Checking coil

Ok got a question on any xj coil how do you check the secondary resistance. It seem every where I look say one of two ways for the primary wires to the plug wire or from the the two plug wires.

 

You can do it either way, but if you leave the caps installed, their resistance will be added to the secondary winding resistance....thus you'll get a much higher reading. The factory specs are for the secondary windings of the coil ONLY, but the service manual mistakenly shows the measurement being done with the caps attached. For precision, you should measure the coil secondary without the caps installed, and measure the cap resistance (each one individually) separate.

 

All of the service manuals have errors.
The proper way to check primary coil resistance is across both primary (small gauge) leads. Secondary resistance is checked between both spark plug wires (ideally with the plug caps removed; lefty loosey, they screw off. Plug cap resistance is checked across both ends of the cap to make sure that the reisistors haven’t failed.

 

ok because when checked with caps remover and from small coil wires primary I got 0 ohms from any on my plug wires .didnt do it from plug wire to plug wire was going from what the service manual said to do it the first way primary to plug wire

 

There are two "sides" (circuits) within each coil: the PRIMARY side (the small wires coming from the main wire harness, with the white plastic plug-in connector shell), and the SECONDARY side (the heavy wires to the spark plug caps). Primary resistance is measured between the two thin wires in the plastic connector shell; secondary resistance is measured between the two thick spark plug wire ends.

 

My cap read #1 is 8.75 #2 is 7.65 #3 is 6.67 and #4 is 7.63 is this with in spec. for got it a xj700n 1985

 

for got its a xj700n

 

NOTE: "K" is abbreviation for a thousand units, so "5K" ohms = 5,000 ohms of resistance, etc.

NOTE: some models within this era could have been fitted with "noise suppression" plug caps (these caps are evidenced by a metal "shield" wrapped around the plastic cap body) and such caps may have used a higher resistance rating as opposed to their stock ratings listed below (for non "noise suppression" style caps).


5K +/- 20% = 4,000 to 6,000 ohms per cap acceptable range:
all XJ650 models
1985 XJ700 air-cooled models
all 1981-84 XJ750 (except XJ750RL) models
all 1983-84 XJ900RK and RL models
all XJ1100 models
all XS1100 models


So if these are original caps (marked T-134 on the outer cylinders, and T-133 on the center cylinders) then they are out of spec, which is not uncommon if they are 35-year-old original caps! Also, assuming that they were measured at "room temp", i.e. about 70-F. NOTE: if there is corrosion on the brass terminals, particularly the "spike" or "screw" terminal that is fitted into the plug wire itself, this can cause added resistance, and a sandblaster (or the like) can be used to clean those terminals. Additionally, some original caps can be taken apart (from the bottom, where the plug enters); the big brass terminal --- which the threaded stud on the spark plug snaps into --- can be removed on some plug caps (there will be a straight slot in the brass receiver, such that a large, flat-blade screwdriver can be used to turn it out), and if so, then you might find some corrosion on the spring, the wafer-thin spacer disc (if it doesn't disintegrate in your hands), or on the backside of the brass terminal. Again, these can be cleaned / abraded to remove the corrosion, which could be the cause of the elevated resistance.

If I recall correctly, the T-133 caps can be taken apart as described above, but the T-134 caps cannot.

 

yes outside T134 inside T133

 

The service manual is wrong in this instance (and a few others).
Plug wire to plug wire is correct. Primary wire to primary wire is correct.

 

What about the one coil primary is 3.7 ohm should I replace it?