Voltage drop to 12v while driving

[station]

I feel embaressed to ask this as these cars are known for their electrical gremlins, but here goes.

 

I had a problem with the car dying due to dropping charge. I found out the belt wasn't tight, so I put genuine Mitsubishi belts on today, tightened everything up and have had 14v all day. Tonight while driving, the car ran at just over 12v, before dropping to 'around' 12v.

I have cleaned all the terminals to and from the battery (but not the fusable links).

 

Is this normal as I read the temperature affects the voltage regulator and reads below? The car started on numerous occasions, so it seems to be charging, but on a worrying 'constantly looking at the voltage gauge' kind've way.

[TexasQuest]

Nothing new, it's a common issue with the 75 amp alternator. The more load you put on it, lights, radio, blinkers, etc. the more it draws down.

[mikec]

The hotter the alternator gets the lower its output voltage... that is documented in the factory service manuals. Many folks see the dash voltmeter reading close to 14 volts right after starting the engine... then it drops to 13 to 13.5ish later on... and think that means the alternator recognizes the battery needs a re-charge right after starting the engine and then, a bit later, sees the battery is charged so it lowers the voltage. Nope... that's just the temperature sensitivity of the alternator. Right after engine start-up the engine bay is pretty cool so the regulator outputs a higher voltage... as the engine bay and alternator heat up the regulator drops the output voltage. The "voltage reference" circuitry inside the voltage regulator is just very temperature sensitive.

 

The alternator guts need a source of +12volts to function - the regulator and field coil pieces. On StarQuests, that 12volt feed suffers the most from wiring issues... leading to low charge voltages. This is the exact same wire that feeds your dash voltmeter too.

 

Read the last post in Alternator isuses from the FAQ for theory and some ideas on cures. Worn/arc-damaged contacts inside the ignition switch are another source of voltage problems.

 

mike c.

[station]

Thanks for the advice!

 

Looking at it again tonight, I messed around with earths, fusible links, etc.

It still remained at 12v!

I gave the belt another tighten and then it went to a healthy 14v!

But is squealed under load/acceleration! The v shape of the belt isn't 'filling' the alt pulley and is getting worn at the sides. The front of the engine had a film of black rubber dust.

I've since put a new replacement on and properly tightened it without squeals or voltage drop.

 

Is this normal? What would cause this? An under tightened belt causing the belt to warp?

[tsi_tom]

Your belts should never squeal. Also you should not overtighten them. Sounds like you have the wrong belt. When asking questions it is good to have pictures. Edited November 9, 2014 by tsi_tom

[mikec]

The belt should not bottom out in the V of the pullies. If it does the belt is the wrong width... or your car has 1 or more incorrect pullies from parts swaps, previous owners, etc.

 

With the belt off, try turning the pullies by hand. All should be easy except of course the crankshaft pulley. Any that are tight have belt-eating problems. Also, examine the two larger belt spots on the crankshaft pulley... they attach to the pulley core via a rubber dampener that eventually separates. When that happens those two belts are not driven at full engine speed. Usually you'll hear clunking too.

 

mike c.

[kidjc]

The belt should not bottom out in the V of the pullies. If it does the belt is the wrong width... or your car has 1 or more incorrect pullies from parts swaps, previous owners, etc.

 

With the belt off, try turning the pullies by hand. All should be easy except of course the crankshaft pulley. Any that are tight have belt-eating problems. Also, examine the two larger belt spots on the crankshaft pulley... they attach to the pulley core via a rubber dampener that eventually separates. When that happens those two belts are not driven at full engine speed. Usually you'll hear clunking too.

 

mike c.

 

& when the rubber "dampener goes?"...

[mikec]

When the dampener fails, the two larger V-groove rings are no longer attached to the metal core of the crankshaft pulley. Those v-belt races will slip (turn less RPMs than the core), can wobble, etc. The intent of the rubber part is to smoothen (dampen) the natural slight RPM variations present in any piston engine. The rotation rate increases slightly each time a piston is on a power stroke and reduces slightly when the next piston is deep into its compression stroke. Remember, a piston engine does not produce smooth & continuous power; the power comes in distinct pulses. The flywheel averages those out a bit so you don't feel the lumpy power as small MPH variations. The crank pulley dampener helps isolate these small variations from the water pump and alternator to reduce stress on their bearings and on the v-belt.

 

The 83 StarQuests and many Mitsu-engined pickups have a solid metal crank pulley so the dampener is not essential. There are aftermarket pullies for StarQuests that are solid metal as well - no dampener.

 

mike c.

[station]

The mk1 MR2 had a drive pulley on the crank puller separated by a rubber band. This also separated and made a hell of a noise, made all the other pulleys extremely hot and destroyed the belts in minutes.

The new belt seems to be doing ok, but time will tell, maybe it wasn't tight enough in the first place?

 

[hunter85]

Mine did the same thing turned out to be my alt/water belt groove on the pulley was wiggly as all get out just put a new one on and it charges alot higher/ runs smoother its a pain really to get the aftermarket pulley on I would imagine even crappier having to take off the radiator and fans

[station]

OK, I do reckon the pulley on the alternator is at fault, it is the only part that is squealing!

[Starfighterpilot]

Station please fill out your profile.

 

To address your alternator belt issue. Sounds to me like you have a 5/16' wide belt for a 83 to 87 Starquest driving a 88/89 alternator.

 

What year is your Lady? The reason that I ask is that there were different valley widths of harmonic balancer & water pump pulleys; 83 through 87 had 5/16" pulley valley widths for the alternator belt; 88/89 had 3/8" widths. Same thing with the pulley on the alternator. Sounds to me like you have a 5/16" wide belt on a 88/89 3/8" width alternator pulley which is why the belt is slipping as it wears itself into the pulley valley. See this link for what I'm talkin' about.

 

http://starquest.i-x...r=asc&start=175

 

Thanks PQ (wherever you may be ) for that great write up and pictures.

 

If your Lady is a '87 or earlier, then you should get a 5/16' wide pulley, MD61 1373, and mount it on your 88/89 alternator to match the other 5/16' pulleys on the water pump and harmonic balancer. Or, as PQ suggests for a "fix," get a shorter 5/16" wide belt.

 

For What It's Worth.

 

KEN

 

PS - Or you have a 88/89 Starquest and your using a 5/16' wide belt.

[station]

Sat here waiting for the AA as my belt snapped on the motorway. It squealed for about 30 seconds and then the battery light.

 

I've just put a new belt on and it went. I previously ground the surface of the v in the alt in case, but I assume it's something else. I've tried all sizes and put it down to a mechanical problem, one of the pulleys must be crooked.

[tsi_tom]

You should show a picture. They always help. Does the alternator spin freely?

[station]

Yes it spins fine! I can't honestly see anything wrong at the moment.

[mikec]

StarQuests (or almost any car for that matter) with dying water pumps can eat V-belts. The typical dying water pump problem is a worn bearing on the shaft... that lets the shaft wobble a bit. When it gets bad enough, the water pump impeller moves enough to rub against the pump housing or the front of the engine - very bad. That'll

* scrape metal chunks into the coolant passages and

* could jam the impellor. Now the water pump pulley is jammed too - burning the belt.

 

When the bearing first starts going bad the usual symptoms are:

* teeny coolant leak from the "weep hole" in the underside of the pump housing around the shaft... down the front of the engine.

* a fairly distinct sound (like marbles rolling in the bottom of large coffee can)

 

Easy test: with the v-bolt off, grab the water pump pulley and try to move it up/down, left/right, and in/out. If it wiggles at all the bearing is shot. You can do the same test on the alternator. Any "slop" in a bearing supported shaft is generally bad news.

 

mike c.

 

p.s. it could be worse: on many OHC Honda engines the water pump is driven from the backside of the camshaft with a short V-belt. If the water pump fails and jams it'll jam the camshaft too. Since most (all?) Honda OHC engines are "interference" designs and use timing belts instead of chains that means the pistons will smack into any open valves, destroying the valves and possibly doing even worse damage. Oh, the teeth of the camshaft belt will be sheared off too if the failure happened while the engine was at high RPM, especially on a stick-shift car where the wheels can keep the crankshaft turning even when the engine itself isn't "running" any more. Happened to a friend of mine that didn't heed my warnings that his water pump - making that oh-so-distinctive-sound - was about to die. Cost almost 900 bucks to put that CRX engine back together. It could be ugly on the Caravan versions of the 2.6 engine too since that also uses a camshaft driven belt to drive stuff... if the camshaft were to sieze at least the valves wouldn't suffer damage as the 2.6 is a non-interference engine. But, since it is a chain driven camshaft, something metal is going to break somewhere - no whimpy teeth on a timing belt to shear off instead. Still gonna be ugly.

[station]

Thanks for that write up, I'm going to change the belt and tensioner (it's a 2.0), I'll see if I can get a water pump. Although I can see the belt change shape and slacken just before the alternator when I rev the engine.

 

BTW are shogun/montero altar the same? Connectors are identical, but they have two pulleys (like the crank pulley).

[station]

Got a 2.6 Shogun/2.0 Sigma alternator, apart from different connector, it fits perfectly! Charge is slightly lower than 14v but it's all charging and running fine!

[station]

Four days later - charge is back to 12v on new alt, and belt is squealing very slightly over 2000 rpm - check belt, it was tight as normal but pulley was red hot.

Now what?

 

edit: Went back up and checked - belt is loose (and still a bit warm), but tightening bolt on alt mount is still where it was - assume the belt has stretched enough to be loose?

I've got a water pump on order - incidentally, the 'weep' hole on the pump, is this there when the seal packs in to indicate pump fail?

Edited November 26, 2014 by station

[Starfighterpilot]

Four days later - charge is back to 12v on new alt, and belt is squealing very slightly over 2000 rpm - check belt, it was tight as normal but pulley was red hot.

Now what?

 

edit: Went back up and checked - belt is loose (and still a bit warm), but tightening bolt on alt mount is still where it was - assume the belt has stretched enough to be loose?

I've got a water pump on order - incidentally, the 'weep' hole on the pump, is this there when the seal packs in to indicate pump fail?

 

Yes - you would be surprised how much a new belt stretches during it's first couple of hours of run time - especially a Chinese made one. I always check/readjust a new belt's tension after a hour of run time - then again after 3 hours run time. Especially that long A/C compressor drive belt.

 

If the pulley was "red hot," you probably fried the belt. If it was me I'd replace it.

 

The weep hole in the engine coolant pump housing is there to indicate that the seal is starting to go or is gone.

 

For What It's Worth.

 

KEN

[station]

The belt was a genuine Mitsubishi 'Mitsuboshi' one! The third one so far - have another one on order now lol. The car wasn't equipped with AC (thankfully) - it's like cars in Thailand don't have interior heaters fitted, five months of warm summers over here doesn't warrant it really.

I could be wrong and say the top bolt has somehow loosened, but I checked the bottom pivot bolt, and it was missing the nut/washer on the back (mustn't have been tight enough and unfastened off).

Everything is tightened up again now, so will see how it goes (it's back at 14v now).

[TexasQuest]

Sounds like something is not staying tight whether it be the mounting bracket or a bolt.

[station]

Yes, retightened everything on the top, and put a nut on the bottom bolt when I got home, has been fine for the past three days (350 miles).

[station]

Weird - driving home tonight - 12v!

Check the belts, power steering is very loose (I noticed some 'deadness' in power steering at a standstill), alt belt is loose also. It's at it's highest bolting point as well, on both belts.

Would love to know what's going on here. There's no squealing.

[Starfighterpilot]

Weird - driving home tonight - 12v!

Check the belts, power steering is very loose (I noticed some 'deadness' in power steering at a standstill), alt belt is loose also. It's at it's highest bolting point as well, on both belts.

Would love to know what's going on here. There's no squealing.

 

Where the alternator bolts loose again?

 

Is the PS pump belt new. If so, it is belt stretch.

 

For What It's Worth.

 

KEN