Join Date: Dec 2008
Location: Tyler, TX
Thanked 407 Times in 347 Posts
If you have an IDI (6.2/6.5L, 6.9/7.3L) then it *may* be wise to replace all 8 if you find a bad one IF they have all been in there for a couple of years.
With the PSDs, I have only replaced two or three GPs since 1994, and only one was not murdered by a bad IDM harness (they will NOT tolerate 115V), it was just bad - had an open circuit. So with the PSDs, I am very much in the "fix as fail" camp.
With the IDI engines, it depends also on the brand of GPs you have. If, for example, you have a Ford/IH IDI engine, and find non-OEM GPs in it, get rid of them ALL the first time and use OEM replacements, then fix-as fail.
'93 F-250 HD, 7.3L IDI, 5spd - FARM TRUCK
I Support: Trailer brakes an every axle over the towing vehicle's GVW; CDLs for RVers; Safety inspections for ALL vehicles and 6 axle trucks (97K GVW proposal).
Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is a well-armed lamb contesting the vote - Benjamin Franklin
I vote for LIBERTY!