Technical Engine will not start (Green Flag can't fix)

[The Sultan]

I just been out and measured mine in a similar way and it comes to the same 4.75v

not sure iv voltages have changed on different models or year but mine is 1998 1242 spi



the wire going to pin 18(not 19 misread there very small on my wiring diagram) is indeed the earth as it goes directly to the ecu but It carry s 4.5 or 5v
and the other should be 12.5 as your battery is probably getting a bit low pluss the starter drain I would expect the drop to 3.5v on the earth aslong as the other stays somewhere around 12 to 10v you have a difference between the 2 of at least 5v as the injector runs on 5v

ready for bed is right there is a 12v comon feed from the relays but the injector runs on 5 and when you measure it to ecu earth that is 5v you get a potential difference between them to run the injector

the idea behind all this is the ecu can vary it's earth voltage to keep the injector voltage common in all battery conditions

it is unlikely the test meter will be able to measure the voltage as it pulses due to the speed it happens so you will need to try the led both ways unless you know which is anode and cathode on it if it does not flash and the continuity between the wires is reasonable then you have a faulty ecu

I would mainly concentrate on the continuity of the wire you had the voltage drop on but I'm sure this is the ecu compensating for the battery voltage at the time

there are plenty of engine ecus code ecus and red keys for sale on ebay for between 50 and 100 quid and if you want to know anything about making them work on your car wile avoiding having to change your locks then contact me or post on the forum there are many ways of doing it

 

[markos]

Hi Littlepip,

Is it possible to check if the voltage stays at 4.75 even when you crank the engine? In theory the ECU should ground it in order to fire the injector..

 

[The Sultan]

the ground can be whatever the ecu wants it to be there is not much point in testing it really what you need to test is that the wires are OK from one to the other


when the key is at mar without the engine running or being cranked the engine ecu earth will sit at a pre-set amount ie the 4.75v+ you tested


but without the battery voltage 12v on the other wire I don't know how you got a reading without the engine turning yet it wont open the injector sounds wrong should only be able to measure this to battery earth

when the engine is running or being cranked the relay supply goes to 12v+ or battery voltage

and the earth to the ecu should then start pulsing at various voltages to keep the potential difference between the 2 the same

as the 12 volt battery feed drops and rises the ecu drops and rises it's earth feed to keep the potential difference between them constant so that fuelling is not altered when the battery is low or you turn on the lights excetra

most test meters will not be able to measure such a short pulse so the led is the only way to be sure

to test with the led you should put the led poitive terminal on the relay feed and the negative on the wire with 4.75 from the ecu then turn the engine over if it don't flash there are no pulses

but you haven't tested the continuity of the wires to the injector from one end to the other yet

turn your test metre to 200 ohms the one with the omega symbol

if you touch the tester leads together you will see 000. or 001. almost no resistance

test each injector wire end to end

if you see anything above 015. or 020. when you test the wires end to end then that's to much resistance and you found the fault

if they are below this then your ecu is most likely faulty from here on its gona be one thing or the other really the injector wires damaged or the ecu not pulsing

just a thought if you turn the ignition on and the ecu earth is at 4.75v then you can earth the other wire to battery and in theory it should open the injector even thou your now passing power through it backwards maybe that's why the ecu earth is kept at 4.75 without the engine running for diagnostics purposes

 

[markos]

Ok, tried a different approach..

With the engine off, I supplied the injector with 12V directly from the battery.

The injector clicks open (you can hear it clearly without the engine turning).

I then got my girlfriend to turn the engine over while I energised the injector manually (like above) for a short duration (just touched the ground wires together). You can clearly see a burst of petrol squirting into the manifold but the engine didn't show any sign of life.

I repeated the above, energising the injector in short bursts, while the engine was turning but nothing...

Ok, I didn't expect the engine to fire up normally with my "manual" injector pulses but shouldn't I get a judder of life at least??

So now I am totally confused.. Could it be that everything is fine regarding the injection system but the timing is off?

Is it possible for the timing belt to slip?

I will check the timing marks tomorrow morning..

 

[The Sultan]

you haven't checked the timing marks already

it is possible for timing to slip without damaging or knocking the belt off but highly unlikely normally happens when people go from 5th to 2nd instead of 4th then let the clutch up quick very common mistake believe it or not

but your car has been stood since the last time it ran

as for your manual fuelling it's very surprising how difficult it is to light fuel air mixtures even if the mixture is slightly off especially under high compresion

the injector pulse width is tenths of a second open time so your 1 to 2 second open time will be far too much fuel but timing out will also cause it we will see when you inspect the timing marks

also do not ever power the injector again from the battery you will cause it to over heat and burn out the internal windings you will have already shortened it's life considerably also depending on how you did it you may have damaged the engine ecu

all you have proved from the exercise is that the injector will open at 7.5v not 5v

it's much safer to just use a test meter across it to measure the impedance

also you can use the earth voltage to run it by earthing the other wire when the key is at mar that is indeed the reason why the ecu does this when the engine is not running

you still haven't told us things we need to know are the wires to the injector ok and does the led flash try it both ways if your not sure about anode and cathode

if after you check the timing is correct and it is you have shown us so far that you have no basic electronics knowledge to speak of and it's about time you took it to a dealer and got it plugged in

advantages of doing this in five minutes you will have your car diagnosed

and here's why the fiat examiner can tell the tech using it weather you have a cps signal (witch you do as you have a spark) and will then also tell the injection timing if this is wrong then you have a faulty ecu

the examiner can also manually trigger the injector to fire for diagnosis

 

[markos]

Actually the manual trigger of the injector it is quite a good troubleshooting technique and one readers of this forum should be aware of (I wish someone had told me to begin with).

It proves that the fuel pump works, the fuel filter is not blocked and the injector is functioning correctly.

The injector is rated up to 16 volts (according to the fiat documentation which I have in front of me) so your claims of ruining the injector etc are wrong.

The anode of an LED can be identified easily as it is the longest of the two pins (anyone with a basic knowledge of electronics should know this ) I did try your suggestion and it stays lit permanently. I am not sure though if this means that the ECU is not switching it on/off or it is so fast that it looks like it is permanently on.

Have you actually tried this yourself? Can you clearly see it flashing?

Finally I checked the continuity of the all the wires leading to and from the injector and they are all fine.

PS Just measuring the impedance of the injector is NOT a good troubleshooting technique as it just proves the electromagnetic winding is OK. The injector could be malfunctioning for other reasons (e.g. defective reaction spring) therefore my method is much better

 

[T14086]

...but how do you know if the correct quantity of fuel (and pattern) is being released by injector?

As for injector voltage once magnetic field collapses it will rise well above 16v.(45-60v when I have scoped them out)

No resistance check is guaranteed.....component must be under load (working) when tested.

 

[The Sultan]

16v interesting I was always told never more that 5 for that engine from work mates must have a read of the technical manual I have probably safer not to power things if your not sure of the voltage but I trust you looked that up before you tried it

well the led is basikly what's in some node testers I have at work

the only difference mine are from snap on and have the correct terminals for various makes and models on car so yes you should see them flashing not like a tungsten bulb they don@t take a long time to dim

funny how there's power to light an led but not open the injector

(ps I know about led anode and cathode I just didn't know weather the one you had had it's terminals the original length's or not could have been cut

well with every thing that's been done so far it looks like the injector is working so is the pump that's new

the spark plugs are working that proves the phonic wheel and sensor are fine

I trust you have checked the cam belt timing now

the wires are fine as you say

so I'm afraid there's only one thing left now ecu faulty

 

[T14086]

When any magnetic field collapses a 'surge' is induced.When (if!) you get spare few minutes at work scope out a injector or coil pattern.

 

[reddy4bed]

Actually the manual trigger of the injector it is quite a good troubleshooting technique and one readers of this forum should be aware of (I wish someone had told me to begin with).
It proves that the fuel pump works, the fuel filter is not blocked and the injector is functioning correctly.

I did tell you this 2 weeks ago!!
The waveform of the injectors clearly shows that the injector is closed for potential difference of 13v - 5v (8v) and open for a differnce of 12 volts


Dont see how you would expect to see a LED go off for a millisecond or so, if you wanted to go that route you could have made a trigger/timer. Remember if the voltages available for testing are 0v injector on, 5v injector off, and 13v. the only place for a response would be between the 5v signal and earth, For a Led to turn off the the injector signal would need to drop to <.7v
..mm
The notion that the ecu earth is +5v is nonsense, its zero

PS Do you really measure impedence? I just use a dc ohmeter. (resistance)

 

[The Sultan]

all very weird

the earth wire to my injector from ecu is +4.5 constant volts when the ignition is at mar if i earth the other wire the injector will open and dump what pressure is there without the pump running

but when the engine is running or being cranked the other comes up to battery voltage from ignition relay for example +12

but wile the engine is running the earth pulses on and off and varies voltages depending on load if you turn on the lights for example it will rise for a second and fall back down to 4 or 5 volts again if you turn them off it will fall again

I used my test meter measuring peek voltage to measure it wile it was running

I have also used nodes on them and you can see them flashing

yes resistance not impedance oops

I never scoped one yet must give it a go with fiat examiner must say it's the best scope and test meter there is

 

[T14086]

Have you actually tried this yourself? Can you clearly see it flashing?

Yes

 

[The Sultan]

just lay a scope of the current over that voltage trace and you'll see there is no current flow when your getting the peeks

 

[[email protected]]

Try the fuse in the engine bay that feeds the injector .
don't just look at it replace it with one that you know is good as I have two that looked good but were not

 

[T14086]

I think he has burnt it by now.

 

[The Sultan]

Try the fuse in the engine bay that feeds the injector .
don't just look at it replace it with one that you know is good as I have two that looked good but were not

he did that pages ago