| DTC 44 and wildly split BLMs at idle |
Subject: DTC 44 and wildly split BLMs at idle by screamin_conure on 2014/6/7 17:44:58 Here's a fun one for you Gurus... A couple days ago, I picked the Vette ('92 coupe with 75k miles) up from the mechanic where it received a new brake master cylinder. Drove it home with my wife following behind in her car. I pulled in the driveway and while waiting for my wife to park her car and jump in the Vette, my SES light comes on. I decide to check it when we get back from dinner. After driving away, the SES light goes out about half way to the restaurant. When we got home, I pulled out the scan tool and found a DTC 44 - Left O2 sensor lean. I started the engine to check out the live data on the scan tool and found my BLMs wildly split at idle. I had 160 on the left and 108 on the right. I believe both of those figures are the max of the available range. The car has NEVER idled smoothly in the five years we've owned it, but when we were driving to the restaurant my wife commented that the car felt like it was "chugging" a bit more than usual while idling. Like I said, it has always had a rough idle with a very slight miss here and there. Yesterday, I went out with the scan tool again and started the car cold. Once the system went into closed loop, BLMs at idle were showing rich on both sides, around 110-115. When I applied a little throttle, everything smooths out and BLMs hover around 124-132; about normal. Left and right integrators were right on at 128 +/- a couple of digits. Take your foot off the accelerator and BLMs dropped back to 108 - 110 on both sides and the idle gets rough. I let the car sit there and idle, feeding a little bit of throttle every so often until the coolant temp got up to normal range. Now get this: once the coolant temp hit about 200 degrees, I actually watched the BLMs start to split at idle, the left slowing climbing until it hit 160, and the right slowly dropping until it hit 108. How in the world does the system go from being so rich to being so lean? I'm guessing the crappy idle is due to the system being so unbalanced in its fueling at idle, and I'm also guessing the imbalance is somehow related to changes in engine vacuum. The car accelerates strong with zero hesitation and runs smooth when driving. I even gets decent gas mileage. It's running a 52mm aftermarket throttle body, a K&N filter, Racetronix OE equivalent aftermarket injectors, Magnaflow high-flow cats and a Corsa cat-back system. Otherwise, its all stock. Plugs and wires are about three seasons old. O2 sensors are Denso units and are also about three seasons old. I still need to check fuel pressure and put a vacuum gauge on it to see what's going on in those areas. What is it with LT1s that causes this crazy split BLM? I've done a Google search on that and there are TONS of threads about it, but nobody really seems to have discovered the root cause of it. A lot of the cases are guys who've installed aftermarket cams and such, but that's not the case here. Ron |
