It might be obvious by the title, but I'm generally an idiot when it comes to wiring/electronics. I get how a test light works, but that is about the extent of electronic diagnostic tools I can use! Here is my issue and why I think I need to find out how to use one.

I did a 5.3L swap on my 80' Buick Century; rewired it myself to a 4 fuse/2 relay setup. It fired up right away and I drove it all summer without issues. Most of the winter it sat in either my garage or driveway, and would be fired up/moved when moving snow or short trips (mini spool in Fargo ND). One of the last times I needed to snow blow it fired up right away and sat and idled. I shut it off so it wouldn't be blowing exhaust against my house while I worked the snowblower on a different part of the driveway. When I went to restart it it wouldn't fire; even with a jump start. Weird, but didn't have time to look into it.

Now, I finally have had some time. I traced it down to no spark, what seems to be at all cylinders using my timing light. The power coming from the fuse block tests good. (test light, I can understand lights, ha!) The ground also test correct. All my grounds appear tight/good yet.

But how do I test the other two coil wires that run to the PCM without frying it? If I read it correctly my test light would fry the PCM if I tried to use it to ground the light. I generally consider myself fairly competent, but for some reason I've never been able to figure out a multimeter. (yes, even after lots of youtube videos, again, I feel really dumb about it!)

Just looking to test out the ignition grounds on the PCM as my next step!

I'll add some photos of my Buick in the next post, because who doesnt like pictures eh?! It ran a 20.8 sec quarter with the 3.8L v6, 16.2 sec with a 305 and a 14.2 sec with stock 5.3l. So its been a fun experiment so far!

Thank you!

 

 

 

i'm not sure how you would go about testing the coil triggers but it might be better to take a step back and look at something else as the likelyhood of all the ignition coils/triggers not operating is pretty low if they were working fine before. if none are working it point mainly to power supply, ground or a antitheft but i'm pretty sure that's done on the fuel side and it was starting/running before so that probably isn't it.

when you say the power to the coils is good is that with the key turned to the "start" position as well as "run" or "on"?

is it possible that there is +12v to the coils with the ignition in the on/run position but when you turn the key to "start" that it drops out?

 

I agree, I seriously doubt your PCM just died. More times than not it comes down to a wiring problem, especially on a swap. Are you positive you checked all the grounds? The one behind the power steering pump is the one that will shut the coils off if it isn't hooked up and is easy to miss. I would start there and just double check the harness.

 

Thank you for the responses! I didn't check to make sure it still had power while cranking; good idea!

I'll recheck the grounds, but pretty sure they did all look good. It could be something inside the harness, but I'm hoping not!

Thank you!

 

Don't just look at the grounds, physically check them. Place a wrench on the bolt and make sure it's tight. Even better, take them loose and ensure you're getting good contact between the ground and the surface. I've seen intermittent issues caused by poor grounds - even when they looked good.

 

Well I checked all my grounds and everything seems to check out OK.

While cranking it with my computer hooked up, I noticed I wasnt showing any RPM while cranking. I put a new crank position sensor in and it then read RPM, started, ran poorly then died. Now it doesnt show RPM again while cranking and wont start again. If it was a faulty crank sensor, what would cause the new one to go out again? I'm hoping thats not the case. I looked over the wiring before putting the new sensor in and it all looked ok. Taking a break from it right now, got frustrated, ha!

Thanks for any thoughts.

 

It seems to come and go whether it reads RPM or not. Sometimes it will stumble a bit but still wont run.

 

So i've found I have spark in 2 cylinders, numbers 3 and 8. Going to see what those two have in common.

 

They have nothing in common. This really sounds like a $45 crank position sensor. DO NOT buy anything but the AC delco one. I literally spent 2 months chasing a problem where I had spark on 1, 3, 7, and 4. Nothing else. Engine would not fire, and I "assumed" that the cheaper ICT Billet sensor was doing it's job. It wasn't. Put a brand new AC Delco in and it got spark on all 8.

It could literally be that simple. Trust me, I was both happy and pissed at the same time when I figured that out. Pissed that I had spent so much time chasing wires when it was just a sensor issue.

If anything, check your crank sensor. That's where the PCM is going to get the proper signal to fire the coils.

You could also go down to Autozone and rent a noid light if this doesn't work out, and check your injector harness too. The injectors fire before the spark does, so the light should come on while cranking. This can help troubleshoot wiring too. Since you know how to read lights, should be easy lol.

The PCM fires the coils by grounding them, so you know. So they should ALL have a 12v supply. Check that with a multimeter. It's rally not that hard brother. You're gonna have to get smart on that if you have LS wiring issues.

I would start with that sensor though, just saying.

 

Got it running!

I hosed down the cam position sensor connector and main coil connectors in electrical cleaner, fired it up and rev'ed it up quickly to 3-4K, then went to WOT and did a crank relearn. Seems to be running well now.

I dont think I mentioned that if I let it sit for awhile (guessing drying out the cylinders) it would usually stumble a little bit, my guess is the two cylinder actually firing.

I have to fix a leaking power steering connection then I'll see how it keeps firing up again and running. It feels like summer here in Fargo and I have some old tires I need to go burn off

Thank you for all the help and suggestions!