can0fspam Posted November 5, 2018 Share Posted November 5, 2018 Hey guys, I discovered a new feature tonight on my 1983 f150 inline six. I turned on the headlights and the engine loaded up a bit and started idling about 50 rpm lower (pretty slight but noticeable). I turned them back off and the engine immediately went back to a normal, smooth idle. Didn't think much of it but kept an eye on things. Then I had to drive a friend to the auto parts store and I turned my lights on to drive since it was dark. It idled down again and as I started driving, I definitely felt some subtle hesitations this time. When I was coasting towards a red light the engine decided to stall out completely, but it turned right back on when I turned the key again. I checked things out under the hood but I didn't see anything obvious. Battery tested with the engine running pulls 14.2 volts with the headlights off and 14.0 with them on. Is this a sign of a bad voltage regulator or something? Seems like the headlights are drawing so much power that it's hurting the engine's spark ability. Thanks for any advice, Jake Link to comment Share on other sites More sharing options...
Gary Lewis Posted November 5, 2018 Share Posted November 5, 2018 Your voltage is a little lower than I would have expected, like maybe .2 volts or so. But it varies by the regulator, temp, etc. So I wouldn't worry. However, the engine loading up and stalling isn't right. What is your idle RPM? Perhaps it is too low. Or, maybe the idle mix is too rich and it truly is loading up. I'm really just guessing. Grasping at straws. Link to comment Share on other sites More sharing options...
can0fspam Posted November 5, 2018 Author Share Posted November 5, 2018 Your voltage is a little lower than I would have expected, like maybe .2 volts or so. But it varies by the regulator, temp, etc. So I wouldn't worry. However, the engine loading up and stalling isn't right. What is your idle RPM? Perhaps it is too low. Or, maybe the idle mix is too rich and it truly is loading up. I'm really just guessing. Grasping at straws. Yeah, I don't blame ya, it seems like a really weird issue! My friend commented saying it seemed like a bad ground to him, but I'm not the most electrically fluent guy out there. Idle RPM when hot is around 800 RPM, it does more like 650 cold. I know whatever the problem is, is related to the headlights or general electrical load since the idle changes so immediately. I'll do some more driving tomorrow and see what happens! Also I just remembered: The truck used to erratically, on its own whim, move between a normal idle and a really, really bad idle around 200 RPM. It would die if I let it do it for more than a few seconds without giving it gas. But I -thought- I'd fixed that problem in January when I got rid of some vacuum leaks. This might be related, although it's had a pretty good consistent idle for a long time now until today. What is a bad ignition switch like? I've read that the cold weather can make them act up. But I have a non-tilt column so that's probably less likely to be it. I also have an aftermarket tach. A friend has a 65 mustang and his tach started making his engine cut out when it started going bad, because it would ground the ignition out. Link to comment Share on other sites More sharing options...
Gary Lewis Posted November 5, 2018 Share Posted November 5, 2018 Yeah, I don't blame ya, it seems like a really weird issue! My friend commented saying it seemed like a bad ground to him, but I'm not the most electrically fluent guy out there. Idle RPM when hot is around 800 RPM, it does more like 650 cold. I know whatever the problem is, is related to the headlights or general electrical load since the idle changes so immediately. I'll do some more driving tomorrow and see what happens! Also I just remembered: The truck used to erratically, on its own whim, move between a normal idle and a really, really bad idle around 200 RPM. It would die if I let it do it for more than a few seconds without giving it gas. But I -thought- I'd fixed that problem in January when I got rid of some vacuum leaks. This might be related, although it's had a pretty good consistent idle for a long time now until today. What is a bad ignition switch like? I've read that the cold weather can make them act up. But I have a non-tilt column so that's probably less likely to be it. I also have an aftermarket tach. A friend has a 65 mustang and his tach started making his engine cut out when it started going bad, because it would ground the ignition out. A bad tach can easily kill and engine. But if yours is working I don't think it is part of the problem. Ignition switches have several sets of contacts, and if the switch doesn't come back to the "RUN" position, which can easily happen in colder weather as the grease sets up, some things like turn signals won't work. But if your ignition works then that's all it takes. Bad grounds do bizarre things, so I can't say it isn't a bad ground. But I don't think that's likely. However, do your headlights appear to be as bright as they should be? As for the idle, 800 is plenty fast and bringing the headlights on shouldn't cause the speed to drop much. I'm really at a loss. So maybe someone else will chime in. Link to comment Share on other sites More sharing options...
grumpin Posted November 5, 2018 Share Posted November 5, 2018 A bad tach can easily kill and engine. But if yours is working I don't think it is part of the problem. Ignition switches have several sets of contacts, and if the switch doesn't come back to the "RUN" position, which can easily happen in colder weather as the grease sets up, some things like turn signals won't work. But if your ignition works then that's all it takes. Bad grounds do bizarre things, so I can't say it isn't a bad ground. But I don't think that's likely. However, do your headlights appear to be as bright as they should be? As for the idle, 800 is plenty fast and bringing the headlights on shouldn't cause the speed to drop much. I'm really at a loss. So maybe someone else will chime in. I thought vacuum leak, but you said you fixed them. May want to check for a vacuum leak again. Link to comment Share on other sites More sharing options...
Dyn Blin Posted November 5, 2018 Share Posted November 5, 2018 A loose ground can make things a hard troubleshoot, but I would start with the battery. If there's a bad cell, it'll hold a surface charge showing normal on a test meter, but under load it'll falter and fail to sink current coming off the alternator evenly. Most auto stores will do a load test for free. Link to comment Share on other sites More sharing options...
BuggTruck Posted November 5, 2018 Share Posted November 5, 2018 I thought vacuum leak, but you said you fixed them. May want to check for a vacuum leak again. He said he fixed the vacuum leak in january. Its now november. Plenty of time for another leak to develop or one to have gotten big enough to cause issues. I second to check for vacuum leak. Link to comment Share on other sites More sharing options...
Gary Lewis Posted November 5, 2018 Share Posted November 5, 2018 He said he fixed the vacuum leak in january. Its now november. Plenty of time for another leak to develop or one to have gotten big enough to cause issues. I second to check for vacuum leak. Having thought about it overnight, I like all of those ideas. But here's another one - the voltage at the coil and/or ignition module. If that voltage is low then when the headlights come on it may drop to the point the spark gets weak, and that will cause subtle running issues. Using this as a reference (http://www.garysgaragemahal.com/start--ignition-gasoline-engines.html) I'd check the voltage on the red/light green wire going to the coil, both with and without the headlights on. And, I'd check the voltage at the white/light blue to red connection at C321, which is the connector near the ignition module - with and w/o the headlights. Link to comment Share on other sites More sharing options...
Steve83 Posted November 8, 2018 Share Posted November 8, 2018 Battery tested with the engine running pulls 14.2 volts with the headlights off and 14.0 with them on.Where exactly were each of the meter probes during each of those tests? Did you clean the surfaces down to shiny metal that the probes were touching? Check voltage between the core support & battery (-) post with headlights off & then on. Then check from the engine (near the coil mount) to the battery (-) post: https://supermotors.net/getfile/825495/thumbnail/cont6.jpg Link to comment Share on other sites More sharing options...
can0fspam Posted November 11, 2018 Author Share Posted November 11, 2018 Battery tested with the engine running pulls 14.2 volts with the headlights off and 14.0 with them on.Where exactly were each of the meter probes during each of those tests? Did you clean the surfaces down to shiny metal that the probes were touching? Check voltage between the core support & battery (-) post with headlights off & then on. Then check from the engine (near the coil mount) to the battery (-) post: https://supermotors.net/getfile/825495/thumbnail/cont6.jpg I tested it with the voltmeter leads both pointing straight down on the top of the posts, with enough pressure to get a good connection. The posts are pretty clean and free of corrosion. I'll try to check voltage from the rad support and the engine to the negative post next time I have some free time -- maybe that will show something. I will check the voltage to the ignition box and the coil too. Does the coil have a connector I can unplug and test or do people usually just bury the needle lead in the insulation to get a reading? I am new to the art of electrical diagnosis! As for vacuum leaks, I think I have an exhaust leak at the manifold, which means I might also have an intake leak at the manifold since they bolt together. Me and a friend tried to put in a gasket a month ago but it didn't make much of an improvement. I might have to have them planed flat. Thanks all for the ideas! I'll get some results soon, let me know if you think of anything else to look at. Link to comment Share on other sites More sharing options...
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