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Old 04-18-2019, 11:44 PM
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1990 GMC Suburban no spark

Hey fellas, I realize this isn't a HotRod but, my 1990 GMC V1500 Suburban (stock 350 TBI) is acting up again. Got home the other night from a friend's place, parked in my driveway, no problem. Went out to start it the next morning to go to work and it cranks but doesn't fire. Since I was able to fix it about a year ago with a new intake coolant temp sensor and it had been acting up lately like it wasn't getting the right amount of fuel, I replaced that tonight and it didn't fix the problem. So, I checked for spark and found none while cranking. I see now burnt fuses in the fuse block under the dash and all the wires appear to be connected as they should be. Where should I go next? I have little experience with more modern automotive ignition but I do understand the basics. Needs ground, could are lazy, plugs need to be relatively clean, etc. I would like to use this vehicle Sunday to go pick up my Dad's aunt and bring her home for Easter so time is of the essence. Thanks in advance!

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Old 04-19-2019, 01:17 AM
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The spark is controlled by the emc module. Pull the cap and check the plugs at the sides there is 4 terminals on the module and sometimes the wires can become loose in the plugs.

Pull the module and clean the surface underneath and test it. If you need a new one install the grease with it. It is not a expensive but a important one. I usually replace the coil, rotor, module, and cap over time as preventive maintance inspecting terminals for damage or being loose.
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Old 04-19-2019, 07:57 AM
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Quote:
Originally Posted by RustyRedneck View Post
Hey fellas, I realize this isn't a HotRod but, my 1990 GMC V1500 Suburban (stock 350 TBI) is acting up again. Got home the other night from a friend's place, parked in my driveway, no problem. Went out to start it the next morning to go to work and it cranks but doesn't fire. Since I was able to fix it about a year ago with a new intake coolant temp sensor and it had been acting up lately like it wasn't getting the right amount of fuel, I replaced that tonight and it didn't fix the problem. So, I checked for spark and found none while cranking. I see now burnt fuses in the fuse block under the dash and all the wires appear to be connected as they should be. Where should I go next? I have little experience with more modern automotive ignition but I do understand the basics. Needs ground, could are lazy, plugs need to be relatively clean, etc. I would like to use this vehicle Sunday to go pick up my Dad's aunt and bring her home for Easter so time is of the essence. Thanks in advance!
Verify no spark at ignition coil by disconnecting the coil wire from the distributor, put a spark plug in the end of the wire, and ground the spark plug to something metal with vice grips - then crank the engine. Do you see spark?

If not probe terminal B of the grey connector on the coil (leave it connected) with a test light connected to ground. With key on you should have 12V here. Probe terminal A of the grey connector with a test light connected to 12V (on the battery terminal) - the light should flash when you crank the engine. If not, a no-spark problem is in the distributor. (If it does flash, problem is the ignition coil)

In the case of still no flash and without access to a module tester, just go ahead and replace the easier part - the ignition module (7 terminal), and retest for flashing light at the coil connector. If still no flashing, the distributor will need to be removed and disassembled to install a pick up coil.

I don't understand your statement about burnt fuses?????

Good luck

Last edited by 2001Blazer4x4; 04-19-2019 at 08:03 AM.
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Old 04-19-2019, 02:38 PM
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Thanks. I'll see if I get time to check it out tonight after work. The burnt fuses thing is about the ECM and IGN fuses in the fuse block.
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Old 04-19-2019, 02:43 PM
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Thanks. I'll see if I get time to check it out tonight after work. The burnt fuses thing is about the ECM and IGN fuses in the fuse block.
Probably you should start by replacing those fuses.
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Old 04-19-2019, 02:52 PM
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I think "now" was a mistype and should have been "no"
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Old 04-19-2019, 03:17 PM
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Once again, fuses are fine. Poncho, I guess I don't see what you're talking about for typo.
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Old 04-19-2019, 03:19 PM
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Nevermind, you were right.
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Old 04-19-2019, 06:32 PM
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How do I test it after I clean it? Crank? Use a volt meter?
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Old 04-19-2019, 11:10 PM
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Using the vise grip grounding, spark plug in the coil wire method, I have spark when I let off the starter and that's it.
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Old 04-20-2019, 12:03 AM
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Started to perform the terminal A test on the grey connector. I hooked my test light up to terminal A which was a white wire. Then went to connect the other end to the positive post on the battery and upon touching the post, the test light came on and I heard a click down near the starter, so I immediately took the test light wire away. Didn't want to let out any secret smoke. Should I be seeing/hearing this?
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Old 04-20-2019, 12:03 PM
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Quote:
Originally Posted by RustyRedneck View Post
Started to perform the terminal A test on the grey connector. I hooked my test light up to terminal A which was a white wire. Then went to connect the other end to the positive post on the battery and upon touching the post, the test light came on and I heard a click down near the starter, so I immediately took the test light wire away. Didn't want to let out any secret smoke. Should I be seeing/hearing this?
You won't hurt anything with a test light.

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Old 04-20-2019, 01:07 PM
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You won't hurt anything with a test light.

Sent from my Moto G (4) using Tapatalk
p.s. the testing is done with the connectors still hooked up to the coil. Probe the back side if the connector is open, or gently pierce the wire with the test light. Just want to make sure you are not misunderstanding. Terminal B should have 12V power when key is on. If there is power there and the module is triggering the coil, then Terminal A of the grey connector is the tach terminal and it should flash a 12V powered test light when cranking. If it stays on all the time or never comes on - that tells us different things. Sorry, but you're either going to have to do all the tests correctly or use the SWAG system and start replacing parts. Good luck and best wishes for a successful repair.

Last edited by 2001Blazer4x4; 04-20-2019 at 01:33 PM.
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Old 04-20-2019, 02:37 PM
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Did the terminal A and B tests as described and we have 12 volts to B and the test light is on constant while the key is on when connected to terminal A and ground.
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Old 04-20-2019, 03:10 PM
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Did the terminal A and B tests as described and we have 12 volts to B and the test light is on constant while the key is on when connected to terminal A and ground.
"Terminal A of the grey connector is the tach terminal and it should flash a 12V powered test light when cranking". This means probe terminal A with the connector still on the coil and hook the other end of the test light to battery positive - then crank the engine and watch the test light. What is the result when cranking?
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