Ok so my BLM's are at 108 basically at all times, which explains the low gas mileage recently, but my car seems to be running fine. As a test I unplugged my MAF sensor and the BLM's bounce around 128 (am I right in thinking that if I just unplug the MAF the PCM runs in speed density mode?). To me this says the MAF is wrong and since I did the ZO6 MAF "conversion" from ls1speed.com which is suposed to be "calibrated" for an lt1. But it would not surprise me if the MAF is reading incorectly (BTW I did the conversion becuase my stock MAF died).

Now if I were to calculate the mass air flow based on speed density info, compare that to what the MAF is reading, and then adjust the MAF tables acordingly do you all think that would help the problem? Or should I just buy an lt1 MAF?

On a side note I also noticed that when I accelerate, basically press the gas any at all, I am getting some spark retard (1-2° or even less) WITHOUT getting any knock......any ideas why?

 

I have MAF table numbers for a stock Z06 MAF that have been scaled to fit LT1 tables if you want them. May help.

Jeff D.

 

The MAF could very well be throwing you off.. Do you still have the stock one to try?

Only other cause's of 108 BLMS would be leaky injector /s, leaking fuel pressure regulator OR there is a possibility that you have your injector harnesses mixed up, check the lil numbers on the side of them and see if you have taken them off recently...

 

If you got some real knock, the computer remembers this for a short period of time, and any time you press on the accellerator, it will pull a few degrees until the engine is cut off, or you drive for a while without getting any real knock.
If its ral knock, then the knock counts will increase.
This is to compensate for bad gas.

 

Thats exactly what is happening to me right now. I have the OEM MAF. original from factory. My quick reaction was to think my MAF was crap but then I began to ask questions... as in at idle what is the normal grms/sec reading on stock LT1s that are in good shape and runing good...also at WOT and the numbers I got match with my MAF numbers. No wanting to buy a new MAF and end up with the same problem I did some searching around and I came across this info:

The "old age" failure mode is that the sensor slows down on the lean to rich switch and causes the car to run extremely rich

I have found other places that match the information... it seems like the sensor takes too long to switch from lean to rich... the PCM reads all this time and confuses it with the car running lean and sends more fuel to the injectors but then the 02 maximum and minimum values shift lower .... indicating a reach mixture and the PCM begins to pull fuel.... however the 02 takes too long during the swing from lean to rich and the PCM adds fuel to compensate again..... its a vicious circle..


My theory is that PCM on a OBD1 is totally analog when it reads the 02's. Its intended to read maximun and minimun 02 readings and calculate and average but if the 02 spends a disproportional amount of time on either lean or rich the PCM interprets it as being to rich or too lean. In other words it doesnt memorize the max or min but acts purely on a voltage average method... if the voltage swing its fast then it works good but when the pcm is calibrated to expect a swing in lets just say 1/2 second from lean to rich and rich back to lean... once the oxygen sensor begins to take longer that that time... the pcm thinks 1/2 a second and it was all rich... time to pull fuel. the opposite hold true...


do I make sense? Anyway I am buying a new set of 02's and as soon as I get them I am gunna have them installed and then I will log my PCM again... if I am right this will fix my BLMs problem.


Find info about "lazy" oxygen sensors... thats what I believe our problem is. not the MAF.


Marvin

 

A lazy O2 could be the cause, but its easy to diagnose if thats the problem, your O2 Cross-counts, X-CNT should cycle from 0-255 in less than 90 seconds watching it on your scan tool. If it takes more than 90 seconds at full operating temp, then they need replacing.

 

good idea:

His and Mine are OBD1 though. Our PCM do not track X-cnt. Or maybe my scantool is not reporting it. I however can tell by looking at the O2's millivolts and I can tell you right now it takes about 1/2 second to go up and 1/2 second to go down. when I gun it though they both go up instantenously, thats what kept me confused. Last night I ordered two 02's from GM parst direct. I will get them in about a week I guess. In the meantime I am not going to seat down and count crosscounts anymore

Marvin