Need a bit of help with a 94 Camaro not sparking

[Talyn]

I've been working on this 94 3.4L Camaro not producing spark. It won't even produce spark to make it start. If you aren't familiar with the ignition system I'll fill you in as to what it needed to at least produce spark to make it start. It has a 7x crank sensor, ignition module, wires, plugs and coils. The ignition module can create spark on its own even when unplugged from the PCM if it has a 12 volt supply and the crank sensor input. It produces a spark until the PCM tells the ICM that the PCM is taking over. Unplug the PCM and it runs on a built in spark map, mainly used for starting.

It came in with a no start issue which I traced to no spark. The coils resistance checked good. I don't believe the coils to be an issue and the ICM isn't supplying voltage to the coils as well. The ICM also isn't supplying the PCM with an RPM signal. The symptom is very intermittent spark. When it does spark the tach moves. When no spark, no movement.

The crank sensor (the 7x/3x sensor, not the 14x) has a suspect looking connector which had been butt connected prior. I replaced that with a new plug, soldered and heat shrinked. I checked the resistance of the sensor and it is in spec. I also checked the wires and nothing was found wrong with them. I also used a multimeter to check for ac voltage while cranking and that checked out as well. I wasn't satisfied with that so today I put the sensor plug to the ICM on an oscilloscope and the wave form is what it should be (if interested I can post that). So that input to the ICM checks out.

The 12 volt to the ICM also checks out. Same diagnostics as I used on the crank sensor. DMM, wire check and scope. It checks out fine with constant voltage.

So that leaves the ICM. I replaced the ICM with a used one. Same thing. I then got a new one and it seemed to work better but the the sparks were still not 100% constant. There was more spark, but it still took a break. This was verified through a spark tester on the coils as well as removing the coils and using a DMM to watch for voltage. Now, after I replaced the ICM the spark became more consistent but still had a hiccup. However, now its more inconsistent requiring more cranking than seeing spark or voltage to the coils.

I also checked the female on the sockets and they are nice and tight on the ICM pins.

Any ideas?

 

[Keithmania]

I am sure you checked this already, but it sounds a lot like a grounding issue to me. I know that some of the GM cars had a wiring harness were several grounding straps mated into one connector and then was grounded to firewall and if that connector fell apart it would cause grounding issues...

 

[Talyn]

all the grounds are good

 

[jeeptech1]

ah. gm and their stupid ignitions! i swear they make em way more complicated than need be! well, not gonna try to solve ur issue for you cuz without looking at the car i will just be wrong and mislead you. but i have always found that when the problem is this complicated looking its always something stupid causing it and when you find it you kinda just smack your for head and go duh! but if ALL your wiring is good then possibilities are bad new icm (seen that before), possible bad ecm. but leanin towards the icm since you have good signal to it and when it works you get a tach signal and spark.

 

[eflores]

Have u pulled codes on it yet?

 

[Talyn]

Just tried another ICM

I haven't pulled the codes.. needs some form of an OBD I reader. Key cycle nor does paperclip method work on that system.

 

[jeeptech1]

snap-on modis scanner has obd 1 capabilities.

 

[Talyn]

I am not sure a scan tool would help as the ICM should produce spark on its own w/o PCM help.

 

[jeeptech1]

im sure you already have this but... you didnt say the other signal into the icm was checked. id make sure all the inputs and signals were there. i cant find any info on which signal it wants more. gotta love headache cars!

 

[Talyn]

Yeah I have that. Went through Alldatadiy's no spark flow chart and it says replace the ICM. Which I have. The one that was on it, a spare one, and two new ones. They tell you to check the ohms on the coils, check the voltage into the ICM and then check the crank sensor. If all those check out replace the ICM.

Starting form the top of that diagram:
BA: is 12 volt in. That is constant. Come on with ignition and doesn't drop out.

ACB: is the crank sensor. Only A&B are used. That checks out 100%. Wave form looks good, ohms out good, correct voltage, wires check out, new plugs on both ends. It sends an AC wave to the PCM when notches in the trigger wheel pass the sensor

The only thing that concerns me about that is that both C and B have 0 ohms to ground on the ICM. Which I don't understand but all teh ICMs show that. And I have found no specs on how to actually check the ICM besides diagnosing its inputs.

ABCDEF:
A: Ignition bypass: 0 volts when cranking 5 when running. This signals the engine that the PCM will be controlling the timing, not the ICM wheni t has 5 volts. Shows 0 volts
B: Ignition control. Pulsed signal from the PCM when ignition bypass is 5 volts. Shows some activity sometimes, but still o volts on Ignition bypass.
C: Tach signal. Self explanitory. Only shows activity when it is actually sparking, which is intemittent
E: sends a square wave to the PCM based on crank revolutions. Shows nothing until it sparks then it shows a square wave. Also, when hooked up to a function generation with a 5 volt square wave injector system is activated.
F: This is actually the ground between the PCM and ICM. Checks fine.

The only two that the ICM gets from the PCM are A and B. And only when the engine is already running above a certain RPM.

ICM is grounded to its mount as well. Ground is good and clean.

Also, the injectors don't fire until it actually sparks, which is based on the E output.

 

[jeeptech1]

sorry for the all data link. didnt realize it changes everytime you change the page on the website. anyway. the only thing that concerns me is the b wire on the crank sensor into the icm that you said had 0 ohms to ground. it doesnt look like there should be any continuity to ground on that wire. are you checking the crank signal with the connector disconnected at the icm or back probing with it connected?