Hi guys,

Back in July I had posted regarding a similar issue -- my BLM's were very high (usually in the 145-160+ range) during any acceleration. At first I thought it was a crossed wire and the resulting misfire was causing my cells to read abnormally, but this wasn't the case. I made sure that none of the wires were arcing, or melting on the exhaust pipes -- everything was OK. I had purchased a set of AC Delco O2 sensors and put them in, just to see if that would help. I then tested each cylinder for spark -- all were firing normally.

I had a spare PCM which I swapped into the car, which had the same tune as my old PCM. I then retested the car, with similar results.

I am still in the 145-160 range for most of the drive -- the only time I seem to get anywhere near 128 is on deceleration or at idle. I noticed that upon acceleration my MAP readings go into the 60s-high 70s. This is also where my readings seem to go off the chart in the "lean" direction. I have read that this could be indicative of either a vacuum leak or that the car is not getting enough air into the engine. This seems odd because the engine doesn't exhibit signs of a vacuum leak at idle and I am using the Corvette "snorkel" style KN air intake filter system (for space concerns). You can see a picture of the setup here:

Air Filter Setup

Air Filter Front View

I'm sending out another plea for help in figuring out what I need to do to get this engine running properly -- almost every part is new. Here are links to the test run, which I made with DataMaster -- you have to right click and "save as" to download the .uni:

August 26th

Any light that could be shined would be a big help.

Thanks,

Tyler

 

When you open the throttle (accelerate), the MAP increases (MAP is conceptually the opposite of vacuum, which drops when you open the throttle).

Sort of a contradiction... if fuel is held constant, a vacuum leak let's extra air into the combustion process = lean, If fuel is held constant, not getting enough air into the engine = rich.

A leak in the bellows between the MAF sensor and the throttle body, or a loose bottom plate on the throttle body could account for a lean condition. It's likely that the leak will open up more as engine air demand increases. Is that the correct LT1 MAF sensor?

 

1. it's a new MAF for a 1995 Camaro z28.

2. The bellows are clamped onto the TB and the MAF and the Air filter nice and tight. The bellows are a year old and were new when purchased.

3. the bottom plate being loose: which component is that? I had put in a new gasket on the top of the TB (the gray plastic rectangle) and a gasket on the bottom component (the piece that is connected to the IAC). Is this the piece you are referring to?

4. I am using a Walboro 225 external fuel pump -- if my fuel pressure drops while under high load conditions (like fast acceleration, or any acceleration for that matter), wouldn't that create a lean condition as well? At idle, the BLMs read a normal 128. Perhaps the pump is causing the problem, even though it is relatively new?

5. Since my MAP readings go up to the 60s-high 70s upon acceleration, this would lean AWAY from a vacuum leak, correct?