Ok, my mom's '95 van stalled at Church this past Sunday. I spent most of the following Monday and part of tuesday, first replacing the fuel pump (it was not running when you turned the key, was getting noisy beforehand.). Once the new pump was in, I tried to start it, and the pump was now working, was definitely getting pressure. But the van just cranks and won't start. When I test for spark, there is no spark. The ignition module (EDIS-6) tests good on the bench, my backup one works no better. I have replaced the crank sensor.

I don't know what I did, but I got it started, and drove it home. But now that its parked at home, it doesn't start, same issue as before.

So, I've looked at the schematics. I have power to the ECM, and power is getting to the EDIS module too. The crank sensor has continuity. I also tested the ground, and it seems fine too. What are some other issues that can cause a no-spark condition (the is no spark on any cylinder, so plug bad wire, plug, coil pack is ruled out.

 

My next step would be to look at the cam sensor.

 

Ignition switch failing?
ECM failing?
Inertia switch?
Wiring harness connector unhooked recently? (Bent/poor pin connections on re-connecting)

 

I don't think its the ignition switch, as the ECM and EDIS module are both getting power when the key is on. If the ignition switch were bad, then there would be no power to those components.
ECM failing, maybe. Thats a last resort.
Inertia switch does not cause the ignition system to cut out. The fuel pump is running, I'm getting pressure. The inertia switch cuts out the fuel system, but does not tie into the ignition in any way.
No connectors were unhooked. Nothing has been changed recently, save what was involved in the changing of the fuel pump, which is working correctly.

I don't recall there being a camshaft sensor on this model. My '97 had a cam sensor, but I thought the '95 only uses a crank sensor. Doesn't the cam sensor have to do with sequential fuel injection, which was introduced in '96? I don't recall my motor having one, and if it didn't work, I should still get spark, and would get a code for a bad cam sensor. I have no error codes at all.

Here is the wiring diagram I am using.


I'll take a look at that.

 

Not to sure about that, Catalog lists a syncro/cam sensor from 1/1/95-12/31/95 F3TZ 12K073-A NR. and then a separated Syncro 1/1/96-12/31/97 F67Z 12A362-AC/F67Z 12A362-AAB & cam sensor F58Z 12A112-AA.

 

here's a good troubleshooter:

Engine Won't Start No Spark

 

None of those troubleshooting tips are any use.

The crankshaft sensor has already been replaced.
The ICM has already been tested and confirmed good and swapped out with a spare, made no difference. Too expensive to experiment with, they cost ~$200.
Can't be bad coil because these use a coil pack with three coils. All three coils would have to fail to cause an ignition failure.
Ignition switch has already been tested, the ICM is getting power when the key is on, so the ignition switch is good.

The camshaft sensor is only found on the late model '95 (i.e. prerelease '96) Those are the ones that got the OBD-II computer before the '96 model year began. Trust me, I built this motor, it has a dummy oil pump drive and cap with a retaining bolt, no sensor. Even if the cam sensor were to fail, the computer would set an error code, and lock it out, and use a limp mode instead. Even in limp mode the vehicle will run and start, it would just have lower performance.

I will need to get a scope to test with, I'm starting to think there is either a broken wire or bad ground, or the computer has an internal fault.

 

if you think the computer may be at fault, then disconnect both cables from the battery and reconnect after 25 minutes to "refresh" or "cold boot" the computer.

 

Off the top of my head, I like the broken wire theory.

I know it's a PITA to get to, but you've covered the plug-n-play possibilities. This is where I'd use a breakout box and 'scope the crank sensor line at the ECM. AFAIK, the crank sensor signal is the only input required for the ECM to signal the ICM to ground/unground the coil pack.

You know the coil pack, ICM, & ECM have power, so it stands to reason that either the ECM is not receiving a valid crank trigger signal, or the ECM's driver transistor(s) have fried -- not as likely, since there's three of them.

Or it's something else

[later]

Oh . . . easier next step: 'scope the tach line (Tan/Yellow) to the ICM, since it's easy to get to. If a tach pulse is present, that would verify the crank sensor signal and the ECM are not the no-spark culprit.

 

Wow what fun!

I have a hard time thinking the pump and spark were bad at the same time. Although possible..So the pump primes? When you crank does the pump run indicating a crank signal?
When you couldn't get it to run after the fuel pump change and then it did maybe that indicates a wire shorting out or opening. Maybe something you were touching...Maybe the orig problem was related to no crank signal? Seems strange you got it home then no go...


Dick

 

I'll look into that.

But heres a few things. The ECM never sees the crank signal. As shown in the schematic, the crank sensor connects to the ICM module. The ICM module decodes and interprets the crank signal, and then sends a tach signal and PIP signal to the PCM. The PCM uses those signals to time injectors, etc. If this signal is broken, you will get spark, but no injector pulse. My symptom is that there is no spark, so the theory of a broken wire between the ICM and PCM is not likely. This is why the EDIS modules are sought after for custom ignition applications, they can run independent of the main computer, so they act as a standalone ignition controller, all you need is the crank sensor, a 36-1 toothed pulley, the EDIS module, and a power source. Several OEM and aftermarket computers can interface with it, so EDIS is a popular choice for Megasquirt.

The PCM then sends a SPOUT signal back to the ICM to let it know how much to advance or retard timing, and how much to adjust dwell. If the ICM does not get a SPOUT signal, it defaults to 10 degrees fixed advance. The ICM is capable of operating independently of the PCM.

I will try to test for a tach signal. If there is no tach signal, it means either the ICM is not reading the crank signal (back to broken wire) or the ICM has an internal fault, even if it tests good.

 

Ah, yes, you have it correct, forgive my not looking closer.

 

Looking at the schematic, one thing I haven't tested is if the coil pack is getting power. Looks like the coil gets power from the red/lt-grn wire, and the coils are fired when the ICM grounds the respective coil.

 

Duplicate post deleted.

 

Losing the clutter, this should be the ignition system isolated.

Click HERE for larger


C103 looks a good place to backprobe for coil power supply. It's the left connector of the two main engine harness connectors.

Click HERE for larger



I haven't ever had a bad harness splice on an Aerostar, but I sure have on old Nissans!

I'm sure you know this, but for others reading: when suspecting a bad connection (broken wire, corroded splice) you want to check voltage with a load on the circuit. If you pull a connector and measure power, that does not mean that you have power when the connector is plugged back in and the circuit is loaded. If possible, check the circuit for power with the circuit in the malfunctioning state (ie don't unplug & plug connectors randomly). Backprobe and if there's no voltage, then unplug & inspect.

I think I'd just connect a tachometer to the tach line and see if it wiggles J/K, I doubt modern tachs wiggle at 300 RPM, but the old ones did.