ECU current draw conundrum. help me?

Hi folks, So I'm starting to go a little bit crazy. I've got a mk3 Suzuki swift gti that I'm daily driving and this is the latest in a long line of dramas it's given me.

Here's the problem, with everything tuned off, doors closed and amp metre hooked up, I'm getting a bit over 300mA of current draw. So far I've been able to hunt it down to the ECU circuit but from there I'm kind of drawing blank.

If I unplug the ECU connector containing it's constant power feed, the current draw stops. I figured maybe the ECU isn't in the good unmolested condition it appears to be so swapped it to another ECU that I know works, although I am not using as its been chipped. Identical current draw, different ECU.

At first I began thinking maybe I'm chasing a ghost and that's just what these ECU's draw, but 300mA just seems to high for me to be willing to believe that.

I disconnected each sensor 1 by one, and while the air flow meter made about a 50mA difference, nothing else seemed to. I don't have any stereo gear in the car, it doesn't have a clock or interior light connected and if I pull the supply fuse to the ECU my current draw goes away. I also disconnected the ignition barrel whilst checking just in case there was a short or electrical issue there.

My next plan of attack is to double and triple check there isn't some alarm, immobiliser or bodged up electrical up under the dash. From there I guess its time to probe the ECU pinouts one by one to see what circuts if any are receiving voltage.

Just wondering if there are any auto elects or ECU gurus here that might be able to impart a bit of wisdom or direction that'll help me regain my grasp on sanity and find the true cause of this parasitic little voltage sucking menace. Thanks.

ECU's will always draw a little- to keep the volatile memory alive. But I agree that 300mA seems too much.

You mentioned disconnecting all of the sensors- did you do the same with the actuators? Fuel pump, injectors, ignition, and then the rest of the stuff? Maybe something is stuck there.

Also, if you take it all off with the meter, and then walk away- after 5-10 min, is it still drawing .3A?

THIS^^^^^^^^^^^

Thanks for the prompt replies.

300mA would be more than I'm happy to accept even with an alarm and aftermarket stereo etc.

Yeah, I pretty much pulled anything associated with the running of the engine. I say pretty much, just on the off chance that I missed something. So fuel pump, relay and gauge, all sensors, the coil and igniter, primary relay, air valves, anything else I could find.

No, I didn't do the walk away for 10 or so minutes and retest. I'll have a go at that and see what goes.

Added bit

Because I can't help but think its somehow related. The engine can be a bit hard to start after running the car up to temp and then shutting it off for about 5 minutes. Cranks but fails to fire immediately the way you'd expect an efi car to. I haven't been able to get that fault to stay long enough to see if it's an ignition or fuel control issue which makes diagnosing it a bit of a non event.

Does the ECU drive any relays, like a fuel pump relay? Pull the relays one at a time and see if the draw changes. Does this ECU drive the voltage regulator? VRs can malfunction and cause a draw, but still work normally when its running. I doubt an old Suzuki has the VR connected directly to the ECU, but who knows? Try disconnecting the wires on the alternator.

Start checking the wire harnesses carefully. When my niece's Mitsu had a problem blowing fuses for it's ECU, I eventually found a tiny nick in one of the wires going to the upstream O2 sensor where it had been rubbing on the head of a bolt, I only found that by inspecting the harnesses, looking from above there were no signs of trouble in that section of harness.

In reply to HappyAndy:

daeman- doing what HA just suggested is a good idea- and looking for that kind of thing, too. If I read your note correctly, you at least know that the fault in in the powertrain system- since all you do is disconnect the ECU, and the draw goes away.

Taking off the sensors and actuators is a good first step, but now you need to look in the harness between the sensors and actuators AND the ECU.

I'd start with the ECU power relay- perhaps it's sticking.

Ecus stay energized for a while before going into sleep mode. The act of unhooking the battery then hooking up the amp meter will "wake it up." As stated above, hook up the meter, make sure everything is off, and wait 10-20 minutes without touching anything. See if it still has the sizable draw.

Thanks guys, I knew this was the right place to ask. I'll try and do some more checking today if I can. The whether here in Sydney has been less than conducive to going outside for the last few days.

Well, the sun is shining today, so I put my amp meter on during my morning break, I'll see what its doing come lunch time.

Ok, just checked my amp Meter after about 3 hours connected and its still drawing the same.

Pulled the main efi relay, no change, pulled the fuel pump relay, no change.

I pulled the conecter on my airflow meter (hotwire type) and it dropped down to 230mA I'll leave it off and the amp meter connected till home time and see if there's any change.

I haven't had a lot of time to investigate my voltage vampire over the last few days, but its looking like I may have a wiring issue. Its going to give me the E36 M3s if that does turn out to be the case, I stripped and inspected the loom and rewraped it prior to installing the engine so I would have to deal with this sort of E36 M3.

I'm going to re check sensors and the like over the next couple of days, and then I'm going to either print out or draw up the ecu pin outs and unplug the connecters and probe them 1 by 1 and mark down what's been tested and what has voltage. I'd also like to remove the standby power wire from the ECU plug and see what happens then.

After leaving the AFM off the other day, nothing changed after the initial drop in current draw despite the multi meter being left hooked up and the car left undisturbed for several hours.

The alternator reg doesn't appear to be computer controlled, it has 3 wires total. Power cable, idiot light and Excitor wire. Though I have heard of dodgey diodes causing strange problems, disconnecting the alternator didn't seem to make any difference.

I appreciate the help so far, i need to get to the bottom of this problem sooner rather than later.

Two different ECU's both behaved the same, right? If so, I'm thinking it's not the ECU. Now, someone has been into this wiring before? Most ECU's have a switched and a not switched line. Is something that supposed to be on the switched line connected to the not switched?

In reply to Dr. Hess:

Yeah Dr Hess, I tend to agree with you, I'd find it strange that 2 different series of ECU would fail with exactly the same behaviour, just wouldn't make sense.

Someone had been into the whole car, and not very well at that...I got another wiring loom when I fitted the engine because the old one had had several poor quality repairs and I wasn't up for headaches so stripped checked and rewrapped it.

There may be a fault with some of the dash harness wiring? But its pretty independent to the engine loom. I've got an ECU pin out diagram so I'm going to probe the loom without the ECU attached to see if something a shorting.

Looks like I've located my little voltage vampire!

Some incredibly intelligent shiny happy person (one of the previous owners), decided to twist and join the constant ECU power feed wire to the ecu ignition powerwire an inch or so from the fuse block. Meaning the ECU never sleeps.

I'm hoping that I haven't uncovered a larger problem, but it should be all good from here. I appreciate anyone who took the time to lend a hand on thus little conundrum. I'll let you all know what the full extent of my findings are once I'm done.

Cheers

So, what you're saying is: Something that supposed to be on the switched line connected to the not switched?

HA HA, couldn't help myself. Glad you got it found. Now, the question is why some DPO did that. Make sure the always on line is actually always on and not getting turned off when the ignition switch is off.

In reply to Dr. Hess:

Haha, yeah, that's pretty much it in a nutshell Dr. It was just a case of finding where, how and why.

I just separated the conjoined wires and checked everything was as it should be. I'm absolutely bewildered as to why it was done.... Even if the relay was dicky it would have been as hard as just putting in a jumper on the switched side of the relay