2002 Chevy Venture will not start

c130

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#1
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.
 

billr

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#2
I wouldn't condemn the PCM just yet. I would try disconnecting the cam-sensor from the harness and powering it up directly and reading its output without connection to the harness; there may be a short in the wiring that is pulling that signal low. Yeah, the short could also be in the PCM, but let's hope for that to be OK. From the way you describe it, I think that cam-sensor is an "active" type and should give a signal when open-circuit like that; but you may have to use a pull-up/down resistor. If you have the old sensor still, experiment with it a bit; you should be able to see that voltage state-change by just passing a steel object near or through the sensing area.
 

c130

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Thanks Billr

What did you mean by powering up the cam sensor directly? Actually running wires from battery dircetly to the cam sensor power leads then read the volts on the sensor output wire that would go to the PCM.

From the way you describe it, I think that cam-sensor is an "active" type and should give a signal when open-circuit like that; but you may have to use a pull-up/down resistor. If you have the old sensor still, experiment with it a bit; you should be able to see that voltage state-change by just passing a steel object near or through the sensing area.
Not sure what a "pull-up/down resistor" is. As far as the old sensor, I should use the 12v power to the leads and measure the voltage state-change, correct?
 

billr

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#4
Yes, try that with the old sensor, see if the sense line swings between 0 and the 10V indicated in the manual. If that doesn't work, then I'll go into detail about the resistors.
 

Gus

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#6
Cam sensor has nothing to do with spark.......It tells the PCM when to fire the injectors.....

Should check for spark at all six terminal of coils....if none on all six, then ICM, crank sensor, or wiring(connections) in between....

If spark on one or two coils, bad coil(s) that didn't fire.....
 

billr

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#7
Are you sure Gus? I thought most systems needed the cam-sensor to determine TDC; especially necessary for ignition timing.
 

nickb2

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#8
actually Bill, in a waste spark ignition system such as this engine, the cam sensor will only tell you which cyl is #6. A cam sensor has NOTHING to do with ignition timing in this particular engine, or most engines for that matter. It has much to do with pulse width injection patterns however. only way to adjust timing in an engine such as this one is to physically alter the crank pulley, reluctance teeth or crank sensor mounting holes. So if there is a no spark condition, in no way is there a correlation with the cam sensor circuit.
I'm with Gus on this one, check for crank sensor/no spark malfunction. I will include a crank sensor/no spark troubleshooting chart to help here.

[attachment deleted by server]
 

billr

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#9
How does the crank sensor show TDC for ignition timing? Is there a missing tooth or two on the crank trigger wheel that is detected?
 

nickb2

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#10
Here you can see the reluctance wheel for this type of engine. It shows the 24x and 7x. Spacing between teeth will tell PCM when cyl#1 is at TDC. The other type I show shows a crankshaft pulley with only a 24x type wheel, notice the absent notch.

[attachment deleted by server]
 

c130

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#11
Well I rechecked the old cam position senor on my bench utilizing a battery charger on a 2amp setting for a power source. Results were the same (60mV) as when the sensor was installed on the engine. When I selected 10amps on the charger the voltage on the sensor wire jumped to around 300mV. I check the new sensor installed on the engine but disconnected from the harness using battery power and the results were as before (60mV).

Thanks for the additional information Nickb and Gus. It looks like the crank sensors operate much like the pulse generator for the propeller system on the aircraft fly. It is used to feed the syncrophaser with the #1 blade position and the sync adjust the lead and lag of the props to keep the blades from passing at the same time at the closest point, thus reducing noise and vibration.

Nickb, I printed out the Troubleshooting guide and will try them tonight if I have time. A few acronyms I want to clear up; DMM: Digital Multi-meter? Mil:?

In step 3, is the scan tool a specific type. I have an fancy Actron (I believe it is the 9180) that reads all kinds of information in it.
 
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#12
I see no mention of "engine rpm while cranking" data. Is your Actron capable of showing "live data"?

You are correct about DMM. Mil is Malfunction Indicator Light. (or mother-in-law) CEL check engine light. SES service engine soon light.
 

billr

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#13
C130 (Hercules?),

"DMM" is digital multi-meter, and I think "MIL" is the check-engine-light. I wouldn't use a battery charger for checking things, most have huge amounts of AC ripple and voltage peaks up to 15-16V. When a charger is connected to a battery the ripple and peaks are smoothed out, just like a filter capacitor would do, so it would be OK that way. But then using the charger too for a quick test is just added nuisance. Now, back to those resistors. Those sensors may not be designed to "drive" the output terminal to 10V. They may be a "switch" that connects a load (circuit in the PCM) to ground thus energizing it; the other side of that load being always connected to a + voltage. So, when you try to bench-test the sensor it is only switching your DMM on-and-off to ground and the 60 mV is probably just noise on the leads when the switch is "off" and the + lead is open. One way to get a real reading is to put a dummy load, a resistor, between the sensor output terminal and the sensor + terminal; use about 10K ohm or more. That should be enough load to get a reading, but won't pass enough current to hurt anything no matter how you might connect it wrong. Another way is to put the DMM "ground" lead to the sensor + terminal and use the DMM itself as the "load"; that should work too, but not quite as sure-fire since the DMM input is a very high resistance and the sensor switching circuit may have enough leakage to turn the meter "on" all the time. That all describes a "pull up" mode; the same basic scheme is possible with loads always connected to ground and switched to the + voltage ("pull down"), but those aren't as common.

Nickb2 and Gus,

I know very well how the "missing tooth" wheel can find TDC, as well as the pulley with two toothed elements (and two sensors?); I was unaware those schemes were used along with a cam-sensor, since they are redundant. I would have thought the cam-sensor would have been eliminated to reduce cost. And I still say we don't know whether the PCM is using the crank-sensor or cam-sensor, or both, to enable and time ignition unless we have (and understand!) the software program the PCM is running. I don't think anyone posting here has access to that stuff or is allowed to share it.
 

c130

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#14
I see no mention of "engine rpm while cranking" data. Is your Actron capable of showing "live data"?
Yes it does show live data. I remember watching the RPM on the scanner while turning it over. Not positive but thought is was like 125-150 rpms.
 

Gus

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#15
Bill, since this uses the waste spark method, it will fire paired cylinders at the same time(1/4, 2/5, 3/6)......all the ICM wants to know is where is #1 cylinder....when the synch pulse comes from the crank sensor, the ICM knows when #1 is at TDC......doesn't make any difference if it's compression or exhaust stroke, the ICM fires 1/4 coil.......if #1 is on compression, almost all of the spark goes to #1....if #1 is on exhaust stroke, all the spark would go to #4....

So the ICM doesn't need the cam sensor to fire the coils......

The PCM needs the Cam sensor signal to know when #1 is on the compression stroke, to start sequential firing of the injectors.....