Crank no start when is cold
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Joined: Nov 2023
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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.
Thank for the tip, but it cranks fine. I'm just trying to fix the "no spark when is cold". Battery and alternator are good.
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Beginning Member
Joined: Nov 2023
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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.
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Joined: Oct 2014
Posts: 4,334
From: North Central Indiana
1. Verify no start condition and no spark directly from ignition coil while cranking before beginning.
2. Disconnect connector from ignition coil. Leave connector hooked to ignition module.
3. With a test light hooked to 12V battery (not ground), probe pin C of ignition coil connector (ckt 1847 - white/blk) while cranking. If light flashes, then all through (and including) ignition module is working.
4. If test light flashes in #3, plug the coil back in and disconnect the ignition module. Ground pin D (ckt 1847 - white/blk) off and on rapidly. Coil should fire each time the circuit is disconnected. If coil doesn't fire we will test it electrically next.
Report please.
Last edited by LesMyer; Dec 20, 2023 at 05:12 PM.
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Beginning Member
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Unless you have an oscilloscope handy, lets do some easier checks and we might just catch the problem in the meanwhile. I was betting you would find a broken wire to the crank sensor. This is what we should have done at the start. Must admit I am puzzled by the no RPM signal on your scanner.
1. Verify no start condition and no spark directly from ignition coil while cranking before beginning.
2. Disconnect connector from ignition coil. Leave connector hooked to ignition module.
3. With a test light hooked to 12V battery (not ground), probe pin C of ignition coil connector (ckt 1847 - white/blk) while cranking. If light flashes, then all through (and including) ignition module is working.
4. If test light flashes in #3, plug the coil back in and disconnect the ignition module. Ground pin D (ckt 1847 - white/blk) off and on rapidly. Coil should fire each time the circuit is disconnected. If coil doesn't fire we will test it electrically next.
Report please.
1. Verify no start condition and no spark directly from ignition coil while cranking before beginning.
2. Disconnect connector from ignition coil. Leave connector hooked to ignition module.
3. With a test light hooked to 12V battery (not ground), probe pin C of ignition coil connector (ckt 1847 - white/blk) while cranking. If light flashes, then all through (and including) ignition module is working.
4. If test light flashes in #3, plug the coil back in and disconnect the ignition module. Ground pin D (ckt 1847 - white/blk) off and on rapidly. Coil should fire each time the circuit is disconnected. If coil doesn't fire we will test it electrically next.
Report please.
3. No test light flahsing from White/blck from coil plug.
4. When I ground pin D from the ignition module (with the ignition module disconnected) i got no spark from coil. I got spark from the white/black cable when im grouding it.
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Joined: Oct 2014
Posts: 4,334
From: North Central Indiana
two different problems and two different directions are doubtful.
Are you sure test light cord was clipped onto 12 positive on the battery. Test light should light whenever you touch it to metal on the vehicle (ground). Then it should flash when you probe Pin C with test light and crank engine.
If the coil is working, you should be getting a spark each time you ground and then disconnect pin D from ignition module.
Probably it would be useful to compare these cold results to warm results when engine is in running condition (recently started). Then you know exactly what to expect.
Sorry to be so inconclusive and ask for repeat testing, but we have to find the correct direction to proceed.
Are you sure test light cord was clipped onto 12 positive on the battery. Test light should light whenever you touch it to metal on the vehicle (ground). Then it should flash when you probe Pin C with test light and crank engine.
If the coil is working, you should be getting a spark each time you ground and then disconnect pin D from ignition module.
Probably it would be useful to compare these cold results to warm results when engine is in running condition (recently started). Then you know exactly what to expect.
Sorry to be so inconclusive and ask for repeat testing, but we have to find the correct direction to proceed.
Thread Starter
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Beginning Member
Joined: Nov 2023
Posts: 13
two different problems and two different directions are doubtful.
Are you sure test light cord was clipped onto 12 positive on the battery. Test light should light whenever you touch it to metal on the vehicle (ground). Then it should flash when you probe Pin C with test light and crank engine.
If the coil is working, you should be getting a spark each time you ground and then disconnect pin D from ignition module.
Probably it would be useful to compare these cold results to warm results when engine is in running condition (recently started). Then you know exactly what to expect.
Sorry to be so inconclusive and ask for repeat testing, but we have to find the correct direction to proceed.
Are you sure test light cord was clipped onto 12 positive on the battery. Test light should light whenever you touch it to metal on the vehicle (ground). Then it should flash when you probe Pin C with test light and crank engine.
If the coil is working, you should be getting a spark each time you ground and then disconnect pin D from ignition module.
Probably it would be useful to compare these cold results to warm results when engine is in running condition (recently started). Then you know exactly what to expect.
Sorry to be so inconclusive and ask for repeat testing, but we have to find the correct direction to proceed.
I will do the test tomorrow again.
I was testing some cables today and if put 12v to the pink wire on the ignition module and than crank the engine it will start, if I remove the cable it die. There is 12v when the key is in ON position. Could it be something with the ignition switch?
Moderator
Joined: Oct 2014
Posts: 4,334
From: North Central Indiana
Sounds like you have stripped the wire insulation back so you have access to the wire with the connector plugged in? Please advise if this is the case. Not the best thing to do, but we can work with that and discuss the practice of doing it later. Guess it doesn't matter if the vehicle won't run. Please tell me what you have done with wiring at the ignition module and coil.
It is really odd to test 12V at disconnected connector with key on, but require 12V be externally supplied for the vehicle to run. If this is true, I think there are 2 possibilities.
1. Bad connection somewhere on the original 12V wire/fusebox/ignition switch etc.
2. Something on the 12V circuit is pulling the voltage down to the point that it won't start. This could be a bad coil taking too much juice to run it, or even other things like ignition switch, etc.
So please verify that you have the insulation already stripped back so you can get at the pink wire circuit with both connectors plugged in. If so, monitor voltage with digital meter on this circuit while cranking (no start) and report. If not, don't strip any insulation - monitor voltage on the back side of the ECM 1 fuse in the underhood relay while cranking (no start) and report (same difference).
The plot thickens!!
It is really odd to test 12V at disconnected connector with key on, but require 12V be externally supplied for the vehicle to run. If this is true, I think there are 2 possibilities.
1. Bad connection somewhere on the original 12V wire/fusebox/ignition switch etc.
2. Something on the 12V circuit is pulling the voltage down to the point that it won't start. This could be a bad coil taking too much juice to run it, or even other things like ignition switch, etc.
So please verify that you have the insulation already stripped back so you can get at the pink wire circuit with both connectors plugged in. If so, monitor voltage with digital meter on this circuit while cranking (no start) and report. If not, don't strip any insulation - monitor voltage on the back side of the ECM 1 fuse in the underhood relay while cranking (no start) and report (same difference).
The plot thickens!!
Last edited by LesMyer; Dec 22, 2023 at 09:46 AM.
Moderator
Joined: Oct 2014
Posts: 4,334
From: North Central Indiana
Don't worry about these charts right now, but I just wanted to get them posted for possible future use, if necessary. A few additional things to check.
Last edited by LesMyer; Dec 22, 2023 at 10:07 AM.
Thread Starter
|
Beginning Member
Joined: Nov 2023
Posts: 13
Sounds like you have stripped the wire insulation back so you have access to the wire with the connector plugged in? Please advise if this is the case. Not the best thing to do, but we can work with that and discuss the practice of doing it later. Guess it doesn't matter if the vehicle won't run. Please tell me what you have done with wiring at the ignition module and coil.
It is really odd to test 12V at disconnected connector with key on, but require 12V be externally supplied for the vehicle to run. If this is true, I think there are 2 possibilities.
1. Bad connection somewhere on the original 12V wire/fusebox/ignition switch etc.
2. Something on the 12V circuit is pulling the voltage down to the point that it won't start. This could be a bad coil taking too much juice to run it, or even other things like ignition switch, etc.
So please verify that you have the insulation already stripped back so you can get at the pink wire circuit with both connectors plugged in. If so, monitor voltage with digital meter on this circuit while cranking (no start) and report. If not, don't strip any insulation - monitor voltage on the back side of the ECM 1 fuse in the underhood relay while cranking (no start) and report (same difference).
The plot thickens!!
It is really odd to test 12V at disconnected connector with key on, but require 12V be externally supplied for the vehicle to run. If this is true, I think there are 2 possibilities.
1. Bad connection somewhere on the original 12V wire/fusebox/ignition switch etc.
2. Something on the 12V circuit is pulling the voltage down to the point that it won't start. This could be a bad coil taking too much juice to run it, or even other things like ignition switch, etc.
So please verify that you have the insulation already stripped back so you can get at the pink wire circuit with both connectors plugged in. If so, monitor voltage with digital meter on this circuit while cranking (no start) and report. If not, don't strip any insulation - monitor voltage on the back side of the ECM 1 fuse in the underhood relay while cranking (no start) and report (same difference).
The plot thickens!!
Yes I stripped the wire insulation back and i plug a jump wire giving 12v with the key ON and it start. Now I check voltage in the pink wire (same wire that I stripped the insulation) while I'm cracking the engine and there is no voltage going to it.
