Hi 'Space - I did a complete tune up (plugs/wires/pcv/air filter/fuel filter) the first week of last May. All parts are AC Delco with the exception of the wires which are Belden Premium. At that time I also cleaned the MAF and IAT sensors and inspected all sensor connections. I cleaned all of them with CRC Electronics Cleaner. The car also got an oil (Valvoline Synthetic) and filter (K&N) change that same week. It's been running great since then. The mpg dropping off started after I installed the CAI, but the rich condition wasn't apparent until the last couple of days. That's why I really don't think the CAI is the culprit, but I will put the stock air box back on to eliminate that possibilty.

 

Hi `Mike, thanks for your detailed reply. Cooler weather & winter gas will affect MPG's, but your CAI could cause a richer mixture with the change...& being richer could cause it to block/clog the PCV ? ? ? Maybe ? Hope you check your PCV to make sure...Just a suggestion...I'm not a GM Tech 4-Sure & I hope one of our expert tech's reads your thread & replies with some suggestions...Good Luck & keep us updated on your resolve/solution to your problem...

 

Go ahead and do a tune up, change plugs, wires, fuel filter, PCV, etc

And keep your heavy foot off the gas. I know the intake sounds cool, but a heavy foot will kill your gas mileage...

 

Reading > You

 

I haven't read any part of the thread, other than the brief description when you scroll over it before you click it

ha

What the hell is reading anyway?

 

Well at this point I'm leaning heavily towards the possibilty of having a problem with the injectors(s). I put the stock air box back on this morning and after letting the car sit it still runs rich when I fire it up. No difference in performance either...still bogging. Another thing that makes me suspect the injectors is when I checked my fluids I noticed my oil has a gas smell...not good. Now I need to determine if I have an injector that the pintle is hung open on or if the PCM is dumping fuel in the other cylinders to compensate for a lean cylinder caused by an injector with flow restriction. The weird part is I'm not getting any codes. I'm going to give my friend a call on Monday and see when I can take it in to his shop for further diagnostics.

 

If you have a good enough scan tool at your disposal, you might be able to check the injector pulse width.... My Grand Am a couple years ago had an issue where it was running like crap (intermittently) and when it ran like crap (stumbling and such) it was running rich. I found the injector pulse width was WAY high when it ran like crap.
Long story short, I had a failing coil pack. I found it purely by accident. Since, I found this write up from the Bonneville guys:
View topic - Comprehensive guide for troubleshooting Ignition coils : PontiacBonnevilleClub.com

Might be worth reading over and checking to ensure you don't have a messed up coil (doubtful since you are running rich, not having a performance issue, but could be worth a quick check).

If you are smelling gas in the oil, I'd pop the plugs off, inspect them. Something tells me one may smell of gas and look different from the others. If that is the case, you now know which cylinder and if it is an injector messed up, you know which cylinder to mess with injectors.

 

I'm doing all of this between rain showers and with this cold I have I'm not feeling too well right now. I don't feel like pulling the plugs at this point in time. Maybe tomorrow but it looks like more rain heading my way. Right now I just want to get the chill off my bones and try to get rid of this pounding headache I have. I'll definitely mention the coil packs to my friend though and have him check 'em out the same time he looks at the injectors - thanks for the tip!

 

I had a few minutes yesterday between rain showers so I grabbed my mulimeter and tested my coils. I talked to my friend this morning and told him my readings. He said that one of the coils is way out of spec (1.3 ohms primary resistance) and another is 'boarderline' (0.8 ohms). He said they should all have a primary resitance between 0.3 and 0.7 ohms and suggested that I replace those two coils. I only pulled the front three plugs, but #3 smelled like gas and was beginning to show signs of soot. That cylinder is fired by the coil pack that has the 1.3 ohm resistance. So, I just ordered three new coils (AC Delco) and hope it cures the problem. It was only a couple of bucks more to order a 'three pack' than to purchase two seperate coils so I figured what the heck...may as well replace them all. Thanks again Jason for the tip about the coils.

 

Well the new coils have been installed. The car didn't smell rich when I started it, it seems to be idling smoother and it accelerates now with no more bog. The big test will come when I calculate mileage after burning through a tank of fuel, but so far all indications are positive.