Crank no start when is cold
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Beginning Member
Joined: Nov 2023
Posts: 13
Crank no start when is cold
I have a 98 blazer 4.3L 2WD. I have no spark from the coil when it is cold in the morning 40°. Change the ignition module, distributor cap, and rotor, but it will start when already warm around 60°. Plug my scan tool, and I don't have reading from the RPM when it is cranking. Already test my crank sensor and cam sensor. (Got good fuel pressure).
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Joined: Oct 2014
Posts: 4,343
From: North Central Indiana
How did you test your crank sensor? That takes an oscilloscope. What about testing coil?
no rpm should indicate no crank sensor signal. Before you replace it, remember they are VERY simple devices and not prone to failure. Just a magnet. More likely wiring to crank sensor.
no rpm should indicate no crank sensor signal. Before you replace it, remember they are VERY simple devices and not prone to failure. Just a magnet. More likely wiring to crank sensor.
Last edited by LesMyer; Dec 19, 2023 at 01:30 PM.
Thread Starter
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Beginning Member
Joined: Nov 2023
Posts: 13
How did you test your crank sensor? That takes an oscilloscope. What about testing coil?
no rpm should indicate no crank sensor signal. Before you replace it, remember they are VERY simple devices and not prone to failure. Just a magnet. More likely, wiring to crank sensor.
no rpm should indicate no crank sensor signal. Before you replace it, remember they are VERY simple devices and not prone to failure. Just a magnet. More likely, wiring to crank sensor.
Moderator
Joined: Oct 2014
Posts: 4,343
From: North Central Indiana
Attached are the schematics for the ignition of your blazer. Also included are the pinouts on your VCM (computer).
Disconnect battery. Remove blue connector from the PCM.
With your meter set to ohms, check resistance on purple wire to crank sensor by probing across pin 28 of the blue PCM connector to pin B of the crank sensor connector (should be near zero ohms) - wiggle the wires and wiring loom and see if anything changes.
Then do the same resistance check for the yellow wire to crank sensor by probing across pin 31 of the blue PCM connector to pin C of the crank sensor connector - again wiggle the wires and wiring loom and see if anything changes.
If all is OK, then put back together and check for 12v with key on at crank sensor connector terminal A (pink wire) - again wiggle the wires and wiring loom and see if anything changes. If OK, then check pins in connectors for 12v on pink wires going to Ignition module and coil).
Report findings and we will go on. Be advised I'll be away from my keyboard for a while.
Disconnect battery. Remove blue connector from the PCM.
With your meter set to ohms, check resistance on purple wire to crank sensor by probing across pin 28 of the blue PCM connector to pin B of the crank sensor connector (should be near zero ohms) - wiggle the wires and wiring loom and see if anything changes.
Then do the same resistance check for the yellow wire to crank sensor by probing across pin 31 of the blue PCM connector to pin C of the crank sensor connector - again wiggle the wires and wiring loom and see if anything changes.
If all is OK, then put back together and check for 12v with key on at crank sensor connector terminal A (pink wire) - again wiggle the wires and wiring loom and see if anything changes. If OK, then check pins in connectors for 12v on pink wires going to Ignition module and coil).
Report findings and we will go on. Be advised I'll be away from my keyboard for a while.
Last edited by LesMyer; Dec 19, 2023 at 02:05 PM.
Thread Starter
|
Beginning Member
Joined: Nov 2023
Posts: 13
Attached are the schematics for the ignition of your blazer. Also included are the pinouts on your VCM (computer).
Disconnect battery. Remove blue connector from the PCM.
With your meter set to ohms, check resistance on purple wire to crank sensor by probing across pin 28 of the blue PCM connector to pin B of the crank sensor connector (should be near zero ohms) - wiggle the wires and wiring loom and see if anything changes.
Then do the same resistance check for the yellow wire to crank sensor by probing across pin 31 of the blue PCM connector to pin C of the crank sensor connector - again wiggle the wires and wiring loom and see if anything changes.
If all is OK, then put back together and check for 12v with key on at crank sensor connector terminal A (pink wire) - again wiggle the wires and wiring loom and see if anything changes. If OK, then check pins in connectors for 12v on pink wires going to Ignition module and coil).
Report findings and we will go on. Be advised I'll be away from my keyboard for a while.
Disconnect battery. Remove blue connector from the PCM.
With your meter set to ohms, check resistance on purple wire to crank sensor by probing across pin 28 of the blue PCM connector to pin B of the crank sensor connector (should be near zero ohms) - wiggle the wires and wiring loom and see if anything changes.
Then do the same resistance check for the yellow wire to crank sensor by probing across pin 31 of the blue PCM connector to pin C of the crank sensor connector - again wiggle the wires and wiring loom and see if anything changes.
If all is OK, then put back together and check for 12v with key on at crank sensor connector terminal A (pink wire) - again wiggle the wires and wiring loom and see if anything changes. If OK, then check pins in connectors for 12v on pink wires going to Ignition module and coil).
Report findings and we will go on. Be advised I'll be away from my keyboard for a while.
New Member
Joined: May 2023
Posts: 6
2001 blazer check your powers and grounds
Checked my alternator power to battery and body grounds when I was experiencing slow crank, no starts. After cleaning chassis and engine grounds cranks normal. The time before that my negative lead to battery became loose not allowing battery to charge normally and harder to crank because of the small gap the power had to jump on the connection. Installed extended bolt and washer kit from O'Reilly's for side post battery and connection has stayed tight ever since. Voltage drop on terminals to battery are not the easiest to check but I'd start there and then check vehicle grounds before condemning battery, starter, alternator or wiring.
Moderator
Joined: Oct 2014
Posts: 4,343
From: North Central Indiana
Checked my alternator power to battery and body grounds when I was experiencing slow crank, no starts. After cleaning chassis and engine grounds cranks normal. The time before that my negative lead to battery became loose not allowing battery to charge normally and harder to crank because of the small gap the power had to jump on the connection. Installed extended bolt and washer kit from O'Reilly's for side post battery and connection has stayed tight ever since. Voltage drop on terminals to battery are not the easiest to check but I'd start there and then check vehicle grounds before condemning battery, starter, alternator or wiring.