I'm trying to get to the bottom of a no-start condition caused by only 2V at the coil positive terminal when ignition is in RUN position. Engine cranks when ignition is in START, but won't run.
I'm familiar with the factory service manual and the factory electrical troubleshooting guide as well as the "Engine Controls - 4.2L" and "Starter" electrical schematics in the troubleshooting guide. My references to wire colors and splice comes from those schematics.
Here is what I've measured:
When ignition is in RUN:
Yellow wire from ignition switch has 12V at splice E (going into the red coil resistance wire) but voltage measured at splice F where the red coil resistance wire connects to (1) yellow wire to coil positive and (2) green w/ tracer wire of solenoid I terminal, is only 2V (The resistance of the coil resistance wire is within spec at 1.35 ohms).The voltage at splice F should be more like 5.5 - 6.5 V per spec when ignition is in RUN.
If I disconnect green / tracer wire at I terminal, voltage at splice F jumps to 12 V. The same thing happens if I instead disconnect the black w/ tracer wire from the bottom of the starter solenoid.
When everything is hooked up correctly, and there is only 2V at splice F, there is sort of a "sizzling" sound apparently coming from the black w/ tracer wire at the point of connection to the solenoid. Per the schematics, that wire is connected to the backup neutral safety switch, so I'm wondering if a malfunction in that switch could be drawing down the voltage at the F splice when everything is connected?
Anyway, any thoughts on how to get to the bottom of this low voltage issue would be much appreciated.
It sounds like a bad connection somewhere. Most often that is a bad ignition switch, but since you hear some sizzling, yours might be elsewhere. Why don't you just try jumping across the neutral switch and see if voltage returns to normal? You can also jump 12v directly to the coil and see if it will run properly. As long as you don't leave it a long time, your coil won't be damaged.
Seems like you've got a good handle on the problem already. You just need to follow up on the diags.
Actually, i'm not so sure how good of a handle I have on it as I'm been staring at the diagrams and engine bay on and off for quite some time now. Getting back to it now with the warmer weather. Having same issue regardless of whether I use existing or spare ignition switch, so i've ruled that out. It prob would start with 12V to the coil, but wouldn't solve the problem. Not sure how to jump across the neutral safety switch. Thanks.
You have the schematic. So look at the starter page for the 4.2L. Your starter solenoid is grounded through the Backup/Neutral switch. So if that switch fails, you don't have a ground and the solenoid won't close.
But that is only going to make the starter not work. That won't be low voltage on the yellow engine controls circuit. So I don't think that is your issue.
Jumping around that switch is as simple as grounding the starter solenoid right at the solenoid (which is how the manual trans are wired). I was following on your suggestion, but now that I've looked at the schematic, that isn't going to help you.
Check voltage on splice "E" yellow wires. In RUN position, should be full battery voltage. Your resistance wire is connected in that splice. Then check voltage on the other end of the resistance wire. I would disconnect it from the coil and check it alone. Should be around 7 volts.
If you pull the - wire off the coil with the ignition on do you read 6 to 12v at the + wire?
The Motorcraft Duraspark (duracrap) ignition system on the 4.2 will ground the ignition coil if the ignition is turned to on and engine is not running. That's probably the sizzling you hear in the coil.
Measure the resistance of your coil on both the primary and secondary. The FSM will give you specs.
It's highly likely your problem with no run but will crank and crank is a bad ICM and coil. I went through them things every two years because I couldn't keep Grammy from sitting at work and leaving ignition on to listen to the radio. I solved that whole situation by putting a MSD6 on it I had lying around.
Voltage upstream of resistance wire at splice E is battery voltage and at splice F is 2V. The latter does not increase to battery voltage unless I disconnect either I-terminal or G-terminal wires from solenoid. Sizzling is from solenoid area not the coil. Also, when I reconnect either of those two wires (resulting in a voltage drop to 2V, I hear two relays click - 1 is either the idle relay or the manifold heater relay near the battery and the other seems to be on the drivers side of the carb (don't know what that one could be).
Voltage upstream of resistance wire at splice E is battery voltage and at splice F is 2V. The latter does not increase to battery voltage unless I disconnect either I-terminal or G-terminal wires from solenoid. Sizzling is from solenoid area not the coil. Also, when I reconnect either of those two wires (resulting in a voltage drop to 2V, I hear two relays click - 1 is either the idle relay or the manifold heater relay near the battery and the other seems to be on the drivers side of the carb (don't know what that one could be).
Voltage upstream of resistance wire at splice E is battery voltage and at splice F is 2V. The latter does not increase to battery voltage unless I disconnect either I-terminal or G-terminal wires from solenoid. Sizzling is from solenoid area not the coil. Also, when I reconnect either of those two wires (resulting in a voltage drop to 2V, I hear two relays click - 1 is either the idle relay or the manifold heater relay near the battery and the other seems to be on the drivers side of the carb (don't know what that one could be).
I would switch to crt hei if everything was in working order. My concern is that the low voltage to the I-terminal could still present a problem. However, am I correct in assuming that crt hei would get rid of the icm, the coil and the old distributor, but everything else could remain stock?
I would switch to crt hei if everything was in working order. My concern is that the low voltage to the I-terminal could still present a problem. However, am I correct in assuming that crt hei would get rid of the icm, the coil and the old distributor, but everything else could remain stock?
If it is an ignition coil problem, its fixed
if it is an ICM problem, it is fixed.
If it is something else, this was still worth it to find the culprit and adds an upgrade with inculded replacement tuneup parts.
I think the CRT HEI should solve my problem, which is low voltage to the coil when ignition is in RUN position. As I said, the jeep cranks with no problem, so likely not a starter solenoid issue. If I do the HEI upgrade and keep the Carter carb (w/ electronic control) can I also still keep the ECU connected? I also still have all of the computer controlled smog stuff hooked up and would prefer not messing with it.
I think the CRT HEI should solve my problem, which is low voltage to the coil when ignition is in RUN position. As I said, the jeep cranks with no problem, so likely not a starter solenoid issue. If I do the HEI upgrade and keep the Carter carb (w/ electronic control) can I also still keep the ECU connected? I also still have all of the computer controlled smog stuff hooked up and would prefer not messing with it.
It will be exactly the same as if you did the nutter to it. No more PCM control of the timing.
Someone mentioned doing a stealth HEI. That would be less expensive, but if you have an original 25+ year old distributor, it probably needs a rebuild anyway. And the YJ mechanical advance does not have a very good curve for use with either nutter or HEI.
If you go with a stand alone dizzy (HEI) your BBD carb will center the stepper pin needles and that's it.
I kept the Motorcraft distributor (it was the non MCU distributor so it had the advance head with more timing) and paralleled the pickup wires with the MCU for my MSD6. So in essence it's "Half Nuttered". I control the spark and the MCU still controls the carb. Look on my YouTube Chanel "Eugene King" I have some help stuff on there for the carb and proper choke operation.
It will be exactly the same as if you did the nutter to it. No more PCM control of the timing. Someone mentioned doing a stealth HEI. That would be less expensive, but if you have an original 25+ year old distributor, it probably needs a rebuild anyway. And the YJ mechanical advance does not have a very good curve for use with either nutter or HEI.
It seems like the easiest thing to do to get the jeep back on the road is the crt hei. I need a new distributor anyway as the vacuum advance on the original one does not hold vacuum well anymore.
If I go the hei route, can I simply disconnect the wire to the i-terminal on the starter solenoid as a way of terminating the resistor wire part of the "run" ignition circuit given that i'm also removing the coil? I'm afraid to leave it connected b/c when it is connected, the 2v at the coil end of the resister wire (and consequently at the I terminal of the solenoid and the coil pos) results in the resistor wire getting hot.
That I terminal on the starter solenoid is only suppose to be active during a start condition. If your problem happens as soon as it's connected you need to replace the starter solenoid no matter what you chose for a ignition system.
A Motorcraft dizzy was around 54 dollars a few years ago. And chances are good that that dizzy will have the preferred advance for doing a nutter over the lazy 7r advance head that came with the emissions 4.2.
For the HEI instal. Use the coil plus to energize a relay and use that relay to feed battery voltage to the HEI.
I thought the solenoid I terminal is supposed to get 5.5 - 6.5 V (as does the coil positive) when ignition is in RUN position, but is "bypassed" in START position during which full battery voltage is supplied to the starter "S" terminal. That's why I thought I could simply remove the wire to the solenoid I terminal if I went with hei.
From what I can remember, I swapped in a new starter solenoid in Dec when this low voltage condition started without any increase in voltage, so I ruled out the solenoid starter.
Th mods you're suggesting are beyond my skillset. Thought I could just add hei and energize with 12V from yellow wire that was going to the ICM, and I'd be done with it except for determining how to terminate the wires from the F Splice (i.e., the yellow to the coil positive and the green w/ tracer to the solenoid I-terminal.
I thought the solenoid I terminal is supposed to get 5.5 - 6.5 V (as does the coil positive) when ignition is in RUN position, but is "bypassed" in START position during which full battery voltage is supplied to the starter "S" terminal. That's why I thought I could simply remove the wire to the solenoid I terminal if I went with hei. From what I can remember, I swapped in a new starter solenoid in Dec when this low voltage condition started without any increase in voltage, so I ruled out the solenoid starter. Th mods you're suggesting are beyond my skillset. Thought I could just add hei and energize with 12V from yellow wire that was going to the ICM, and I'd be done with it except for determining how to terminate the wires from the F Splice (i.e., the yellow to the coil positive and the green w/ tracer to the solenoid I-terminal.
What does your FSM say? One wire is from the start part of the ignition switch and the other puts 12v on the coil during start. I may have them backwards in my head. (But I'm 99% sure the I terminal of the start solenoid is the contact that puts battery voltage on the ignition coil while the starter is energized) It's been a while. But know this. When you turn on ignition the ICM will ground the coil. So just turning on ignition you will see low voltage on the + of the coil. It's how the duraspark ignition operates. And why you should never leave the ignition on without the engine running. The duraspark ignition is only rated at 2a. Turning in ignition without engine running will pull about 4a while the coil is energized. Not good for either one.
If you hear sizzling noise in the start solenoid with the wire on the I terminal at the minimum you need to change the start solenoid. I've had one go bad and keep the engine running with key removed. I'm sure they can also fail and short.
I'm my opinion you have a bad ignition coil, ICM, and start solenoid. And the start solenoid may have caused it all. Or you left the ignition on for more for a little while. (Listening to radio etc....) shorting out the coil and ICM and the I contact in the start solenoid fried trying to start it repeatedly with a bad ICM and coil.
The mods you're suggesting are beyond my skillset. Thought I could just add hei and energize with 12V from yellow wire that was going to the ICM, and I'd be done with it except for determining how to terminate the wires from the F Splice (i.e., the yellow to the coil positive and the green w/ tracer to the solenoid I-terminal.
When I put in the MSD I just left the coil horseshoe hanging incase my MSD failed and I needed to go back to the stock (with stealth HEI in the factory ICM place). I used a Pachard blade connector pushed into the power wire slot of the factory ICM connector to feed the MSD it's power. If that's your yellow wire just leave the coil connector hang (as long as it's still the ford style coil connector).
Ok thanks. Gotta rethink this. I've got 3 spare ICM's so doubt it's that and the coil is an MSD Blaster that is only a couple of years old and when I tested resistance it seemed to be in spec. I can get a new stock coil and starter solenoid and try replacing what's there now and also swap out the ICM to see if that fixes low voltage issue to coil positive issue before proceeding with the hei upgrade.
Ok thanks. Gotta rethink this. I've got 3 spare ICM's so doubt it's that and the coil is an MSD Blaster that is only a couple of years old and when I tested resistance it seemed to be in spec. I can get a new stock coil and starter solenoid and try replacing what's there now and also swap out the ICM to see if that fixes low voltage issue to coil positive issue before proceeding with the hei upgrade.
you need to remember that the ICM grounds the coil at ignition on. You need to remove the negative wire to the coil to see if anything else is dragging it low.
Removing negative wire to coil has no effect - still just 2 V at coil pos. I swapped 3 diff ICM's - no difference. Also plugged in a new stock distributor - no difference - still 2V. Also checked resistance on disconnected coil: .9 ohms and 5,300 ohms, so within spec. Only thing left to do is get a new starter solenoid - will be a couple of days.
One thing came to mind -I remember a dragging noise in steering column that occurred for a while before I experienced the no start 2V to coil pos condition. Can a short in the steering column be causing this? How can I test for a short there? Or do I have to take the steering column apart for a visual?
Removing negative wire to coil has no effect - still just 2 V at coil pos. I swapped 3 diff ICM's - no difference. Also plugged in a new stock distributor - no difference - still 2V. Also checked resistance on disconnected coil: .9 ohms and 5,300 ohms, so within spec. Only thing left to do is get a new starter solenoid - will be a couple of days. One thing came to mind -I remember a dragging noise in steering column that occurred for a while before I experienced the no start 2V to coil pos condition. Can a short in the steering column be causing this? How can I test for a short there? Or do I have to take the steering column apart for a visual?
what I remember on that stuff is that jeep only had 1 10awg wire out of the ignition switch that feeds everything. At least on the 1986 CJ. If you pull the wire off the I term of the starter solenoid and the voltage goes to normal it's probably your smoking gun. Take a wire and connect it between the battery positive terminal. (Eyelet with a 12awg wire and inline fuse) to that removed wire from the I terminal and see if it starts. (It won't shut off but if it starts like that, the starter solenoid is the issue if it starts )
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Related Threads
?
?
?
?
?
Jeep Enthusiast Forums
18.5M posts
726.8K members
Since 2000
A forum community dedicated to all jeep owners and enthusiasts. Come join the discussion about performance, engine swaps, modifications, classifieds, troubleshooting, maintenance, and more!