Extensive tests of space charge compensation, at the energy of.8 GeV, in similar conditions to those of the e+e− configuration are reported. Stability regions, smaller in size than those observed in that configuration, are found to decrease rapidly with current. Up to the limit, the beam cross-section stays constant. The value of ξ rather than the residual compensated value sets the limit. Comparison of the results is made to various predictions of the 4-beam instability: proximity of the integer and of non-linear resonances.