My ck engine light came on and Autozone pulled this code PO441. A search revealed more questions than answers. I hear talk of INT and BLM #'s, what do these mean? I have no carbon puddles under the car, and there is usually a lot of pressure in the gas tank when I refuel. The car seems to run fine. If anyone can give any insight here I would greatly appreciate it, I have a dyno session this weekend and I want the car running right.

 

ttt Anyone, please don't be shy... :seeya


[Modified by C4DC, 9:29 PM 3/19/2003]

 

OK, here goes.....
PO441 means no EVAP system flow during purge. The EVAP system is the one that traps fuel vapors in a charcoal canister. When the conditions are right the computer opens a solenoid and vacuum takes those vapors and burns them. In between the vacuum solenoid and the canister there is a vacuum sensing switch. The computer looks at this switch during purging to verify that there is vacuum present. If no vacuum is seen at that switch (during purging) two trips in a row your Service Engine Soon light comes on and code PO441 sets.

Here's a couple of things to check:
1. Make sure the vacuum lines to the purge solenoid, the vacuum switch, and to the charcoal canister from the intake are hooked up, not split, plugged, etc.
2. Make sure the wires are hooked up to the switch. The picture I have shows the switch to be on the passenger side of the engine, next to the throttle body. It should have two wires going to it- a light blue one and a black one.
3. If you have an ohmmeter and a vacuum pump you can test the switch. It should have very low resistance with no vacuum applied and infinite resistance (no continuity) with vacuum applied. Apply vacuum to one side and plug the other. It is probably OK with no vacuum applied or it would have set a different code.

Outside of this, it's hard to diagnose this stuff over the internet. If all of this checks out you may need to find someone with a scan tool to help check it out further. As a last resort, if you'll hold your monitor up to the hood of the car, I can try to faith heal it. The good news is it shouldn't hurt your dyno run at all because there is no EVAP purge during wide open throttle operation.

Your other question involving BLM (block learn memory) and INT (integrator) is a fuel trim matter. When your engine runs rich or lean according to the O2 sensors the engine must modify it's fuel delivery programming. It does this through BLM and INT. If only small corrections are needed for short periods of time INT moves to add or take away fuel to correct this. If INT has to move a great deal or stays moved away from center for a long period of time BLM moves to correct the delivery. Ideally these two don't vary more than 10% from the factory setting of 128. If the engine is running rich the numbers will drop (taking away fuel) and if it is running lean the numbers will be above 128 (adding fuel). Integrator jumps around with the O2 sensor so it's hard to use as a diagnostic tool. BLM, however, tracks long term conditions so it's a very valuable diagnostic tool. There are 16 blocks in the ECM's memory based on RPM and Load, and each one of these has their own stored BLM number, INT starts over every time you shut the key off. Now that you know what they are, it's time to tell you that they don't use these terms any more. They're called Short Term Fuel Trim (INT) and Long Term Fuel Trim (BLM). They're now given in positive and negative percentages. They still do the same thing.

That's probably alot more than you bargained for when you asked the questions, but you happened to catch me when I had a few extra minutes to write. I'm always happy to answer stuff like this when I can. If I don't know the answer, I can usually hunt it down. I'm lucky to work at a place with great resources. If you need more help, just ask.

JIM :chevy

 

Thanks so much for your great explanation. Il'l try to check what you mentioned this weekend. :thumbs:


[Modified by C4DC, 9:29 PM 3/19/2003]