PLT OF SMA SUFFERS LOSS OF VACUUM SYS AND SUBSEQUENT GPS INACCURACIES. ABANDONS ATTEMPT TO DSND THROUGH SEVERE TURB INTO MYF AND DIVERTS TO PSP.

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DEPARTED ELP ON VFR FLT. 1 HR INTO FLT; EXPERIENCED A FAILURE OF MY MAIN VACUUM PUMP; PWRING PRIMARY AND SECONDARY ATTITUDE INDICATORS. I VERIFIED THAT STANDBY VACUUM PUMP WAS OPERATING; BUT LEFT IT OFF TO CONSERVE. I ELECTED TO DIVERT AT THAT TIME TO MY MAINT BASE AT MYF. NEARING DEST; WITH FLT FOLLOWING BY ZLA; I WAS ADVISED THAT MYF WX WAS CLR; 10 NM VISIBILITY WITH 1200 FT BROKEN; 2500 FT BROKEN 3600 FT OVCST. I ADVISED ZLA OF MY ACFT CONDITION AND TOLD THEM I WOULD EXECUTE ENRTE LETDOWN TO MAINTAIN VFR; AS I WAS NOT CONFIDENT OF MY STANDBY VACUUM PUMP. I WAS THEN ADVISED OF PIREPS RPTING SEVERE TURB BELOW 9000 FT; AS I DSNDED TO MAINTAIN VFR INTO MYF. I REQUESTED A POS FIX AND WAS ADVISED I WAS 1.5 NM SE OF THE JLI VOR. AS I REACHED 3600 FT; ATTEMPTING TO MAINTAIN VFR; I WAS EXPERIENCING SEVERE TO VIOLENT TURB AND BARELY ABLE TO CTL THE ACFT IN THE DOWN/UPDRAFTS. DUE TO DETERIORATING VISIBILITY AND LIGHT RAIN; I ELECTED TO DIVERT TO PSP; AND COMMENCED A CLB TO MAINTAIN VFR TO 8500 FT. I HAD BEEN UNABLE TO RAISE SOCAL APCH ON THE ASSIGNED FREQ AND RETURNED TO ZLA. I ADVISED CTR THAT I WAS 3.3 NM FROM MYF; ON THE 262 DEG RADIAL. CTR ADVISED THAT I WAS IN CLASS B AIRSPACE WITHOUT A CLRNC. I REQUESTED A POS AND IDENTED. CTR ADVISED I WAS AGAIN WITHIN 1 NM OF THE JLI VOR. AT THAT TIME I DETERMINED MY NAV SYS WAS GIVING ERRONEOUS POS DATA AND REQUESTED VECTORS TO PSP; WHERE I LANDED WITHOUT INCIDENT. I DO NOT BELIEVE THAT I PENETRATED CLASS B AIRSPACE AT ANY TIME; BUT BOTH GPS UNITS WERE GIVING SEPARATE AND APPARENTLY ERRONEOUS POS DATA. HAD I RECEIVED WARNING OF THE SEVERITY OF THE TURB; PRIOR TO MY LETDOWN AND ENCOUNTER WITH IT; I WOULD HAVE IMMEDIATELY DIVERTED TO PSP. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR ADVISED THAT HIS DISORIENTATION WAS THE RESULT OF INADVERTENT SELECTION OF A DIFFERENT EFIS MODE THAN HE THOUGHT WAS ACTIVE DUE TO THE EXTREME TURB. HE WAS; INDEED; RIGHT DOWN IN THE MOUNTAIN PASSES WHEN HE MADE THE WISE DECISION TO CLB AS RAPIDLY AS POSSIBLE AND EXIT THE AREA. HE HAS ARRANGED TO TAKE FURTHER INSTRUCTION IN THE USE OF HIS EFIS SYS AS HIS EXPERIENCE AND SKILLS IN ITS USE WERE CLEARLY INADEQUATE FOR OPS UNDER SUCH ADVERSE CIRCUMSTANCES.