testing coil output
 

was curious how to check for coil output. suspecting a wire issue causing the leading coil not to fire at full making for a weak leading spark and running rich with some backfires. if there was a weak ground on the coil would this be caused?

also what should the input voltage be during cranking? it was showing down around 9v while the motor was cranking is this normal?

thanks

bump please. i'd just like to know if a 9v drop is normal

ref the work shop manual for testing coils...but for starters, coils are given 12V power from switched ignition, and then the ECU grounds it to fire.

9V is low. Coils to have a max Ohm res. of 1 Ohm.

i just put the multimeter between the + and - leads with the coil off to test if the coil was getting power from the ignitor and ofcourse with out the motor cranking there was nothing since the ecu wasnt closing the ground. i have found nothing in the fsm about this. i'd like to know the voltage coming from the ignitor should be more close to 12v when it fires or if 9v is normal...

I'd like to know about this too. Since you were using a voltmeter and the signal you are measuring is AC in nature you can't really say that it is 9V. The signal is changing too quickly. It would be much more useful to measure with an oscilloscope or something that could capture the rapid change. You could at least measure the resistance between the coil +input and +battery (with key ON) to look for an obviously poor connnection.

If you suspect you have a bad coil, I have a known good coil removed from a low mileage car/engine for sale.

New from the dealer they sell for $142.

IM asking $50 shipped USPS Priority mail.

i was using the multimete in dc mode, and had it hold the peak voltage signal. of course you cannot just see for a quick second what the signal from the ignitor is at the moment the ignitor tries to fire the coil...pretty much what i'm saying is that it seems the coil is only receiving 9v of power and i'm curious if this is what it should be seeing or if there is possiblly a bad ground connection to the coil or something :)

for that i would get an msd coil or just use a t2 coil like i am now

So, you are using T2 coils and not FD coils? Do you have an ignition amp?

i was using a mallory box but i took it off...

imonly using a t2 coil for the leading

Here's some info:

hm didnt know that. i mean i knew the t2 coils held up better to ignition mods that the stocker fd ones. althought this still doesnt connclude my initial question of coil INPUT. the amount of voltage that the coil is seeing. this should be irrelevant to the type of coil i'm using.

However, that statement does correlate to trying to figure out why you have weak leading spark; i.e. the stock FD ignitor isn't strong enough for the FC leading coil.

yea i know, i do appreciate the info i didnt know that was the case. i'll either be reconnecting my mallory box or just droppingin an fd coil without the box (fried the fd coil...hence the t2 lol)

but if anyone can tell me about the coil input voltage and what it should be that would be great, as now it's mroe of a case of my curiosity since mahjiks info is sure to solve my problem

I you read the wiring schematic you will see that the coils are connected direct to ignition switch +12v.That mean that if you turn the key to on and measure the voltage between coil +12v and chassis ground you have to see >12v.
If you measure <12v then check your harness.
The igniter switch only the ground.
So the coil input voltage on fd must be the same voltage who have the battery.

If you're measuring below 11V while the motor is cranking, it's likely that your battery is low.

How long since it's been charged?


This thread might help you also:
https://www.rx7club.com/3rd-generation-specific-1993-2002-16/you-pro-troubleshooter-ignition-problem-569498/

-s-

1: The battery was connected to a car starter...yes a big shop one at full cranking power since we had the alternator belt off so there wouldnt be a voltage drop and the battery had been charging prior so either way thats out of the question.

2: I did not check between the positive lead and the chassis ground i checked between the positive lead and the negative lead of the coil. the circuit between the + and - wires is only closed when the ecu closes the circuit by closing the Negative side that goes through the ecu. If the coil was seeing a constant closed circuit it would melt...trust me...and ooze..and crack..and smoke..

If you want to measure the voltage on coil connector you would need oscilloscope.
But there are no reason to measure like that.If you have >12v from chassis to coil connector then you are ok.

i do have another questions ort of pertaining to this... the ground that goes through teh coil (not from the - lead but the ground that grounds the coil through the bracket) if this ground were weak could it cause ignition break up? could you ground this ground straight to the chassis? i mean it seems it would be anyway since it's mounted on the motor...but there is a ground cable from the harness that comes with a loop and bolts to the bracket also.

If you check with a dc voltmeter between the positive and negative leads of the coil with the ignition on and not cranking, you should read zero volts, since the ECU is not pulling the negative side of the coil to ground... the ECU should look like an open circuit to ground, no current through the coil, and so both ends of the coil are at the same voltage.

If you check between the positive lead of the coil and chassis ground under the same condition, you should read +12 volts.

If both of those readings are OK, and the resistance of the coil primaries (both leading and trailing) is below 1.0 ohms, and the resistance between the L1 and L2 coil tower terminals is between 9.6 Kohms and 16.0 Kohms, and the resistance from the trailing coil tower terminal to chassis is infinite, then the coils are OK as far as can be tested without a "Megger."

(The ground wire to the coil assembly bracket seems to work fine on my stock FD.)

hmmm

well i dropped my mallor on there but still getting break up...i'll make sure the grounds are okay and the tps is adjusted right and a few other things in a few days. seems to be running stink rich because of an aparent lack of spark, hence the break up. no wideband but just looking at and smelling the exhaust is pretty much a dead give away. for all i know the tps needs adjusting and think the throttle is half open when it's at idle.

alsi it wont idle below 1500 rpm..which i can see as being because a combo of rich afr's and low spark. any lower rpm and the motor wouldnt be spinnign fast enought o expell the excess fuel and would die..makes ense i guess