1999 GMC Suburban 1999 Suburban no spark

Tiny
HAWK1061
  • MEMBER
  • 1999 GMC SUBURBAN
  • V8
  • 4WD
  • AUTOMATIC
  • 120,000 MILES
This is the 7.4l V8, K2500.

Tested for spark, no joy. My question is how do I determine if the ignition module is bad, if there is a problem with the coil, if the distributor/rotor is shot, etc? I removed ignition module and coil, took to a local parts store who 'checked' module and said was bad. I asked them to check the new module to verify it was good, he tested and it was bad. Tested another module from their stock, was also bad. I assume the counterperson had no clue how to test. Can I test it and if yes, how?

Same question on the coil, how do I know if it's shot or good?

Thanks guys.
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Monday, June 15th, 2009 AT 10:58 PM

3 Replies

Tiny
JDL
  • EXPERT
Hello, With a distributor ignition, I take the coil wire loose from the distributor, hold close to engine ground, have helper crank it, while I watch for spark to jump from the coil wire. If there is spark, but, nothing at the plugs, I change out the cap and rotor. If no spark and the coil wire is good, I check for input and output signals from the ignition module, if there is input and no output, I suspect the module. I also check primary circuits to the coil, small wire connector. There is probably an ohms spec for your coil, don't have it in front of me. I probably over-simplified just a little.
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Sunday, June 21st, 2009 AT 9:47 AM
Tiny
HAWK1061
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Thanks jdl. Turns out it was the ignition module. It starts now but.

While working on the truck I had the battery disconnected. Once I got everything put back together (say 2 days without battery power), I was able to start it up VERY easy (like the settings were lost and so it was running on default settings). Over the next few days, it seems that sometimes it takes two or more cranks to start, it seems to run rough at first (sometimes) and I'm smelling unburned gas in the exhaust. There is no check engine light on which I would expect to see if there were some serious problems. The air filter is completely new so it's not a lack of air getting in. What would cause it to run rich in this day of electronic engine controls? And shouldn't a rich/unburned gasoline condition trigger a DTC?

One final observation. When I took off the air intake system while working on the truck, I noticed that the bottom of the inside of the throttle body has what appears to be a brownish/yellowish stain. At first I thought it was oil and tried to wipe it off, but it's not liquid, it appears to be solid. Almost seems like gasoline that has pooled over time and turned to laquer. What is this a sign of?

Thanks for your help.
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Sunday, June 21st, 2009 AT 10:31 AM
Tiny
JDL
  • EXPERT
I'd want to see what the 02 sensor/s are doing and look at the fuel trims. You can put a fuel pressure gage on it, do some testing.
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Sunday, June 21st, 2009 AT 11:01 AM

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