Flowmaster+injector cleaner=bad mileage!

After the BG injector cleaner I got a check engine light, reset the computer, light stays off. Still mileage is down to 190 per tank. Was about 230 to 250. I'm thinking o2 sensors. Will the computer store a code, even if I have no check engine light? I have a 99' and last time I checked the o2's were pretty expensive and I have 2 of them. Dont want to replace if not necesarry. 99' XJ 126K. Thanks

If you reset the ECU, you most likely lost your code. If the CE light comes on again have the codes read.

I can think of two reasons why your mileage is down.
1. Converter might be pluged from the cleaning you did.
2. The ECU has to relearn the correct fuel ratio and that may take a few hundered miles.
3. The cleaner ruined the O2 sensor and is only running in open loop.

You know its very intresting you bring this up i have the same exact issue. LAst week before my smog test i ran a can of bg44k cleaner and now i am gettign a check engine light with horrble mileage. THe code i am getting is 51 which means i am running lean.

LEt us know what code you get.

pete

tompatjr said:

3. The cleaner ruined the O2 sensor and is only running in open loop.

Click to expand...

Thanks for the help guys. I'm thinking #3, at almost 130K, I'm sure it wouldn't hurt to replace my o2's anyway. Hasnt thrown any more codes yet, but mileage is still down. I'll post another responce when I have the o2's replaced and let you know.

I'm in a similar situation.. I'm getting ready to switch over to a non-oil filter.. I know my cat is pretty screwed up right now and one of my O2 is throwing a code..

I'm not entirely blaming the oil from the K&N... but after I thought about it, I don't like the idea of oil getting into the intake system.. Even though it is suppose to be ok, I can imagine that oil from the filter still gets sucked up.

Also, your O2 sensor still could be bad without throwing a code. If it's not reading right, the ECU will adjust the air/fuel ratio.

Elias

Update. Well, my mileage is coming back this last tank. 16.5 mpg! 75% highway, and about 50 miles in 4 high. Not too bad for 31's and 3.55 gears, driving mountains. I think the injector cleaner did have something to do with the last three tanks of horrible mileage. I'm hoping the flowmaster will bump up the mileage a bit.