Tango Mike
Well Known Member
Manifold Pressure Mystery:
The airplane: RV-4 with VM-1000 and dual Electroair ignitions (left gold Gen 1 unit with the MP sensor mounted on the EIS beside the coil packs, and right purple Gen 2 unit with a rev 1 MP sensor mounted separately).
Symptoms:
1) VM-1000 MP reads barometric pressure when the engine isn?t running.
2) After start, the MP advances to mid to high 20s with about 900 rpm.
3) Left advance reads 17 degrees
4) Right advance reads 28 degrees
5) Neither advance reading changes when the manifold advance is turned off.
6) During runup, the VM-1000 MP and the advance on each side remain the same as when the rpm is below 1000.
Discussion:
1) It appears to me that the VM-1000 and both Electroair EISs are operating normally.
2) It?s important to note that the Gen 1 units have a different RPM advance curve than the Gen 2 units. I don?t have my notes with me at the house this evening, but I think the Gen 1 units are programmed to 18 degrees once RPM is above 800, and the Gen 2 units are programmed to 25 degrees. (I also think the Gen 1 units added a degree or two of advance for every 100 RPM above 1000, but that?s not germane to this problem.)
3) With MP advance turned on and working on both sides, the advance readings at low taxi manifold pressures should be high. They?re not, and they remain at the fixed advance settings based on RPM, close to the programmed, fixed advance of 18 degrees on the left and 25 on the right.
4) Turning off the manifold pressure advance causes no change in advance readings.
5) If the VM-1000 were reading normally, I?d troubleshoot the manifold pressure ignition advance system.
6) If the manifold pressure ignition advance system were working properly, I?d investigate the VM-1000. (It?s important to note that last year I followed forum member Reggie?s procedures for cleaning the MPT and solved a problem with erroneous MP readings. That and the fact that the MP reads atmospheric pressure in static conditions appears to eliminate the VM-1000 as a suspect in this mystery.)
7) I?ve removed the hose from the fitting on the engine and gently applied pressure and vacuum, both of which resulted in about .2? increase and decrease, respectively.
What?s next?
Investigate the possibility that no MP is being supplied through the fitting on the #3 cylinder to the VM-1000 MPT and the two MP sensors?
Any suggestions would be much appreciated. Thanks.
Tosh
The airplane: RV-4 with VM-1000 and dual Electroair ignitions (left gold Gen 1 unit with the MP sensor mounted on the EIS beside the coil packs, and right purple Gen 2 unit with a rev 1 MP sensor mounted separately).
Symptoms:
1) VM-1000 MP reads barometric pressure when the engine isn?t running.
2) After start, the MP advances to mid to high 20s with about 900 rpm.
3) Left advance reads 17 degrees
4) Right advance reads 28 degrees
5) Neither advance reading changes when the manifold advance is turned off.
6) During runup, the VM-1000 MP and the advance on each side remain the same as when the rpm is below 1000.
Discussion:
1) It appears to me that the VM-1000 and both Electroair EISs are operating normally.
2) It?s important to note that the Gen 1 units have a different RPM advance curve than the Gen 2 units. I don?t have my notes with me at the house this evening, but I think the Gen 1 units are programmed to 18 degrees once RPM is above 800, and the Gen 2 units are programmed to 25 degrees. (I also think the Gen 1 units added a degree or two of advance for every 100 RPM above 1000, but that?s not germane to this problem.)
3) With MP advance turned on and working on both sides, the advance readings at low taxi manifold pressures should be high. They?re not, and they remain at the fixed advance settings based on RPM, close to the programmed, fixed advance of 18 degrees on the left and 25 on the right.
4) Turning off the manifold pressure advance causes no change in advance readings.
5) If the VM-1000 were reading normally, I?d troubleshoot the manifold pressure ignition advance system.
6) If the manifold pressure ignition advance system were working properly, I?d investigate the VM-1000. (It?s important to note that last year I followed forum member Reggie?s procedures for cleaning the MPT and solved a problem with erroneous MP readings. That and the fact that the MP reads atmospheric pressure in static conditions appears to eliminate the VM-1000 as a suspect in this mystery.)
7) I?ve removed the hose from the fitting on the engine and gently applied pressure and vacuum, both of which resulted in about .2? increase and decrease, respectively.
What?s next?
Investigate the possibility that no MP is being supplied through the fitting on the #3 cylinder to the VM-1000 MPT and the two MP sensors?
Any suggestions would be much appreciated. Thanks.
Tosh