1993 Brooklands Charging at idle - Rolls-Royce and Bentley Forums
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post #1 of 12 (permalink) Old 08-08-2019, 12:10 PM Thread Starter
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1993 Brooklands Charging at idle

Looking for some advice, ideas to bounce off of. I have checked the idle of my 1993 Brooklands to make sure it isn't idling too low and it doesn't seem to be (600 RPM at idle in gear). I have checked the Bosch ISV and it seems to be performing correctly. My continuing issue is at night with headlights on and AC fan running when I come to a stop from highway i can watch the lights dim, voltage gauge drop to below 12 volts and then the engine dies (most likely due to low voltage at the ECM). I can start the car right back up no issue what so ever every time. I have a battery that is consistently at full charge as I keep a very very small trickle charger on it at all times. The alternator has been rebuilt twice (first time it needed it, second time because I told them I didn't think they fixed the issue the first time). Shop tells me it charges perfect, and at highway speeds it is. If at idle I can catch it quick enough it only takes the tiniest blip of the throttle to make the voltage gauge go up to 13.5 volts or so and car idles fine. So, my question is, do I need a smaller alternator pulley, or does it sound like I'm having a huge voltage drop in the wiring of the vehicle somewhere? I would assume the battery would keep enough voltage to the ECM at idle with loads, but it is not seeming that way. Any help or advice would be appreciated, its becoming unsafe to drive at night. The alternator shop told me that they have in some cases found a smaller alternator pulley for the older Rolls/Bentley or older Cadillacs that use this design engine and it solves the problem.

Last edited by kylel2838; 08-08-2019 at 12:12 PM.
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post #2 of 12 (permalink) Old 08-08-2019, 12:39 PM
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You have a voltage issue when headlamps on . It pulls more current (amps) and the alternator is trying to replace it. Remove the alternator and have it tested under load conditions. Also, check belt tension and all connections from the battery to the alt. Remove battery connections, clean, grease and tighten.

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post #3 of 12 (permalink) Old 08-08-2019, 01:48 PM Thread Starter
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The shop that rebuilt it told me that they load tested it to the max amount and it charged fine. That was why I took it back and had them re look at it. My theory is that at such low RPM it simply can’t keep up with the heavy load of headlamps , ac blower fan, and all other lights at night. I will also check all connections, I’ve pulled battery terminals and cleaned many times over. I’m curious if they are able to load test it at very low RPM to simulate the idle speed of these engines. I’m at a point now to try buying a different Gm alternator that does 100 amps min at idle such as what was posted in the other thread for the Turbo R..
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post #4 of 12 (permalink) Old 08-09-2019, 02:26 PM Thread Starter
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So I have checked and cleaned connection at the starter, and batteries today. Even during the day today with A/C on full fan without headlights it died on me at almost every stop light when I came to idle (can watch the voltage meter drop to 11 then engine dies). So question begs now has anyone upgraded their alternator to a higher amp? I read the other thread for the Turbo R and someone recommended a 12SI alternator that does 100 amps at idle, has anyone tried this on a SZ car? Looks to be somewhat straightforward, would just have to change some wiring for the 3 wire plug that looks like it goes to the dash data center, down to the starter, and has 12V fed to it to excite the alternator.

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post #5 of 12 (permalink) Old 08-09-2019, 08:34 PM
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I wouldn't rush into replacing the alternator just yet especially since the shop that tested it cleared it as OK. Your problem could be something as simple as a bad engine to body earth wire. I don't know how many earth straps your engine has since I'm only familiar with the Silver Shadow but there's more than one. Have a look underneath and undo any earth straps, clean the contacts and apply a small dab of electrical contact grease on them, there's probably another earth strap from the rocker cover to somewhere near the bonnet/hood latch and maybe another one from the gearbox housing to the underbody. The symptoms you're experiencing could be down to something that simple. Also, if the lights flicker it's a sure sign of a bad earth. Replacing the alternator before ruling out other possibilities could land you back at square one with an unnecessary dent in your wallet.
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post #6 of 12 (permalink) Old 08-10-2019, 03:58 AM
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I wouldn't rush into replacing the alternator just yet especially since the shop that tested it cleared it as OK. Your problem could be something as simple as a bad engine to body earth wire. I don't know how many earth straps your engine has since I'm only familiar with the Silver Shadow but there's more than one. Have a look underneath and undo any earth straps, clean the contacts and apply a small dab of electrical contact grease on them, there's probably another earth strap from the rocker cover to somewhere near the bonnet/hood latch and maybe another one from the gearbox housing to the underbody. The symptoms you're experiencing could be down to something that simple. Also, if the lights flicker it's a sure sign of a bad earth. Replacing the alternator before ruling out other possibilities could land you back at square one with an unnecessary dent in your wallet.

I agree with Shadow 11, the car should not stall just because the alternator stops charging at idle speed. Look to see why the engine stalls, rather than the alternator, especially as it tested ok.
If this was the problem, why do other Brooklands not have the same problem?

Jake.
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post #7 of 12 (permalink) Old 08-10-2019, 06:13 AM
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How this problem happened ? Since you own it ? Was it working fine before ?



Have you run the onboard diagnosis ?
Have you used booster to start your car on another , or a nother car to start yours, in thepast ?

97 Continental R
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post #8 of 12 (permalink) Old 08-10-2019, 07:53 AM Thread Starter
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Yes, the car has done this off and on since I’ve owned it (3 years now). At first it’s classic bad diode pack symptoms, I can always tell when it’s going to happen. Car idles Fine, then I can watch my voltage gauge drop down towards 11 volts, check engine light illuminates when it hits that low voltage and engine cuts off. It starts right back up. If I can catch it quickly enough I can just barely touch the throttle to get the voltage back up to 13 or so and it’s good. As long as the voltage at my gauge stays up towards 13-13.5 or so the car will sit and idle all day no issues. During the daytime it’s typically never an issue unless I have high current loads on like yesterday with a/c full blast. The other night it was bad when I had the headlights on, in fact voltage stayed up at one stop sign until I hit the brakes and when the brake lights lit up I saw my dad lights dim and voltage dropped. It’s gotten to the point to where I have no idea when it’s gonna stall on me.
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post #9 of 12 (permalink) Old 08-10-2019, 09:25 AM
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You should run the onboard diagnosis, and see if it reports faults.
Also, you should chechk battery connexion, clean with sand paper.
Same for main ground on the car, track oxydation / rust...


If you have a master switch, make sure everything is tight on it and no oxydation.

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post #10 of 12 (permalink) Old 08-10-2019, 05:48 PM Thread Starter
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I’ll take a peek at ground straps, and something hit me last night to maybe check the battery cutoff switch in the back also, so I’m glad someone else brought that up also. The main lead from alternator goes from alternator to starter, then to battery cut off and battery. I can’t believe they used the positive side to put a cut off on most vehicles kill the ground.
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