If your Fiero was running good but now it won't start - watch the tach as you crank the engine. If you see the needle bouncing as the engine cranks, the ignition system is working. But if the tach just lies there at zero - here's how you figure out what the problem really is. It'll take a few minutes - but it'll save you time and dollars in the long run. Many good parts get replaced chasing Fiero ignition problems.

You need a voltmeter or test light; connect the negative lead to ground. Now, gently remove the two pin connector from the side of the distributor and measure the voltage on both pins in that connector with the ignition ON. Also, wiggle the wires as you're measuring the voltage.

Results:
Solid 12 volts on both wires: bad ignition module.
Solid 12 volts on only one wire (the pink one): bad coil.
No voltage on either wire: bad fusible link.
If the voltage varies as the wires are moved, the cable between the distributor and coil is bad.

That little 2 wire cable from the distributor to the coil is a known trouble source. The wires break where they bend coming out of the connectors; when they do it usually results in an intermittent connection. What happens far too often: wire in that cable breaks, car dies. Owner says "ignition module" or "coil" and replaces the suspect part. While doing this, they move the bad cable and the wires make contact. Car starts; it's a successful repair. Nope - they just replaced a good module or coil. In a little while they'll do it again.

Save your money and avoid an unreliable car - use this simple procedure to pinpoint the failure.

quote Originally posted by Whuffo: You need a voltmeter or test light; connect the negative lead to ground. Now, gently remove the two pin connector from the side of the distributor and measure the voltage on both pins in that connector with the ignition ON. Also, wiggle the wires as you're measuring the voltage.

Gently remove the two pin connector. Is this the wire that plugs into the ignition module? or somewhere else? Does anyone have a photo to show me which one it is?

quote Originally posted by Gecko: Gently remove the two pin connector. Is this the wire that plugs into the ignition module? or somewhere else? Does anyone have a photo to show me which one it is?

The same one you had pictured in your thread looking for the part number of that pigtail. The other connection off the dist has 4 pins.

Thank you.

Now for a stupid question. Am I testing from the side that plugs into the ignition module or the side that plugs into the coil?

Great thread to reference, but i want to add a little bit of plain experience to it to elaborate on the simple electrical test.

-Car stalls and can't restart, but you see the tac bounce around when you try to start the car = its probably your ignition coil (btw the "coil" described in the first post in this thread is the 'ignition coil' not the 'pickup coil'). I've had people tell me that if your tac goes up while starting, your ignition coil is good - Wrong! You ignition coil It could very well - and very likely be bad. Also a lot of the time when your ignition coil goes out you can occasionaly start the car, like once a day out of a lotta tries. If you get it started and you try driving it, it will bog under hard excelleration and possibly stall. Once it stalls, its another 100 tries to restart or another day or two of trying on/off.

-Car stalls and can't restart, but your tac doesn't move at all/moves backwards to 0 = its probably your ignition modual or your pickup coil. If your ignition modual goes out then most likely you aren't gonna ever restart it. If its your pickup coil try jiggling your pickup coil around/back into place - my old pickup coil fell apart from old age and would bounce off its ground over bumps in the road - causing the car to stall and make me pull the distributor cap off to put the pickup coil back in its place...

Also two 12v lines in the first test can mean its your ignition modual OR your pickup coil! So do an omh test on the two wires comming from the pickup coil to make sure thats ok, should be btw 750-1500omhs. Note u gotta take ur distributor cap off, and its the plug going into the back of the ignition modual, its a 2 minute job. If it tests good but its falling apart (like into two peices or getting wobbly) - you probably need to replace it. Have Autozone do atleast 15 tests on your ignition modual to figure out if thats bad or not (occasionally will test 20x good and still be bad, but mine tested bad on the 6th try when mine went out).

Hope this helps someone! (especially me when another ignition component breaks nxt year )

edit: double 12V on that connector just means ignition coil is ok - NOTHING MORE! but usually if the ignition coil is ok its gonna be a icm or a pcu.
edit: Note to self, read this:
https://www.fiero.nl/forum/F...HTML/094757.html#p18

[This message has been edited by cloaked (edited 09-09-2008).]

My future solution to this sort of problem for mine........intalling my 3.8sc and getting away from GM's crappy ignition. I hate distributors! Yeah, I know, its an expensive way around the issue. LOL

Holy freaking crap! If this is the problem on my car I will... do something.

I have a nonworking tach that I have not started to diagnose yet due to other problems. I niticed that both connectors going into the module both have one wire that is half cut going into it and I am talking FLUSH with the connecor, so I can't solder it. Where can I buy new connectors for an exact fit? Or do I just find someone elses Fiero and cut theirs off for myself? Bwahahahaha!

A bad ignition coil wont neccesarially cut power to the module. And just because the module has power but no RPM register, doesnt mean the module is bad.

ICM - Ignition Control Module
PUC - Pick Up Coil

If you dont get RPM when cranking, its either the ICM or the PUC **

In the 2 wire connector on the ICM, check the white wire resistance to ground. If its open, the module is bad. Even when not cranking, it will show some resistance to ground.

If you get medium resistance to ground, crank the engine, if you dont get pulses of lower resistance, then the PUC is probably bad.

Test the PUC, it should read ~820 ohms across the 2 terminals, and have no connection between any terminal and ground. Theoretically the PUC should put out a miniscule AC voltage when the engine is cranked, I havent tried that myself.


You can also take the module to any parts store to have it tested for free.

A new ICM should cost ~$35, PUC ~$12, Ignition coil ~$14. Obviously costs vary, but incase anyone wants a ballpark.

The coil will often fail when hot, but work fine when cool. So the car may cutout, miss, backfire, or stall after it heats up (usually all 4 in that order) then fire up fine once it has set and cooled. Modules usually, but not always, fail once and thats it. Since the coil may only fail when hot its hard to test.


** it could also be the tach filter shorted, but its rather uncommon

Some the below file has been covered but checkput the rest it may save you money and hair:

Your’s could be a common problem and don’t cost anything to check.
Try this:
Watch the tach when cranking if it don’t move you're not getting pulses from the distributor. If so, it could be a faulty module in it or more likely simply corroded connectors at the base of the distributor. Reseating those connectors a few times could clean the pins some and also do the same to the connectors on the coil etc. These cars are old, and old connectors corrode. Such can also manifest itself as intermittent misfires, and engine cutouts.

BTW: lots of folks keep replacing modules and coils thinking they are bad because the new ones FIX the problem, when in actuality the fact that they simply unpluged the connectors and repluged them into the new unit cleaned the contacts enough to make it work again, at least for a while. It's smart, to replace those old connectors with new ones.
BTW: Cliphouse has those connectors

A little more insight just from first hand experiences today helping someone solve a no spark issue:

Preface:
ICM = Ignition Control Module
PUC = Pick Up Coil
"Coil" = ignition coil

Just to give you an example, im sitting in my fathers Fiero right now, the one I said before we had just fixed. Im a little lost, but here is my best account of what has happened.

For the last month he has driven it, sometimes it would cut out in the middle of driving and stall. He would get out, wiggle some wires, start it up and drive away.

So he called me 3 days ago, asking if we had any ECMs laying around. He had replaced this and that and couldnt get it to run. He also had code 42.

So I went over that day, brought an old module I found in the garage, checked it out, he was installing a PUC when I got there.

We got to checking and his module was bad. Replaced it with the one I brought after a lot of testing and it ran. So I left him there to put everything back together.

He calls today, the car quit running before he got it out of the garage, he has picked up a coil and a ICM and still cant get it to run.

Well I brought over my oscilliscope and really dug into it. Bottom line, his original module was bad, apparently his original coil was bad as well, he had replaced the coil with an old spare before I got there today, and had a new one hanging on top of it, but it still wouldnt run because his new module was bad.

So he had
old module bad+ old coil bad + good PUC and he replaced the PUC
spare good module + bad old coil
new bad module + good spare coil
new bad module + good new coil

So you can see how you can get bad new parts, and how one bad part in the mix, if you switch things up wrong, can leave you scratching your head for 3 days. Its very important to start at the top of the "food chain" and test each componet before making assumptions or buying parts.

One thing for anyone who wants to know how to test these componets. Here is what I have fine tuned today.

1: The PUC will generate AC current when it is turned. Test across the two PUC terminals when cranking, you should see low AC current.

2: With a known good PUC, to test the ICM, unhook the coil and the 4 wire plug from the ICM. Take the 2 plugs from the coil, jumper pink to pink to power the coil, and when you crank, you will get pulses on the white wire from the module. Unfortunately, I dont know how to measure these pulses with out an Oscope, if you have a multimeter with frequency setting, you may well see 28 hz when cranking. you may see volts, and Id be willing to bet, if you test continuity to ground, you will see it pulse (an analog meter would work better for this). If anyone wants to contribute to the Fiero community, try these methods and report back. I would, but I dont have a stock Fiero engine anymore.

3:To test the coil, if you have confirmed the ICM is working, then there must be power at the coil, so if its not sparking, then its bad.

The ECM has no input on sparking when the engine is not running, so its fault, or lack of, is completely irrelevant until you get the system sparking.

[This message has been edited by 86GT3.4DOHC (edited 09-01-2008).]

quote Originally posted by Whuffo: No voltage on either wire: bad fusible link.

I am having this problem with my 88GT but it will start after being hooked up to a battery charger for ~10min. The battery is good, had it tested. What is the "fusible link" I should be looking for?

got anything for the DIS systems? im haveing some "no spark" issues right now. ive been looking everywhere for a flow chart. nada so far.

i did just win a GM Ignition System Operation & Diagnostic Manual off ebay. so i know this is going to help. good find, and i wasnt even looking for it!

------------------
First LX9 Fiero GT, 1987
If you can't fix it with a hammer, you've got an electrical problem
Fiero's are people too. We pay just as much attention to them, if not more than our loved ones
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Google Videos of My GT

The DIS system is fundamentally the same, but a little simpler.

The Crank Posistion Sensor (CPS) has replaced the PUC, but still acts the same and performs the same functions.

To test a CPS, just check for AC voltage between the two pins while cranking. Voltage means its good, flatline means its bad. Its signalling right off of castings on the crank, so theres no 2 ways about it (other than bad wiring)

The DIS module (ICM) is very simple. Just feed it 12v, ground, and CPS signal and it will spark.

So confirm you have 12v and ground to it, confirm the CPS is outputting AC voltage, and take all the plug wires off and crank. You should be able to watch the spark jump from tower to tower in sequence. If any one coil isnt firing, its painfully obvious. If none of them are firing, I would take the module in to be tested and plan on buying a new one.
As far as the car only starting on battery charger, Im gonna go with the battery has to be bad, or you have a bad connection that is being remedied by the charger. If you had a blown fusable link, then its blown, and theres no way for it to ever work again until its replaced. And think about it, all you are doing with the battery charger is forcing more power into the battery, thats not going to effect anything else.

So, its either got to be the battery doesnt have the power to crank the engine, or there is a bad connection and the battery doesnt have the power to overcome the resistance AND crank the engine under its own power. OR you are changing something, wiggling something, when you connect the charger.

I have a brand new ICM in the car, so I know that portion is good. Is there a way to test the 4-pin connector that attaches to the ICM to read the voltages with the ignition on? To make sure the ICM is getting power?