECT or failed TC lockup/ OD failure(controlled by PCM). may be engine mechanical problems also.

codes are the place to start.

 

inaccurate MAF reading... yep, I agree, it happens. try another MAF, ore clean your MAF....

 

Engine computer relies on certain critical sensor values to optimize efficiency. If a reading is missing or too far outside parameters, the computer uses a default setting instead. This sounds like what is happening in your situation. As mentioned above, you need to find out if your other critical sensors (MAF, oxygen, ECT and AIT) are working properly.

Such poor fuel economy indicates a rich fuel mixture and a lot of fuel being "dumped" into the catalytic exhaust system. This tends to continually overheat the catalysts. If not corrected it can lead to damage and a plugged exhaust system.

 

So if I take it to Autozone will they be able to diagnose a bad O2 sensor?
I just don't want to make the investment unless their device is capable of detecting it.

Thanks again for the advise!

 

just have AutoZombies read the codes. they'll try to sell you parts, not mechanics, just parts pushing clowns on commission.

post the codes here and we'll help you.

search this forum for MAF cleaning. a good starting point.

 

I've been checking my mileage on my 92 3.0 lately when I fill up and I'm surprised to see that I am still getting 20-22 MPG; considering the van has 135k.

 

Not necessarily. If it is bad enough to set a code, then yes, they will be able to diagnose it. But autozone does not use scanners capable of monitoring fuel trim. Without that, it is impossible to diagnose outside codes. O2 sensors are maintenance items to be replaced at 60K - 80k intervals. So don't worry about replacing them. O2 sensors are supposed to be replaced before they fail.

 

Yeah, that's what I thought, Autozone wouldn't be able to do it.
Thanks to all for the advise.
Will take it to a specialized mechanic that used to work on Aeros and he may be able to help me with the info you people gave me.

My EB 4.0L Van has the green LED factory digital Dash and integrated trip computer for 92 year.

Does it have and emissions indicator?
Where would it be?
I've been trying to find it to see if someone tampered with it, but so far I've come out blank.

 

I had a "lazy" O2 sensor that did not trip a code but let the engine run rich.......had to use a oxi acetylene toech to get it out!

 

I'm thinking the o2 sensor is out of spec. Maf sensor is also possible but symptoms of rich mixture does not sound likely. Tie off the o2 sensor wire & see what the MPG goes to then. The engine will run on theoretical tables values, & should run pretty well even without the o2 sensor, however as mentioned above the engine will not be able to run in closed loop mode & the CEL should come on.

 

My wife was driving our '93 through a different town about a week ago. The check engine light came on and she telephoned me. I said to take it to AZ and have them read the codes. This store could not read an OBD1 system and tried to sell her some fuel injector cleaner and a new O2 sensor. I told her to keep driving. I can guess as well as they can. (Will hook up my code reader to it tomorrow)