Diagnostics: Ohm reading for TCI pick up coils

[Pat Conlon]

I'm chasing a high rpm studder on my '84.
The bike starts and runs fine (really good actually) until above 7.5k rpm where a intermittent studder kicks in.
I've replaced the 32 year old oem ignition coils with new Dyna green 3 ohm coils. I have the coil relay mod done..good juice to the coils.
I checked continuity and ohms of the coil trigger wires from the TCI plug to the coils...wiggled the connector wires looking for bad connections.

My question is: In both the Clymer/Haynes Workshop manuals they specify a ohm resistance reading on the TCI pick up coils (orange to black and gray to black at the TCI plug) of 120 ohms +/-10% at 68*F (108-132 ohms) I warmed up the pick up coils with a hair dryer.

I checked mine and they are 159 and 160.....I have a spare back up set of pick up coils and checking those they are at 160-161.

Are both sets of pick up coils bad or is the ohm value wrong?
I can see one (of the 2) pick up coils reading high...but both sets? (all four pick up coils? unlikely)

[FJ1100mjk]

Don't play around with it. Call Randy and discuss. Might even be a sticky valve or...?

[Pat Conlon]

it's definitely a ignition studder...

Valves are good, plug readings look good.

email is sent to Randy.

I have a back up TCI ignition box I'm going to swap in.

[red]

I'm chasing a high rpm studder on my '84.
The bike starts and runs fine (really good actually) until above 7.5k rpm where a intermittent studder kicks in.
My question is: In both the Clymer/Haynes Workshop manuals they specify a ohm resistance reading on the TCI pick up coils of 120 ohms +/-10% at 68*F (108-132 ohms) I warmed up the pick up coils with a hair dryer.  I checked mine and they are 159 and 160.....I have a spare back up set of pick up coils and checking those they are at 160-161.
Are both sets of pick up coils bad or is the ohm value wrong?   I can see one (of the 2) pick up coils reading high...but both sets? (all four pick up coils? unlikely)

Pat,

Do you get the stutter when parked, or only at speed?  If it is good at high RPM standing still, then I would look for a dirty air filter, or anything that changes the way the engine gets air (inlet boots, altered covers and panels, et c.).  

You may be starving for gas at high RPM, also.  When riding with half a tank of gas or less, run the engine up to the start of the stuttering.  Back off the throttle, pop the gas cap for a second, close the gas cap, and see if you still have the stutter then.  The gas cap vent may be plugged, or partly plugged.  Do this next part outdoors, as you will create lots of gas fumes.  Use a siphon hose to "vacuum out" the bottom of the gas tank into a clean plastic catch bucket.  If you get a lot of rust and crud in the catch bucket, the tank needs cleaning.  Apply a suction to the vacuum hose of the petcock, strong enough to let the petcock flow the fuel.  Blow compressed air generously from the carb end of the fuel line, back up into the tank, to clean the screen in the tank.  Then clean out the gas tank.

No matter what the pickup coils read in Ohms, coil values are best measured in Henries, not in Ohms.  If an electronics geek there can show you that the Henry values of the pickup coils are all the same, then they are all good.  An Ohms reading usually can not spot the slight failure in a coil that might cause your problem.

Cheers,
Red

[TexasDave]

With it being electrical there are so many things it could be. If swapping the TCI doesn't cure it I would unplug your tach and see if the problem is still there.  Dave

[Pat Conlon]

Thanks Red, gas is good, tank is clean, cap is vented, carbs clean, carb jetting is good.
Again...it is a ignition studder...very slight, intermitent, comes and goes.
I only rev out my engine under load in 3rd gear (sometimes 4th and 5th) never in neutral standing still.

My primary question is why the "apparent" low ohm value for the coil pick ups?
....or is it really a low ohm value? (120 +/-10%) All 4 of my coil pick ups are within 2 ohms of each other.

Has anyone else noticed this?

Swapped in the back up TCI, and the problem still exists.

Thanks Dave...I'll disconnect the tach wires and see what happens.

[FJ_Hooligan]

Maybe try temporarily wiring around the coil relay.  Where is the relay mounted?

At high RPM maybe vibration could be jacking with the relay connection?  Maybe try a new relay?

Just a wild idea....

Let me know if you want to swap over to a Dyna.

(I "might" have an extra one lying around)  :-)

[Pat Conlon]

Thanks Hooli...
The relay is up front above where my charcoal canisisters used to be.... I'll plug in a new relay. I put heat shrink on all the spade connectors on the base plug, I would hate to have cut that all open.

Hooli, you just gave me an idea....if the relay (that powers both coils) was acting up, the studder would be severe and dramatic...which is not the case...

Hmmmm.

Perhaps 1 plug is acting up? Sure feels like it....I'm gonna put a new set of plugs in and see what happens.

Sometimes (most of the time) it can be the simplest of things....wouldn't that be something?

[copper]

your books are wrong. my GYSM says pickup resitance is 149~182 ohms at 68*F

so the pickup is not the trouble

[Mark Olson]

Hey Pat,    wow third gear is where the fj lives.

I recall the coils for the tci are different from the dci ign , if you use the hot coils on the tci you will cook it. ( one of those things i learned and forgot why. )

I like the check the plugs idea, and you may have a sprk boot or wire having a crack . spray with water and see if it causes a miss while running and lights you up.

A tear in one of the diaphragms of the carbs will act similar but don't you have flatsides on that bike?

Lots of ideas tossed around Post up what you find.

[Pat Conlon]

Thanks Coop!  

Randy at RPM just e-mailed me and said the same thing. Correct values = 149-182 ohms at 68*F

Randy tested several pick ups, both early TCI dual pick up, and late model DCI single pick up, and they all came in at the 160-165 ohm range....

My suspicion is confirmed.

So, let it be known that both the Clymer and Haynes Workshop manuals are WRONG WRONG.

Thanks Mark, the Dyna green 3 ohm coils are compatable with the early FJ 2.8 ohm TCI ignition.
You do not want to run coils with a lower ohm value than your ignition (like the Dyna gray 2.2 ohm coils)
Fresh plug wires/boots (Dyna gray resistor core) remember the problem existed before the new coils.

[FJ_Hooligan]

....if the relay (that powers both coils) was acting up, the studder would be severe and dramatic...which is not the case...

Good point.  If the power was intermittent then it would be very severe missing and probably cause a lot of backfiring from mis-timed plug firings.

Spark plugs may be a good idea.  You said you were using Dyna wires?  On mine, I have to watch out for the screw-on tip of the spark plug loosening up.  Seems like everytime I pull a wire, one or more of the screw-on tips is loose.

[Mark Olson]

Hey pat I just remembered something that happened to me similar to your problem.

The run/kill switch was acting up on my 86 and would cause a miss at the rpm you are talking about.
problem only in the fun rpm zone in third gear.
Check that out.
I took it apart and cleaned it and used the dielectric grease on the contacts.

Good luck.

[FJmonkey]

Now that you mention it Mark, I have a strange Kookaloo issue. Many times when entering the Kookaloo zone I will discover my turn indicator starts blinking. Many times I have been riding for some time on the road so I know the signal would have timed out many miles ago. But after the fun acceleration I find it blinking away.... Since the impact to my riding enjoyment is very low I have not bothered to root cause it. I know I have already cleaned the switch contacts a few years ago. So it may be from vibration or the G's pulled during a good run.

Back to your regular channel...

[Mark Olson]

Now that you mention it Mark, I have a strange Kookaloo issue. Many times when entering the Kookaloo zone I will discover my turn indicator starts blinking. Many times I have been riding for some time on the road so I know the signal would have timed out many miles ago. But after the fun acceleration I find it blinking away.... Since the impact to my riding enjoyment is very low I have not bothered to root cause it. I know I have already cleaned the switch contacts a few years ago. So it may be from vibration or the G's pulled during a good run.

Back to your regular channel...

Yeah , just cause you did it once upon a time dosen't mean you won't have to do it again.
Part of my spring maintenance schedule.