96' K1500 5.7 no crank/no start after swap

[Lazarus96]

This has been a project truck for the better part of 3 years so I will attempt to keep it brief. Thanks in advance for any help/tips y'all can offer.

I bought this truck 4 years ago with a "mild misfire" that quickly went from a new cap, plugs, and wires to a full top end rebuild, valve job, ect. That engine ran briefly, then lost compression in cylinders 4 and 6. I tore the top end back off, had the heads checked by a local shop and verified the heads were holding compression properly. At that point I didn't want to dive any deeper into bottom end rebuilding, I worked in a hydraulic repair shop then a machine shop for years, but I'm not a mechanic and I know when I'm outmatched. So I picked up a verified running donor engine and swapped it out.

*Note* I used the heads, both upper and lower intake, and water pump(new) off the old engine. I spent a boatload of time cleaning everything, putting a new spider in, gaskets, ect. So I figured why let it go to waste?

When we were lowering the engine in my dad was running the hoist and I was guiding it in. He twisted the handle the wrong way and dropped the ending about 6 inches into the bay. It pinched a couple wires, broke the distributor, and a fan blade dented the radiator but that was all I could find after inspection.

So I bolted it in, wired it up, filled fluids, fresh fuel, ect. Hit the key, all dash lights come on, fuel pump kicks, then nothing. The starter has juice, I replaced the Neutral safety switch(the connectors looked fine) and Ignition relay.
Still nothing.

So what would be your next move? I'm grasping at straws at this point.

*Attached pictures show results of testing all 4 female starter relay contacts in the fuse box.*

-Adam

 

[Scooterwrench]

Check the starter solenoid circuit. Could be a wire got pinched in two when the motor fell on it. I recommend downloading the wiring schematic for your truck here;

88-98 Service Manuals

Over the years I have collected a bunch of GM service literature. Links to PDF Scans of service and STG manuals and a links to the Parts manuals. You'll need the FREE Adobe Acrobat reader to open these files. Get it directly from Adobe here {http://get.adobe.com/reader/} If you're not...

www.gmt400.com

 

[Schurkey]

Four most-likely issues:

Damaged starter/starter solenoid

Purple (sometimes fades to pink) wire connected to wrong terminal of starter solenoid. Needs to go on "S" terminal, not "R" terminal. Many newer solenoids don't have an "R" terminal.

Not enough power on purple wire, due to corroded contacts, damaged/corroded wire, etc. Typically more of a problem when the engine/starter is hot.

Faulty ground connection between starter and block, or between block and negative battery cable.

But there's plenty of other causes--faulty ignition switch, faulty "trans position" (neutral safety) switch, faulty starter relay, bulkhead connector, etc. Some of that you've checked already.

 

[Cpufreak101]

To rule out the "easy" issues, you getting 12V on the big wire to the starter solenoid at all times? and when you crank are you getting voltage to the smaller wire? As they said above could just be a case of the starter solenoid wire got damaged when the engine dropped.

 

[Lazarus96]

Four most-likely issues:

Damaged starter/starter solenoid

Purple (sometimes fades to pink) wire connected to wrong terminal of starter solenoid. Needs to go on "S" terminal, not "R" terminal. Many newer solenoids don't have an "R" terminal.

Not enough power on purple wire, due to corroded contacts, damaged/corroded wire, etc. Typically more of a problem when the engine/starter is hot.

Faulty ground connection between starter and block, or between block and negative battery cable.

But there's plenty of other causes--faulty ignition switch, faulty "trans position" (neutral safety) switch, faulty starter relay, bulkhead connector, etc. Some of that you've checked already.

 

[Lazarus96]

To rule out the "easy" issues, you getting 12V on the big wire to the starter solenoid at all times? and when you crank are you getting voltage to the smaller wire? As they said above could just be a case of the starter solenoid wire got damaged when the engine dropped.

I'll double check the starter voltage in the morning and let you know. However I'm not getting any voltage to the small purple wire when the key is turned.

 

[Schurkey]

I'll double check the starter voltage in the morning and let you know.

Good plan. Not likely to be a problem, but worth verifying. Ideally, you'd do a voltage-drop test on that cable, but the starter has to be cranking the engine to do that.

However I'm not getting any voltage to the small purple wire when the key is turned.

That's a problem.

Broken wire, faulty relay (if equipped), bad connections, faulty ignition or safety switch, or POPPED MAXI-FUSE.

 

[Cpufreak101]

alrighty. doing some extra looking, thanks to this post: https://www.gmt400.com/threads/88-98-service-manuals.43575/post-1246113 I was able to grab a wiring diagram of the starting system and got it colored in to make it easier to follow.

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from what I can see, assuming there is power to the starter solenoid on the black wire directly off the battery, if there is *no* power to the purple wire when turning the key, then there's only a couple things that could be wrong. off the ignition switch is a yellow wire that either goes to your clutch lockout switch or your neutral safety switch depending if it is an automatic or a manual, and off of these will then be a purple wire. if you're able to access these to check for power, if the yellow wire has power *at the switch* but the purple doesn't, then the switch is bad (it would be safe to TEMPORARILY bypass the switches for testing purposes though). however if you have power *at the switch* on the purple wire and still no power on the purple wire at the starter relay, then it has a break somewhere. Similar thing for starter relay as well, make sure it's getting power from the purple wire when trying to crank as this is what activates the relay (and if you're unsure if the relay is good, you can just apply 12v to the control side and it should click, and if you really want to be sure, get a cheap multimeter with a continuity test or resistance test mode, with the relay activated the switch side should have fuil continuity or almost no resistance) if everything up to this point is good and there is STILL no power to the purple wire, then there's a break between the starter solenoid and the starter relay in the fuse block.


similar procedure for the yellow wire if there's no power *at the switch* when you turn the key. make sure there's voltage at the key, if there is and there's none at the switch still, then there's a break in the yellow wire somewhere. if there's no power at the key though, then there's bigger issues we'll need to figure out.

I hope I was able to explain it well enough!

EDIT: seems I accidentally made a purple wire orange, fixed now

 

[Lazarus96]

Howdy all, I figured I'd post a long belated update on what I found.
Long and short? It was the starter...
Then cyl 5 was full of water somehow, but once that got sorted it's been running pretty decent

Thank you guys again for helping me work to narrow that all down.