Guys I am having a problem. 97 XLT 102,000 miles. Truck starts up, runs great, small shudder at warm idle but it has always done that. Recently I have had the plugs changed OEM, fuel filter, fuel induction service done and fuel injector service done. Since the plugs have been changed and the fuel induction service done, my gas milage has gone from 14mpg to 9mpg. I am not a mechanic so have no idea. I have no check engine lights on. Would the truck throw a code even if there was no cel on? Could it be my o2 sensors? I do notice a pollution smell when I start it up in the cold a.m. here in Buffalo. Wouldn't bad o2 throw the cel on. I did learn to clean the MAF and have done that and put a bottle of Lucas tune up in a bottle in the gas tank to no avail. Sorry for the long post and I appreciate any advice

 

PCM can set a pending code without turning on cel. Be careful about cleaning maf. It is much like a lightbulb filament and can be stretched or damaged with improper cleaning. When diagnosing fuel economy issues, I first like to look at o2 values in the datastream and status of long term fuel trim. If LTFT is much above zero, it means the PCM is adding extra fuel to the mix and step 2 would be finding out why!

 

this may sound a little corny but the typical dirty air filter can cause bad gas milage. check her out!

 

Thanks guys. Kingkoz, funny you mention the air filter, I went out and replaced it today. Hope that is the issue. I will keep you aLL informed