I am having problems diagnosing this problem. Here is a little history. After replacing injectors with #24 ones and adjusting fuel pressure and prom accordingly I am getting a backfire. I have scanned the ecm and find that my O2 voltage is low at idle and after going into closed loop the BLM and INT values climb above 140 meaning I am running rich since the ecm is dumping in fuel because it is running lean. The O2 sensor is new and it is heated since I am running headers. Is there a test that I can do to check the O2 sensor or is there something else the would cause this low sensor reading and high BLM and INT values. This problem has been happening since last year.

 

ttt

 

So let's use some logic here:

1. O2 says it's lean
2. The ECM is working its guts out to dump in more fuel
3. It's still so lean that it backfires

Changing the O2 sensor isn't going to fix that.

It's REALLY TRULY GENUINELY lean. The O2 sensor is not lying.

Fix the lean problem. Check the fuel pressure UNDER LOAD, not just sitting there idling; and if it stays where it should (38ish at low load, 45ish at high load) then you need PROM work. If the FP goes low (instinct tells me that's what you'll find), you likely need a fuel pump, but you should at least try a new fuel filter first.

 

Alright - thats something that I have not checked yet. I have adjusted the fuel pressure up to 53 psi, but have not taken a real close look at the fuel pump itself. Thanks for the advice.

I have not done load testing due to the high BLM values. I am a little concerned about breaking something due to a lean condition.

 

Load testing = duct tape your FP gauge to your dash and hit an expressway ramp

Remember, if your O2 sensor is telling you that it's lean (low O2 voltage), and the ECM is trying to dump in all the fuel it can, and it's still lean, then the O2 sensor is telling the truth. The truth is, it needs more fuel than it's getting. All you have to do now is figure out why it's not getting enough. Your choices are: low FP, incorrect programming, bad injectors. Eliminate them as potential sources of error in that order: check FP under load, put the stock BIN back in it and see what happens (or adjust your injector constant, whichever is easier), try some other injectors.

No rocket science. Just a Stone Age fuel injection from back in the 20th century.

 

Excellent - that makes sense. I will definately give that a try. Thanks

 

Just one final thing. I have a prominator installed in the vehicle so adjusting the injector constant is a snap. I have lowered the constant from 24 to 22 and I noticed an improvement in the BLM. How much lower can that number safely go - is 19 too low of an injector constant for #24 injectors on a stock fuel pump??