Non-start ..the saga continues!

Hi,

I have to say I admire your persistance

I have read down through the thread and I think I may have a few points to add which may help you.

Since you have the ECU pin outs then I think this should be your starting point. To put it simply, if the ECU has it's required feeds, earths and sensor inputs, if the ECU is ok, then the outputs should be ok too. You need to prove that each of these works ok.

First thing is to prove the supply and earth. Never mind testing the relays. Go to the pin at the ECU because if this tests ok then the relay and wiring must be good too. Make sure the battery is fully charged. If you have battery supply at the pin then you have to test if the supply is good. A reading on a multi-meter or lighting a test light does not prove it is good. 99 times out os a hundred it will be ok but to be sure you need to check it. Easiest way to do this is to use a headlamp bulb. Take a supply from the terminal of the ECU plug and earth it on the battery, if the bulb lights fully then the supply is ok. MAKE SURE YOU USE THE CORRECT TERMINALS FOR THESE TESTS so as to avoid frying the ECU. Check the earths the same way except feed the bulb from the battery + and earth it at the ECU terminals. These tests are done with the ECU disconnected.

Also check the supplies under cranking load. Measure the voltage at the ECU as well as at the coil + terminal and see how much it drops when cranking. Again, make sure the battery is charged for this test.

I know you have checked the ECU in another car but you should be aware that these suffer from dry solder joints. It is possible that you have a faulty ECU which just happened to work ok at the time when tested in the other car.

Strip the cover off ECU plug so you can gain access to the back of the terminals with the plug attached. Remember that just because you have tested a sensor does not mean the the signal is getting to the ECU intact. By checking at the ECU plug you also check the wiring at the same time. Start with pin one and work your way through every pin to check that you have what you should on each one. If you do not know what should be on any pin just give me a shout and I will tell you. If you are unsure of any test procedure or results just ask. 

It can be difficult to be sure that the crank sensors are working right. One simple way to check this is to put a capless bulb across the fuel injector terminals and crank the engine. If the bulb flickers then the ECU is commanding the injectors. It will not do this unless it has good crank signals. If it does not flicker then check for supply at one side of the injector.

Hope this helps some

Good luck

Alan

 




A reading on a multi-meter or lighting a test light
does not prove it is good. 99 times out os a hundred
it will be ok but to be sure you need to check
it. Easiest way to do this is to use a headlamp bulb.
[/QUOTE]

Er, no - the best way is to use a proper multi meter
(cheap enough now from Halfords) which will yell
you EXACTLY what voltage is there. A headlamp bulb
will illuminate with less than 12 volts which gives a
false impression.


Hi Drew,

I hope I did the Quote thing right.

I am afraid you are mistaken regarding how to check voltage supplies. When you measure a voltage with a meter all this tells you is how much potential energy you have in the circuit. This potential (measured in volts) can be present even in an open circuit, so is no indication of if the circuit can do any work. If the supply is not strong enough then the circuit will fail. To measure the integrity of the circuit you need to know if it can handle the required current (measured in amps). The only way to do this is to place a load in the circuit. The load has to be heavy enough to test but not too heavy. I suggested a headlamp bulb because this way it is easy to see if the supply is right because the bulb will light brightly thus no need to measure with an ampmeter. Even measuring the resistance of the circuit will not prove for sure if the circuit is ok as there is no load involved. The method I outlined is far more acurate. This is basic electrics which is well proven and has been around a long time. It is known as Ohms law.

HTH

Alan

Yes, but the wonderful thing is that here we are reading about Ohms Law! It might not fix the Beemer in question, but I like it nevertheless. The 635csi and Tsiolkovsky's rocket equation next please! Makes me want to go for a drive already! Tsiolkovsky's law says that "for any maneuver or any journey involving a number of maneuvers . . .", and so on and so on. Might well be a useful law as we hit p.7 of this posting, after all. All best wishes. ;-)

So does mine!

Hi all,

@ brucey. Very good advise on connecting an ampmeter. This is one of the reasons I didnt mention it. The other being that an ampmeter would be useless to prove the ECU supply unless, as you correctly stated, there was a load in the circuit to cause the current to flow. If you are going to put a load in.then a bulb is likely to be easily available to the average DIY man so it makes sense to use one.

@Drew. "You're absolutely right of course - but most (if not all)
multi meters also test for amps. Mine does anyway."   Which is why you said that the correct way is to check volts?

HTH

Alan

 

To add to this to those who don't under stand how
electricity works;

Electric current is the flow of a thing called ‘charge’.
All metals are full of charge, period. Charge is
measured in units called AMPS. Imagine a hose
pipe. Amperage (or Amp Hour...Ah) is like gallons
per hour going through that pipe, just like amps
along a wire.
Whenever charge within metals is flowing, electric
currents (charge flow) are created. This is measured
in Amps.
The faster charge moves, (or the more it moves
through a fatter wire), the higher the amperage.
Think back to that hose pipe. A FAST flow of water
through a NARROW pipe has the same ‘Amps’ as a
SLOW flow of water through a FATTER pipe. Get it so
far?
If you doubled the speed of the water in a pipe you’d
double the ‘current’ - right?.
What are Watts? All energy is measured in “joules’.
A joule can move along a wire. A Watt is simply the
flow rate of energy, or one joule per second. So what
is ten watts.........?!

VOLTS:
Voltage is effectively an electrical pressure and static
electricity is mostly volts from an oppsitely
unbalanced charge. The static-electric field is the
voltage, an electrostatic state. (Christ this is hard
work)

OHMS
Go back to the water hose again, now conencted to a
pressurised water tank. Take your thumb off the end
- you will have a flow of water right? Now double the
hose length and the flow of water halves. Imagine
the surface tension of water (or friction) - by doubling
the hose length you’ve doubled the friction or
RESISTANCE. The longer the hose, the slower the
water.
Now imagine the water tank is a battery, the hose is
a wire and the water is charge. The friction or
resistance is OHMS.

 The ecu is definately o.k, i know because we tried it in a festering poobox of an e28 in my garden!, i wriggled it i hit it i swore at it and the car continued to run perfectly . So i think we can safely eliminate the ecu from the equation , mind you that was several weeks ago! 

Edited by Hiabboy

Not only was the wire almost completely severed, I'd
add that when stripped back the wire was quite
'black' through corrosion.

Can we get back to the subject in hand now please?

Edited by Drew540i

Hi Drew,

I agree, the origional topic is the point  and we should get back to it.

My reason for posting was to offer some sound advice as I thought some posts in this thread, while mostly correct, were possibly somewhat misleading. Unfortunately you chose to, incorrectly, contradict what I had posted and then further defend your position thus confusing the issue even more. I was under the impression that the goal was to help the man, not confuse him.

Re your Pug fog lamp. You had 12v potential but a poor earth. The poor earth could not handle the current so the lamp could not light. IF your meter showed the poor earth then you were just lucky as a meter loads the circuit so little that it is not conclusive. Now do you see the point?? You were in effect using the bulb to test the circuit.

To be fair, I should point out to you that I am a professional diagnostic technican, information specialist and I write training courses on this subject.

My appologies to the thread starter. Hopefully you will find something useful in all this. 

 

Alan

autofix wrote: IF your meter showed the poor earth then you were just lucky as a meter loads the circuit so little that it is not conclusive. Now do you see the point?? You were in effect using the bulb to test the circuit.

Yes, I see what you mean about using a bulb to test
the circuit and see if it can actually light a bulb -
rather like a regular test light but more demanding?
I always (wrongly) assumed that to light up a bulb in
a test light there had to be current flow but as you
say, a 55 watt bulb sorts the men from the boys. But
all I'm saying is that the multimeter I have (nothing
special at all) measures DC and AC voltage, DC
current, resistance, diodes and hFE. I used it to
determine (or guestimate) that the earth was
inadequate, simple as. In this instance it was rusty
screws holding the thing on, typical French scrap.

But I admit you're vastly more qualified on this
subject - I won't argue with you again!

As for the analogy between bhp/torque and
volts/amps it was merely that, an analogy - volts and
bhp are the 'obvious' power values, yet it's torque
and amps that really do the job.......
No scientific connection whatsoever though.