Is this issue fixed? I didn't see the result.

No, it is not fixed as of yet. The car continues to run each and every time I have tried to start it over the past week though...

Many thanks to phonedawgz for sending me an ICM to Coil connector, as well as a pigtail to splice in for the other connector. I will try to get that done and wired in the coming days.

I am getting the Fiero parts car in 3 weeks, and I will then swap in the ECM from that car to mine. (It is also a 2.8 with auto trans).

Replaced so far:

- New Coil
- New ICM (3 times)
- Fuel pressure is at 45 PSI when I turn the key on, and 40 PSI while cranking
- I am getting solid spark on Cylinder one, (checked with an inline spark detector)
- New Cap & Rotor
- New TPS
- New fuel tank innards (Fuel pump, sending unit, & all rubber lines that are fuel submersible rated)
- New Fuel Filter

Soon to replace, ICM to Coil harness / ICM to ECM pig tail

At this point it is virtually impossible to trouble shoot, as it starts and runs perfectly. I have to wait till it does this again. The first thing to check when it does happen again, is to see if it will fire up with starting fluid. Till then I am kind stuck waiting for the car to not run again......

Reasoning things out: When the car starts, it idles perfectly, no missing, no bucking in any way.... just runs smooth as it should. So, It is highly doubtful that all the injectors are bad. It is also doubtful that both of the injector circuits in the ECM would go out, but then start working again, on and off sporadically. If one bank went out, the car would start, or at least try to fire. When the car "acts up", the engine does not fire at all, just cranks as if the car had no spark, or no fuel. (of which I have both, at least fuel pressure)

Thinking this through, what actually tells the ECM to fire the injectors? There is no crank sensor on a 2.8. SOMETHING has to tell the computer to fire the injectors. It is not just a "Key On" event, as that would have the injectors firing simply with the key in the on position. Could whatever it is that tells the ECM to fire the injectors be faulty? If it is the ICM that sends this signal, that would rule this though out, as I have tried 3 ICM's thus far.

The ICM senses the engine is rotating via the pick up coil.

That signal is amplified and sent to the coil (under 400 rpm), and it is also sent to the ECM via the Purple/White wire.

The ECM uses that signal to figure when to fire the injectors, and to see what the RPMs are, and if the RPMs are over 400 rpm .....

Over 400 RPM the ECM sends a signal on the Tan/Black wire to the ICM to tell the ICM to now follow...

The adjusted (advanced) ignition pulse signal on the White wire.

The Black/Red wire is a ground between the ICM and ECM

---

The Purple/White wire signal is also used by the ECM to determine if it should keep the fuel pump relay energized. The fuel pump relay will be energized when the ECM sees pulses on the Purple/White wire and for two seconds beyond it/


----
So if the Purple/White wire fails the ECM won't fire the injectors during cranking/running. If during running the engine will just shut down. No backfire. No restarting while the Purple/White wire is not making connections.

If the Tan/Black wire fails the engine continues to run, but the ignition timing won't be advanced.

If the White wire fails, the engine will still start. The ICM has special programming in it that if the engine is running and it is sending pulses on the Purple/White wire but the ICM is no longer getting a signal on the White wire it defaults back to running on it's internal spark signal. If this failure occurs during operation you will get a code 42 and you will notice a short loss of power usually followed by a backfire in the exhaust when the ICM starts again firing the plugs after the injectors have still been injecting. If you hear someone complain about a loss of power followed by a backfire and the check engine light comes on it is almost always this signal/connection.

I am not sure what would happen if you lost the Black/Red wire connection.
===

Note also - while I described this as loosing the wire connection, it can also be caused by the ICM not producing the signal, the ECM not receiving the signal, the ECM not producing the modified signal, or the ICM not receiving the modified signal. Since the ICM is the easiest part to swap, it is normally the first one to be swapped for these problems. It also is the most likely to go bad.

[This message has been edited by phonedawgz (edited 10-14-2014).]

I thought in one vid you had no fuel at the rail?

To answer your question, "what actually tells the ECM to fire the injectors" the pick up coil talks to the ICM wich talks to the ECM.
The pick up coil acts just like a crank sensor, as crank sensors don't plug into the ECM but into the ICM. if that makes sense

edit to add: above was posted while I was typing

[This message has been edited by sardonyx247 (edited 10-14-2014).]

if the car is running good now, maybe its a good time to test out those used ICM's you have??

..and while its running, do the tap tap tap on all the connectors & stuff to see if the car will stall.

@sardonyx247: I never really did even remotely think that it was the cap and rotor, as it is so very, extremely, highly unlikely that it would cause the symptoms I am having. I just replace it as ro 100% rule it out.

@phonedogz Thanks, that all makes perfect sense, and the good reason to change the ICM <-> Coil cable, as well as the pigtail on the ICM. Thank you again for sending those, it is much appreciated!

quote Originally posted by Alex.07.86GT: if the car is running good now, maybe its a good time to test out those used ICM's you have??

Now THAT is a good idea! Why didn't I think of that?

quote Originally posted by Alex.07.86GT: ..and while its running, do the tap tap tap on all the connectors & stuff to see if the car will stall.

I did think of that. When the car will not start, I wiggled every plug, cable and wire I could find, nothing. Now that it is running, I started it, and again went and wiggled every plug, wire, cable, tapped on the rotor and all around it with a small rubber mallet, tapped on the ECM and wiggled the plug and wires going into it. The car kept running and never skipped even the slightest beat.

[This message has been edited by JohnWPB (edited 10-14-2014).]

John, was your avatar from before or after your series of unfortunate events?

Your luck doesn't seem to run in a favorable direction lately.

quote Originally posted by tshark: John, was your avatar from before or after your series of unfortunate events?

My vote is before, as the car is now blue.......................................

Yes, the avatar is from before. That is the very day that I brought the car home on a flat bed tow truck. Blown engine, 4 dry-rotted tires....Here is the thread where the saga began! LOL The large version of my Avatar is in that thread

I said the cap wasn't your problem, but it is something to look at as far as new caps go, they just suck, really really, suck. but look for crooked pins anyway. EVERY brand is like this, from high $$$ to cheap ones. All the same problem. cheap china crap.

I like phondawgz explanation above. It always seems these things boil down to bad connectors/wires in the area of the coil/distributor. My SE has done some of the same things, it cut out momentarily while driving, wouldn't start one day and now only cranks. When I replaced the ICM in May the lock broke off the bigger connector. It's now quite loose. The car also runs, hesitates, then backfires. These all seem to fit the explanation above. It makes sense to me that they are similar to your problems except everything else is in great shape on your car. It might not take much of a break or weakness to shut things off temporarily. The heat in our engine bays is more intense than front engine applications, so the insulation cracks and the wires flex and break strands, leading to intermittent problems.

I agree with 85 SE VIN 9 Member, I would bet a vapor lock.

quote Originally posted by 1Fred: I agree with 85 SE VIN 9 Member, I would bet a vapor lock.

Thats one of the things I said too, but the post whore dismissed it, he says it can't happen. So wrong. I imagine FL can get as hot as Vegas. Might not happen untill next summer, I fight this all summer long here.

To remind everyone that is is NOT an ign, ECM, ICM problem

quote Originally posted by JohnWPB:

no fuel pressure at the rail. It IS a fuel problem.
You are on the right track of starter fluid when it happens again.
Could even be possible to be the fuel pressure regulator, a possiblity. Hasn't been mentioned yet. I would invest in a fuel pressure gauge. Fiero store sells a nice perment one too. A little high price, but good still http://www.fierostore.com/P...px?s=52603&d=246&p=1

[This message has been edited by sardonyx247 (edited 10-16-2014).]

Johns brand new fuel pressure gauge says it has proper pressure.

My questions,

1) are the the fuel injectors getting a pulse when the no start problem happens???

2) Does the car start with starter fluid??

3) is there a problem with the TPS or its Cable?

John has two problems. They are both intermittent. One is shown in the video. The ECM is running the fuel pump correctly when he first turns the key to on, however the ECM does not re-energize the fuel pump relay when he cranks it. That would be caused by the ECM not receiving an ignition pulse signal.

A bypass regulator with a properly operating fuel pump pushes fuel through the fuel rail, and the regulator bleeds the excess pressure back into the tank via the return line. If you drove the car and parked it and it hot soaked the fuel rail, and the fuel in the rail were to boil - 1 - the excess pressure of the boiling fuel will push any excess pressure/fuel past the fuel pressure regulator and into the tank, and 2 - once you turn the key to on, the fuel pump will run and push any remaining fuel vapor also out of the rail and into the tank. The new cool fuel from the tank won't be boiling and you won't have vapor lock.

The fuel pump itself sits in the fuel tank. It is both surrounded by fuel and pumps fuel through itself. It would have to heat the whole fuel tank to near the boiling temp of gasoline to be able to vapor lock the pump located in the fuel in the tank.

[This message has been edited by phonedawgz (edited 10-16-2014).]

I still think you are suffering electrical gremlins that are either a poor connection or an iffy ground. I believe that the reply I posted on page two of this thread still applies:

quote Originally posted by lateFormula: https://www.fiero.nl/forum/Forum4/HTML/066267.html From reading this post, I suspect that the problem lies in the wiring and/or interconnects in the ignition system. I see three items that could be a possible root cause here: 1) The ICM to coil cable linked above. 2) The pickup coil on the distributor 3) The four wire pigtail from the engine harness (ECM) to the ICM. If you replace item 1 from the list above, that is a relatively inexpensive and easy swap to see if that solves the problem. Number 2 is something that if you wanted to replace, I would simply swap out the entire distributor with a Cardone reman unit. They have a newer design pickup coil on them. This repair has higher cost and more labor involved, but might solve the problem. Number three could be fixed, but would require a costly specialty tool to do right. If it came down to this, I would cut the connector off the pigtail right at the connector, and then install a new weatherpack connector and crimp new terminals on the ends of the cut wires. To do this requires a special crimping tool that is not cheap ( http://www.summitracing.com/parts/LNG-44905/ ). This would put a new connector on the engine harness with new terminals to connect to the ICM. EDIT: let me add to this that you could also buy a pre-made pigtail for this and splice it in. These are available from the Fiero store, and you could probably also get them from Napa or Rock Auto ( http://www.fierostore.com/P...px?s=65503&d=248&p=1 ). I would cut off the old connector and install a new connector myself, but I do have the tools, experience, and I would choose to do this rather than splice in a ready made connector. But that's just me.

And this:

quote Originally posted by lateFormula: The only other suggestion I could offer is to check continuity on terminal A on the 4 terminal connector on the ICM. That should be a black and red wire and is a ground path through the ECM. In my experience electrical gremlins are almost always the result of faulty grounds.

[This message has been edited by lateFormula (edited 10-16-2014).]

I did send John both a new ICM to Ignition coil wire and a new 4 pin ICM connector last week or early this week. Not sure if he got them on yet however.

quote Originally posted by phonedawgz: I did send John both a new ICM to Ignition coil wire and a new 4 pin ICM connector last week or early this week. Not sure if he got them on yet however.

I know, I saw that in the recent additions to this post. Much respect to you for sending those items to him as well as the detailed troubleshooting info you have provided here!

I'm now on the four wire connector to the ICM band wagon. Vapor lock wouldn't cause the tach to not register when cranking which has happened. The ground in that connector sounds promising because the actual ground is the one under the console (correct?) and therefore wouldn't be detected by the wire wiggle test.

i know John said he had an exhaust leak. I dont know where it is but it could be pointing hot air to the harness or it could have damaged the harness.

please check this out

Vapor lock DOES happen, I don't care what you think, I fight it EVERY summer with a lot of cars here. The theory is sound as why it shouldn't, but it DOES happen. Mabey not in your "cold" climate, but it gets damn HOT here, I would think FL could be the same. You even been in 130+ temps? Imagine that poor little engine bay with an exhaust leak pumping in hot gases in addition to outside temps. Exhaust leaks amplify the problem.

In the vid he has NO fuel, I can pull the fuel pump fuse, crank, crank, crank, still get some fuel to spurt out of the rail, so if pressure is built, then the ecm doesnt energize the pump, the oil pressure sender will when oil pressure builds, regardless of ECM. he should still have fuel at the rail, thus why I say a fuel problem. You can unplug the ECM, crank it till oil pressure builds, you STILL get fuel pressure. HE HAS A FUEL PROBLEM. That is at least one of his major problems, regardles of other problems.

[This message has been edited by sardonyx247 (edited 10-18-2014).]

Contrary to what one would think, Florida does not get that hot where I live, within a few miles of the coast. The humidity, yes, that's bad for sure! However for the temperature to hit the mid 90's here is as hot as it gets. There have been rare cases that it has gotten into the upper 90's.

I agree, vapor lock can happen for sure, I just don't think it is playing a role in my particular case. The one time the car died, I had been driving for maybe 5 minutes, and it was around 85 degrees, and the engine cut out as I was cruising along at 45 MPH. It was 3 days before I got it to start again that time.

quote Originally posted by sardonyx247: You even been in 130+ temps?

Nope. Nor have you ever been if you were in Nevada or Florida.

https://en.wikipedia.org/wi...temperature_extremes

I do have to say you must have some magic going there if you are able to get your fuel pump to run after you pull the fuel pump fuse.

[This message has been edited by phonedawgz (edited 10-18-2014).]

quote Originally posted by sardonyx247: if pressure is built, then the ecm doesnt energize the pump

I had wondered about this, and asked a couple pages back. Someone mentioned that the Fiero does not sense the pressure, and the fuel pump is always on for 2 reasons, when the key is first turned on for a couple seconds, and while it is running (Determined by the Pick-Up Coil --->ICM ---> ECM).

So from my understanding, is there is no Fuel Pressure Regulator, at least not in the electronic sense. There is however some sort of bleed back valve and hose to return the excess fuel back to the tank if I am understanding things correctly.

[This message has been edited by JohnWPB (edited 10-18-2014).]

Correct on ECM not sensing the fuel pressure. The fuel pressure regulator is mechanical and moderated by a vacuum connection. It is a bypass fuel pressure regulator. So it 'leaks' fuel back into the tank at the pressure it is set at. It does this via the return line.

Right hand side - black 'hat'. The vacuum port of the FPR connects to the T near the MAP sensor. The only other thing on this line is the MAP.





Sometimes the FPR diaphragm will rupture leaking gas into the intake manifold. If this occurs you would have fuel in that vacuum line.

The FPR should regulate the fuel pressure to about 42 minus the vacuum reading of the manifold

There is a back up switch for the fuel pump in the oil pressure switch. Whenever the oil pressure is above something low like 5 psi, the oil pressure switch also closes to supply power to the fuel pump. It is redundant to the fuel pump relay. Either being on will cause the fuel pump to run. Having both on or just one one makes no difference. Usually the oil pressure switch will turn on after a few seconds of cranking. Also if you shut off the engine right after it starts the oil pressure switch will keep the fuel pump running for up to about 45 seconds from the residual oil pressure.

I did notice the fuel pump not turning on when you cranked it. Usually the test is just a bump. Like about 1/2 second of cranking. Anyways I didn't say anything because I think it will just confuse things to also look at the redundant oil pressure switch. Up to you if you want to. If the oil pressure switch is closed (on) you will see the light being ON on your ALDL cable the same as if the fuel pump relay turned it on.

[This message has been edited by phonedawgz (edited 10-18-2014).]

Was the pickup coil replaced? Or the entire distributor?
Please excuse me if I missed it, but I read back through the previous 4 pages, and didn't read that it had.
===========
On a properly working EFI system, the fuel pump will easily overcome any vapor in the system. Even if it has to pump the vapor out through the injectors (which should NOT be the case) it should be clear in a couple of seconds.

Which reminds me of a situation that I observed...
Check your fuel tank vent line and make sure it is not plugged. It's also possible that the vapor canister is plugged, and not allowing the tank to "inhale". If that happens, it will create a vacuum in the tank as the fuel is pumped out, which the fuel pump will NOT be able to overcome. I HAVE SEEN this happen. Took the owner (our designated club mechanic, BTW...) several weeks to figure out what was going on, as it only happened during a longer trip. Took that long to build up the vacuum. The symptoms resembled "running out of gas". It stumbled a bit, then died. It was not a dead stall.
A quick check, when it stalls again, is to crack open the fuel cap. If there is a rush of air, you may have found your problem. If it immediately starts up, that would further support this.

[This message has been edited by Raydar (edited 10-18-2014).]

I went digging around in the shed today, and I found a distributor that I pulled out of the original engine that was in the car. It has, what I can surmise from the odometer, 60,000 miles on it, unless it had been replaced at some point. The engine it came out of ran, but it had a severe knock.

It appears to be in good shape, cosmetically just by looking at it at least.



I really am not familiar with the distributor, or how to tell if it is good or worn. When I grab each end, and I try to "Bend it" back and forth, there is no give whatsoever. When I spin it, it turns smoothly between the "magnetic stops". When I pull up and and from the ends, there is about 1/16th to 1/8th inch gap right above the gear. Is this normal?

This is where I am talking about, same distributor pictured side by side: pushed together, then pulled apart to show the gap:


The rubber O-ring is still soft, as I depressed my thumb nail in it, and it bounced right back. I do have a new pickup coil here on the desk next to me that I can put on this distributor just to be sure.

So, is that play in the above photo normal, does this distributor look like a good option to swap in to alleviate one more thing that it could be?

[This message has been edited by JohnWPB (edited 10-18-2014).]

quote Originally posted by phonedawgz: Nope. Nor have you ever been if you were in Nevada or Florida. https://en.wikipedia.org/wi...temperature_extremes I do have to say you must have some magic going there if you are able to get your fuel pump to run after you pull the fuel pump fuse.

What they show for temps, ask anyone who lives here, add 10 degs to that number, the reading they show is taken is the shade, I have seen thermometers read over 130.

I didn't say the pump would run with out the fuse, but I said that there is still some residual pressure left after pulling a fuse and cranking it a bit.
Then I said that if the ECM doesn't engergize the pump the oil sender will. Read carefully. 2 different things. Sorry, I worded it in the wrong order.

I said that if the ECM doesn't engergize the pump the oil sender will
I said that there is still some residual pressure left after pulling a fuse and cranking it a bit.
Reads better this way. sorry for the misunderstanding.

quote Originally posted by JohnWPB: I went digging around in the shed today, and I found a distributor that I pulled out of the original engine that was in the car. It has, what I can surmise from the odometer, 60,000 miles on it, unless it had been replaced at some point. The engine it came out of ran, but it had a severe knock.

John, that is not an original distributor, it is a reman unit. The pickup coil is what gives it away (the star on the shaft and the triangles around the perimeter pointed towards the shaft). There should be a small amount of "play" in the shaft but I think what is shown in your second picture may be too much. I cannot recall off the top of my head what the acceptable range/measurement is, but I'm sure someone will chime in with that value.

RE distributor gap:

That's not an original distributor. It has the star tongs. The original would have the big fin things.

The gap should be much smaller. To fix that you have to take the gear off, and insert washers. The proper ones can be found at rockauto.com, but they're pretty expensive at ten for ten dollars or so. A hardware store washer will probably do. If you're going to replace the pickup coil you could put some washers on at the same time. This gap probably doesn't do much for the original problem. When it's way off you may see the distributor cap moving as the rotor turns and you might find dust from the distributor cap inside.

One thing to mention though. If the distributor was replaced in a relatively low mileage car it may indicate that a PO was having the same problem way back then.

If I find the tolerance in the service manual I'll edit to include. Haven't been able to locate the tolerance information or a picture of an original distributor.

I've been looking at wiring diagrams and ground locations in the SM. Have you checked the ground for the ECM? I think that's under the console. From what people have said the ECM uses this ground in controlling both fuel and spark. Since the car was open for awhile this normally safe ground may have become rusty/loose. It's location would also be immune to the wire-wiggle test that otherwise might explain intermittent operation.

+1 on it being a replacement distributor.

When the distributor is being turned, the angled cut of the gears tends to drive the distributor upward. Thus the wear patterns on the washers on the bottom of the dist. Excess slack in the axis of the distributor would only effect timing scatter. - http://www.covvc.org/COVVCTech--TimingPart2.doc

The Black/Red wire is the only Low Reference (ground) wire that is used by the ignition.

The ECM and thus the injector grounds are the two ring terminals on the two sets of wires that connect to the studs on the front (far side) of the bellhousing bolt/studs.

http://www.fastfieros.com/t..._diag_vin9_part2.GIF
http://www.fastfieros.com/t...es/ECM_diag_vin9.GIF

Ok, now knowing that this distributor is a replacement, I am content to swap it in as a replacement. My thinking being the engine had 62,000 miles on it. I would imagine that the distributor was fine for quite a while, so it tends to make me think it probably has 30,000 or less miles on it, probably less.

I will put the new pick up coil on it, with Buddy's help, and get it installed. This takes the guessing away, and will rule out one more thing for certain.

[This message has been edited by JohnWPB (edited 10-18-2014).]

quote Originally posted by JohnWPB: I will put the new pick up coil on it, with Buddy's help, and get it installed. This takes the guessing away, and will rule out one more thing for certain.

Buddy's distributor is the old style. Yours is a newer style. I would imagine that the pickup coils do not interchange. I would install the distributor as-is.
(If you feel the need to do anything with it, just add a washer between the gear and the housing to take up the up/down slack. I probably wouldn't even do that.)

Dont add any new parts, they might add new problems.

if the pickup coil on the distributor ohms out ok (pin to pin -low or zero. pins to ground-infinite) leave it alone.

if your distributor doesnt move around a lot in its bearing - leave it in.

-anyway you can tape or patch up that exhaust leak?

Ok, the car is up to it's shenanigans again. I THOUGHT it was solved after replacing the ECM.



Took it for a drive Sunday about 30 miles north. Parked the car for 6 hours. Drove back 25 of the 30 miles and the car died again. Driving at a nice leisurely and steady 50 MPH, the engine just died. No sputtering, no nothing, just as if you turned off the key.

Since my last post I replaced the ECM (Main Computer), the coil and the pigtail harness from the coil to the ICM, and the pigtail from the Coil to the wires going under the intake manifold. After the ECM swap, The car idled and actually ran a bit better. That has been 3 months ago. Since then the car has not been driven too much, as complete suspension work has been done, and it was in the paint shop for a month.

I am not getting any spark from the coil when I just checked it a few minutes ago. I have an inline spark checker that I put between the coil and the distributor. I have replaced the ICM 3-4 times. Each time the car starts to run again, I swap the ICM's and test them. All 4 appear to be good. When I crank the car, it will not start, but the RPM gauge does pulse.

I currently have great fuel pressure.

It appears to be narrowing down to some sort of electrical problem, but I have NO CLUE what. I have replaced just about everything electrical on the car.....

Replaced so far over the course of trying to figure this out:

- New Coil
- New ECM (Main Computer)
- New ICM (3 or 4 times)
- Fuel pressure is at 45 PSI when I turn the key on, and 43 PSI while cranking
- New Cap & Rotor
- New Throttle Position Sensor
- New fuel tank innards (Fuel pump, sending unit, & all rubber lines that are fuel submersible rated)
- New Fuel Filter
- All grounds are clean, and solidly connected
- New fuel pump relay
- New gas cap (In case other was not venting properly)
- New Coil harness / ICM to ECM pig tail
- New Coil harness / ICM to coil pig tail

NOTES:
- There are NO check engine codes in the ECM when checking it with my laptop.
- The previously mentioned exhaust leak is on the trunk facing side. It is a leak in the manifold gasket, almost dead center, and blowing away from everything. It is blowing up towards the deck lid. It's a small leak, as I can hold my hand over it about 6 inches away, and not get burned.

[This message has been edited by JohnWPB (edited 02-17-2015).]

Pick up coil?

quote Originally posted by jmbishop: Pick up coil?

Through this thread, I have been told it would not cause the intermittent problems I am having. The car runs PERFECTLY when it runs. No missing, no lack of power or hesitation. Then like a switch it dies, and will not start for hours / days and sometimes weeks. Then it again runs PERFECTLY.

From what I have read from others, the Pick-Up coil dies slowly, and if completely went, would not start working perfectly again.

I was going to change the distributor, but was advised against introducing new parts possibly causing problems such as throwing the timing off by doing so.


I am at the end of my ropes here. I have tried to track down this problem for over a year now. I think I have it fixed, and take it for a drive, and all is well! Then out of nowhere, it does it again without warning. I was so mad the other night when it happened, for the 7th time leaving me stranded on the side of the road, that I lost it and threw my car keys at it and did one hell of a number on the brand new, 2 week old paint job

It does not look like I am going to Daytona with the car for the 3rd year in a row

[This message has been edited by JohnWPB (edited 02-17-2015).]

I had a similar problem and i actually forgot about it. I was driving along, no warning and the engine died. Just like the key turned off. No tach movement....nothing. 2.5 minutes in a well lit waffle house parking lot revealed a tach filter wire grounding out on the valve cover bolt. Problem solved. Check that out too.. one of the white wires.
Ron

Could your new coil be bad, sometimes when a bad coil gets hot it "opens up" inside and doesn't produce any spark.