check engine light/31 codes
I am having some trouble trying to solve a intermittent check engine light problem. The self test indicates a code 31, a problem with the EGR system, specifically EVP circuit below min voltage.
I have done the following:
1. Checked all the vaccuum lines & subsituted new temporary lines to the from the can to the EVR solenoid and from the EVR to the EGR.
2. Vaccuum tested the EVR both energized and deenergized, it tested within spec. I also switched it for a known good EVR off another engine.
3. Vaccuum tested the EGR, moves freely, holds vaccuum, opens with manually applied vaccuum at idle causing engine to stumble as it should.
4. Checked resistance at the EGR position sensor while applying vaccuum to the EGR, it was within spec (3700 ohms closed/700 ohms at 10 in. hg.) and increased and decreased smoothly with vaccuum changes.(This is a new EVP and the test results are the same as the one on another engine)
5. Cleaned the electrical connectors at the EGR position sensor and at the EVR solenoid and reassembled them with dielectric compound.
The engine light still persists. It won't come on till several miles of driving. At first it will come and go, with throttle movement seeming to trigger it. The longer you drive it the more it will stay on, then, if you leave it idle for a while it will stay on. This is a 1988 F-150 351W.
If anyone has any ideas I would sure appreciate hearing them.