Undertaking a 350 Motor Build

[GalDemSuga]

good job

Thks to all that gave such great info. Did some research and 108 BLM is lean. I'll log on the way back to the hotel and see how it changes.

 

[Russell]

Yep, engine thinks that exhaust is lean. 108 BLM is as low as the ECM is possibly able to register (the O2 sensor is likely reading even leaner than the ECM can read it to be). That tells me that either your O2 sensor needs to be replaced, or you still have a fairly significant exhaust leak upstream of the O2 sensor yet.

 

[GalDemSuga]

Yep, engine thinks that exhaust is lean. 108 BLM is as low as the ECM is possibly able to register (the O2 sensor is likely reading even leaner than the ECM can read it to be). That tells me that either your O2 sensor needs to be replaced, or you still have a fairly significant exhaust leak upstream of the O2 sensor yet.

I plan on having the exhaust manifold gaskets changed on Saturday. Code 45 just popped up an hour ago. The O2 is new (week old) and it's the third Bosch I put on in two weeks.

I logged the ECM last night and the BLM's never dipped below 108 nor get above 123. I've attached the Log Files.

 

[Russell]

You are shooting for 128 BLM which means that the ECM is fuelling a perfect mixture and with a perfectly programmed ECM it shouldn't deviate from that value at all. However, since no ECM is perfectly programmed from the factory, the BLMs will deviate the mixture from the programmed fuel maps to get a good mixture reading as according to the O2 sensor. Generally speaking, if you are 118 - 138 your chip is within factory specs. BLMs will always go to 128 once you hit PE (Power Enrich) as the ECM ignores the O2 sensor and follows the programmed fuel maps only. Just to be clear, below 128 the ECM is adding fuel to richen what it is detecting as a lean condition, and above 128, the ECM is removing fuel to lean out what it detects to be a rich condition.

I'd normally expect to see a 350 running around 130 - 134 BLM at part throttle as they are programmed to be a bit rich from the factory. A reading of 108 is lean enough to cause engine damage if that is the actual mixture passing through the engine, and above 140ish is so rich that the injectors would have such a narrow pulsewidth that the injectors midaswell be wide open at all times. The engine would smell very strongly, and would probably stall out like if you were to choke a carbed engine at full operating temp. If you are seeing a reading of 108 and not getting lean pops / overheating then it is almost always an exhaust leak or bad O2 sensor.

 

[GalDemSuga]

You are shooting for 128 BLM which means that the ECM is fuelling a perfect mixture and with a perfectly programmed ECM it shouldn't deviate from that value at all. However, since no ECM is perfectly programmed from the factory, the BLMs will deviate the mixture from the programmed fuel maps to get a good mixture reading as according to the O2 sensor. Generally speaking, if you are 118 - 138 your chip is within factory specs. BLMs will always go to 128 once you hit PE (Power Enrich) as the ECM ignores the O2 sensor and follows the programmed fuel maps only. Just to be clear, below 128 the ECM is adding fuel to richen what it is detecting as a lean condition, and above 128, the ECM is removing fuel to lean out what it detects to be a rich condition.

I'd normally expect to see a 350 running around 130 - 134 BLM at part throttle as they are programmed to be a bit rich from the factory. A reading of 108 is lean enough to cause engine damage if that is the actual mixture passing through the engine, and above 140ish is so rich that the injectors would have such a narrow pulsewidth that the injectors midaswell be wide open at all times. The engine would smell very strongly, and would probably stall out like if you were to choke a carbed engine at full operating temp. If you are seeing a reading of 108 and not getting lean pops / overheating then it is almost always an exhaust leak or bad O2 sensor.

This makes sense but the performance of the motor isn't adding up.
She's not stalling but rather runs good. I'm sitting in the truck watching the Data logger at the moment. The BLM's are at 108 but I'm getting a code 45 (O2 Rich). Does this mean that an exhaust leak is causing the O2 to read Rich and as a result the ECM is leaning the mixture?

 

[Russell]

You're right, that doesn't make much sense. Pull one of your spark plugs and see what the engine has to tell you. The color of the end of the plug will say volumes about how your engine is actually running most of the time. Another thing that can really screw with BLMs is timing, if your timing is so far off that the fuel isn't getting a complete burn (possible PO band-aid fix to the exhaust leak?), it will still run rich.

Did your engine straighten out a bunch when you tightened up the exhaust manifolds and got rid of the tick? There is a possiblity that the ECM hasn't re-learned that the O2 is gone and still enriching the truck even though it doesn't actually need it. The ECM stores previous BLM changes in the ROM to speed up the process of self adjustment. It won't re-learn BLM information unless the truck is driven faster than 45 mph first.

 

[GalDemSuga]

You're right, that doesn't make much sense. Pull one of your spark plugs and see what the engine has to tell you. The color of the end of the plug will say volumes about how your engine is actually running most of the time. Another thing that can really screw with BLMs is timing, if your timing is so far off that the fuel isn't getting a complete burn (possible PO band-aid fix to the exhaust leak?), it will still run rich.

Did your engine straighten out a bunch when you tightened up the exhaust manifolds and got rid of the tick? There is a possiblity that the ECM hasn't re-learned that the O2 is gone and still enriching the truck even though it doesn't actually need it. The ECM stores previous BLM changes in the ROM to speed up the process of self adjustment. It won't re-learn BLM information unless the truck is driven faster than 45 mph first.

It did run better after tightening the bolts, but I fear that the gaskets are bad. The truck sounds like a Harley when I drive her. She roars man.
She is showing me lean BLM's and a Rich Flag at the same time. I just drove to Shinnston,WV from Pittsburgh and back, and I hammered on her 75 MPH etc She ran good but was loud as hell. I made sure to clear the codes when I replaced the O2 sensor.