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Headlights make engine run rough

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can0fspam

Headlights make engine run rough

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

- Jake

1983 F-150, 300-6, NP435, NP208

Gary Lewis

Re: Headlights make engine run rough

Administrator

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.

Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

can0fspam

Re: Headlights make engine run rough

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.

- Jake

1983 F-150, 300-6, NP435, NP208

Gary Lewis

Re: Headlights make engine run rough

Administrator

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.

Gary, AKA "Gary fellow": Profile

grumpin

Re: Headlights make engine run rough

I thought vacuum leak, but you said you fixed them.

May want to check for a vacuum leak again.

Dane
1986 F250HD SC XLT Lariat 4x4 460 C6-Sold
1992 Bronco XLT 4x4 351W E4OD
1998 GMC Sierra SLE K1500 350 4L60E
Arizona

Dyn Blin

Re: Headlights make engine run rough

In reply to this post by can0fspam

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.

Sonoma County,CA
1982 F150 Flareside XLS
NP435 4x4
351W Motorcraft 2150

BuggTruck

Re: Headlights make engine run rough

In reply to this post by grumpin

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.

1986 f150 2wd standard cab w/ac 302 5l v8 efi 175,000 miles.

Gary Lewis

Re: Headlights make engine run rough

Administrator

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.

Gary, AKA "Gary fellow": Profile

Steve83

Re: Headlights make engine run rough

Banned User

In reply to this post by can0fspam

can0fspam wrote

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:

can0fspam

Re: Headlights make engine run rough

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.

- Jake

1983 F-150, 300-6, NP435, NP208

Gary Lewis

Re: Headlights make engine run rough

Administrator

You can test the voltage at C321, as shown below. I don't suggest piercing the insulation as it can allow moisture in to degrade the wire itself.

And, you should check the voltage at the coil on the red/light green.

You should check the voltage from those points to the battery's negative terminal, with and without the headlights on.

Gary, AKA "Gary fellow": Profile

vjsimone

Re: Headlights make engine run rough

In reply to this post by can0fspam

Try unplugging your headlamps from the harness, that will eliminate the headlamp load.
Any change between H and L beams ?

Vinny... "Do All Scheduled Maintenance Prior To Troubleshooting" "Resolve All Known Issues Prior To Troubleshooting"

can0fspam

Re: Headlights make engine run rough

This post was updated on .

In reply to this post by Gary Lewis

Just went and tested the voltage at the coil and solid state. With headlights off, both of them showed 12.2 volts. With parking lights on, 12.1 volts. With headlights on, they went down to 11.8 volts.
I replaced the solid state over the summer, so it should be good. The coil is of unknown age but the voltage seems alright.

Edit: Tested battery positive terminal to the valve cover. 14.2 volts running, no lights; 14.0 with lights, 14.0 with high beams.

- Jake

1983 F-150, 300-6, NP435, NP208

Gary Lewis

Re: Headlights make engine run rough

Administrator

There's something wrong with regard to the voltage going to the ignition module. As you can see here, in Run you should have battery voltage to the module. So something is wrong if you have 14.2 volts at the battery and 12.2v at the module.

But, the voltage you are seeing at the coil is what I expected since there's a resistor in the circuit that drops the battery voltage to the coil.

I think the low voltage at the ignition module may well be what is causing the miss. I suspect that the module isn't always triggering the coil, either at the appropriate time or every time, and that causes the engine to miss. You could prove that by running a jumper, preferably fused, from the battery to the ignition module and then taking the truck for a drive and turning the lights on.

To fix it we need to know where the voltage loss is. As you can see in the page linked to above, it is a fairly simple circuit: A fuse link is attached to the solenoid, and that leads to the yellow wire that goes to the ignition switch, then from there it goes directly to the ignition module. I guess it is possible that the ignition switch is failing, but that's rare. And given the age of the wiring it is possible there's a bad connection.

But the first thing I'd check is the fuse link. A fuse link is a smaller sized wire with a heat-resistant insulation. I'd pull on that link to see if it appears to be compromised. If not, then I'd start checking voltages down the line from the solenoid, and you may have to use a pin to probe into the wire. While I don't like to do that, it is going to be difficult or impossible to determine where the problem is w/o doing that.

Gary, AKA "Gary fellow": Profile

can0fspam

Re: Headlights make engine run rough

I do appreciate the thorough analysis, but before we get too far along the diagnosis, make sure you understand that I checked the ignition voltages with the engine off since I had to unplug things.
The battery shows something like 12.2-12.4 volts when the engine is off, and my 14.0 to 14.2 figure was tested with the engine running. Therefore I don't think there's a big jump in voltage from my test, unless the jump from 12.2 to 11.8 is enough to worry about; my apologies if my wording was unclear.

- Jake

1983 F-150, 300-6, NP435, NP208

vjsimone

Re: Headlights make engine run rough

In reply to this post by can0fspam

ChecK the 2 grounds for the Headlamps.

Vinny... "Do All Scheduled Maintenance Prior To Troubleshooting" "Resolve All Known Issues Prior To Troubleshooting"

Gary Lewis

Re: Headlights make engine run rough

Administrator

In reply to this post by can0fspam

Sorry, I misunderstood. At this point I like Vinny's idea - check the headlight grounds.

Gary, AKA "Gary fellow": Profile

can0fspam

Re: Headlights make engine run rough

Alrighty, just went and gave it another look!

The headlights' positive contacts to ground both returned 10.8 volts with the lights on -- not tooo bad. Same voltage from the high beam contact too.

The headlights' negative contacts to battery ground both showed a resistance of 0.01 ohms -- seems like the ground connection is fine.

In the meantime, I thought I would investigate the rest of my wiring -- my alternator idiot light works once in a blue moon and my brake idiot light never works. Could be bad bulbs; how hard is it to get to the bulbs in the cluster?

- Jake

1983 F-150, 300-6, NP435, NP208

Gary Lewis

Re: Headlights make engine run rough

Administrator

You should install a headlight relay harness, as discussed here: Electrical/Lighting/Headlight Wiring Harness. You'll get essentially battery voltage to the headlights and, therefore, have much brighter lights. Plus, your headlight switch and wiring will only be carrying a very small load - just the relay coil's pull-in current of less than an amp.

And, as I think about it, this might fix the problem of the engine missing when you pull the headlights on. I don't like fixing problems when I don't know exactly how it fixed it, but there's something bizarre going on here that I don't understand. So, fixing the headlights and the miss in one go wouldn't be a bad deal. A relay harness will for sure help the headlights and may fix the miss as well.

Oh, as for the ground, you really can't measure connection resistances with a digital volt meter - at least not the kind we mortals possess. The current our DVM's use to assess resistance is far, FAR too small to find a bad wire or connection as the electrical properties change with increasing current. For instance, I've seen battery connections that will run the headlights just fine but won't crank the engine. However, you can measure the voltage drop across a wire or connection, as explained here: Electrical/Voltage Drop Testing. In this case you'd put your DVM on the 20v scale and put one lead on the headlight's negative terminal and the other on the battery's ground post. With the headlights on you should see a very small voltage, but if the connection is bad you may see several volts of drop.

On the gauge bulbs, you have to pull the cluster. Start by pulling the wiper and headlight knobs, then the shroud around the steering column, then the instrument bezel and then the cluster. To do that you'll have to reach behind and disconnect the speedometer cable and the wiring connector to the cluster.

Gary, AKA "Gary fellow": Profile

can0fspam

Re: Headlights make engine run rough

That sounds like fun. I definitely could use brighter headlights! Sounds like redoing the electrical system may be in order. How difficult and time consuming is it to put in relays? I want to do it but I don't want to tear it apart and get lost or stuck somewhere with a truck w/o headlights.

Also I'll read up on voltage drop testing and try that out too!

--

As for electrical I just remembered I wanted to ask you about this:

I was looking at the voltage regulator trying to troubleshoot the charge light the other night.
There are four "ports" on the voltage regulator, but there are five wires coming out -- two from the "A" port -- and one of those (orange wire) ends with what looks like a rubber heat shrink connector and nothing on the end of it. Is this supposed to connect to something?

The rest of the wires go into a wrapped harness towards the alternator. I think the "I" wire is the idiot light. It showed 12 volts with the key in run but I couldn't make the light turn on by grounding it.

- Jake

1983 F-150, 300-6, NP435, NP208