I just got this 87 rex, the guy toled me it wan fine then he parked it. the next morning it would not start for him. so its ben sitting for 2 years now. i look at the sparkplugs and found that the trailing is sparking but not the leadings. i looked in my shop manuel and it tells me to connect an ohm mether to test the ressistence, from .2~1 dose that mean if its with in .2 to 1 it passed? and her is how i tested it. i pluged the voltemerter to the 2 wiers + and - on the coil and it was reading .5
dose that mean that the coil its still good? and if so what else can i look at to solve this problem?
thank you for your time

 

I personally would look for spark by plugging a spark plug into the plug wire, and grounding the electrode. No spark? Then swap the coil

rat

 

First off, you should be on the resistance scale on the meter, not volts. The resistance of the coil windings should be less than 1 ohm (although I've heard of several people with slightly higher resistances that seem to have no problems).

IF you were on resistance, and you read .5 ohms, then you're good. Next step is to check for the input voltage to the coil with the key on. Should be 12v (battery voltage) on the black/yellow wire at the connector near the coil.

 

Nah..

Swaptronics owns..

 

ok so the power wiers on the leading coils read 2.43volts, now whats my next thing to look at?

 

Lol, you must be an aircraft mechanic

 

2.43v with the key ON? That ain't good...Can you hear the main relay clicking when the key is turned? You must, if you're getting trailing sparks.

If it's as you say, you must have a wiring problem between the main relay and the coil...

2.43v DC with one probe in the connector at the black/yellow wire (or backprobed while the connector is still together) and the other on a good ground, right?

 

AVIONICS SIR!!! 14.5 years USAF!

 

Ahh, then that explains a lot, since you guys have no idea what kind of tron magic goes on in the black boxes, swapping 'em out is a whole lot easier than troubleshooting. Then you call in us electricians to fix it if the black box didn't. That's how it worked in the Navy (4 years was enough for me- big airline A&P money too much to pass up, lol)) anyway.

Just messing with ya man

Retiring in 5 1/2 years?

Glad to see your car's back on the road, BTW....

 

ok i did the test using both wires from that plug when it was off il run the test once agin like you sayed

 

ok i ran the test and found that it dose have 12V but i turned it over at night, the leading flashed one just as it started turning over but only one small flash 2 times. then nothing but still has 12V at that wire. whats next?

 

Now you need to start looking at the CAS and ECU, because they're responsible for the timing signals to the ignitor/ coil that you say is petering out.

Are you sure your plugs aren't fouled?

The plug wires in good shape?

 

i know the plugs are good cause i wsaped them from leading to traling and still nothing il swap the wires in the morning tho, i just figured that it would be odd to have 2 bad wires buy hey i could be, il look in to the CAS and ECU now that we have kind of narowed it down thank you much saved me lots of time.

 

i know the plugs are good cause i wsaped them from leading to traling and still nothing il swap the wires in the morning tho, i just figured that it would be odd to have 2 bad wires buy hey i could be, il look in to the CAS and ECU now that we have kind of narowed it down thank you much saved me lots of time. ok next question what is the cas?

 

I was reading that you should do this: Take the old cas. Put the cas's electrical plug on the old cas which is now in your hand.

Turn the key to ON.

"Lay the two lower sparkplug wires on the left fender near the left strut tower.

Spin the cas's lower gear rapidly. Actually you don't have to spin it very fast at all. IF the fuses are good the thing should make spark at the plug wires on the fender. "
is this how you test the CAS? or is there an other way?

 

i was wundering if there is a way to test the ecu's, and the cas? and if there is an other ways to make the leading coil fire (at the wright time like can i take the traling coils and advance the timing so much that the trailing will run my leading and just not use traling?

 

I think that is a splendid way to checkout the CAS and the ECU at the same time.

It's quicker than ohming out the wiring b/t the ECU plug and the CAS.

You could take the CAS out and put a meter on the appropriate wires/pins on the cas and spin the cas gear while looking for A/C voltage at the meter. You might see as much as 1-2 vac.

Spinning the gear on the bottom of the cas with your finger is best as long as you know how to reinstall the cas and have a timing light to set the timing when your through.

Actually you can pull just ONE wire out of the Lead Coil's bore (leaving all other wires alone) and lay it just outside the bore of the coil. Then spin the cas gear. If the cas/ecu are good there will be a bodacious spark b/t the bore and the wire that lays just outside the coils bore.

 

cool thanks il look ing to it as sonne at the weather get to plus 10 C its -5 here lol

 

ok heres an update on this problem, i ohming out the wiring b/t the ECU plug and the CAS, and the from the ECU to the leading Coil with the ECU off that is. all wires are good, the next thing i did was take all 3 coils aparts and noticed that the traling white wire on the modual seamed to have a little buble coming out of the wire, i all so took 2 wires off the traling coil and installed it on the leading coil and i did get spark, so im left to conclued that eather A the ECU is faulty (witch i took apart and found no burt spots or any thing that looked abnormal) or B the leading modual is the problem. dose any one know how to test the ECU or the leading coil modual? and is there any ways i can advance the timing so much that I would be able to use the traling coil as my timing? i do understand that i would have to make a braket to hold the cas in place to hold the timing, but can this work? and is it ok to quit using the traling plugs (leaving them in lol)

 

I thought you tried the "Hailers" test and rotate the CAS with your finger while looking for external spark? That would've tested the ECU for you.

Unfortunately, I don't think you could swap the trailing igniter into the leading position to see if the ignitor is bad.

You ohmed out the leading coil & it was good, right? That leaves the igniter, if the ECU is good. If you want, put everything back together and check for the timing signals the ECU sends to the leading coil assy via the green/yellow wire (on the plug leading to the igniter wiring). Leave the plug connected, and backprobe it with the meter (other lead to ground). You should get about .8 volts at idle, which means you'll probably get a bit lower than that during cranking, maybe .4 or .5v. ...If you get nothing, then suspect the ECU. If you get at least something over 0v, suspect the leading igniter.

Probably be easier to do it Hailer's way, though, you think?

 

Shoot, you could have just done a swap and been done with this whole thing!

 

Lol, Rat speaks wisdom

No spare parts to play with?

 

no I dont yet might just go out and get an other partss car that dam igniter is like 600$

 

and the other thing that i thot it could have ben is the condensor but according to the wireing diagram it looks like if the condensor is fryed it the loading and traling would not owrk so i think its the igniter all so thank you much for all your help
ps what are you talking about J-Rat when your saying to swap?

 

He means to "swap" known good parts in to the system for troubleshooting. It's a military and airline thing, because there are usually plenty of spare parts to play with. We usually don't have that luxury on our cars, unless you happen to have a good parts car sitting nearby...

If the condensor shorted out, the fuse would have blown. And if it "fried" and opened, you just wouldn't have any electrical "noise" protection for the low voltage timing signals, which may screw with the igniter's head.

If you think this may be the case, make sure any spark plug wires are at least 2" away from any wire bundles that the leading igniter may use for its signals...If any plug wires are sitting on the wiring harnesses, push them out of the way and try it all again...