ms85er

Electrical circuit issues

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Hi all,

So I have an old ms85 crown with an efi conversion in it. So strange thing,

The car works perfectly running from the battery with no alternator. With an alternator in the circuit something strange is going on with the electrical system where the rpm affects the power in the whole car. So with the alternator hook up, I idle and put some load on the car and release the clutch, the lights dim, the fuel plump strains and the whole electrical system is pissed off. I unplug the main feed from the alternator to battery and run the car off the battery and everything is perfect. I have a new alternator so this is not the problem, there was nothing wrong with my old alternator either. The battery appears to be ok. I think I'm in the more advanced area of troubleshooting, maybe the electrical system is changing is reference to ground in relation to alternator output. I don't know its strange I've disconnected as much as possible to troubleshoot but as soon as a put the main feed from the alternator charge terminal to the battery on, I get rpm varied voltage throughout the whole car.

 

Help is much appreciated.

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I have no idea why you would want to run the car without the alternator connected.   However, your very first test is to ensure all major "power" connection points between battery & alternator on both the +12V side, and the chassis side.  Check all earths between chassis & engine block.

Make sure every other electrical load in the car is turned off. Lights, radio fan etc.

Then connect a multimeter across the battery terminals, without the motor running, & note the DC voltage reading.

Then start crank the motor & note the mulitimeter DC voltage reading, during cranking.

Then run the motor at a fast idle, & note the DC voltage reading on the multimeter.

What ECU are you using for the EFI conversion ?

If you feed us back some answers to the above questions, we might be able to provide some more suggestions.

Hopefully, your inspection of all electical "power" connections, will find the culprit, & all will be fixed.

Cheers Banjo

 

Edited by Banjo

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everyone always starts their post with no introduction to when or how the issue started. But then there are those like me who give their life stories haha
So ill ask

Did you install the conversion kit then this problem began??
or have u just bought the car and its giving a problem and ur just describing whats in it (the EFI conversion)?

I have no idea why, but I'm just going to say EARTH STRAP, because most issues like this are caused by engine to chassis earth strap issues.
And instead of criticising that suggestion, which i know will happen from someone, lets just let the OP open his eyes and check it, its free and easy to check.

Edited by rebuilder86

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Thanks for the replies

 

Banjo, thanks for the suggestions. Alternator is good, charging fine much diagnosis says Good! 14v+ for days. I've checked all connections between engine and chassis to the negative terminal of battery, All is well. ECU has nothing to do with charge its ancient motor very simple efi. I added some earthing wires between engine to the car chassis just for the hell of it. Alternator is brand new no problems there. So something strange happened. I measure the resistance between the case of the alternator and another spot on the top of the engine 0.01 ohms or something like that. I turn the car on and I get 12 ohms. WTF? I get a reading of 36 ohms between the alternator case and the negative terminal of the battery with the car on as well. with it off it's about 1/3rd of that. Something strange is going on when the alternator is in the circuit and I'm ultra confused. Took the car to battery world, did a few tests said battery fine, could raise the idle a little bit to help the alternator out but that's just a band aid fix to get some more supply to the fuel pump/lights still sure electrical system has issues major issues.

 

Rebuilder86 thanks for the suggestions, as mentioned above I have a 4gauge wire from engine to battery terminal and its hooked up fine with no corrosion. I don't have it going to the chassis though. I guess that's why I added some smaller cables going from the engine head to the chassis.

Edited by ms85er

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20 hours ago, ms85er said:

. I measure the resistance between the case of the alternator and another spot on the top of the engine 0.01 ohms or something like that. I turn the car on and I get 12 ohms. WTF? I get a reading of 36 ohms between the alternator case and the negative terminal of the battery with the car on as well.

haha i remember when i first discovered this phenomenon.. but someone (best mate with electroics engineering degree) pointed out to me, that when doing a voltage drop test we must have the accessory or thi g being tested turned on, because the resistance changes based on current going throught it.

so if u are seeing a difference between on and off engine like that, it would suggest something is corroded. my brains not functioning too wrll right now so i cannot visualize exactly what it would mean, but perhaps someone else can step in here and diagnose this particular phenomenon further.

off the top of my cloudy head right now, I am thinking that more current causing a higher resistance from alt to engine would be either a... nah sorry my brain is not working, but there is something odd going on there. I am sure someone here knows what I am getting at and can step in here.

something to do with a bad path to earth (engine or chassis) from the alternator.

Edited by rebuilder86

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Ok thanks Jeremy.

It's a full chassis car, so it's not quiet like most peoples corollas. The body panels are basically bolted to the solid frame. Makes it awesome for removing body panels to access the engine bay but could be causing issues with grounding. The car did come with more grounding straps than usual. So I have a 4 gauge wire from the engine to the negative battery terminal, A short 4 gauge from the battery terminal to the side body panel next to the battery. Obviously the engine is grounded to the solid frame by the engine mounts. Considering its a full chassis car with the body panels bolted to the frame you would think that the ground would be fine, but I'm considering running a 4 gauge wire from the engine to the frame, it seems redundant considering the engine is bolted to the frame with engine mounts, but I'm running out of ideas.

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ive found engine mounts to be completely insulated actually. theyre rubber.

anyhow I'm suspecting the issue is with the alternators path to ground through its contact with the engine, like through its adjustable mounting bolts seeings as thats effectively the path u tested that gave erroneous results with the multimeter.

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also, the best advice i can give is to change ur thinking from this:

On 10/01/2018 at 3:31 PM, ms85er said:

still sure electrical system has issues major issues

to 

"there is something very simple wrong and I'm going to kick myself when i figure it out" 

u will figure it out, and it will then appear so simple

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20 hours ago, rebuilder86 said:

also, the best advice i can give is to change ur thinking from this:

to 

"there is something very simple wrong and I'm going to kick myself when i figure it out" 

u will figure it out, and it will then appear so simple

 

Yah I wish.

 

Went to supercheap bought one of these http://www.supercheapauto.com.au/Product/SCA-Battery-Lead-18-Lug-Lug/15022

Put it between the car chassis and the nut holding the back of the alternator. Also bought some new battery terminals, hooked them up.

Took the battery out of the misses' car, hooked it up.

Problem Persists.

The only thing I can think of is that the engine block is painted so maybe I should scrub it back with a wire brush for the ground cable going between the block and the negative batt terminal.

Pretty sure my next step is to buy another alternator, failing that, give up.

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haha shit.

id say a bolt hole and its exposed thread should be enough contact for earth. so that might eliminate paint being an issue, unleas the bolt was individually painted aswell....

in all cars ive worked on, the negative battery terminal goes straight to the engine and that is a direct source (negative side) for the high current that the alternator puts out.

so perhaps just try running that cable u bought directly from the alternator body to the negative battery terminal before moving on.

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also just resettingy brain and rrading ur original post again, i have a few questions..

is the alternator a self regulating (2 wire plus charge) one or is there an external regulator??

the changing power load on rpm is simply evident of a malfunctioning regulator and I'm not sure how i negated to mention that originaly. and this is probably what banjo was getting at with his questions i think.

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Old MS85 Crowns are now a bit over 40 years old, & could well have had an alternator originally with an external regulator.

My check of the web indicates that.

image.png.d2eded270b5d408c38af345fba7519c2.png

However, when a car gets to 40 years old, anything can change in that time. Very easy to identify.

If it is an alternator with an external voltage regulator, & you have to replace it, I would be upgrading it with one, with an internal regulator, with a bit more output than the origial 50A.

Cheers Banjo 

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Thanks for all the suggestions.

 

I've thrown a 100amp MR2 alternator on it already :P

So I noticed something interesting when I drove one of my other cars today. It does it as well! just not as bad. So apparently the current draw of the fuel pump just cannot be sustained at low rpm. When I reverse into a car spot I can hear the frequency of the pump drop as well. So basically the only solution is to probably bump up the idle a bit. It strange though because I would of thought if the alternator drops its output below 13.8v that the 12v battery would take the hit and act kinda like a capacitor to keep the voltage up to the fuel pump since it can handle large current draw from the starter I would of thought the small amount drawn from the fuel pump would be no problems, apparently not.

So long story, me being paranoid about killing the fuel pump is just me being paranoid. The lights do dip a bit but they aren't so much of a problem. It would appear some fuel pumps don't get the required juice at low rpm is my conclusion. Think I might buy a voltage regulator to throw on the fuel pump to maintain longevity so I don't have to pull my fuel tank apart again. https://www.powerstream.com/dc2.htm looking at the PST SR500 13.8v output with 15 amps continuous supply. I saw a guy on a supra forum threw one on his fuel pump to maintain a solid power supply for his 2jz supra making big power.

 

 

 

 

 

Edited by ms85er

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Have you checked the volts at the pump terminal at idle to prove your theory. If you find  the issue is bad volts at the pump why not increase your cable size to the pump or parallel up the existing cable. 

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There is an old saying that says "what gets measured, gets managed". 

You certainly will not solve this issue with lots of hypotheticals. With electrical issues, you commonly need measurements, to work out exactly what is actually happening.

You seem to feel that the fuel pump is an issue, & Graeme's suggestion to measure the volts supplied to the fuel pump itself, to see if there is a voltage drop between battery & fuel pump, is a good one.

Voltage drops do not occur unless there are loads.  It is imperative that the fuel pump load on the electrical circuit is measured.

Most cheap multimeters have a 10A DC current range.  Very few fuel pumps draw more than 10A.  The average car's fuel pump will draw about 4-8 amps.

Fuel pumps can overwork, & draw excess current for a number of reasons.  A blocked inlet filter.  A pinched inlet pipe or line.

A faulty motor in the pump itself.

Here's a video, that shows you how to measure the current very simply. Just remove your fuel pump relay, and place the meter between the NO & COM terminals on the relay socket.

Once you have this info, about the amps the pump is drawing, you might be surprised, that the answer to your problem is simple, & easily fixed.

Remember, this car has had an EFI conversion, so someone at some time, has added wiring etc. that may be undersized.

https://www.youtube.com/watch?v=ibJW8lHugNI

Cheers Banjo

 

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