Troubleshooting a no crank/no start situation
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Joined: May 2003
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From: Kennesaw, GA
Re: Troubleshooting a no crank/no start situation
Took a look at the starter, a previous owner replaced it recently and all the connections are very good. Not going to bother pulling it for now. Could not get to the other PCM ground, but it looked good.
Cleaned up the battery ground point after seeing that giving it a cleaner path to the block perked things up a bit.
Ordered an Opti, I can decide if and when it goes on but I can have it ready. Tested the ICM harness again, got 12v and ground fine, but that pesky B terminal still doesn’t hit 1VAC. I have good grounds and power connections now, low resistance to the block on ground. I can’t think of what else it could be at this point. Worst case I can simply pull the Opti and inspect it.
Still planning on running compression test and replacing spark plug wires.
Cleaned up the battery ground point after seeing that giving it a cleaner path to the block perked things up a bit.
Ordered an Opti, I can decide if and when it goes on but I can have it ready. Tested the ICM harness again, got 12v and ground fine, but that pesky B terminal still doesn’t hit 1VAC. I have good grounds and power connections now, low resistance to the block on ground. I can’t think of what else it could be at this point. Worst case I can simply pull the Opti and inspect it.
Still planning on running compression test and replacing spark plug wires.
Last edited by It's Cochese!; Sep 22, 2023 at 04:53 PM.
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From: Duvall, WA
Re: Troubleshooting a no crank/no start situation
if you don't get the few hundred rpm on the tach then the computer is never going to supply a spark signal to the coil.
its like wiring your house, and you get no power at the outlet, you check the breakers, wires, all look good, but if power company doesn't supply power to the house you will never get power at the outlet!
its like wiring your house, and you get no power at the outlet, you check the breakers, wires, all look good, but if power company doesn't supply power to the house you will never get power at the outlet!
Thread Starter
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Joined: May 2003
Posts: 268
From: Kennesaw, GA
Re: Troubleshooting a no crank/no start situation
if you don't get the few hundred rpm on the tach then the computer is never going to supply a spark signal to the coil.
its like wiring your house, and you get no power at the outlet, you check the breakers, wires, all look good, but if power company doesn't supply power to the house you will never get power at the outlet!
its like wiring your house, and you get no power at the outlet, you check the breakers, wires, all look good, but if power company doesn't supply power to the house you will never get power at the outlet!
Thread Starter
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Posts: 268
From: Kennesaw, GA
Re: Troubleshooting a no crank/no start situation
Before I take anything else apart though, I’d be happy to check for continuity or etc that would explain not getting enough voltage on that line. I did check one of the PCM connectors and found no issues.
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From: Kennesaw, GA
Re: Troubleshooting a no crank/no start situation
Checked the Optispark harness, all values checked out. Changed the Opti, still got less than 1VAC. Decided to try and start it anyway, didn’t start but I did get a couple of puffs of fuel vapor out of the intake.
While I could have gotten another bad one, I’m going to scour shoebox’s site and elsewhere to figure out why I would get less than one volt on that signal line. New plug wires will also go on tomorrow, may get the ICM checked and I also need to test the coil.
I suppose the other bit of investigation I need to do is the wiring. Outside of the Opti harness, is it just taking apart the entire engine harness or can I do some continuity/resistance checks?
While I could have gotten another bad one, I’m going to scour shoebox’s site and elsewhere to figure out why I would get less than one volt on that signal line. New plug wires will also go on tomorrow, may get the ICM checked and I also need to test the coil.
I suppose the other bit of investigation I need to do is the wiring. Outside of the Opti harness, is it just taking apart the entire engine harness or can I do some continuity/resistance checks?
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Re: Troubleshooting a no crank/no start situation
Only things I can think of are a bad ICM ground, problem with the ICM, or the PCM isn’t supplying the required reference voltage on the white wire. I'll see if I can get
@GaryDoug to look at this. He's the electrical wizard. Even has built a complete LT1 simulator with PCM, Opti, most of the sensors and actuators.
@GaryDoug to look at this. He's the electrical wizard. Even has built a complete LT1 simulator with PCM, Opti, most of the sensors and actuators.
Thread Starter
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Joined: May 2003
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From: Kennesaw, GA
Re: Troubleshooting a no crank/no start situation
Only things I can think of are a bad ICM ground, problem with the ICM, or the PCM isn’t supplying the required reference voltage on the white wire. I'll see if I can get
@GaryDoug to look at this. He's the electrical wizard. Even has built a complete LT1 simulator with PCM, Opti, most of the sensors and actuators.
@GaryDoug to look at this. He's the electrical wizard. Even has built a complete LT1 simulator with PCM, Opti, most of the sensors and actuators.
I will get the ICM tested tomorrow. I was thinking to trace that white wire back to the PCM and check continuity/resistance. If there is a bad connection in the wire, it would show a high ohm number?
I hope it isn’t the PCM, but I suppose that can be overcome as well.
E: I found on which PCM harness the white wire runs to, first thing I’m checking is that.
Last edited by It's Cochese!; Sep 23, 2023 at 08:56 PM.
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From: Hell was full so they sent me to NJ
Re: Troubleshooting a no crank/no start situation
The black ground wire from the ICM doesn’t go directly to the stud that holds the ICM/coil bracket to the head. It goes up into a harness bundle to a splice that couples it with other ground wires. Than a single black wire comes out of the bundle, with an eyelet that goes on the stud. The other eyelet with 2 wires on it is one of two PCM grounds. Then there should be a braided ground strap from the chassis. I don't know what effect a problem in the harness splice, or something messed up on the other ground wires that feed into the splice would have.
Just grasping at straws with that one.
Just grasping at straws with that one.
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From: Duvall, WA
Re: Troubleshooting a no crank/no start situation
Is the tach showing any RPM's when you try to start it and how many?
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From: Kennesaw, GA
Re: Troubleshooting a no crank/no start situation
I haven’t been the one to start it lately, but it would basically only twitch a little. Not really going above the 0 line.
E: as a note to self, the other thing I could try is de-pinning the ICM connector and test again.
E2: Also this, quoting because direct linking isn’t working on mobile.
E: as a note to self, the other thing I could try is de-pinning the ICM connector and test again.
E2: Also this, quoting because direct linking isn’t working on mobile.
Start with the ign control signal on the white wire of the ICM pin B and at the PCM is on the black connector pin 5. The first thing to do is disconnect both connectors and check continuity from pin B of ICM to pin 5 of the PCM connector. You may need a second wire to reach it with meter. Obviously if there is no continuity, you have a wire to fix.
If ok, connect both ends and put the meter on AC Volts. While cranking the engine, look at the signal on the white wire of the PCM. It should have between 1 and 4 volts AC on it. Remember to ground the black lead.
If no AC signal, pull the connector at the PCM (black connector) and check the signal coming out of pin 5. If there is no signal coming out of pin 5 then most likely (notice I said most likely), the PCM is bad.
If the AC signal is getting to the PCM on the white wire, you must now look at the signals from the ICM to the coil. Ignition off. Meter set to DC Volts. First check for a good ground to the ICM. Put a meter lead on the + battery terminal and probe the black wire pin C on the ICM with the other lead. It should show a full battery voltage (12 or more volts).
If not you have a bad ground.
Ignition on. Meter set to DC Volts. Now check the pink/black wire on pin A of the ICM and the white/ black wire on pin D of the ICM for battery voltage (12 or more volts) remember to ground the other lead.
If the voltage is there, the problem is the coil. If it is not on those 2 pins, you have to determine if the wire from the coil to the ICM is broken, or if the connectors are bad or the coil is bad.
Also if the voltage is not on those 2 pins, check the #11 fuse (10 amp) the supplies the ignition. If blown, no voltage either.
If the AC signal is getting to the ICM and the ICM has 12 volts on pins A and D, the ground is good to the ICM, and you still have no spark the ICM is probably bad.
One other thing, do yourself a favor and put the screen back in your MAF.
Dave
If ok, connect both ends and put the meter on AC Volts. While cranking the engine, look at the signal on the white wire of the PCM. It should have between 1 and 4 volts AC on it. Remember to ground the black lead.
If no AC signal, pull the connector at the PCM (black connector) and check the signal coming out of pin 5. If there is no signal coming out of pin 5 then most likely (notice I said most likely), the PCM is bad.
If the AC signal is getting to the PCM on the white wire, you must now look at the signals from the ICM to the coil. Ignition off. Meter set to DC Volts. First check for a good ground to the ICM. Put a meter lead on the + battery terminal and probe the black wire pin C on the ICM with the other lead. It should show a full battery voltage (12 or more volts).
If not you have a bad ground.
Ignition on. Meter set to DC Volts. Now check the pink/black wire on pin A of the ICM and the white/ black wire on pin D of the ICM for battery voltage (12 or more volts) remember to ground the other lead.
If the voltage is there, the problem is the coil. If it is not on those 2 pins, you have to determine if the wire from the coil to the ICM is broken, or if the connectors are bad or the coil is bad.
Also if the voltage is not on those 2 pins, check the #11 fuse (10 amp) the supplies the ignition. If blown, no voltage either.
If the AC signal is getting to the ICM and the ICM has 12 volts on pins A and D, the ground is good to the ICM, and you still have no spark the ICM is probably bad.
One other thing, do yourself a favor and put the screen back in your MAF.
Dave
Last edited by It's Cochese!; Sep 23, 2023 at 10:23 PM.
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From: Duvall, WA
Re: Troubleshooting a no crank/no start situation
You need to find out WHY you don't have RPM's!
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Posts: 191
From: Duvall, WA
Re: Troubleshooting a no crank/no start situation
Go read post #2 & 11
the only thing you said was the tach twitched.
the tach needs to read 100+ rpm while cranking the engine over, otherwise you get NO Spark or Fuel.
the computer controls the tach, if the tach isn't showing the engine is turning then the computer is not going to send spark or fuel signals, because the computer thinks the engine is not turning.
the only thing you said was the tach twitched.
the tach needs to read 100+ rpm while cranking the engine over, otherwise you get NO Spark or Fuel.
the computer controls the tach, if the tach isn't showing the engine is turning then the computer is not going to send spark or fuel signals, because the computer thinks the engine is not turning.
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From: Kennesaw, GA
Re: Troubleshooting a no crank/no start situation
Go read post #2 & 11
the only thing you said was the tach twitched.
the tach needs to read 100+ rpm while cranking the engine over, otherwise you get NO Spark or Fuel.
the computer controls the tach, if the tach isn't showing the engine is turning then the computer is not going to send spark or fuel signals, because the computer thinks the engine is not turning.
the only thing you said was the tach twitched.
the tach needs to read 100+ rpm while cranking the engine over, otherwise you get NO Spark or Fuel.
the computer controls the tach, if the tach isn't showing the engine is turning then the computer is not going to send spark or fuel signals, because the computer thinks the engine is not turning.
There doesn’t seem to be an easy answer that we have stumbled across here. Wiring, PCM, or maybe ICM are best guesses at this point. I have gotten near zero ohms on various ground to ground and harness to ground. My Opti harness I bought is optimal according to the tests.
What it kinda seems like is the PCM sees that the engine is turning, but very weakly or inconsistently. They question is why.
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Re: Troubleshooting a no crank/no start situation
Go read post #2 & 11
the only thing you said was the tach twitched.
the tach needs to read 100+ rpm while cranking the engine over, otherwise you get NO Spark or Fuel.
the computer controls the tach, if the tach isn't showing the engine is turning then the computer is not going to send spark or fuel signals, because the computer thinks the engine is not turning.
the only thing you said was the tach twitched.
the tach needs to read 100+ rpm while cranking the engine over, otherwise you get NO Spark or Fuel.
the computer controls the tach, if the tach isn't showing the engine is turning then the computer is not going to send spark or fuel signals, because the computer thinks the engine is not turning.