Electrical gurus: How can my charging system be doing this?

[oldcorollas]

hmm, i forgot about boost and fuel pump... any chance you can get a 20A ammeter and put inline to the fuel pump?

or.. (just for me ) can you get a bike pump, and put pressure to the fuel reg with the pump running and see what happens? i guess it is not easy to do with the engine running, but it may not make it stall at idle...or low rpm...

perhaps the pump is pulling a lot of amps when loaded (as mentioned?)

injectors will nto be doing it. spark? i didn't think they pulled more current when resistance of the spark plug got higher but...

what else is there?

does it have AFM? any chance it could be shorting at boost (i guess you would see this in fuellign too).
heated O2 sensor power wire hitting underbody when engine tilts?

do you have fuses on everything? can you temporarily change fuse for each circuit to the mac anticipated current and then see what melts

[1JZ-Rolla]

each pump has a dedicated relay & circuit with a 20A fuse, surely this would have blown by now if the pump was pulling crazy current.

No AFM, aftermarket ECU.

Can't be coils either as that circuit has a 15A fuse.

Keep them coming!

Cheers

[BradW]

An alternator would need the electrical load on it to exceed it's output by a reasonable amount for it to read such a low voltage. That means a current drain in excess of 100A in your case. This would blow fuses or burn wiring UNLESS the wiring is capable of handling that sort of current (ie battery cable).
Something to think about.

[river]

Hi,

The cables, even if capable of withstanding such current, would be quite warm to touch,

Does the voltage drop exactly with boost? As soon as boost is off the voltage goes back up? No lag or anything like that, in relation to the voltage drop and boost?

Also, does the engine seem strong when the voltage drops? That is, you cannot detect any drop of performance if the electrics are not getting the full voltage?

Does the voltage drop when the engine is cold or hot? I am wondering if, in your installation, the alternator is not getting enough air to effectively cool it, and the heat is affecting it's performance (ie high ambient temp for the diodes etc).

seeyuzz
river

[BradW]

I was thinking about this today and thought of a way to test if it is belt slip.

Think of it like this. If your tires aren't up to scratch and you accelerate hard, when the engine comes on boost the tyres loose traction and spin. Now, if you back off the tyres get traction again and drive the car. If you don't back off, and hold the revs high in the rev range, the wheels continue to spin and the car slowly moves forward. Eventually, as the car speeds up, the wheels start to regain traction and drive the car.

Now, this would be the same for a slipping belt. If you accelerate hard and the belt slips, the alternator wont charge properly. But, if you hold the revs steady, the belt will start to regain traction and the alternator will start charging.

If you can get the car on a dyno it will be safer to check, if not you could do it on a long stretch of quiet road and a passenger to read the voltmeter for you. Hook up a volt meter and run up the engine to get it to play up. When the voltage drops off, hold the revs up (obviously not reving it's ring out, say 1000-1500 rpm under redline). If it is a slipping belt you should see the voltage start to come back up as the belt regains traction. Obviously you may need to hold the revs up for a short time to let the alternator catch up to the crank in terms of rpm.

This might help you eliminate belt slip as the cause of your problem once and for all.

[river]

Hi,

Nice idea, but I find it hard to think it's belt slippage.

The alternator doesn't need to spin fast to output the necessary voltage, so if it is belt slip the alternator must be going very slow while the engine is going faster. This would burn up the belt and you'd see severe scorching and belt damage if it continued for anything more than a short time.

You'd probably smell the belt burning, plus you could actually feel it for how hot it is.

seeyuz
river

[1JZ-Rolla]

River: yes, as soon as you back off the voltage comes straight back up.

The problem occurs even in Canberra's cold air at night after only a short drive, no chance to heat soak the alternator.

I tested the voltage drop between the output post of the alternator, and the battery terminal last night. Max drop was 1.2v as the engine hit full boost, then settled on around 0.9v to redline.

Interestingly, I checked the relay & fuse for the 044 EFI pump, the 20 amp fuse was not blown, but had melted the plastic around one terminal. Odd since the bosch specs rate the maximum current draw as 15.5 amps.

BradW: i'd like to test that belt slip theory, will give it a go once the car is back on its wheels, as I had to do some other work on the car today.

[oldcorollas]

so if the alternator is only dropping from 14.5 to 13.2, it is still charging, and the lower voltage is from current draw.

melted is not good. what size wires do you have running power to pump? how are they terminated?

can you borrow a 20-30amp ammeter?

[Squid]

Any luck yet phil?

[Toobs]

Its a long shot but have you checked your harmonic balancer?
I've heard a few cases where J series harmonic balancers seperate at the rubber joiner... this could cause the symptoms you describe and would be reasonably hard to notice unless you take a really close look at the harmonic balancer.

[1JZ-Rolla]

Toobs, I had thought about that, but surely with slippage so often (if that is the case) then it should be falling off by now?

Anybody got a pic of the harmonic balancer so I can see where the join is? I can't see mine in the car (too close to the rad) but wouldn't mind checking out a pic before pulling things apart

Cheers

[DX20VT]

Toobs, I had thought about that, but surely with slippage so often (if that is the case) then it should be falling off by now?

Anybody got a pic of the harmonic balancer so I can see where the join is? I can't see mine in the car (too close to the rad) but wouldn't mind checking out a pic before pulling things apart

Cheers

Just get a white paint pen and draw a line from the centre of the pulley right out to the ribs where the belt runs.

Run the car till the fault has occoured.

Stop and see if the marks still line up.

If the outer piece of the crank pulley is slipping on the inner part, chances are there is no way it will spin round and line up again.

[1JZ-Rolla]

Just get a white paint pen and draw a line from the centre of the pulley right out to the ribs where the belt runs.

Run the car till the fault has occoured.

Stop and see if the marks still line up.

If the outer piece of the crank pulley is slipping on the inner part, chances are there is no way it will spin round and line up again.

Good thinking, that's exactly what I did earlier tonight after Toobs mentioned it Will find out tomorrow if the marks stay in place.

[Ribfeast]

Get a clamp-style ammeter and clamp it around various wires, and take the car for a spin, see where the load is coming from. This means you don't need to cut any wires.
Belt slippage should be fairly noticeable by the smell

Mine sits on around 11.5-12V on idle if the thermo fans are running (30-35A draw), and around 13V on idle without the fans going. If I rev it over 1000RPM it goes to around 13.5-14.2V if the fans are off.

Injectors, ignition, fuel pump are probably the only things I could think of that would maybe increase current draw with revs. Or a bad earth as stated by people earlier.

[The Witzl]

Do you have an electric turbo charger that you arent telling us about Phil??