i have an 85 car with an 87 TPI 305 in it, it has an LT1 cam (.451 lift) as well as headers and a 3 inch exhaust system and 19 pound multitec 2 injectors. here's my problem, the car starts and runs beutifully, revs fast and hard and its VERY smooth and has plenty of power. sounds wonderful right? heh, here's whats bothering me, my A/F ratio guage is reading VERY lean and when i punch the gas it shoots up to stoich, then drops back off the chart when its warming up at idle in park, when it hits closed loop, it even reads pretty lean, in drive with my foot on the gas it switches between stoich and lean. my BLMs stay around 128 -130, my iac counts are all good. i put an AFPR on it which put me in the sweet spot im in now with the way it runs and i HAVE adjusted it too far in a d adversely affected the run qualitfy, the the A/F guage did NOT show much different. what do you guys think? (im also posting this in the TPI board for their opinions)

 

Exhaust leak ?

 

When you adjust the fuel pressure, do you get a response change in the BLMs? You see, the ECM should correct for a fuel pressure increase so that the BLMs will change accordingly but the drivibility will remove about the same, unless you peg the BLMs to one side or the other. What you will change and feel would be the WOT response.

 

i adjusted it so the that BLMs are about 130 cold and 125 hot, but i still have no real change in the o2 readings, i am thinking my o2 sensor is too far downstream and it's not getting hot enough, weather permiting i want to try installing a heated o2 sensor

 

Oh yea! you are in Illinois. When I lived in Ohio and Michigan, my '87 went into storage for the Winter on about December 1st. I would not get it back out till April 1st.

When you say that your BLM is 130 (or whatever), do you realize that there are 16 different fuel trim cells (FTCs)? You have a unique BLM and INT for each FTC. When I drive around in OD, I am in FTC 6 or 10 most of the time.

 

im reading what the scanner says, tells me my block learn is 130-125

 

What fuel trim cell are you in at that time? You are nearly perfectly tuned for the specific FTC that you are in if your BLM ranges from 125 to 130. Baseline is 128, so you are next to perfect.

 

Now I'm confused ?
Here you say you have absolutely the most perfect BLM numbers I've ever seen anyone report, yet you think there's a problem ???
You also say your AFR gauge shows lean. This tells me your AFR sensor, whatever it is, is not reading the perfect 14.675 AFR your BLM's are telling you that you have. About the ONLY way a real AFR indicator can show lean in a perfect burn environment, is that the AFR ( but NOT your real narrowband O2 sensor ) is getting unburned air AFTER the burn.
I say again, exhaust leak, and specifically AFTER the O2 sensor, but BEFORE the AFR sensor, unless your AFR sensor is tailpipe and it's seeing back-draft.

 

Is your AFR gauge working off of a wide band O2 sensor or a narrow band? Also, where along the exhaust path is the factory O2 sensor and the AFR gauge sensor,,, Is your AFR gauge working off of the factory O2 sensor?

 

AFR is running off of the vactory single wire o2 sensor (replaced 3 months ago) it is in the header, but t think it is too far downstream, it's about 3 inches further downstream in the collector than it was on the stock manifold, again, im telling you guys what the scanner is reading, the only time the AF meter and scanner move up to stoich or past stoich is when i give it gas or there is load on the engine, which should increase exhaust temperatures getting the 02 hot enough to read, or so this is my thought, id installl my heated o2 sensor but with the snow beating down on us right now i can't (this is not a daily driver anyways) what is driving me bat **** insane is how the hell my BLM is in such a good range with the factory o2 not reading right? is the a/f ratio set soley on what the MAF, TPS, and CTS tell the ecm? because with what my o2 is reading it shouldnt run this good! and if it was as lean as the o2 is reporting this stupid things headers would be glowing bright enough to light my basement up at midnight. >.>

 

You've just told us what we needed to know. Your AFR is totally bogus !!
IF the single wire O2 wasn't reading, then you'd get an error, and a SES light.
That single wire is accurate from about 14.6 to 14.8 AFR. Anything else is completely bogus. As long as it oscilates full rich ( 14.6 or anything richer ) to full lean ( 14.8 or anything leaner ) about once per second it's fine.
Believe the BLM and ditch the AFR gauge, or get a wideband.

 

well thats what is throwing me off, it doesnt oscilate, it dropps lean and stays lean, even the scanner shows this, then when i give it gas, it jumps up then slowly comes back down again, shouldnt the a/f guage reflect this switching rather than dropping lean and staying lean? that's whats worrying me, i dont want to damage my engine at all, I have no codes, so thats a good thing, but i guess a LC-1 where the y comes to a single pipe would be a better way to measure >.>

 

Here fellas, taken just now straight from my snapon MT-2500's display so you know im not BS'ing, also a pic of my AFR staying steady lean

 

OK, the crosscounts is telling.
Suggests your sensor is not getting hot enough to work.
Mine is in the ex manifold, about 6 inches from the number 7 exhaust valve, just as FYI.
Replace the single wire unheated with a three wire heated, and you should be fine.
Meantime, your AFR is completely meaningless, and will be questionable at best once the narrowband is working. I'd still rely on the BLM after crosscounts is counting.

 

ok so what your saying is i really did get it into a nice sweet spot then?

 

No, I'm saying that you don't have any real, measured, data on which to conclude anything other than that you're not getting complete data.
I'd say that since you posted zero cross counts, either your SES light is burnt out, or the ECM is seeing JUST enough swing in the O2 sensor to not quite throw an error. You should be seeing a swing on that narrowband full rich to full lean and back about once per second anytime the ECM is in closed loop.

 

How can the BLMs be correct if the O2 sensor is not operating properly?
If I understand things correctly, it's the O2 readings that are used by ECM
to derive the BLM. That's why BLM is static on 128 until O2 sensor heats up and provides voltage signal. The 128 sweet spot is defined in the cal by the
RML tables. 128 does not necessarily mean 14.7:1.