vdambros

Hello all. Long time reader, first time poster.

For about the last 10 months now I have been trying to get a long-term project car to pass smog. It’s got very high HC (hydrocarbon) levels and CO (carbon monoxide) levels. It smells rich but the wideband 02 sensor and other indications seem to be just fine.

The car’s computer is from a 1992 TBI Firebird, and is equipped with an early version of the Embedded Lockers from Dynamic EFI and the Prominator. There is a Zeitronix wideband 02 sensor which connects to one of the analog inputs of the Embedded Lockers unit. The engine is a 350 with a fairly aggressive cam and there are some high-flow injectors in the throttle body. Some of the details have been lost with the previous owner, but the important thing is that this whole setup passed smog when it was in the Firebird.

My dad and I transplanted the engine into a 1984 z28 Camaro. We added an in-tank Walbro fuel pump to the original fuel pickup (which was intended for carbureted engines). The fuel runs through the original supply line to the engine, but we replaced the original too-small return line with AN-6 hose. The fuel pump may be operating at a different pressure or flow rate than the original fuel pump, but no adjustments were made to the regulator. We gauged the pressure once, if I recall it was in the 13-14 psi range. Otherwise, the setup should be identical. All sensors were preserved including VSS.

Along the way, we flashed the ROM by accident and turned the car into a driveway ornament until we found what we believe was the last-known-good .BIN and flashed it again. Initial drivability was OK but not great until we hooked up the VSS.

The first time we went to smog the car, HC levels were high (6465ppm at 15mph and 6763ppm at 25mph), and so were CO levels (5.81% at 15mph and 6.25% at 25mph). In addition, there was a leaky gas cap and a fuel system leak at our modified fuel tank sender. The car definitely smelled like it was running rich.

We repaired the fuel system leak and replaced the gas cap. We imagined that HC problem was due to the ¼” return fuel line being too small and thus causing too much pressure at the throttle body and replaced it with AN-6 hose. Back to smog.

The second time we went to smog, we passed the fuel system leak items, but the HC levels were essentially unchanged (6449ppm at 15mph and 6460ppm at 25mph) as were the CO levels (3.68% at 25mph and 6.05% at 25mph).

We then installed the Wideband 02 sensor which had been collecting dust and tried to do some tuning. We did three or four rounds of driving / logging / tuning using the Learn VE and/or the Wideband 02, until the corrections approached zero.

For a 3rd time, we returned to smog only to see similar results with high HC levels (6098ppm at 15mph and 6504ppm at 25mph) and only slightly lower CO levels (3.26% at 15mph and 2.97% at 25mph).

This is what I’m having the most trouble understanding. Both the BLM and the Zeitronix Wideband oxygen sensor tell me I consistently run very lean (up to 17.0), though, anyone standing near the car can easily tell it smells extremely rich. Also, corrections on the Learn VE table are both positive AND negative, up to 13% change in either direction.

I am at the point where I am not sure what to do, as even if I were to start making drastic changes to the cars tuning with Tuner Pro, I would not know what to change or if any changes were helping, due to the sensors. I have of course already double checked my wiring on both, and also verified the air-fuel-ratio reported by the Embedded Lockers What’s-up-Display (analog sample) matches that sent by the Zeitronix control unit to the laptop via serial cable (digital).

The owner of the engine and computer set up prior to me passed smog, and the only difference I can think of in the fuel system is the Walbro high flow fuel pump. I did not change the base pulse width. While this could certainly explain the excess fuel, it does not seem to explain the discrepancy between the high HC reading and the oxygen sensors.

Thank you ahead of time for any responses. All are greatly appreciated. I do have actual data logs for the tuning sessions and the last smog, if that would be useful.

RBob

iTrader: (1)

Sounds (reads) like there is a bad misfire.

RBob.

vdambros

Hi RBob,

Wanted to say thanks. It was indeed TWO misfires. After your post, I checked all of my spark plug wires with a timing light, and found a plug that was melted all the way through. I returned to smog, and it cut my numbers in half. When I took a closer look at the engine the next weekend, I found that a plug wire had melted to the headers and was arking to it--hence why I did not catch it with the timing light.

After fixing that, as well as installing a new cat, I passed smog with readings approaching (and in some cases), zero.

I am 18 and have been working on this car since I started high school, and for the first time I am able to drive it (legally). Thank you.

p.s. Any idea about the O2 sensor saying lean?

Ronny

iTrader: (1)

With misfire and incomplete combustion the NB02 would show lean. Same on WB. Sees unburned 02 and reports lean. Once combustion is compete it will report accurately.