Another no start LT1
Another no start LT1 Was out for a drive (in my 97) and all of a sudden the car started running like crap, no power, missing/bucking/stumbling/almost dying. I did make it home, albeit barely. Now the car won't start at all. Anyone run into something like before? If so what was the issue?
Tests done:
No pulsing ground at the injectors.
Optispark harness has both 5v references, 12v battery voltage, and 0-1 ohms ground.
At the ICM harness it's being weird. Terminals A and D both have battery voltage. Terminal B... the first time I tested it had AC volts while cranking (about 2v AC). Now it has 0. Terminal C... the ground is also acting very strange. I've tested it several times. Sometimes it has 0 ohms to ground, sometimes it has 15-20 ohms to ground. This is with the key off of course.
All fuses checked and work fine.
EDIT: Should add I tested for fuel and have it with a fuel pressure gauge.
I took a spare opti and did the drill test. Key on engine off. I spun the spare opti with the drill and still didn't didn't get spark or injector pulse.
EDIT2: Just noticed my PCM ground to ground and battery ground to ground are also giving funky readings. Bad battery or bad battery cables?
Tests done:
No pulsing ground at the injectors.
Optispark harness has both 5v references, 12v battery voltage, and 0-1 ohms ground.
At the ICM harness it's being weird. Terminals A and D both have battery voltage. Terminal B... the first time I tested it had AC volts while cranking (about 2v AC). Now it has 0. Terminal C... the ground is also acting very strange. I've tested it several times. Sometimes it has 0 ohms to ground, sometimes it has 15-20 ohms to ground. This is with the key off of course.
All fuses checked and work fine.
EDIT: Should add I tested for fuel and have it with a fuel pressure gauge.
I took a spare opti and did the drill test. Key on engine off. I spun the spare opti with the drill and still didn't didn't get spark or injector pulse.
EDIT2: Just noticed my PCM ground to ground and battery ground to ground are also giving funky readings. Bad battery or bad battery cables?
Last edited by Z28Roxy; Jun 17, 2020 at 01:07 PM.
I had something similar happen this spring. The car would run like crap for a bit, then it wouldn't start. I could reset the trouble codes and it would usually start up and run great for a bit, I'd get a code 42 and it'd start running bad again. On each no start I wouldn't have injector pulse. Ended up being a couple of bad wires between the pcm and the icm, and the icm connector itself was corroded. Replaced the icm harness with a new one and fixed the wires and she's run great since.
I had something similar happen this spring. The car would run like crap for a bit, then it wouldn't start. I could reset the trouble codes and it would usually start up and run great for a bit, I'd get a code 42 and it'd start running bad again. On each no start I wouldn't have injector pulse. Ended up being a couple of bad wires between the pcm and the icm, and the icm connector itself was corroded. Replaced the icm harness with a new one and fixed the wires and she's run great since.
I'd definitely check the continuity while moving the wires around to see if they're dropping signal. If it is a code 42 that's shutting down the injectors you should be getting a check engine light. I think disconnecting the battery for a few minutes would reset the codes and maybe allow it to at least start. I also switched out the coil and icm with spares that I had, but the randomness of the wires losing signal made it a pain to try and track the problem down. Good luck.
Trending Topics
I get high ohms from the PCM grounds to ground when the battery is plugged in (negative terminal is connected to the battery). I get low (0-1) ohms when the battery negative is disconnected.
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
Amazing '71 Camaro Restomod Is Modern Muscle Car Under the Skin
Verdad Gallardo
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
TECH Resident
Joined: Jun 2013
Posts: 853
Likes: 32
From: Kernersville, NC
These charts should help out.....from a 96 manual.
No crank....
http://www.ace1252.com/1996_Z28_Fact...hots/No_start/
Crank, but no run....
http://www.ace1252.com/1996_Z28_Fact...ut_no_run1.JPG
http://www.ace1252.com/1996_Z28_Fact...ut_no_run2.JPG
http://www.ace1252.com/1996_Z28_Factory_Manual_Snapshots/crank_but_no_run3.JPG
No crank....
http://www.ace1252.com/1996_Z28_Fact...hots/No_start/
Crank, but no run....
http://www.ace1252.com/1996_Z28_Fact...ut_no_run1.JPG
http://www.ace1252.com/1996_Z28_Fact...ut_no_run2.JPG
http://www.ace1252.com/1996_Z28_Factory_Manual_Snapshots/crank_but_no_run3.JPG
TECH Resident
Joined: Jun 2013
Posts: 853
Likes: 32
From: Kernersville, NC
https://www.testequipmentdepot.com/a...ge-drop_an.PDF
I removed all the under hood grounds (2 on the passenger side of the block, the one on the head with the coil, the one with the strap, the two by the headlights, the one by the jump post, and the battery terminals themselves) and cleaned the ring terminals and bolts/nuts up with a wire brush and even re-ground bare metal on the 4 chassis grounds (the one for the ground strap near the air filter, the one on the driver's side above the headlights, the one on the passenger side above the headlights, and the one by the jump post). I haven't tested it yet because I need to make trip to the hardware store plus I think I'm going to clean up the positive ring terminals as well.
TECH Resident
Joined: Jun 2013
Posts: 853
Likes: 32
From: Kernersville, NC
Your unpowered must mean key off. By unpowered I mean, battery disconnected. I was concerned that something might be interacting with the ohm meter with the battery connected....even with measuring on the gnd side. I did a quick test on mine just to double check. With the battery connected,key off, from the negative battery post to the alternator shell is 000.7ohms. Taking out the meter lead resistance, the reading drops to 000.2.
Sorry I mean key off or key not in ignition at all, doors closed, headlights off, etc.
After cleaning all the ring terminals, bolts etc I got it to be 0-1 ohm at the battery negative to chassis ground. I still couldn't get 1-4v AC at the ICM or get injector pulse though, even using a drill to spin a second opti. Then I noticed it went back to 18 ohms to ground ONCE but then back to 0-1 ohm. I'm wondering if I have a slightly but not completely broken wire or bent terminal pin somewhere. Frustrating. I have a scan tool coming tomorrow so I'll see if it stored any codes.
After cleaning all the ring terminals, bolts etc I got it to be 0-1 ohm at the battery negative to chassis ground. I still couldn't get 1-4v AC at the ICM or get injector pulse though, even using a drill to spin a second opti. Then I noticed it went back to 18 ohms to ground ONCE but then back to 0-1 ohm. I'm wondering if I have a slightly but not completely broken wire or bent terminal pin somewhere. Frustrating. I have a scan tool coming tomorrow so I'll see if it stored any codes.
TECH Resident
Joined: Jun 2013
Posts: 853
Likes: 32
From: Kernersville, NC
Which way are you spinning the drill? It would need to be reverse to simulate the proper engine direction. I'm also not sure how well that works....never tested it myself but the dude I saw do it in a youtube vid one time was spinning the thing in the wrong direction. 
No 1-4 volts AC when cranking puts the problem between the opti and PCM according to the buick know how opti vid. Timestamp below where they speak to that point. Edit: timestamp is 17:25.....can't disable this video embedding that breaks the timestep link.
No 1-4 volts AC when cranking puts the problem between the opti and PCM according to the buick know how opti vid. Timestamp below where they speak to that point. Edit: timestamp is 17:25.....can't disable this video embedding that breaks the timestep link.
Last edited by ACE1252; Jun 20, 2020 at 01:45 PM.
HOPEFULLY solved!
Since this is so strange it has to be an open circuit (or the PCM) at this point since even the spare opti won't do anything... I had previous checked terminals A, B, C, and D on the PCM side of the harness to B2, B20, B14, and B3 on the PCM. All checked out fine. But then I have a spare opti side harness (for spinning the spare opti) and I tested B2, B20, B14, and B3. They were bad so I tested the short harness and terminal A at one end works with terminal A on the other etc. I took the OEM opti side harness and backbrobed. Same deal. Very spotty connections between one end of the connector and the other!
Side note: after cleaning the grounds the car cranks much better, lol.
Since this is so strange it has to be an open circuit (or the PCM) at this point since even the spare opti won't do anything... I had previous checked terminals A, B, C, and D on the PCM side of the harness to B2, B20, B14, and B3 on the PCM. All checked out fine. But then I have a spare opti side harness (for spinning the spare opti) and I tested B2, B20, B14, and B3. They were bad so I tested the short harness and terminal A at one end works with terminal A on the other etc. I took the OEM opti side harness and backbrobed. Same deal. Very spotty connections between one end of the connector and the other!
Side note: after cleaning the grounds the car cranks much better, lol.