Need a bit of help with a 94 Camaro not sparking

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SilverXJ
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Need a bit of help with a 94 Camaro not sparking

Post by SilverXJ » Fri Aug 05, 2011 9:55 pm

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?

Tom K
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Re: Need a bit of help with a 94 Camaro not sparking

Post by Tom K » Fri Aug 05, 2011 10:37 pm

Ruling out the module, coils, poor connection and broken wire scenario and concentrating on trigger signals. Are you checking the High ( 3 wire) and the low resolution ( 2 wire)crank sensor output? The low res. sensor will trigger direct to the ICM the high res. sends the PIP to the PCM If you are getting a clean scope trace on the low res CKP and hi res CKP and CMP at the PCM but you are not getting an EST output to the ICM and the wiring checks out the PCM has likely failed. I am assuming you have checked cranking voltage at the module. Have you checked for injector pulse during crank / no start?
Tom

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Re: Need a bit of help with a 94 Camaro not sparking

Post by SilverXJ » Sat Aug 06, 2011 9:40 am

I am concentrating on the low resolution 7x/3x sensor now as it is responsible for starting. I haven't even checked the cam sensor and 24x crank sensor as I can't even get it to spark when turning it over, which the ICM and 7x sensor handle. The ICM has 12 volts going to it when the ignition is on.

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Re: Need a bit of help with a 94 Camaro not sparking

Post by Tom K » Sat Aug 06, 2011 11:52 am

Check all the input outputs at the ICM including cranking power and grounds.

B - Pink 12VDC run and crank
A - Black white ground

A - Yellow
B - Shield CKP VR signal.
C - Purple

A -Tan / Black Bypass should have zero volts while cranking and 5 volts otherwise
B - White EST from ECU
C- White Tach Output
D
E purple / white (reference) should be square wave anytime the engine is cranking or running
F black / red Ground.

Do you have injector pulse when you get a crank no spark condition ?

I also want to clarify when you say the ICM is not supplying voltage to the Coils. Are you getting 12VDC to the coils? The Coils should have 12VDC at run or crank. The ICM sends the ground to the coil.

Sincerely,
Thomas R. Kise
Holley Tech Service

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Re: Need a bit of help with a 94 Camaro not sparking

Post by SilverXJ » Sun Aug 07, 2011 11:44 pm

Tom K wrote: B - Pink 12VDC run and crank
A - Black white ground
That checks out.
A - Yellow
B - Shield CKP VR signal.
C - Purple
Checks as well, see waveform above.
A -Tan / Black Bypass should have zero volts while cranking and 5 volts otherwise
Shows 0 volts while cranking.
B - White EST from ECU
Shows something but not very consistent.. mostly 0 volts
C- White Tach Output
Only shows voltage when spark happens
E purple / white (reference) should be square wave anytime the engine is cranking or running
Usually 0 volts but shows square wave, albeit irregular & with spark. Also corresponds to injector firing.
F black / red Ground.
Shows ground when either/or the ICM voltage supply (pink & black/white) is connected or ICM is grounded.
I have waveforms for B&E if it would help.
Do you have injector pulse when you get a crank no spark condition ?
No injector pulse when there is no spark
Are you getting 12VDC to the coils? The Coils should have 12VDC at run or crank. The ICM sends the ground to the coil.
Yes, that is what it is. +12volts w/ ignition and ground when it rarely fires the coils.

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Re: Need a bit of help with a 94 Camaro not sparking

Post by Tom K » Mon Aug 08, 2011 11:41 am

I do not want to get into a debate about how the module should function on its own. It Sounds like a crank sensor or PCM issue, You should have injector pulse. Scope the cam and crank sensor. Is it a manual transmission car? If so check the crank thrust. They are known for thrust wear on the crank resulting in CKP sensor errors.

Sincerely,
Thomas R. Kise
Holley Tech Service

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Re: Need a bit of help with a 94 Camaro not sparking

Post by SilverXJ » Mon Aug 08, 2011 1:03 pm

It does sound like a crank sensor problem. However the sensor, wires and signal checks good, as does the crank end play (was a though of mine as well).

I am not trying to debate, but asking for clarification. The way I understand ignition to work (in theory at least) is that during starting the ICM has complete control of spark. It gets 12 volts and the crank sensor inputs. Creates spark and sends a 3x signal to the PCM on the purple / white (reference) wire as well as RPM on the white tach output wire. Once the engine is running (how does the PCM know this, just after a certain RPM?) the PCM will apply 5 volts the the tan/black bypass, which tells the ICM to get timing from the PCM on the white EST wire. So, with 0 volts on the bypass wire the ICM should be working on its own. Is that correct or am i understanding it wrong?

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Re: Need a bit of help with a 94 Camaro not sparking

Post by Tom K » Mon Aug 08, 2011 5:25 pm

The PCM has a programmed crank to run RPM. I do not know specifically what it is for that vehicle. If the PCM is getting erroneous signals from the sensors it may be causing it to go into run mode essentially disabling the bypass crank mode. If all the sensor signals power and ground check out after have back probed and scoped them at the PCM & ICM terminations. The coils test good, Power and grounds are correct and you have changed the ICM ( assuming it is good) the only thing left would be the PCM.

Sincerely,
Thomas R. Kise
Holley Tech Service

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