My pickup has been running and driving just fine except that for the last several months the engine has randomly been stalling. At first it was so brief that the engine would recover before it died and it was only happening about once every other week. I wasn’t to concerned because unless were you paying close attention to the engine you might not even notice it. However the last month or so it all of sudden became much more frequent and significant. Now the engine is actually dying almost every time I drive it. So I’ve parked it and started driving a spare vehicle we had. When the pickup dies the engine does not spit or sputter at all, it just cuts out cleanly which makes me believe the problem is electrical in nature. However I did check fuel pressure which was fine and also checked the spark when it was acting up. There was not any spark. So I checked voltage at the ignition control module with a full charge on the battery (over 12VDC) and even with the full charge there was only about 7VDC. I’m having a heck of a time locating where the voltage drop is.
An interesting piece of information is that the circuit for my horn and dome light is receiving too many volts, about the same amount the ignition control module is missing. I’ve known about the problem with the high voltage in the horn/dome light circuit for a while. That problem first arose when I tilted the dash forward to replace the heater core. So it’s possible the some wires may have been crossed or shorted, I’m not sure.
I’ve been trying to locate the wiring schematic showing how the voltage is brought to the ignition control module, I did find a couple but they seem incomplete. I appreciate any advice that can be shed on this. THANKS!!
Define too many volts? What are you reading with the engine off and on? These circuits don’t just receive too many volts.
The ignition module is just a sensor, 7 volts maybe be all its supposed to get.
Take off you distributor cap, turn the engine until one of the vanes on the shaft lines up with the line down the center of your ignitor. The gap between these should be about 0.010". Stick a feeler gauge in the gap and then push the shaft away from the ignitor. If a new gap appears, you will need to get a new/reman distributor.
I don’t believe that truck has a distributor. And without a good wiring diagram it would be difficult to determine which wire at the module was the key on circuit and which ones were circuits to sensors and the ECU.
The circuit for the horn and dome light blows fuses consistently, so much that I’ve left the fuse out. During the brief time the fuse does last there is 15-16VDC.
Yes, this is a distributorless ignition. I was reading a troubleshooting flow chart a little while back for GM 2.2l that stated there should be 12VDC powering the ignition control module.
If you can confirm voltage >15 there is a problem with the alternator. And if you remove the module and carry it to a McParts store they should be able to bench test it. If it is tested and passes the test cycle ask the parts man to repeat the test 3 times. Any failure is total failure.
Bench test the ignition control module? That would be great! I thought the only way to truly test those was to look at the waveform on an oscilloscope.
I can understand why you might blame the alternator for not regulating the voltage to around 12VDC but if the alternator is causing >15VDC then I would think just about the entire fuse block would have blown fuses. Not just one fuse.
High voltage will not blow fuses. 1,000 volts wont burn a fuse. Exceeding the amp rating at any voltage burns fuses. Although you should check and confirm the voltage for attention it is very unlikely to be causing your problems. Somewhere in excess of 16 volts the computer might be programmed to drop out in self defense. And most of the McParts (chain stores) have a bench tester for modules that is quite reliable. The tester often indicates a part is good yet it fails on the car after running and getting hot. Quickly repeating the test several times will often heat the internal board and the problem will show up.
If the alternator isn’t grounded properly the voltage regulator can be tricked into putting out too much voltage.
So put one voltmeter lead on the battery negative terminal and use the other to confirm the body, engine and alternator case all read 0 volts.
Thanks for all the advice. Hopefully during some upcoming vacation time I will be able to figure out what’s going on. Still thinking the root cause is the low voltage (7VDC) at the ignition control module. Thanks to all you I have a better idea of what to look for that is causing the low voltage. BTW, here’s the link to a diagnostic procedure I followed last time I was working on this problem.
If the module is failing and becoming a short to ground the voltage at the key on terminal will be reduced. You might disconnect the harness from the module and retest the circuit.
From what you stated in the orignial post it kind of sounds like there is a grounding problem that is causing you to see these irregular voltage readings along with a shorting problem on the horn circuit. It would be good to know where the ground reference for your meter was when you took the ignition voltage reading.
To check for a bad ground issue tie the voltmeter common lead to the negative battery post and then check the voltage at suspected bad ground points under the hood and the dash areas with the headlights on and the blower on high speed. A good ground connection will show no or very little voltage at the other ground point. Also check the voltage at the positive battery post while the engine is running around 2,000 RPM and with the lights on and blower running on high speed. You should not see more than 14.8 volts at the battery. Check the AC voltage also and make sure it isn’t more than .1 volt.
You would be wise to purchase a factory service manual for the wiring to help guide you in finding the trouble with the dome light circuit. That and a good meter is a must have in my opinion. Happy Thanksgiving!
Happy Thanksgiving everyone! Here’s an update:
Currently the pickup won’t fire at all, no spark at all but it does turn over just fine. I checked the voltage at the ignition control module with the connector unplugged while grounding to the engine and about 8VDC shows up while there’s about 12VDC at the battery. I checked voltage at the junction block which is the same level as the battery which tells me the fusible links are just fine. I’m currently tracing power through the dash while referencing wiring diagrams from Mitchell.
Just to be clear, the only reason I mentioned the horn/dome circuit that has been blowing fuses for the last few years is because I thought it may be related to the voltage I’m missing at the ignition control module. And just to possibly make this more complicated. There used to be a aftermarket cruise control the previous owner installed that stopped working due to what I believe is a faulty control unit which I removed. It was soon after I removed it that I started having ignition problems.
Needed to take a break…feeling frustrated. So here’s another update.
As I was tracing power through the dash I suddenly noticed that I had 12VDC at the ignition module. So I plugged the connector back in and the pickup started right up then died after a few seconds. When I unplugged the connector and checked the voltage again it was back down to about 8VDC. So I’ve been trying to pinpoint exactly what circuit is acting up by pulling the fuses that are wired in parallel with the power for the ignition module. When I pulled the fuse for the instrument cluster I got 12VDC again. However I do not consistently get 12VDC when I pull the fuse for the instrument cluster. Nonetheless, as Cougar mentioned, I’m going to try to locate the ground for the power going through the instrument cluster then check that ground and the others while I’m at it.
oh, and the voltage for the horn/dome light circuit went back to 12VDC.
After looking at some info it shows that the power to the ignition control module comes from the ignition switch on a pink wire. Is that the wire that shows the low voltage? If so then you need to check the ignition switch to see if the bad connection is there.
Yep, the pink wire does show the low voltage. Anytime it has normal voltage my pickup starts right up. I’ve checked the grounds I could find and they’re all fine. There’s just a couple other grounds I need to locate. The ignition switch is something I recently thought about checking. Just need to figure out what contacts to check resistance across.
I’m to the point where I may just tear the dash out, or just tilt it forward. I’ve been trying to eliminate different circuits that could be the problem but I just cant get at all the wiring in the dash. grrrrr…as an engineer I like challenging problems but this is starting to get to me.
You have proved the trouble is somewhere on the connection to the pink wire and the grounding is fine. The trouble is most likely with the ignition switch but the info I am looking at shows there is a wire connection between the switch and the pink wire and there is no color assigned to that wire. So that is a possible trouble spot also. The connection may be close to the switch to change it out when needed so look for that. Pin C5 ties to the pink wire. By checking for voltage on the switch position that has voltage getting to it when the switch is in the run position will be the unknown wire color that ties to the pink wire. If the voltage is low at the switch position then you have proved the trouble is with the switch and not at the connection to the pink wire.