EGR Valve, Throttle Plate inoperative

[Carimbo]

EGR valve and throttle plate are not operating. EGR controller box is apparently operating as I am picking up signals from the test connector (just under driver side dash lower panel) that carries these signals. The air solenoids work correctly when I apply current directly to their immediate connections and test w/ engine running.

First guess is the wires have deteriorated in the troublesome bundle section that passes along the passenger side frame rail in the engine compartment under the fuel filter area. Further testing will tell.

In the meantime: Any bad effects by running the car w/ inoperable EGR and throttle plate (throttle plate is normally open)?

[asavage]

The EGR system toggles the IP housing pressurization somehow -- I forget the details. The timing is advanced while the EGR is operating? I think that's right. In any event, you might want to disconnect the EGR advance solenoid on the IP.

[diesel-man]

In the meantime: Any bad effects by running the car w/ inoperable EGR and throttle plate (throttle plate is normally open)?

I have been running Maxi diesel's with the "throttle" plate open and the EGR hose unhooked since 1987. The only downside is the engine pushes a small amount of oil into the lower end of the air cleaner box. The throttle plate creates a small amount of vacuum to pull the crankcase fumes out of the engine at idle and just above idle. It is also there to lower the sound of the air moving into the intake. Personally I believe all the air it can get is advantageous.

When you can breathe the exhaust, the EPA will finally be satisfied.

[Carimbo]

The EGR system toggles the IP housing pressurization somehow -- I forget the details. The timing is advanced while the EGR is operating? I think that's right. In any event, you might want to disconnect the EGR advance solenoid on the IP.

Yes the IP advance solenoid gets its signal from the EGR control box (driver's side kick panel) and I can't tell any difference connected or unconnected. According to the FSM descriptions, it is supposed to operate in unison w/ the EGR. The easy way to disconnect it is via the inline spade connector between the IP advance solenoid and pass. side frame rail wire bundle, red wire. Tested the solenoid itself w/ a jumper, it clicks, don't really know how to measure what real effect it has, nothing at least at idle that I could tell.

diesel-man, I do get the small puddle of oil in the corner of the air cleaner box.

[cab]

Is there an advantage to running with more injection advance? Would improved performance or economy take place?

[Carimbo]

Maybe, but how would you know your new more advanced setting is not damaging the engine? Timing the LD28 is not a trivial task, and it is not the same as timing a gasser "by ear."

The IP advance solenoid (or PLA Partial Load Advancer as the FSM calls it (p. ec-29) "is designed to contol the formulation of HC emission." It is energized at the same times the EGR valve is, at idle and low-medium loads & RPMs. High loads/high RPMs it is supposed to cut off, also at low or extremely high coolant temps.

I don't know how this reduces HC but it seems like it would spend more time activated than deactivated so I wonder if it wouldn't have been better to design it contrary. That is, set the IP more advanced and have the solenoid retard it at high RPM/loads. Unless they wanted a more fail-safe mode.

[Carimbo]

Turns out this problem (inop. EGR valve, throttle butterfly, and IP advance solenoid) was caused by a faulty rev counter, the one mounted just behind the IP cog pulley, at 7 o'clock position. The faulty rev counter showed no continuity. I replaced it w/ a good one from my spare IP, and the EGR valve, throttle butterfly and (presumably) the IP advance are working again. I say presumably, because I can't tell any effect from the IP advance solenoid.