Author Topic: Headlights/blower drop idle, electrical gremlin?  (Read 377 times)

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Toybrota

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Headlights/blower drop idle, electrical gremlin?
« on: May 20, 2019, 12:03:49 PM »
Hey everyone, I've been having some electrical gremlins on my 85' Pickup, and I can't seem to figure out what the cause might be.

I have my idle set to 800RPM (Weber likes it) and whenever I turn the headlights on, it drops the idle.
If I have a combo of the headlights, blower, AND windshield wipers, it brings the idle down to 700.
Now, 700RPM definitely has a lil rumble in the seat, stock carb did the same. Can't be carb related?

I know this is NOT normal, my other 85' 4WD pickup doesn't do this. It idles the same with the headlights, blower, wipers, and the 800 watt subwoofer on... With the stock output Alternator.

Things I've checked/verified:

- Alternator - Outputs 14.45 Volts at idle (800rpm), and the same with the headlights on

- Battery - Almost new, truck can sit for 2 weeks and have no issues starting. Previous owner mentioned maybe it has a bad cell, but that wouldn't make sense with how it performs?

- Grounding - All three ground wires are present. Intake to firewall, fender to motor mount, and coil to the dipstick bolt.

- Harness - Harness is in good shape, not chopped up.

Anyone have any ideas? I'm not an expert when it comes to electrical, but I definitely have gotten this far with the knowledge I have.
I appreciate the help I've received already on this forum, you guys are awesome! Thanks for helping a younger guy like me out.

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toyodaaddict

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My 1980 w/90 22re swap does this. It is annoying.
My 84 22r doesnt do it. I agree, its not normal. I have checked the same things you mentioned. Hopefully someone has some good ideas
80 shortbed-22re,w56,Marlin 23 spline dual cases,HighAngle drivelines,RUF/63"chevy's,35''mtr's,85 front axle,30 spline Longfields, Allpro highsteer.87 rear axle,5.29 gears,rear spool,BudBuilt cm, marlin HD clutch,ramsey 8000 winch. 
     Also 84 toy DD 22R 4.88s,33'' toyo mt'z, marlin clutch,4inch lift/63's, HA drivelines.

Lewis Hein

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In the absence of any idle-up circuits, this seems to me like normal and expected behavior. The idle on our '93 with a 22RE drops when I turn on the headlights. On my 85 it does not, however the idle is around 1100 RPM. What is the idle set at on your other 85?

To check this, start the truck and then let the battery reach full charge. Unless I am mistaken, the alternator output at this point should be zero amps. Measure it just to be sure! Call this number A0. Now turn on the headlights and measure the current draw at each headlight. Call these H1 and H2. Now measure again the current output of the alternator, and call that H1.

In an ideal world, H1+H2 = A1-A0. A tiny difference is likely not be a problem; check against a known good system for reference. A huge difference means trouble...

Make good and sure you are not charging the battery while this is happening. The amps going into the battery will change with time and potentially throw off your measurements.

Snowtoy

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Appears to be the additional demand for amps from the alternator is causing the alt to put a little drag on the engine.  Do you have a 60amp or 70amp alt on it now?

How high is the idle if you turn everything on, adjust the idle to 800, then turn it all off?  Is it livable with it running a little higher w/nothing running but the engine?
'90 black X-cab mod'd 3.0, 33's/4.88's, rear ARB, custom bumpers, sliders, safari rack, etc.
'91 Blue X-cab 22re, 35's/5.29's,Truetrac front, ARB rear, dual cases, and custom Safari flatbed, bumper, interior.
The money pit '87 Supra resto/mod

Toybrota [OP]

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Appears to be the additional demand for amps from the alternator is causing the alt to put a little drag on the engine.  Do you have a 60amp or 70amp alt on it now?

How high is the idle if you turn everything on, adjust the idle to 800, then turn it all off?  Is it livable with it running a little higher w/nothing running but the engine?
The alternator is stock, I'd imagine it's of the 60amp variety.
As for the idle, if I adjust it how you suggest it would have it idling at 900rpm.
900RPM is not necessarily bad, but I'd rather have it as low as possible. Stock idle speed is 700 for a Manual trans 22R, which is a little too rumbly for my setup (no vacuum leaks, tuned Weber gets 20mpg).
If I set the idle to 700, it would drop it to 600 with headlights+blower+wipers on.


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Toybrota [OP]

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In the absence of any idle-up circuits, this seems to me like normal and expected behavior. The idle on our '93 with a 22RE drops when I turn on the headlights. On my 85 it does not, however the idle is around 1100 RPM. What is the idle set at on your other 85?

To check this, start the truck and then let the battery reach full charge. Unless I am mistaken, the alternator output at this point should be zero amps. Measure it just to be sure! Call this number A0. Now turn on the headlights and measure the current draw at each headlight. Call these H1 and H2. Now measure again the current output of the alternator, and call that H1.

In an ideal world, H1+H2 = A1-A0. A tiny difference is likely not be a problem; check against a known good system for reference. A huge difference means trouble...

Make good and sure you are not charging the battery while this is happening. The amps going into the battery will change with time and potentially throw off your measurements.
1100RPM? Wow, that's mighty high!

My Xtracab will idle at 700RPM. All lights on, wipers, blower and sound system. Idle is not affected, stock alternator.
I'll have to definitely measure and calculate given that formula. Thanks for this write up, I appreciate it!

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liveoak

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first thing you should do is have your battery and alternator tested then go from there

gnob

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Make sure the connection and power lead from alt to battery is good.  Alot of times the sub wire from the battery to fuse box has been monkeyed with.
hold this. . .

Toybrota [OP]

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I just got back from having the alternator tested at my local AutoZone. It passed with flying colors.
Next I'll take the battery in and see.
After that, I'll be going thru the entire Harness.

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Lewis Hein

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I'm curious... what were the results of the multimeter check? Did you post them and I missed it?

liveoak

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Next I'll take the battery in and see.


 :thumbs:

Toybrota [OP]

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I'm curious... what were the results of the multimeter check? Did you post them and I missed it?
I haven't posted anything other than saying it has 14.45 bolts at idle. At AutoZone they usually give you a print out with what your alternator tested at, didn't get it. But they said it works flawlessly.

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Snowtoy

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The amp output and draw when the components are on is the issue, not the watts.  Did they bench test it or on the vehicle?
'90 black X-cab mod'd 3.0, 33's/4.88's, rear ARB, custom bumpers, sliders, safari rack, etc.
'91 Blue X-cab 22re, 35's/5.29's,Truetrac front, ARB rear, dual cases, and custom Safari flatbed, bumper, interior.
The money pit '87 Supra resto/mod

Toybrota [OP]

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The amp output and draw when the components are on is the issue, not the watts.  Did they bench test it or on the vehicle?
Bench test. I asked for solid numbers, and I of course didn't get any. I wanted to know exactly what the Amperage output was, as that's important.

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