Date registered: Apr 2005
Vehicle: 1974 450 SL
Location: Coos Bay Oregon
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Seattle Merc Mechanic Recommendation? Tach/Roughness Problem
Does anyone know of a merc mech in the Seattle or south Seattle/Burien area? (Or maybe someone to stay away from?)
I have given up on solving two specific issues. 1) my tach jumps up and down wildly between idle to 2000 and 2) once or twice a month she runs very rough/rich running for the first 15 minutes or so. The roughness can happen just after sitting for an hour or overnight. I've checked the cap/points/rotor/wires/ignition wiring and it seems good and think my vac system is solid. I don't want to blindly start replacing things or wires that don't need changing. The tach and the roughness don't seem to be related since the tach problem is continuous. But maybe I should just change it all before "shopping" her? This cars old mechanic (in socal) said not to go with electronic ignition, but I wonder if that might solve problems... I heard the EI can improve my 10 MPG, too.
Once I get over 2000 RPM the tach stabilizes and seems to read correctly, but from idle up to there it jumps wildly and reads about double the real RPM. I suspected a bad chassis ground or maybe a dried out capacitor in the tach cluster. But that doesn't seem to be it. I jumped the sender wire from the terminal block near the coil to the back of the tach, but that didn't change anything. That sender wire seems to come from the Ignition Control Module. Could the car run fine (98% of the time) and the ICM be the culprit? They are too spendy to just change out in case.
Ideas or a reference would be appreciated.
1974 450 SL with 212K