Big fuse diag with RS-AJP
Discussion
Hello,
I thought I would share what I did yesterday, first to be sure of my theory, and second because this could be helpful to others.
My newly acquired cerb developped pretty quickly 2 symptoms : first erratic tachometer readings, second and some stuttering at 2k RPM.
As these (especially the first) are typical of the infamous big fuse failure, I decided to log the voltage using RS-AJP so I could check the voltage. This is what I got on a short trip :
As you can see, we clearly see the ramp up of the voltage at low revs, where the alternator does not charge the battery much. We also see the regulated voltage (around 13.2V) from the regulator of the alternator. What bothered me is that there are lots and lots of dots under 13V, so something is wrong. I assume it's normal that there are some low dots, but not that much.
So I changed the big fuse to a 125Amp one, and got this :
We still see the ramp up at low revs and the regulation, but regulation is higher (arounds 13.3-13.4V) and a lot more defined. Results! There are still lots of low dots, but definately less, and not so low. I assume it's normal that the regulation is not 100% precise (if not, tell me!) but the upper line of the regulation is clearly much more defined, and the lower cloud is definately less crowded, in spite of a longer logging session.
In practice, the car performed flawlessly, with no stuttering and accurate tacho indformation.
The old fuse looked perfect at removal, so this is definately interesting.
What do you tink about this? Do the theory sound good? Do the second graph look ok, or should it be more accurate and I have problems with alternator regulation or battery wiring?
Thanks!
Julien
I thought I would share what I did yesterday, first to be sure of my theory, and second because this could be helpful to others.
My newly acquired cerb developped pretty quickly 2 symptoms : first erratic tachometer readings, second and some stuttering at 2k RPM.
As these (especially the first) are typical of the infamous big fuse failure, I decided to log the voltage using RS-AJP so I could check the voltage. This is what I got on a short trip :
As you can see, we clearly see the ramp up of the voltage at low revs, where the alternator does not charge the battery much. We also see the regulated voltage (around 13.2V) from the regulator of the alternator. What bothered me is that there are lots and lots of dots under 13V, so something is wrong. I assume it's normal that there are some low dots, but not that much.
So I changed the big fuse to a 125Amp one, and got this :
We still see the ramp up at low revs and the regulation, but regulation is higher (arounds 13.3-13.4V) and a lot more defined. Results! There are still lots of low dots, but definately less, and not so low. I assume it's normal that the regulation is not 100% precise (if not, tell me!) but the upper line of the regulation is clearly much more defined, and the lower cloud is definately less crowded, in spite of a longer logging session.
In practice, the car performed flawlessly, with no stuttering and accurate tacho indformation.
The old fuse looked perfect at removal, so this is definately interesting.
What do you tink about this? Do the theory sound good? Do the second graph look ok, or should it be more accurate and I have problems with alternator regulation or battery wiring?
Thanks!
Julien
Edited by Jooles81 on Sunday 21st August 10:07
Edited by Jooles81 on Sunday 21st August 10:08
Jooles81 said:
Hello,
The old fuse looked perfect at removal, so this is definitely interesting.
They seem to break down over time. Mine was 0 ohms when I removed it and replaced it with a new one, but the bouncing tacho was resolved.The old fuse looked perfect at removal, so this is definitely interesting.
I do not like my car idling above 1000, and always try to keep it around 900, which is not easy if there is any wear in the throttle bodies.
The problem is not the idle, tbh. adaptatives are really out, there is some slack in the throttle linkage, and the lambdas are making some strange stuff.
moreover, I took the car again today for a spin. It's running great, though voltage is between 12 and 13V at high RPM, and all over the place, so I think there is another problem...
Julien
moreover, I took the car again today for a spin. It's running great, though voltage is between 12 and 13V at high RPM, and all over the place, so I think there is another problem...
Julien
I used to have my idle set around 975.
But I increased it slightly for two reasons.
1) idling in traffic one day, with the lights on and widows down, the phone rang so I wound up both windows at the same time. But the engine started to struggle.
2) When I turn on the air conditioning it causes a 50-60 drop in idle rpm.
The manual doesn't mention if this target idle should be set when the air conditioning is on or off.
But upping the idle by 70rpm solved these issues for me.
You could argue that the first reason might have been caused by a battery nearing the end of its life and not holding its charge.
However, the log above suggests that idling below 1000 rpm doesn't spin the alternator fast enough.
Moreover, you have to consider how high the engine revs too. I have an ecu from a very early 4.2 that has stepper circuitry on it, which suggests they might have expierimented with the idle voltage values?
Aide
But I increased it slightly for two reasons.
1) idling in traffic one day, with the lights on and widows down, the phone rang so I wound up both windows at the same time. But the engine started to struggle.
2) When I turn on the air conditioning it causes a 50-60 drop in idle rpm.
The manual doesn't mention if this target idle should be set when the air conditioning is on or off.
But upping the idle by 70rpm solved these issues for me.
You could argue that the first reason might have been caused by a battery nearing the end of its life and not holding its charge.
However, the log above suggests that idling below 1000 rpm doesn't spin the alternator fast enough.
Moreover, you have to consider how high the engine revs too. I have an ecu from a very early 4.2 that has stepper circuitry on it, which suggests they might have expierimented with the idle voltage values?
Aide
Ditto - I also only knew about the one behind the engine. Where is the other one and what does it do? Is it similarly fragile?
I changed the one behind the engine, without it fixing the bouncing rev counter. BUT, I did learn that you shouldn't over-tighten the nuts. Whoever replaced it before me had done so and, when I tried to undo them, the whole fuse holder came apart (which was a much bigger pain to change than the fuse alone would have been).
I changed the one behind the engine, without it fixing the bouncing rev counter. BUT, I did learn that you shouldn't over-tighten the nuts. Whoever replaced it before me had done so and, when I tried to undo them, the whole fuse holder came apart (which was a much bigger pain to change than the fuse alone would have been).
aide said:
I used to have my idle set around 975.
But I increased it slightly for two reasons.
1) idling in traffic one day, with the lights on and widows down, the phone rang so I wound up both windows at the same time. But the engine started to struggle.
2) When I turn on the air conditioning it causes a 50-60 drop in idle rpm.
The manual doesn't mention if this target idle should be set when the air conditioning is on or off.
But upping the idle by 70rpm solved these issues for me.
You could argue that the first reason might have been caused by a battery nearing the end of its life and not holding its charge.
However, the log above suggests that idling below 1000 rpm doesn't spin the alternator fast enough.
Moreover, you have to consider how high the engine revs too. I have an ecu from a very early 4.2 that has stepper circuitry on it, which suggests they might have expierimented with the idle voltage values?
Aide
Slightly off topic, but also worth pointing out that a higher target idle rpm means that the water, oil and ps pumps spin slightly faster at idle as well But I increased it slightly for two reasons.
1) idling in traffic one day, with the lights on and widows down, the phone rang so I wound up both windows at the same time. But the engine started to struggle.
2) When I turn on the air conditioning it causes a 50-60 drop in idle rpm.
The manual doesn't mention if this target idle should be set when the air conditioning is on or off.
But upping the idle by 70rpm solved these issues for me.
You could argue that the first reason might have been caused by a battery nearing the end of its life and not holding its charge.
However, the log above suggests that idling below 1000 rpm doesn't spin the alternator fast enough.
Moreover, you have to consider how high the engine revs too. I have an ecu from a very early 4.2 that has stepper circuitry on it, which suggests they might have expierimented with the idle voltage values?
Aide
aide said:
TheRainMaker said:
aide said:
1050rpm is 100% deliberate.
Aide
Somethings wrong with your car.Aide
Thanks for your help, it is greatly appreciated.
Can you let me know what needs to be fixed?
Aide
If it was working as it should you would't need to mess around with the idle speed, trying to cover up an underlying problem.
TheRainMaker said:
aide said:
TheRainMaker said:
aide said:
1050rpm is 100% deliberate.
Aide
Somethings wrong with your car.Aide
Thanks for your help, it is greatly appreciated.
Can you let me know what needs to be fixed?
Aide
If it was working as it should you would't need to mess around with the idle speed, trying to cover up an underlying problem.
Many thanks for your insight, it is greatly appreciated
Aide
Interesting but confused (nice graphs BTW)!
The AMP rating of the fuse is the amount of current need to blow the fuse, so 100AMP or 125AMP it shouldn't affect the voltage being passed through I would have thought (*but correct me if that's wrong)
Fuse rating normally = (Power/Voltage) x 125% which based on 100AMPs as the standard big fuse, would mean a Power of about 1000Watts around the engine
x/12 * 1.25 = 100
100 / 1.25 = x / 12
100 / 1.25 * 12 = x
x = 960
Perhaps it was just making a better connection or the original fuse had degraded over time?
The AMP rating of the fuse is the amount of current need to blow the fuse, so 100AMP or 125AMP it shouldn't affect the voltage being passed through I would have thought (*but correct me if that's wrong)
Fuse rating normally = (Power/Voltage) x 125% which based on 100AMPs as the standard big fuse, would mean a Power of about 1000Watts around the engine
x/12 * 1.25 = 100
100 / 1.25 = x / 12
100 / 1.25 * 12 = x
x = 960
Perhaps it was just making a better connection or the original fuse had degraded over time?
The fuse rating will not have anything to do with this.
It's rating determines it's thermal capacity to pass rated current. Its operating (fusing) characteristic is very different. Admitted the fuse will degrade over time and it's ability to pass rated current will be compromised.
This fuse normally fails physically, hair-line crack, which causes intermittent wobbles - e.g. rev-counter bounce.
The fact the battery volts are low at idle would suggest voltage regulator / excitation issue with the alternator.
IMHO
It's rating determines it's thermal capacity to pass rated current. Its operating (fusing) characteristic is very different. Admitted the fuse will degrade over time and it's ability to pass rated current will be compromised.
This fuse normally fails physically, hair-line crack, which causes intermittent wobbles - e.g. rev-counter bounce.
The fact the battery volts are low at idle would suggest voltage regulator / excitation issue with the alternator.
IMHO
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