LT1 Rich/Lean

[brandoncooper]

I have a 383 LT1 with a Comp Cams 306 grind cam, ported heads intake. It is 11:1 with 30# injectors and 50psi of fuel pressure. I have a questionable situation happening maybe someone has some input on it. I am seeing BLM's of 108 (extremely rich) below 3000 rpm, my exhaust temp. gauge reads between 1200-1400f with normal driving under these conditions. The car seems to run good and has good throttle response. Also the chrome headers are starting to turn blue from the heat. The PCM is telling me I am rich, but from the exhaust temperature and the header color I am concerned that I may be running lean. Any help would be appreciated.

Thanks,

Brandon
brandonacooper@alltel.net

[Injuneer]

A BLM of 108 does not necessarily mean the engine is running "rich".... it means IF the long term fuel corrections were not pulling fuel by reducing the BLM's below 128, it would be running rich. If the BLM's were anything below 128, other than 108, it should be running exactly right.

The problem you are running into is that 108 is the minimum fuel flow reduction it can achieve, and apparently, to the O2's, it is still running rich. There are several possibilities:

"true" rich....

-who did your tuning? Did you tell them the injector size and the elevated fuel pressure?

-leaking fuel pressure regulator

-saturated EEC canister

-EGR stuck open

-MAP sensor incorrect, or fuel maps not corrected to elevated MAP readings of a high overlap cam.

-TPS sensor faulty.

-MAF sensor miscalibrated and over-reporting air mass flow.

"false" rich"....

-Leaking injectors

-poor O2 sensor wiring, extensions, wires too close to plug wires.

Fairly normal for "chrome" headers to turn blue. That's why most people chose cerametallic coatings, which add to engine performance, and reduce underhood temps, rather than chrome, which does just the opposite.

EGT's are only a valid measure if you have tracked them as you tuned the engine with a wideband sensor, and can correlate A/F ratio directly to the EGT readings.

[RangerBob]

Injuneer: You just amaze me!