DTC 56 again, no vacuum leak

[petefias]

I'm getting DTC 56 when the engine is hot. No vacuum leak that I can see (pump turns on with key on, cycles a couple times and stops).

Terminal B12 shows 0.035V when the engine is really hot and has the DTC 56. Once the engine cools down B12 shows 0.59V (perfect).

When I ground the solenoid (to open the actuators) B12 shows 2.14V - 2.5V as the air pump cycles once a minute with the key on. When I ground the solenoid with the engine running B12 shows 3.2V. Of course, at this point I get DTC61 since the ECM is not expecting this. This is what I would expect.

Solenoid and actuators seem to work fine.

This is very intermittent. It's driving me crazy. Last year I corrected a major vacuum leak (the rubber connector on the vacuum reservoir) and I thought DTC 56 was behind me.

Any word of advice before I pull the plenum again?

Where do I get the sensor if I need one?

DTC56 is set when B12 is below 0.46V. Do I have a bad sensor?

[Jeffvette]

You working out of the manual Pete?

[petefias]

You working out of the manual Pete?

Yes, the manual is pretty clear on this. The only "hazy" part is that it shows 0.0V at no vacuum and at idle the required voltage for Terminal B12 is above 0.46V. I'll verify this after pulling the plenum this weekend.

This DTC 56 only shows up on a hot engine.

[Jeffvette]

You can get the map sensors at any dealership, you should be able to get them from any of the local parts stores.

You really need to be doing the testing on a hot motor, which sucks. Or either extend the harness and a vacuum tube to outside the plenum.

[petefias]

I did order a new Manifold Density Pressure Sensor from my local dealer. On the MY95 it is installed under the plenum. With it installed the voltage reads 0.59V at idle cold or hot (it's in spec).

Had a great test session at Summit Point without any codes so far.

Unfortunately there was a couple week old Viper with temporary tags that "climbed" a tree. Driver OK, car is totalled. This happened on the first session (still raining). In the afternoon it dried up, had some decent lap times. On the last session noticed a Mustang Cobra deep in the runoff trap at turn 1, must have lost brakes.

There were no other ZR-1's there, but that's nothing unusual. The only C6Z06 had a rookie driver, to his credit, didn't see him off course.

Peter '95 #442

[Jeffvette]

Good to hear Pete.

Yea, I see more Vipers off track when I'm out. I think it's a combo of the car and the driver.

[Lowflight]

I think I have the same problem...falling on its face with the key on...will pull codes in the morning though NO SES light.....I unplugged the VAcuum Sensor under the ECM (1992 location) and plugged it back in and screwed it up I guess...I hope that fixes the problem....because I have not checked for leaks...but the car ran awesome until I changed the braek MC...and still the pump only burps once and that is it....