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Discussion Starter #1
Hi, 5.7 had a couple of spun rod bearings so I pulled the motor and put in a 5.7 out of a 1997 Tahoe. Has fuel pressure, has 12 volts to coil, has power to crank sensor. I'm not getting spark. I get a very weak spark out of the coil. (not enough to make it to the plug) Is there something I'm missing with either the computer or ignition? Do I need to flash the computer for some reason? Thanks for the help!
 

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Discussion Starter #3 (Edited)
Yes, both are from the original engine. I also tried the one from the Tahoe engine, no change. The original motor with the spun bearings, started up and ran fine, even with the spun bearings.
 

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I pulled the #1 spark plug, connected it to the wire and cranked the engine. (nothing). I then pulled the coil wire, did the same thing and got a weak spark or what seems to be weak.
 

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Ok, I will check again. I don't think the drivers side head is grounded? I did check the ground to the coil, to the battery and frame. (With multi-meter and all were good) I didn't see a ground to the drivers side head. The lower aluminum intake manifold has a ground in the front of motor, front of block and back passenger side head is all I see. Also the starter is grounded as well.
 

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Hi, 5.7 had a couple of spun rod bearings so I pulled the motor and put in a 5.7 out of a 1997 Tahoe. Has fuel pressure, has 12 volts to coil, has power to crank sensor. I'm not getting spark. I get a very weak spark out of the coil. (not enough to make it to the plug) Is there something I'm missing with either the computer or ignition? Do I need to flash the computer for some reason? Thanks for the help!
Make sure your engine is grounded. Replaced my 07 Trail Blazer engine with a 05.Vehicle would crank but no start. Drove my mechanic nuts. I told him over and over,sound like a bad ground.After two days,he grounded the block,vehicle started. The 05 has a plastic valve cover,07 is medal. Original ground was connected to the medal valve cover. Check your grounds.
 

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So, I got it to start but it didn't run well at all. (I had to push the gas pedal to the floor to get it to run and stay running) After that I checked all grounds, cleaned them, (each time trying to start the truck) I reset the timing, making sure I was at top dead center on compression stroke. It seems to be losing spark for some reason. Any ideas?
 

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So, I got it to start but it didn't run well at all. (I had to push the gas pedal to the floor to get it to run and stay running) After that I checked all grounds, cleaned them, (each time trying to start the truck) I reset the timing, making sure I was at top dead center on compression stroke. It seems to be losing spark for some reason. Any ideas?
each time you try to start the engine and no start [ignition problem] then the fuel will load up the combustion chamber.. then the plugs get fouled up..

ignition problem check the distributor for rotor bearing worn .. if it wobbles then change it .
post back how its running ..common issue 175K 225K miles.
 
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