Electrical problem - Coil or ECM

[kim.beveridge]

Hi there.

Hoping someone can help me out with an issue. I have a MK3 Golf GL (1997). The story is..

1. My battery died a couple of days ago (battery dead, would not turn over the engine), so I swapped in a old spare battery i had to get me by, which worked ok.
2. Bought a new battery today and put that in, but then car will not start, spins engine over easily but engine not fire.
3. Put old spare battery back in, same issue engine turns over but not firing.
4. But new battery back in, same issue, so i have concluded this is a new issue, must be con-incidence?
5. Started troubleshooting...

a. check all fuses i could find under steering wheel and 1 i found in engine bay, all good.
b. took out spark plug and checked if spark, no spark..
c. followed some troubleshooting from service manual to test the coil and "power output stage"

test-1. disconnect 3 pin connector from coil and test current across pin-1 and pin-3 with ignition on, current is there, test passed.
test-2. connect test-light across pin-2 and pin-3, turn over engine, should see test-light flash, test failed, i don’t see any flashing or light at all. My manual says if this test fails then -> The ignition ground signal from the ECM is missing, check the wire between the ECM and the coil output stage, if not wiring faults, then ECM may be faulty, and should further test the ECM.

I am not really confident in testing the ECM so i skipped that testing, and went on to next test.

test-3. remove small cover from coil terminals, connect test-light, turn on ignition and check light comes on, it did test passed.. Then turn over engine and check light flashes, test failed, light did not flash.

From the 2 tests above i think maybe ECM is not sending the pulses of electricity thru to the coil, does this should correct, do i need to replace whole ECM or could this behaviour be caused by something else.

any tips or thoughts appreciated, otherwise i be off to auto-electrician tomorrow i guess.

thanks in advance
Kim

[Golf Loon]

Most likely to be the coil mate. Very common on these cars.

I dunno if I`d want to be too close to a coil with a testlight or multimeter when cranking the motor. Thats big amps!

[Peter Jones]

Thats big amps!

Big VOLTS Matt!

(Big volts electrocute, big amps just burn. )

Pete

[kim.beveridge]

Hi Matt.

OK i was hoping it would be the coil over the ECM, coil sounds less expensive. I have replaced the coil about 5 years ago, so i guess the time has come again for another replacement.

I stayed well clear when i did that test to avoid the amps, volts whatever.

thanks alot for your reply..

regards
Kim

[peedman]

Big VOLTS Matt!

(Big volts electrocute, big amps just burn. )

Pete

Other way around pete lol. 2 amps will cause cardiact arrest, cranking i think the starter draws 250+ amps. Ouchie is all i can say

[Peter Jones]

Kim, WHere abouts in Melbourne are you? I have a new coil you could try and buy for $100 if you'd like. I'm in Boronia.

Pete

Other way around pete lol. 2 amps will cause cardiact arrest, cranking i think the starter draws 250+ amps. Ouchie is all i can say

Dude. Current does the killing but you can't get enough current to flow through the human body without a high voltage. Your ignition coil is a High voltage low current supply, it can kill you. Your starter motor is a low voltage high current circuit and it won't fatally electrocute you.

What's more deadly?
1. A 1000 volt battery capable of producing 1 Amp
2. A 1 volt battery capable of producing 1000 Amps

According to you the 1000 volt battery is a safe bet when in fact this may kill you.,

On the other hand the 1 volt battery capable of 1000 amps is quite safe because the human body has too high a resistance to allow the 1000 amps to flow.

Humans are typically around 1 - 2 K ohms hand to hand. Children are less.

So applying ohms law V=I*R to the 1000 volt battery case we can see that the current drawn by an average human of 1K5 ohms would be 1000/1500 = 666 mA which is more than enough to kill you. It takes less than 100 mA (0.1Amps) to cause ventricular fibrillation.

On the other hand the 1 volt battery will cause 1/1500 = 666uA to flow which is well below all danger thresholds.

Now the above is a pretty simplistic explanation, there is the difference between AC and DC to consider here as well as what's called the clamping or let go limits and the duration of the exposure.

In a household electrocution scenario death by ventricular fibrillation occurs because the 50 Hz AC messes with the nervous system signalling to the heart which is typically running around 60 Hz (your pulse).

Ac also causes muscular spasms which cause the victim to clamp to the source. Up to a certain current level you can let go, the exact threshold varies by individual, age and gender. This muscular contraction or paralysis can also affect the diaphragm and cause suffocation before cardiac arrest in some circumstances.

In your average car the only voltage source that's usually capable of causing a fatality is the ignition coil. Ignition coils can produce in the the order of 15000 to 20000 volts.The output of the coil is DC so if you catch a single pulse you're usually thrown back rather than electrocuted. There's a couple of scenarios that can apply here. A single pulse from an ignition coil is very similar in fact to the output of the first generation uniphasic defibrillators so it will affect your normal sinus rhythm if you time it just right. A similar to AC electrocution scenario applies if you catch hold of an ignition lead while the engine is running because pulsating DC is just as good as AC for messing with the heart's rythym.

There are some very unique situations where automotive electricity can kill you in other ways. I have read of a pedestrian trapped under a truck for hours died because of electrolysis due to being exposed to 24volts at a low current for a long duration. I don't recall the exact detail but I think it was the body salts that were affected and turned toxic.

Now to go back to my original statement

Big volts electrocute, big amps just burn

The types of electrical industrial accidents you see in High voltage industries like power distribution and generation are usually electrocutions.

In industries that use High currents (smelters, trams, telephony) industrial electrical accidents involving burns are more common. These are typically caused by hand tools shorting out power conductors. 1000 amps is more than enough to vaporise a spanner. If you happen to be holding that spanner third degree burns and flash blinding are typical injuries.

That's enough of a thread hijack for the moment. We can continue this in General chat if anyone's interested.

Work Safe People!

Pete

[peedman]

Jeez so i made a mistake, all u had to say was that at low voltages the skin provides enough protection....far out!

[bboyskidz]

sorry - how does a the newest taser product produce 50,000 volts then?

Peak open circuit voltage: 50,000 volts (V)
Current: 0.0021 amperes (A) (2 milliamperes average)

It doesn't kill you because it only puts out 0.0021 amps...

You are right in the sense that 1000 amps on a 1 volt charge will not have enough power to pass through your body, but anything more than 1 amp across the heart will kill you.

Anyway - have you managed to test the coil Pedro?

[Peter Jones]

sorry - how does a the newest taser product produce 50,000 volts then?

Usually by capacitive discharge into a transformer, much the same as a car ignition system or a flash gun. More advanced models work more like a switch mode power supply and use some cleverly engineered modulation techniques to really get those muscles twitching.

It doesn't kill you because it only puts out 0.0021 amps...

Correct, the power source must be capable of producing sufficient current through the body to electrocute you. Clearly if the source can only produce a few mA then there's no issue regardless of the voltage. This is why static electricity which is also often in the KV range, doesn't kill either. (Doesn't mean it's an enjoyable sensation though)

Tasers can and have killed people which is why they create a lot of contoversy. There's a few ways they can kill, paralysis of the respiratory system, blunt force trauma when your head hits the pavement, they can trigger epiletic fits and so on. Its an interesting topic, try doing some Google research if you're interested. On the whole though I'd rather be tasered then shot.

You might also look into TENS machines (Transcutaneous Electrical Nerve Stimulators) which can be considered to be a medical grade TASER. There's quite lot of information (good and bad) about these on the www.

You are right in the sense that 1000 amps on a 1 volt charge will not have enough power to pass through your body, but anything more than 1 amp across the heart will kill you.

Actually as I said above it takes less than 100mA ( 1/10 of an Amp.) current through the heart to kill you. The exact amout varies by age , gender, health, physiology and a whole lot of other factors. As little as 5mA (5/1000 Amp ) can be fatal to some people. Most Health and safety authorities quote those sort of numbers. To put it another way most of the population will survive 5ma accross the heart and most of the population would be killed by more than 100mA accross the heart. In between 5mA and 100mA you might be lucky or you might not depending on your own individual tolereance levels.

This of course begs the question why are ELCBRs and RCDs ("safety switches") set to trip at numbers like 40mA? But I've hijacked this thread long enough.

Pete

(I am an electronic engineer and my duties include forensic engineering, if there's any Melbourne based EE students that would like a tour of our lab PM me)

[bboyskidz]

fair 'nuf.

i guess i need to do more reading. I've got build a pretty simple circuit for my car pc - I might pm you tonight with more info... could be helpful having the advice of an electrical engineer.

thanks Pete!