We all suffer while our Zs are in hibernation. This website helps us stay sane.
A little.
Frank T
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| headlights cause engine stall? http://forums.ctzcc.com/viewtopic.php?f=4&t=7095 |
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| Author: | shelly [ Tue Oct 16, 2012 11:09 am ] |
| Post subject: | headlights cause engine stall? |
When I turn on the headlights of my 73 240z, the engine begins to idle rough followed by stalling out after a few seconds. I only noticed this a few weeks ago since I don't let it out at night much. Any thoughts? I did a complete tune up this summer including points, condensor, plugs, and replacing the 40 year old ignition coil. The alternator was rebuilt a few years ago, but I think the voltage regulator is original. Thanks for looking. Shelly |
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| Author: | Frank T [ Tue Oct 16, 2012 1:43 pm ] |
| Post subject: | |
Engines develop the LEAST amount of horsepower when they are idling. It's the time every engine is 'weakest'. As the engine speed (RPMs) increases, the power increases. But at idle, we're looking at maybe a single horsepower or less, and some of that horse power is used just to keep the engine turning against friction. Turning on the lights (or other electrical devices) presents an additional small strain to an idling engine, because it is now being asked to generate enough electrical charge to run the engine AND operate the lights, and that requires a small amount of additional workload from the alternator. Normally this additional work is such a small strain, it is generally unnoticed. You might (might) hear the engine idle dip a bit (like maybe 50-100 rpm at most), but not more than that. If everything is as it should be, the engine should continue to idle normally. However, if the charging circuit is not working correctly, or the regulator is not passing enough electricity at idle to keep the battery charged, or if the battery itself is actually running the engine at low rpm (due to a faulty charging circuit), then even the small additional load of the headlamps, or a fan, or the windscreen wipers, or the air conditioner, or other electrical drain could be enough to either lower the idle rpm far enough to cause a stall, or it could divert enough electricity away from the ignition circuit to cause a stall. And of course, there's the possibility that your headlamp circuit has a short or a ground someplace, which is allowing all your electrical output to divert away from the ignition system and go straight to ground. There are a few things to check to determine what's causing your stall: 1. What rpm is your idle set at? What does your tachometer read while the engine is idling? It should be btwn 400-750 rpm when warm with the choke off. 2. With the engine OFF, can you turn the fan by hand? It should have a 'clutch' behind it which allows it to spin freely when you try to turn it. If it doesn't turn easily, the clutch might be frozen or locked up. That places an unnecessary load on the engine while idling and can lead to a stall; 3. If you still have your air pollution air pump (driver's side/front of the engine, below the distributor), check to see if it spins freely or is frozen. They were notorious for 'locking up' and placing a huge burden on an idling Z engine; 4. Is your fan belt adjusted properly? Too loose will allow it to slip, which will result in the alternator not supplying electricity and charging the battery as it should. Too tight can result in worn bearings at the water pump, which can result in heavy resistance to turning at low rpm, which can put your engine at the brink of a stall ~ as soon as you add some more load by turning on something electrical, it could then result in a stall. Your fan belt should dip about ONE HALF INCH when you press it down with your thumb, midway btwn the fan pulley and the alternator pulley,and operate without squealing; 5. Is your battery charged? The battery's only jobs are to spin the starter to start the car, to operate electrical devices when the engine is OFF, and to (rarely) supplement the alternator when demand is too high for the alternator to meet expectations. All other times it just "sleeps", accepting re-charge from the alternator until it is full, then remaining dormant until called upon for one of the three reasons above. If it's under-charged, you must determine why and fix the problem. There is the possibility that your charging circuit (alternator) is not delivering a charge to the battery to keep it charged. In that event, the charging circuit would NOT be running the engine (as it usually does), but making the battery run the engine instead. This is abnormal, but it happens if/when something is wrong with the charging circuit. That results in the battery constantly putting out its stored electricity (to run the engine and operate any electrical devices) until it runs-flat (becomes totally discharged). The use of any electrical devices in that case would only hasten a stall. A faulty voltage regulator will also allow a battery to begin to discharge to ground when you turn the engine off. And a shorted cell inside the battery will allow it to self-discharge, regardless if it's connected to anything or not. On American cars, I always tested for that condition by disconnecting the battery at idle to see if it stalls (indicating that the battery was the only thing providing electricity for the engine, instead of the charging circuit). But I've been warned not to do that on an early Z car, so I won't recommend it to you. Does the car start OK? Does the battery sound strong when you crank the engine? With the engine OFF, turn on the headlamps in a dark garage, then beep the horn ~ do the lamps dim a lot? Frank T |
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| Author: | shelly [ Sun Oct 21, 2012 7:07 am ] |
| Post subject: | |
Frank, Thank you for taking the time for your detailed reply. The battery is fine as the engine cranks rapidly when I start up. The air pump was disconnected years ago. I will check out the other things this week. |
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| Author: | Frank T [ Thu Dec 13, 2012 3:12 pm ] |
| Post subject: | |
So, whatever became of this? Did you find the problem? Frank T |
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| Author: | shelly [ Tue Dec 18, 2012 7:05 pm ] |
| Post subject: | |
I started going through the list you gave me. The battery tested fine with a voltmeter and cranks strong. I increased the idle speed to about 800 rpm. The fan turns freely, and the belt seems tight. The smog pump was disconnected years ago. The alternator was rebuilt a few years ago, and according to the ammeter, it appears to be charging. About a month ago, it starting getting pretty cold. I put the Z in storage for the winter. I will resume the quest in the spring. the next thing I may do is replace the voltage regulator. It's over 25 years old, so I think it's the next logical step. Thanks for the follow up. I already can't wait for spring, and winter doesn't officially start for three days. |
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| Author: | Frank T [ Wed Dec 19, 2012 12:25 am ] |
| Post subject: | |
We all suffer while our Zs are in hibernation. This website helps us stay sane. A little.
Frank T |
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