Secondary Coil Resistance Question
 

Attempting to get this trucks performance /economy at it's peak and before I spend money on data logging @ the Dyno - (Going in for a custom tow/adjust for lean condition.)

I'm pretty close, torque and economy (16/18 without trailering) is good. The truck doesn't sweat a 1900 lb trailer (empty) - No downshifting @ cruise in OD (1900-2100 rpms) (No need to pull in third, as long as I'm empty).

I have 4 coil sets to choose from, - decided to run 8 of the latest set (10 pack) since their new.

I can't seem to get the resistance numbers off my mind tho. My other sets are good (No low grade issues). I was under the impression coils are labeled according to resistance, ie -

Current sets test correctly

Motorcraft - DG491's = 491
Motorcraft - DG508's = 508
Global - - - DG508's = 508

The set I have installed now varied. I ordered a 10 pack of Globals DG508's. Eight of the ten tested out @ 530-540, while the remaining two tested @ 508.

To keep Ignition integrity, I decided to try the 530 - 540's. Truck seems to be running fine, but if I'm thinking correctly - More resistance means less spark or a lower pulse rate in this case. ? Is this correct and should I remove these before wasting time and money on logging ?

Thanks

Dumb question, didn't have time to look yet.

Shouldn't that resistance value be the primary resistance in less then 1 ohm ? Thought that would be 508 is a .508 value ?

The secondary I thought were in the K ohm range ( less then 10K ).

Have not done a coil test in some time on the bike, so I am thinking out loud here.
I'll try t get a chance to check the service manual on coil testing on Sunday ( I hope ).

Not a dumb question, your thinking correct as far as testing for failure. The first to be tested/ruled out is primary @ 0.55 ohms and secondary @ 5,500 ohms.

Most coils don't fail this way, they fail under load = low grade misfire. With low grade misfires, primary and secondary can pass all day long with no success revealing low grade problems.

Techs find those low grades thru stress testing using the Rotunda WDS, the follow procedure - Go to the Oscilloscope Tool and select Channel 3, then select Auto, then select COP_STRESS_TEST_RED. That will find the low grade problem thru pre-configured settings. You might know more about that, I never whiteness this being done, just read about it. I stress test the unconventional way :lol: - Monitoring thru a pulse reader that sort of acts like a noid light, but constructed for coil pulse and wired thru the firewall for drivecycle monitoring.

What I'm curious about is coil rating thru secondary. Tested @ 20k (I don't have the 10k setting- (Fluke/Craftsman meter)) . Resistance readings vary as said. The instruction when this happens is to replace the coil. That's if the coil resistance isn't equal to .55 or 5,500. My good sets range from 4.91 - 5.54 (4,910 - 5,400) @ 20k -Ohms setting.

Yea, I'm checking just secondary, I want to know what's hitting plugs in this case and what's best.

I recall reading a memo or TSB maybe, stating 50% of coils returned for warranty do not have a problem. I wonder if it's because of fluctuating resistance readings. This doesn't mean their bad, but the instruction for service is to change the coil.

I'm not a tech, just a DIY'er trying to get this truck to 300k performing as well she can.

I guess it doesn't matter - DG491/DG508/FD503/FD507 - 97-06 are all compatible. The numbers mean nothing - It's when you don't get any numbers when testing that counts.

Thanks