I just have gotten my PCM back from PCM's for less and now it seems like the mileage has dropped tremendously. What are some of the things to look that could make the mileage drop from my previous tune. Jeff at Carolina Auto Masters did the tune the first time and I know it was running rich but it seemed to get better mileage than it does now. Are there any sensors that can affect the tune? Coolant Temp Sensor? Or anything else? Just trying to get an idea of what could have happened.

 

The A/F ratio for "normal" running (part load/part throttel; not WOT) is hard-coded into the PCM, and there is no reason for a tuner to alter it. Things that could affect part-load fuel economy would be any changes to the spark advance tables, changes to the cold-start enrichment, etc. If the transition to power enrichment (PE) mode and its richer A/F ratios is done at a lower RPM or throtte position percent, it would cause the engine to operate at a richer A/F ratio a large part of the time.

A faulty coolant temp sensor, a faulty O2 sensor, false "leans" caused by misfires and exhaust leaks before the O2 sensors could affect fuel economy. A faulty MAP sensor would give the PCM incorrect data regarding engine load.

Quantify "tremendously"..... what was your miles/gallon before the tune and what is it now?

PS: Might also want to add a "signature" with basic info about your car - year, model, trans type and any major mods.

 

As far a a signature, you I'm afarid guys couldn't really help me much by giving me a base seeing as my LT1 is in a Jeep wrangler. There really isn't any comparison to a Camaro or Firebird. It's kinda like a brick to a bullet if you know what I mean. ANyway, before my tune, I could drive the 120 mile round trip to my friends on about a quarter of a tank. Now it was more like a half to three quarters. Not a good thing. I know the motor has a bunch of miles (150000) but still this was a couple weeks ago that I went down there, (old tune). Then I went the other night and BAM! had to stop for fuel twice. My wallet hurts! Anyway I was just looking for some suggestions and maybe some places to start looking as far as parts that could be worn out. Thanks

 

You still need a "signature", so people know you're not talking about a vehicle that isn't a 4th Gen or an F-Body. Is really shouldn't take that much effort to do it. It's up to you.

 

Fuel economy can be screwed up in tuning via spark tables. Playing with spark affects how much fuel the engine needs to register the right reading on the O2s.