Lean Running on 3 Cylinders
 

Hi All,
I have a 1992 SVX throwing a code 37 (left side O2 sensor). The sensor is pegging itself at .007V, indicating an extreme lean condition. There is no fluctuation to the voltage. I’ve confirmed that the sensor itself is good (switched sensors side to side) and verified the wiring is good (voltage readings are the same at the sensor as they are at the computer). The right side bank is functioning perfectly. So my question is what would cause a lean condition on just the left bank? I pulled the spark plugs and they all looked good. I pulled the fuel injector leads off one by one, and the engine stumbled and ran poorly with any injector disconnected. I have no drivability or other issues, just a code and a check engine light. I’m planning on a road trip tomorrow evening so any ideas before then would be greatly appreciated, but more importantly, am I running the risk of damaging the engine if the problem is not fixed right away? Thanks, Cory

Re: Lean Running on 3 Cylinders
 

Pull the plugs and see what it looks like on piston. . Try to get one from each Try for the area below the manifold on the heads or from the underside. Lean is very bad for an engine. Think holed pistons bad. Until you verify that it is or isn't running lean I wouldn't be planning any trip.

As for possible causes. It is possible both are running lean and then I'd look at the fuel filter but if it is just that one side I'd pull and clean everything. There are plenty of places that bench clean and test injectors for about $20 a pop. Rails to and I'm not sure but I think the SVX has regulators on each rail. That could be bad.

Re: Lean Running on 3 Cylinders
 

I don't think you have anything to worry about, for your trip.:) It shows no sign of being lean, just a O2 sensor code. If the ECU finds that a sensor is reading "out of limits" it will disregard that sensor and work off the other one.
If the sensor is pegged at 0.007V, it is more likely that there is a problem with the wiring on that side.

Harvey.

Re: Lean Running on 3 Cylinders
 

Well that sure sounds better than burning holes in my pistons. But I've confirmed that the wiring is not the issue, both by continuity and resistance checks, and by bypassing the wiring and reading the voltage directly at the O2 sensor (.007v). So I'm still concerned that the left bank is running really lean even if the computer is using the right sensor for guidance. The left side sensor is still indicating an extreme lean condition. Hope that made sense. Thanks for the reply.

Re: Lean Running on 3 Cylinders
 

After reading all you posted and noting the tests you have carried out, I came to the same conclusions as you have now posted and which make perfect sense.

The deciding factor is the plug readings. How long has the fault light been indicating a suspected lean condition? How much running since fault indication? Can you be sure a valid plug reading was in fact registered and obtained?

With left sensor reading 0.007 volts, what does the right read? (Presume this has been measured from the lead which is shielded.) If you are using a high impedance digital meter, the circuit could in fact be open and only induced volts are being recorded. The key to this will be comparing left and right voltages. You may also be able to check at the TCU ends, i.e. connector B59, terminals a6, white wire, and a5, yellow/blue wire. The shield may or may not be visible but is grounded at the TCU end.

If you can not prove faulty wiring and are confident in your test made by means of exchanging sensors, your doubts are understandable. However you must take into account that the fault code indicates a faulty sensor, or sensor signal, and not necessarily lean condition.