They're down around 98-112 constantly- at idle or anywhere except at WOT when the ECM goes into open loop. I had it calibrated to run at the 126-132 range for the longest time, and then something went afoul. Question is, what is the something.

If it were ignition related, I would suspect that the ECM detecting unburnt fuel, would correct in the other direction, that is, up into 140-150 BL range. The way it is now, the computer seems to be detecting a lean condition.

What things should I be looking for? Already verified fuel pressure and injector operation. I haven't checked the fuel filter yet.

 

Sounds like a sweet ride man, any pics?

I do however think you are wrong with your diagnosis though. Low blm readings mean the ecm is reducing fuel delivery, indicating a rich condition, not lean as you indicated.

If you didn't change anything to spur this drop in blm's I would tend to think one of three things: your O2 is giving false readings, your maf/map is giving false readings, or most likely one or more of your injectors are leaking in between pulses. A scan tool and a FP gauge should get you to the bottom of this one.

 

When I had a broken spark plug wire a while ago, the Block Learns were hovering around 150, which is why I'm wondering what's going on now that the BL's are down to 100.

With a broken plug wire, you're going to get unburnt fuel coming out of that cylinder which will make the ECM think you're running rich, so why would the BL's be at 150 for that situation?

I do have a scanner and all sensors are reading what they should. Guess I'll just have to keep poking at it.

I had it running perfectly and didn't touch a thing! That's what's so frustrating.

Pics? Here are some...

 

Wow, your car is the shiznit. I like thirdgens alot, but it is nice to see a good example of some secondgen possibilities every now and again. Back to the problem at hand though...

I assume whatever ecm you use to control that beast works in the same general way a stocker does, so low blm's definetly mean at least your ecm thinks your running rich. I am still sticking to my guns and blaming your injectors. A quick leakdown test with a FP gauge would make or break this leaking theory though. You could also have a faulty FP regulator (vacuum hose still hooked up?), but again this would be obvious with some FP gauge testing. Other than that I would only think to question your map sensor, but if your scanning it that's probobly within spec.

Anyone else have some ideas?

 

Thanks!

Hmmm...Guess I should clarify what I'm running...

The electronics (ECM, sensors, wiring harness) are for a 1990 TPI Camaro.

I don't know if that helps in the diagnosis, but at least it's a stock GM system albeit with a different calibration for the ZZ4.

I'm going to dismantle the fuel system this weekend and see if I can find anything wierd. I've gone through the entire ignition system, wiring harness, and sensors already and everything is in order.

If anyone has any suggestions, please let me know! I'm quickly running out of ideas...

 

YES!!! It is a very nice car! I believe it was featured in either Car Craft or Hot Rod (I always get them mixed up) awhile back. I know that I was/am very impressed!

 

The O2 sensor does just that: senses how much oxygen (not fuel) is in the exhaust stream.
Your dead cylinder put unburned fuel into the exhaust, of course, but what the O2 sensor saw and reported to the ECM was too much oxygen. The ECM saw this as a lean mixture, so it raised the BLMs to get more fuel into the combustion chamber. So, you (or your CAT) probably saw a very rich exhaust AND raw fuel.
In your present condition, the ECM , with its low BLMs, is trying to reduce fuel to the cylinders. So, the O2 sensor is not seeing enough oxygen and is reporting a rich condition to the ECM. As Dustin surmised, something is putting too much fuel into the mixture. Since you have checked the fuel pressure, then leaking injectors, defective O2 sensor or perhaps retarded spark advance may be the root of the problem.

Rich exhaust = low oxygen = high O2 volts = low BLMs
Lean exhaust = high oxygen = low O2 volts = high BLMs

 

Yes, it was actually in Chevy High Performance last May. Only then it was actually running right!!

I had put an O2 sensor on the passenger side of the engine (in addition to the one on the driver side) for diagnostic purposes so I could see what both sides are doing. Hooking the ECM up to the that side revealed that both sides of the engine are behaving the same way. Previously, I could only see the driver side. So apparently, whatever is causing the rich condition is global rather than being localized to one particular cylinder (which would only affect one of the O2 sensors).

 

Wow, you've even been in a magazine, now I am even more jelous!

I was thinking, does your set-up have a 9th injector?

 

No, just the eight. I went with the 1990 precisely because it didn't have the cold start injector (as to the 91's and 92's I believe).

 

Have you checked for vacuum leaks? Check your fuel pressure regulator if you got it from TPIS, I've seen 2 of them go bad already. They use the stock LT1 regulator, and add their 'hat' to make it adjustable.

 

Hmm, temperature change?

When you first tuned the cal, what the temperature alot warmer? or colder?

If so, your MAT tables may need some adjustments.