1997 Chevy Astro Extra spark firing

Tiny
WINGS515
  • MEMBER
  • 1997 CHEVROLET ASTRO
  • 6 CYL
  • AWD
  • AUTOMATIC
  • 122,000 MILES
After the car heats up and after a left turn the engine runs very rough. I put a scope on the coil wire with a trigger from number 1. At idle the spark time is about 30 msec. After failure, there are intermittent extra spark firing between the 30 msec pulses. If I shut off the engine and re-start it is normal. Distributor, wires, coil, ECM have all been changed. At the time of the miss fire the communication to the Snap On scanner becomes erratic. My question is, is there a singular point in the ground circuit that would make the ECM "think" it is getting an extra pulse from the crank sensor. When these extra spark pulses fire you can hear a ping in the engine. Previous to this, the fuel pump and filter have been replaced and the rail pressure is 55# at idle, increases as the engine revs and returns to 55#. This has been beating me up for over 2 months of troubleshooting.
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Tuesday, August 31st, 2010 AT 8:14 AM

20 Replies

Tiny
WRENCHTECH
  • EXPERT
In all the parts listed that you changed I didn't see ignition module. Since the ignition module is the component responsible for triggering the coil, I think it would be highly suspect.
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Tuesday, August 31st, 2010 AT 8:33 AM
Tiny
WINGS515
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Would the ignition module cause the scanner to intermittently loose communcation and display multiple unrelated failure codes?
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Tuesday, August 31st, 2010 AT 10:49 AM
Tiny
WRENCHTECH
  • EXPERT
I doubt it. It can trigger other codes but it doesn't sound related.
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Tuesday, August 31st, 2010 AT 11:56 AM
Tiny
WINGS515
  • MEMBER
Just returned from 3 hours of work on it. The ignition module had been changed during the distributor change out. Just replaced one of the O2 sensor connectors. The heater pins were very corroded. Also changed the ground lug above the drivers head light and the one near the thermostat. The missing now starts without total warmup but I can get it to miss when ever I do a hard left turn. Restart and its fine. BTW MAF sensor has also been swapped out. Getting very frustrating.
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Tuesday, August 31st, 2010 AT 2:44 PM
Tiny
WRENCHTECH
  • EXPERT
The ignition module is not in the distributor.
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Tuesday, August 31st, 2010 AT 4:14 PM
Tiny
WINGS515
  • MEMBER
I was told it was changed. Where is it located? I'll try anythin now!
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Tuesday, August 31st, 2010 AT 9:01 PM
Tiny
WRENCHTECH
  • EXPERT
It's mounted on the intake manifold, near the edge of the valve cover.
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Tuesday, August 31st, 2010 AT 9:05 PM
Tiny
WINGS515
  • MEMBER
If this is the module that has the high voltage output to the distributor, that has been swapped out with no change.
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Wednesday, September 1st, 2010 AT 8:56 AM
Tiny
WRENCHTECH
  • EXPERT
I don't know what your talking about with high voltage output but the ignition module is mounted by itself on the intake manifold.
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Wednesday, September 1st, 2010 AT 9:20 AM
Tiny
WINGS515
  • MEMBER
I'll look for the ignition module. The Mitchell schematics show it as a separate unit but the coil module on the vehicle has two low voltage connectors. Maybe the ignition module is just mounted on the same assembly as the coil.
Could you detail the sequence of spark firing? I think it is, crank sensor sends signal to VCU which sends control signal to ignition module. That triggers the coil to generate spark then through the distributor to the plug. Where does the cam sensor come into this path? According to the schematic, the two sensors are like switches providing circuit closure to the VCU. They do not provide ground.
I am trying to zero in on the places to look since there is very little room to see anything in the engine compartment.
Thank you soo much for your responses.
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Wednesday, September 1st, 2010 AT 11:02 AM
Tiny
WRENCHTECH
  • EXPERT
It's #2 in the picture


http://www.2carpros.com/forum/automotive_pictures/561653_Ignition_module_97_43_1.jpg

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Wednesday, September 1st, 2010 AT 11:30 AM
Tiny
WINGS515
  • MEMBER
Thanks for the picture. It came out kinda small. I think I see a 2 near and to the left of the alternator. Is that it? The front of the engine is to the right, correct?
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Wednesday, September 1st, 2010 AT 11:36 AM
Tiny
WRENCHTECH
  • EXPERT
Yes, that is a view from the right side so it's right behind the alternator. Sorry, the site reduced the picture.
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Wednesday, September 1st, 2010 AT 1:35 PM
Tiny
WINGS515
  • MEMBER
I don't know if my last posting came through but "FOUND IT". The yellow wire from the crank sensor had broken through the insulation and intemittently chaffed against a frame bracket. Once found it was an easy repair. There is one other set of wires, a Yellow and Tan that went somewhere up the drivers side of the engine. The male protion of the connector was severed from the cable. The schematic does not show any 2 wire harness with these color wires. Any idea where this cable assembly goes?
Thanks for your help.
Dan
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Saturday, September 4th, 2010 AT 9:45 AM
Tiny
WRENCHTECH
  • EXPERT
There is a yellow and a tan with white for the MAF
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Saturday, September 4th, 2010 AT 10:00 AM
Tiny
WINGS515
  • MEMBER
I would think the wires you mentioned are on the top of the engine. The wires I wrote about are on the bottom of the engine in the same harness as the Crank Sensor.
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Saturday, September 4th, 2010 AT 12:15 PM
Tiny
WRENCHTECH
  • EXPERT
I have no way of finding out. I have to look at individual circuits to get wire colors.
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Saturday, September 4th, 2010 AT 1:16 PM
Tiny
WINGS515
  • MEMBER
Other than Mitchell, who prints wiring diagrams for individual vehicles. I know Chilton's used to, but they were more generic than for a specific vehicle. I'd like to find out what these wires are for.

I also would like to fix an intermittent radio problem on a 2002 GMC Envoy. Seems this is a "known" problem that GMC can't figure out. I have seen two postings on this problem and each required the replacement of the radio.
Dash display shows all is good, volume bars move, tuning OK, just no sound from speakers. If the fault is there when you shut off the car, it drains the battery. Unique shut down procedure to check radio is working before parking for the night.

Thanks again for all your help.
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Saturday, September 4th, 2010 AT 1:43 PM
Tiny
WRENCHTECH
  • EXPERT
Www. Alldata. Com will sell you a subscription for one vehicle for about $25. They are about the best in the industry.
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Saturday, September 4th, 2010 AT 1:46 PM
Tiny
WINGS515
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Thanks, I have heard of them. I'll check it out.

Bye for now.

Dan
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Saturday, September 4th, 2010 AT 2:33 PM

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