Electric gurus how to diagnose and fix electrical problems

[chnk]

Alright my car has been down for about 2 weeks now because it keeps blowing a fuse. I would love to learn how to track down and fix this issue so any advice on diagnosing this and fixing it would be helpful.

About 4 months ago I had hopped a curb and broken all kinds of things on the bottom of my sc link to the thread

I ended up buying a parts car and replacing the parts myself using jacks, an engine brace, and hand tools. Got the up and running successfully for a couple of weeks. Then I had an ignition interlock installed on it

Then a week after the ignition interlock was installed, the damn thing stopped working on me and I couldnt start my car for two days. Got another one and a day later I blew an efi fuse link to url

that problem was temporarily fixed by removing my foglights

Now the problem came back link to thread
This time the engine cut off when I floored it. The problem of the efi fuse still remains.

- the car -
1995 sc400
mileage 300k+

- mods to the car -
hid low beams,
coilovers
wheels,
led taillight bulbs

- the issue -
keeps blowing the efi (electric fuel injection) fuse as soon as i turn my key on
the fuse is a 30amp fuse so i can't just put a bigger one
starter is clicking,
there is still spark,
no fuel is getting to the engine because this fuse is blowing

- tried failed fixes -
clean the battery terminals
Regrounded the ground wire that was connected to the battery terminal that i forgot to connect
checked and reouted the wiring harness that was under my driver wheel well
bypassed the fuel pump ecu incase my fuel pump ecu was going out
swapped out my fuel pump with the fuel pump from my parts car

 

[ak47prince]

hi

So it kept blowing up the 30A fuse when you turned the ignition to start?
Trace from the blown fuse to the component that the power is supplied to.
Usually too much current drawn by that component will blow fuse but i never blown a 30A before..

 

[marc280]

I didn't look through all of the links that you had there, so I don't know if you've checked the basics, but I'm assuming that you have a multimeter, so I would start by checking the voltage at the terminals for the fuse. You should have battery voltage on the hot side (going to the battery) and nothing on the otherside when the fuse is removed.

On the side where there is no voltage check the resistance between the fuse terminal and ground on the car. If you check the resistance with the ignition off and there is very low resistance (i.e. a short) then your going to keep blowing the fuse. If there is no short with the ignition off try the same with the ignition on.

Once you've determined that you definitely have a short circuit on the EFI circuit I'd suggest getting hold of a wiring diagram and then looking at what is connected to the circuit. Then you can remove connections until the short goes away and you'll know what is causing it.

That is just the way I'd go about it so hope that helps.

 

[sideshow]

its easy
get workshop manual for the car
look at diagrams to see what that fuse powers
disconnect every part that the fuse runs
if it still blows then u have a shorted wire

now this is the hard part
find where the short is

efi fuses normally blow due to old fuel pumps that overload the system just that little bit more
but could also be the accesorries that get powered on the motor by the black/red wire

 

[ak47prince]

Good one

Good one from you Sideshow.at least for me. I never taught of the possibility that those accessories guys will use the Blk/red as a powersource. Good point.

 

[Sudsy]

can also be something that someone in the past has hooked up to that power source so might not show up in a wiring diagram

 

[Thomas DK]

I like sideshows method - removing the fuse. But... I prefer to put in a wired up bulb instead of the fuse. As long as You got a short, it will light up. Now start disconneting the parts belonging to the fuse. Once it goes off... - Ta-daaaa!!

 

[sideshow]

yes my way means u might go thru alot fo fuses hehehe
i have a small unit that is sort of a short finder made by power probe
but the main thing u need is diagrams then its easier to find the circuits

 

[ak47prince]

hi Thomas

I like sideshows method - removing the fuse. But... I prefer to put in a wired up bulb instead of the fuse. As long as You got a short, it will light up. Now start disconneting the parts belonging to the fuse. Once it goes off... - Ta-daaaa!!

I still prefer the Sideshows way of doing it. You didn't specify what type of bulb ratings that one must use. Some bulbes won't light up with little shorts or low Amps even up to 2 Amps. i think it should be better to use a multimeter don't you think?

 

[sideshow]

each way has it's good and bad points
I grew up using the blow the spare fuses way
Hehehehe. but I have heard of using a test light
only prob with that way is u can get false earths thru
solenoids or motors etc on the same circuit
which means u need to male sure every single device is
unplugged from the circuit that is blowing the fuse

 

[ak47prince]

.

i see i see...

 

[Thomas DK]

I still prefer the Sideshows way of doing it. You didn't specify what type of bulb ratings that one must use. Some bulbes won't light up with little shorts or low Amps even up to 2 Amps. i think it should be better to use a multimeter don't you think?

Yes, You're right. One has to do a little math before inserting a bulb instead of a fuse. But its very simple.
I dont belive multimeters when searching shorts or open in circuits using fuses bigger than approx 5-10 amp.

blowing a 2 amp fuse, and You can light up a 12volt*2amp=24watt bulb.(here i woud go for the multimeter)

Blowing a 30 amp ECU fuse as in this case... geee what a lightshow

But again - both methods has a "flip side". My choise depends on the "challenge"(no probleems in my garage...)
The reason why I like the bulb - Use a long wire and bring it to the engine bay, and You'll be the first to know when its solved

 

[sideshow]

go buy yourself a power probe 3 and short
circuit finder kit
best tool u will ever use
trust me

 

[ak47prince]

haha

Yes, You're right. One has to do a little math before inserting a bulb instead of a fuse. But its very simple.
I dont belive multimeters when searching shorts or open in circuits using fuses bigger than approx 5-10 amp.

blowing a 2 amp fuse, and You can light up a 12volt*2amp=24watt bulb.(here i woud go for the multimeter)

Blowing a 30 amp ECU fuse as in this case... geee what a lightshow

But again - both methods has a "flip side". My choise depends on the "challenge"(no probleems in my garage...)
The reason why I like the bulb - Use a long wire and bring it to the engine bay, and You'll be the first to know when its solved

what you said makes sense to me after giving it a second taught... true.. most bulb will lid up but i will also consider sideshows's power probe 3

 

[ihiryu]

Circuit Breaker and an old compass

You get a 30 amp circuit breaker, install in place of fuse. And get an old compass (with a needle) and watch it shake as the breaker turns on and off. The less it moves the further away you are. The strength should be about the same until you get close to the short. It should do massive jumps at that time.

Get it down good enough, and you should be able to find the short within five inches of it. Make sure that you know the routing of the wiring, cause it'llmake your life ten times easier.

 

[Smitherz]

+1 Power Probe. I bought the whole kit and I love it! It's pretty amazing. Go on their website and watch the videos on how to use it and you will see. Think of all the money it's saving you if you can put it to good use. I would just unplug everything fuel related and then plug things back in one at a time until the fuse blows indicating your problem.

 

[Smitherz]

Also check the fuel pump resistor for proper operation. Google: "fuel pump resistor lexus". There are specs on ohm readings you should be getting. Check the EFI relay or maybe swap for your parts car one. You could also bypass that manually and check it that way. I'm assuming your 95 uses the same type of components as the earlier one.

 

[sideshow]

yes if it was me i would sell the sc400 as they r getting to the age where they fk up alot now
and i would use the money to buy 3 or 4 power probe kits
they are the best tool
hahahahahahahahahahahahahahahahh

 

[Smitherz]

One of my neighbors sold their cherry condition SC400 overnight by using Craigslist. A dude came up from LA within 2 days to pick it up with cash. They were scared of the same thing... too many old electronics in those cars. If you own one you better be good at troubleshooting if you want everything to work!

 

[sideshow]

yes
u should goto some wrecking yard and have a look at whats behind the dash in one of these sc400
they have over 10 or 13 computers
thats a fair bit for a 90s model car
ive seen one having the dash being pulled apart didnt look fun
hehehe