cerm78

Hi there.

I have some strange symptoms in my 1991 NA convertible that are not difficult to overcome but sometimes are a little annoying.

Symptom number 1: Every time I start the engine, being it cold or warm, the voltage needle shows bare battery voltage (~12) as if the alternator is not working. As soon as the engine gets revved over ~3500 rpms, idle or gear, the voltage jumps to ~14 and stays there the most of the time. If I turn on various loads it drops a little but never below 13 volts.

Symptom number 2: When I fist start cold (I live in tropical area so "cold" means 20+ Celsius) it revs up to warm up and by the time the temp needle starts to raise the idle is stable around 800rpm, thats good and normal. BUT when it fully warms up, that is when the temp needle reaches half way up (and never past it more than a nedle width up) the idle drops to a not-so-stable 500rpm idle. It sometimes stalls when the engine is fully loaded with AC, headlights and power steering all at the same time.

Now the interesting part that relates both symptoms in a strange way: The times the engine stalls due to the low idle (usually parking or at a stop light, symptom #2) I have to restart it, but the voltage will be low (symptom #1) and now the idle will be fine around 800-700 rpm (symptom #2 fixed) until I reach over ~3500 rpm (symptom #1 "fixed"). At this time, the voltage recovers to 14 volts and the idle goes low again to ~500.

Just for the record: The PO installed a HOT air intake that I haven't fixed yet, the bypass screw for the idle speed is all the way out (oring flush with external surface). Havent checked TPS adjustment.

Any toughs about this strange behaviour?

Thanks!

HAILERS

What they call the L wire on the back of your alternator is not connected up OR that wire is open b/t the alternator and the warning light assy.

When you rev the engine real high, it *self excites* itself though residual magnatizm in the rotor assy. From then on it puts out and is excited by the diode assy inside the alternator. Now I'd wonder if it is being regulated voltage or not. That's up in the air. You need to take a meter to it at the B terninal of the alternator to find out.

So you need to ask yourself, do the Warning lights all come on when the key is put to ON and engine OFF or not. IF they don't all light up, then there is a problem with the wiring b/t the alt and warning light assy. If this is a S5 car.

L wire is one of the two wires on the back of the alternator.

cerm78

Hmmm seems you have hit the nail... When I power ON before starting the engine, some lights come on but definitely not all of them (belts, brake, check engine, airbag, I think that's it)

I'm sure the alternator wiring is all connected, so I'll check the terminals with the voltmeter.

That helps me with symptom number 1, but I'm still intrigued by the idle symptom.

Thanks a lot HAILERS!

misterstyx69

iTrader: (142)

Have you checked the alternator Belt to see if it is tight?..Check it out this way,by pressing on the Outer side of the belt and having a play(deflection when you press on the belt) of a half an inch,between pulleys.If the belt is slipping then it may cause the alternator's voltage to fluctuate.

cerm78

I've done some tests on these days.

Regarding the alternator the belt seems to be tight and I tested voltage directly at the battery, B terminal, L terminal and S terminal and all of them gave the exact same readings when with the engine running at idle. When the voltage was down (before running the engine past 3500rpm at least once) my multimeter showed a little over 12 volts at all the four points. When it was high (after running the engine past 3500rpm at least once) it showed almost 15 volts on all four points.

According to the image posted by Hailers, the L terminal should be somewhat regulated between around 13.1 volts, but my readings where not showing this kind of behaviour.

Another thing that makes me think is that, again according to the image posted by Hailers, the S5 alternator has the B, L and S terminals at the back, but the alternator on my car has that connectors on the top of the alternator, more like the one labeled has S6 alt on that image. Have I the already upgraded alternator on my car?

Regarding my low idle it seemed to be the full range TPS adjustment out of range. I adjusted it using the resistance readings and now it's stable at 700-800rpm and the engine don't stall, but again, when it's fully warmed up and the voltage is down, the idle is a little higher than normal. Obiously, the ECU seems to be calibrated to read the TPS at 14+ volts and when voltage is down it missreads throttle position.

That's all I have to say for now... any inputs are welcome... Thanks!

Napsterfreak15

my tps does the same thing. At really low rpms it wont get enough volts to work right and then my engine will die.

For a quick fix I adjusted my idle to 950 and I bought a marine battery. A capacitor might help too idk

Also when i start my car the rpm tach doesn't work until i rev it past 3000 then it will work fine even at idle.

I've seen my warning lights come on once or twice since i've built my car and thats it.

Napsterfreak15

heres a vid of what mine does. All i'm doing is adjust the dash lights.

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HAILERS

********According to the image posted by Hailers, the L terminal should be somewhat regulated between around 13.1 volts, but my readings where not showing this kind of behaviour.******************************

Take a sewing needle and ***** the L wire. Put your meters neg lead on a known ground, like the alternators case. Put the meters positive lead on the needle that is punturing the L wires insulation.

Key to ON, engine OFF. The meter should read 1-3 vdc with the key on, alternator not turning. This is different than if you had pulled the small plug off the alternator and probed the L terminal of the harness plug. Not the same thing.

So see if you have that 1-3 volts or not. The L wire is white/black on a series four. ON a series five it's a White/Black wire.

The voltage on a tps is a five volt input from the ECU, not the alternator voltage. Most all the sensor use a five volt ref voltage.
I'm not having much success with my alternator posts. I think I'm not being clear enough. Just the way things are out west.

And on a series five alternator, the small plug is on the back for a non turbo and it's on the side for a turbo car. Either works the same. Same output. Same inputs.

ON a SERIES FIVE, the L wire goes directly to the Warning Light assy. When you turn the key to ON, the alternator puts out a GROUND signal on that wire to the warning light assy and that ground should turn on all the warning lights. Especially the CHARGE light, but all of them all the same.

Then you start the engine up and the alternator rotates. It starts putting out and now there is no ground on the L wire and all the warning lights go out.

I've a series five alt on a 86 series four. For a connector I just use two female connectors crimped on the two wires. I saw a post where a fellow had the two wires crossed. So I started my car and let it idle. It was putting out in the low 14's vdc. So I pulled that L wire off the alternator. Volts went to 15vdc. Not desirable me thinks. I think that equals non regulated voltage ....somehow. I put the L wire back on and it read in the low 14's again. All's well.

TPS have to be set with a HOT engine so the water thermowax will have done it's business and now the throttle linkage is fully closed at idle. With a warm engine the throttle plates will be a bit open thus messing up any TPS adjustments you make. Similar to pissing in the wind.

cerm78

Hi Hailers and all other fellows.

When I tested the alternator voltages the engine was running at idle and all the wires where connected, I didn't puncture the wires but reached the metal tabs with the multimeter leads trough the weather caps in the connector. I'll repeat the test with the engine off to take readings and see what comes out.

I'll take readings at the light cluster too, to discard any broken wire.

I'll take some pictures of the alternator as my car is NA but the alternator has both connectors at the top of it, not the back, I'm very suspicious of its origin.

Re-thinking the idle mystery, if the TPS don't get alternator voltage, may be the low - high idle difference when the alternator is - isn't generating right is associated only to electrical/mechanical loads.

When I set the TPS the engine was fully hot, it's much better now and does not stall. Another symptom I didn't mention early was that my car had bucking when coasting in gear, from 1000 to 2000 rpm... but with the TPS adjustment it is gone or at least happens in different situations...

Thanks for the help!

HAILERS

Download the ENGINE ELECTRICAL of the series five FSM.

The first jpg comes out of that section and shows the 1-3vdc check. The connector has to be ON the alternator and key to ON, engine OFF. It verifys the voltage coming from the warning light assy TO the alternator. Supplies the field voltage for the rotor in the alternator to initially get it operating.

The next three jpg: first shows the two different alternators used on N/A and TURBO engine.

Third jpg shows a closeup of the non turbo alternators plug location.

Fourth jpg shows a closeup of the TURBO alternators plug location.

IF you buy a regulator/brushes for one from AutoZone or whereever, you have to make sure you order the one for your particular type alternator because if you try to mix 'em up you cannot install it in the alt case because the plug will face the wrong direction and won't fit the alernator case. The plug is part of the regulator/brush assy.

Either alternator will fit in a turbo or non turbo and work the same. There are *fitment* issues if you try to put a non turbo alt on a turbo, but it's not a BIG DEAL issue. Just some small adjustment to the B terminal so it won't hit the intercooler.

If the small plug is off the alternator, and the key is to ON, and you put a ground on the L wire in the two wire PLUG, then the warning lights should all come on verifying that there is continuity from the L wire to the warning light assy. Thats for a series five or series four car. So there's no NEED to pull the plug off the warning light assy.

HAILERS

I'm guessing the tach problem is related to the alternator. If the ECU sees low voltage it will disable the trail coil assy. I'm GUESSING that what happens is the ECU kills the trail coil on startup and the alternator isn't putting out when you first start up. Then you rev high and the alernator starts putting out and that solves the non operation of the trail coil assy.

Trail coil assy outputs the tach signal, just in case you wern't aware of that.

I think anybody who designs a alternator that depends on the warning light to supply it Field voltage should go out of business. The series four depends not on the warning light, but the voltage from the coil of a relay in the CPU. Now that makes more sense to me than a light bulb(s) in the warning light assy.

And yeah, if you can actually backprobe the L wire connector, that's always bettter than pricking a wire with a needle.

cerm78

Thanks a very big lot Hailers, I haven't had the chance to test things again but with all of this information I hope to resolve the issue or at least clarify where the problem is.

I'll update this thread as soon as I have some more info.

Thanks!

PS: Those FSM pictures show that I actually have the stock alt.

cerm78

I have done some tests yesterday and these are the results:

1. Disconnected S/L plug and grounded L (W/B) terminal. All warning lights did come on, so the wiring and warning light cluster is working fine. Connected everything again after the test

2. Engine OFF, ignition OFF, all terminals connected:

B (B/W) post = Battery voltage
L (W/B) terminal = 0v
S (W/L) terminal = Battery voltage

3. Engine OFF, ignition ON, all terminals connected:

B (B/W) post = Battery voltage
L (W/B) terminal = Battery voltage <---
S (W/L) terminal = Battery voltage

So according to the S5 FSM page G-9 (exactly what was pointed by Hailers in his previous posts) there should be 1-3 volts at L terminal when ignition is ON and engine OFF, being it battery voltage means that regulator IC is not grounding properly and thus not generating alternator field.

I know that regulator IC can be removed from the rest of the alternator but can it be bought separately?

What is better? changing regulator IC only or the entire alternator? Should I think about an upgraded (S6) alternator?

Meanwhile I'm not concerned to much by this fail, because what it produce is low voltage. When revved up tu 3500rpm at least once it seems that alternator field auto-excites with residual magnetism (again, as stated by Hailers before) and it outputs voltage whitin the FSM range, so there is no risk of frying other electronic components.

Hailers, thanks again for pointing me in the right direction. I aready had the FSM but some times I'm a little lazy.

HAILERS

The regulator with brushes can be had from AUTOZONE for fifty bucks. Some places might charge less. Been there, done that.

You'll need a soldering iron though for soldering in the new regulator. As for how the FSM shows a soldering iron being laid against the bearing housing prior to pulling the alternator apart.........I used a common butane torch used judiciously. I mean I just played a small flame against the housing til I determined the thing got hot enough. Now where near red hot. Just hot. Like just hot enough where I wouldn't think about putting my finger on it.

cerm78

Thank you very much for all your help. I'll search for the regulator and change it some time soon (I hope)

I'll post a follow up when done.

Thanks again everyone!