. my revs drop dramatically, they drop so far as to eat into the battery power, then stall the car. My volt meter reads that the voltage is ~14.4 when I keep the revs up, when I take my foot off the accelerator the volts drop rapidly.
i've just had the alternator tested and that is fine.
To me, these are all signs of the alternator problems, but that has just been disproven.
What else could it be?
intrade,
Jun 4, 10:09am
What car year make model are we talking here ? because without that your information is almost useless for the next step.
321mat,
Jun 4, 10:12am
Without knowing the make/model.
I suggest it sounds like a crook spark plug. because the engine is "searching" and failing to find the spark, which confuses the ECU.
machinehead,
Jun 4, 10:14am
Sorry, for the lack of detail!
It is a 1990 Ford Sierra with a Link Plus ECU.
frytime,
Jun 4, 10:17am
Why is the the idle dropping? Most alternators don't charge properly until about 1500rpm. So low idle will cause low voltage. Blocked idle valve?
machinehead,
Jun 4, 10:20am
It idles fine by itself, it just drops/stalls once the volts get really low (which happens very quickly).
intrade,
Jun 4, 10:21am
ok now we have a new problem link plus ecu. a 1990s ford has almost 0 diagnostic possible but we can rule out difficult things like faulty smart alternators and there like. I want you to disconnect the battery and mesure for a parasitic amparage draw with engine off ignition off. then with ignition on what is the amp load with just ignition on? Do you know how to do this?
machinehead,
Jun 4, 10:26am
I *do* have a multimeter, but do not know where to take the measurements from. Just from the cables that are attached to the battery?
gazzat22,
Jun 4, 10:30am
Correct me if im wrong but i,m from an age when most cars had generators and i understand the main advantage of alternators was they charged at lower revs,certainly well before 1500rpm.
intrade,
Jun 4, 10:34am
you need to set it in amparage setting. be warned this setting makes your multimeter in to a straight piece of wire like a jumper cable You disconnect the 1 therminal and hold 1 wire of the multimeter to the + post of the battery and the other wire to the clamp therminal that would fit on to the battery jumping the power in amp setting thru your multimeter . Dont forget to plug the cables on multimeter back to its non amparage plug hole when you are finished or you pop the fuse in the meter.
only do the above if you understand exactly what i wrote. doing stuff wrong can cause damage .
intrade,
Jun 4, 10:41am
do not attempt to start or try to do this with engine running . either for that you need a scope and a different amp clamp meter.
gsimpson,
Jun 4, 11:20am
This doesn't sound right. The engine should still run ok even if the alternator is not working at all. It does start after all.
I would be looking at battery clamps and earth straps. Remove and clean. Do you get a voltage drop across the actual lead terminals of the battery itself when this happens? This would indicate a dodgy battery.
Could also be faulty ignition switch?
cammey,
Jun 4, 11:26am
Yes, assuming the battery is in good condition, the car will run fine for ages without an alternator. So the car stalling when RPM drops is most likely not associated with the alternator. (Unless of course the battery is faulty).
Id suggest always searching for electrical faults with a battery known to be in good condition as an excellent starting point.
intrade,
Jun 4, 11:32am
yes well if there is no parasitic draw then i want the battery at a battery place whom have a electronic diagnostic health checker tool who prints out the battery condition. even do on older cars these things are normally hardly a problem he states he has a Link Plus ECU i would need to do research but it could be that this is modern ecu affected by slight battery faults . also if the Link Plus ECU actuarly has a diagnostic port to see what it data is reporting. but the easy stuff first .
intrade,
Jun 4, 11:33am
like can you revert to stock ecu for a test of same symptoms? or has the wiring been modified so reverting is not easy possible?
skin1235,
Jun 4, 11:39am
just how far do the volts drop back?, and how long does it take, they certainly do not stay at 14.4 in any battery I've ever known
do you have a sub fitted, or an amp fitted, what else is usually running when the engine is running in your tests above are the lights on or off
bigfatmat1,
Jun 4, 5:10pm
The car has a crap Lucas alternator fitted the volts will drop if revs get to low. I would doubt it being related to the stalling. By any chance does this happen while braking. Or deceleration. Obviously car has been modified I don't know the extent. These were carburated cars. Have you checked to make sure your spare wheel is secured in the boot.
towelynz,
Jun 4, 5:19pm
Probably unrelated but don't Link ECUs have a low voltage cut off? Im almost sure they do. If the idle was real low and the voltage was jumping around the ECU could be shutting the car off.
gsimpson,
Jun 4, 5:39pm
Define low volts. Remember the battery itself is 12V Could it be a fuel pump problem?
frytime,
Jun 4, 5:41pm
Yes they charge at lower rpm, but still need some spinning to get voltage/amp up to spec. They also have higher outputs to generators
bigfatmat1,
Jun 4, 5:51pm
Which is why its important the spare wheel is secured so it doesnt smack the inertia switch and shut fuel pump off
towelynz,
Jul 30, 7:20pm
10.something. I have come across it before. Car wouldn't start because the voltage was just dropping below the 10.something volts while cranking. Fixed the problem by rewiring the power source.
If the idle was quite low, and the voltage was jumping around, almost at the stall point, it could turn off the Link.
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