87 Bronco II: O2 Sensor Location & Effects?

[CraigK]

1987 Bronco II, 2.8L V-6 EFI A/T. I have an ongoing problem - once the engine warms up, it begins to sputter and almost die on a cyclical basis. Just as if fuel to the engine is being cut of on a cyclical basis, every 30 seconds or so. Pressing the gas pedal down further seems to return fuel flow(?) and the engine picks up. The problem does not occur under acceleration or load, and is worst at any constant running speed/no load condition. When the engine sputters and dies it does so somewhat slowly, as if gas is running out (takes say 5 seconds or so), but when it kickes back in it is instantaneous. I have replaced every frickin' vaccuum hose and installed a vaccuum gauge, and am convinced it is not a vaccuum leak issue. I have replaced the entire distributor, the TFI unit, and the MAP sensor. Of course, the fuel filter, and the plugs and wires. I've even 'permanently' installed a fuel pressure gauge on the intake manifold to check fuel pressure, and everything seems A-OK.

It's personal now. :angry:

On this vehicle, the EGR system has been disconnected and plugged at both ends, but this problem occurred BEFORE this was done, and is probably not related??? Is it possible the O2 sensor is reading a rich mix and signalling a fuel cutback to the injectors??? Where is the O2 sensor located? It is NOT on the driver's side manifold where my useless Hayes manual shows it.

Any thoughts would be appreciated. Thanks you.

CraigK

 

[Runnin'OnEmpty]

1987 Bronco II, 2.8L V-6 EFI A/T. I have an ongoing problem - once the engine warms up, it begins to sputter and almost die on a cyclical basis. Just as if fuel to the engine is being cut of on a cyclical basis, every 30 seconds or so. Pressing the gas pedal down further seems to return fuel flow(?) and the engine picks up. The problem does not occur under acceleration or load, and is worst at any constant running speed/no load condition. When the engine sputters and dies it does so somewhat slowly, as if gas is running out (takes say 5 seconds or so), but when it kickes back in it is instantaneous. I have replaced every frickin' vaccuum hose and installed a vaccuum gauge, and am convinced it is not a vaccuum leak issue. I have replaced the entire distributor, the TFI unit, and the MAP sensor. Of course, the fuel filter, and the plugs and wires. I've even 'permanently' installed a fuel pressure gauge on the intake manifold to check fuel pressure, and everything seems A-OK.
It's personal now.  :angry:

On this vehicle, the EGR system has been disconnected and plugged at both ends, but this problem occurred BEFORE this was done, and is probably not related??? Is it possible the O2 sensor is reading a rich mix and signalling a fuel cutback to the injectors??? Where is the O2 sensor located? It is NOT on the driver's side manifold where my useless Hayes manual shows it.

Any thoughts would be appreciated. Thanks you.

CraigK

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Craig, have you tried cleaning the IAC? I would try that first, along with cleaning the throttle body where the butterfly meets the housing.

ROE

 

[CraigK]

ROE

Thanks for the input. If the IAC is the Air Control Valve that sits on the side of the intake manifold, that has been replaced already. :blink: Also, I've tried installing a blank gasket at the valve/manifold interface to block flow (since the EGR is plugged). No change. I have disassembled the throttle cover and inpected it several times and there does not appear to be a problem there. I doubt it's the butterfly, but I'll check that next - Thanks.

BTW, it's a 2.9L v6, not the 2.8L. Ya think I'd know that by now . . .

ROE: is there/where is the O2 sensor????