Sudden loss of gas mileage.

[rcengco]

I bought a 1999 Ford xplorer last September. Getting great ga mileage 21-22 mpg. In December I decided to have all the fluids changed. Oil and oil filter, fuel filter, air cleaner and trans flush no filter replacement.

As soon as I drove aaway my mileage dropped to 17 mpg. I was driving 80 miles highway to work every day with a 4 mile and 1 mile city trave at each end. After 3000 miles of this since the JIffy Lube service my mileage is still down at 17 if I'm luck. Someone said the PCM needed to reset itself. Wouldn't it have reset since then. Just recently chnage the trans filter and fluid thinking there may be something there but no change.

Then I heard that the PCM may NOT reset itself......what's the reason for not reseting?????

The only performance difference I notice is that I used to be able to start up with no gas pedal input just fine. Now if I don't use the gas pedal, the truck almost stalls/stumbles then catches.

Any Ideas????? This is driving me nuts !!! Please remember the change was instantaneous after the Juffy Lube service.

TIA

 

[BrooklynBay]

Welcome to this forum! I've moved your thread into the fuel economy section. Check your vacuum lines to see if something got disconnected.

 

[2000StreetRod]

Oily air filter?

If you got one of those cheap oily air filters then your MAF sensor might be contaminated. You might try cleaning the MAF sensor with MAF sensor cleaner.

I usually add a bottle of fuel injector cleaner to the tank after changing the fuel filter.

The PCM adjusts your fuel trims based on data from the O2 sensors. It happens continuously while the engine is running. No "reset" is needed for the things that were done.

Are any diagnostic trouble codes set?

 

[rcengco]

No codes before or after the Jiffy Lube. SOmeone said that if they disconnected battery the PCM would haveto re-learn my driving habits....True/False???? How is this accomplished and how long should it take? Any chances/circumstances where it wouldn't "reset" ?

I have a bottle of injection cleaner that I'm about to use on the next tankfull.

Thanks for the reply

 

[2000StreetRod]

Default after battery disconnect

If the battery is disconnected for more than 5 minutes the values stored in keep alive memory (KAM) are lost. When battery voltage is restored the PCM utilizes default values until new ones are determined. Most of the "relearning" is associated with fuel trims and transmission shift points. New fuel trims are determined very quickly. Transmission shift points may take a few driving cycles.

 

[rcengco]

Performance Chip Option???

Its been over 3-5k miles since the Jiffy Lube incident so I assume this meets the "few driving cycles" Does this mean it won't be any better than it is now?

DO you know anything about performance chips ..... '99, 4.0L, 4x4 Eddie Bauer

SLR has chip for $69...... 50 hp increase, 3-6 mpg gas savings


not interested in the hp but the mileage increase looks good....

any thoughts/inputs?

 

[jonlax]

Its been over 3-5k miles since the Jiffy Lube incident so I assume this meets the "few driving cycles" Does this mean it won't be any better than it is now?

DO you know anything about performance chips ..... '99, 4.0L, 4x4 Eddie Bauer

SLR has chip for $69...... 50 hp increase, 3-6 mpg gas savings


not interested in the hp but the mileage increase looks good....

any thoughts/inputs?

What ever you do, DO NOT buy that. They are cheap resistors that yeld no gains in MPG or performance. They can acutally hurt your truck.

50 HP on an explorer would have to come from forced induction or higher compression.

Jon

 

[BrooklynBay]

Contact James from Henson Performance. He's a vendor on this site, and custom tunes are his specialty.

 

[2000StreetRod]

clean MAF sensor?

Did you ever try cleaning your MAF sensor? A MAF sensor contaminated by oil is not detected by the PCM so no associated codes will be set. Use MAF sensor cleaner as directed on the spray can.

What weight engine oil were you using before getting it changed? If you were using synthetic and it was replaced with a heavy weight non-synthetic then the increased friction could account for some of your fuel economy loss.

Was the old air filter a low restriction unit? Was it replaced with a high restriction unit? That could adversely affect fuel economy. I believe an Amsoil drop in filter is the best choice for superior filtering and air flow.