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Reams have been written about the all too common PO401 code. I think I have read most of them. I have tried to do my homework, all without benefit of a breakout box. I am teed into the EGR motor and hooking a vacuum gage to the tee. I am using a pin to prick the insulation of the EVR leads and clipping a lead from my DVM and watch it in real time driving.

What I know right now:

The DPFE is less than a week old.

The voltage to the EGR vacuum regulator (EVR) is ~12.5-13.5 V (which it should be).

The voltage from the EVR is intermittant, ~12.5-13.5 @ idle (which it should be), ~6.5 V at a steady 45mph cruise intermittantly.

The vacuum signal to the EGR varies inversely proportionate with the voltage from the EVR, ie, the voltage goes down, the vacuum comes up.

Vacuum signal reads a high of about 10 inches Hg at the EGR motor.

The vacuum hoses are in good shape.

The EGR itself is working. A removal and air pressure test verifies it does let the gas through when activated.

The exhaust gas supply line is clear. An air pressure test confirms.

The voltage from the EVR seems to vary from stoplight to stoplight, sometimes 6.5V at cruise, other times 13.5V at cruise.

Two problems:

Question: Why is the voltage signal from the EVR so intermittant? Could the PCM be on it's way out? Everything else about the operation of the car is fine.

The passage in the intake manifold appears to be blocked. An air pressure test to the port and listening at the throttle butterfly is quiet.

Question: What is the correct way to clean the carbon out of the EGR port. It appears to be a blind hole, but there has to be a passage through. Looking through the butterly the floor apears to come up above the EGR port. I would think air pressure would blow it clear but no dice. A wire finds to bottom of the hole and won't go any further. Are there several bends before the passage finally finds its way into the intake manifold?


Bill in sunny Tucson

On edit, I did get the passage into the intake somewhat clear. When I apply air to the port, I hear a noise out of the butterfly.
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