Author Topic: 2002 Chevy Venture will not start  (Read 10452 times)

c130

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2002 Chevy Venture will not start
« on: March 21, 2011, 10:59:40 AM »
I'm at a loss. My 2002 Chevrolet Venture LS will not start, Vehicle is equipped with the 3.4l GM engine, Automatic Transmission, and 147,0000 miles. Engine Cranks over just fine, but no longer will produce a spark. At first it was an intermittant problem, now it won't at all. It is not misfiring, it is not firing at all, just sits there and cranks over. Fuel pump works and plenty of fuel fumes coming from exhaust. I have checked everything I can think of. Here is the run down.

Ignition Relay on Eng Comp Fuse block checks out and has been replaced when it was an intermittent problem.

All Fuses in both fuse blocks are good.

I have 12v going to Ignition Module, and both leads check good for continuity.

Pulled a plug and there is no spark.

All three coil packs check good ohms wise, primary and secondary side. (Can't imagine all three going to bad at once anyway, nor can I buy all 6 plugs and wire going bad at once)

7x Crankshaft position sensor produces upwards of 500mV (200mV min according to manual) when engine is cranked over.

24x Crankshaft position sensor receives 12v from PCM, and 10v of sensor wire, and drops off correctly when crankshaft is manually turned.

Ignition Module has no trigger signal from any of the coil pack terminals. Took module to Autozone twice and both times the Ignition Module bench checked good. Replaced the module with a new one anyway. Still won't start.

Camshaft Position Sensor receiving 12v from PCM, but only showed 60mV on sensor wire, with no change when rotated. (Manual says it should have 10v on Sensor wire with a drop off once every rotation). Replaced Camshaft Position Sensor. Engine still will not start and new sensor checks out the same as the old one.

Using a wiring diagram for a 2002 Venture, I spent today checking power and continuity on every imaginable wire from fuse blocks to the PCM, Sensors to PCM and Ignition switch to fuses. Everyone I could see that is related to ignition checks good.

I am starting lean in the direction that the PCM has died. When I hook my Actron Scanner to the OBD connector, there are not codes stored nor are there any pending codes. Some of the checks I performed were supposed to have triggered a code in the system, but there are no codes to be found in the system.

Before I either spend the money on a new PCM or send it out to be tested (Dealer doesn't have the capability to bench check a PCM, they want the whole vehicle brought in), I figured I would check here to see if anyone or a professional technician has any ideas.

Thanks in advance.

Linkback: http://forum.trustmymechanic.com/b1/2002-chevy-venture-will-not-start/32948/

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conniecartech

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Re: 2002 Chevy Venture will not start
« Reply #1 on: March 21, 2011, 04:01:15 PM »
its possible the timing chain is stretched or broke. or even a broken camshaft. that would explain the low signal on the cam sensor.

take the oil cap off and look in there while someone cranks the engine to see if theres movement on the valve train. u may allso be able to pull back the timing cover enough to see if the chain is loose or broke.

and u could do a compression test and see what results u get from that.

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c130

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Re: 2002 Chevy Venture will not start
« Reply #2 on: March 22, 2011, 08:30:33 AM »
I'll check on that, but being it was an intermittant problem, I find it unlikely a broke camshaft would be the issue.  I bench checked the old cam sensor out of the engine and harness and got the same result.

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conniecartech

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Re: 2002 Chevy Venture will not start
« Reply #3 on: March 22, 2011, 04:14:23 PM »
still wouldnt be a bad idea to check the timing chain and do a compression test before condeming the pcm.

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discretesignals

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Re: 2002 Chevy Venture will not start
« Reply #4 on: March 22, 2011, 07:24:04 PM »
There are two crank sensors on that one as you stated and tested.  There is a 7X VR sensor in the engine block that produces an AC signal and a 24X hall effect sensor behind the crank pulley that produces a digital on and off signal that is used by the PCM.  The cam sensor signal also goes to the PCM to syncronize the injector firing order to number 1 piston when it is at TDC.

The ICM uses the 7X signal for firing the ignition coils in the proper sequence and time.  The 7X signal is also processed inside the ICM and a 3x signal is sent off to the PCM.  The ICM will fire the coils in bypass mode when your cranking the engine.  Bypass mode means that the circuitry in the ICM is controlling the operation of the coils.  Once the PCM gets the 3X signal, the PCM will send 5 VDC down the bypass circuit to switch timing control over to the PCM for advance and dwell adjustments.  Even if the PCM is dead, you should have spark as long as the ICM has power, ground, and the 7X crank sensor signal input.  That's unless the PCM is sending a bypass signal to the ICM, but isn't sending timing signals to the ICM.  You can check that by unplugging the 4 wire connector on the ignition module and cranking the engine.  If you get spark, the PCM is triggering the bypass circuit when it isn't supposed to.  

Also inspect your coils really good.  If you are getting secondary voltage into the ICM from a leaking coil, the ICM won't function.  If you had a scan tool, you could look at the PCM data stream to see if the PCM is getting the 3X signal from the ICM.  Otherwise you would need a scope to see the signal.

On the cam position sensor there should be 12 VDC on the red/white wire to power the sensor.  The black wire should have 12 or 10VDC bias voltage from the PCM with the connector disconnected from the sensor.  The red/white wire is the sensor's ground.  The sensor pulls the bias voltage to ground when the interrupter passes over the sensor.  

When you checked the signal on the middle wire of the cam sensor's connector how did you check it?  The connector has to be connected and you can back probe to connect your meter or you can run jumpers.    Even if the cam position signal was missing or the timing chain or cam snapped, you should have spark.
« Last Edit: December 31, 1969, 06:00:00 PM by discretesignals »

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c130

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Re: 2002 Chevy Venture will not start
« Reply #5 on: March 22, 2011, 08:36:20 PM »
Good info discretesignals.  Will try disconnecting the 4wire connector on ICM, and see if I get spark that way.

I can't seem to find in my Actron 9180 scanner where to find the 3x signal information.

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c130

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Re: 2002 Chevy Venture will not start
« Reply #6 on: March 25, 2011, 08:28:34 PM »
Checked all the sensor wires, all good.   Replaced 7x CKP sensor last night.  Got everything back together tonight, and she fired right up.

Thanks

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discretesignals

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Re: 2002 Chevy Venture will not start
« Reply #7 on: March 27, 2011, 10:23:38 AM »
Maybe the 7x sensor wasn't sending out a strong enough signal or the signal was corrupted to cause the ICM not to fire the coils.  Thanks for the follow up and happy motoring. Very Happy
« Last Edit: December 31, 1969, 06:00:00 PM by discretesignals »

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