Technical onboard computer diagnostics

[Deckchair5]

Well you either have a bad injector or the injector signal wire is going to earth

Your voltages don't make a lot of sense though. All the injectors have a permanent 12v supply and the ECU gives a reference earth to each injector to make it open. There's evidently something wrong with the suspect injector or wiring but you'd need to tell us where you are measuring your voltages, from what pins to where?


All injectors N70 pin 1 should have 12v when not energised coming through pin 3 on connector D81
Pin 2 should have signal earth from ECU. If this wire shorts to earth then injector will be constantly open

Have a look in Stilo Guides for help with injector voltages and resistance

I would check out voltage on pin 2 on the suspect injector. I'm surprised the ECU isn't putting out a fault code if injector is stuck open

 

[gamekeeper]

All the injectors are wired to a common connector just at the back of the engine. Is that connector D81 ? . I was testing between the individual pins on that connector and the battery earth. I did it this morning and thought there was only 5 pins in the connector. From left to right the first 3 pins had the 3.6V on them, the 4th had the 12.6V and the right hand 5th pin was down to to 0V. I was thinking that pin was a common earth but clearly the whole system works the other way round by sinking the injectors to earth when they fire. The problem is more likely to be on that right hand pin that appears to be down to earth. I will test it properly tomorrow in the daylight now I know how it is wired.

many thanks,

winston

 

[Deckchair5]

Have a look here
https://www.fiatforum.com/stilo-guides/112113-checking-injectors-electrical-circuits.html
but that is for a 1.6 engine



On the 1.2 engine D81 connector
Pins 1,2 ,3 and 4 are the injector signal wires and should all have the same voltage and pin 5 is the supply 12v

It sounds like you're getting confused with your pin numbers. Pin 5 will be the one with 12v on it and it is correct to have zero happening at pin 6 as it's not used


Be aware that D81 is a 6 pin connector and pin 6 is not used

 

[gamekeeper]

Sorry to be pain but does anyone know where the supply comes from that feeds the spark plugs and injectors. It has disappeared. The bn wire on your drawing deckchair5. I went to test the injector voltages on their individual plugs (the resistance on all the injectors is identical so that's good) but found no 12V. I tested it again at D81 and the 12V was no longer there. D81 definately only has 5 pins on this car by the way, so I also tested for 12V on the spark plug plugs and it has gone from there also. Needless to say the car no longer starts up. Any ideas thanks.

 

[Deckchair5]

Can you take a photo of your D81 showing inside pin layout and another showing wire colours going in as it will be tricky to know for certain we're on the same wavelength if yours differs from the wiring diagrams,


Injector and coils 12v supply comes in from relay T9 through fuse 22 so check out F22 as you may have blown it whilst testing. Check you have power on the upstream side of the fuse and that will tell you whether relay T9 is energised ON and working

If T9 is working and F22 is ok then you should restore power to the injectors and coils

 

[gamekeeper]

You were absolutely right Deckchair. Many thanks again. I had blown fuse 22. Dithery hands must have shorted the system out.

So back to were I was. It would be very difficult to photograph D81 as it is right at the back of the engine underneath the inlet manifold. So with that plugged back in I get 12V on each of the 4 plugs on each of the 4 injectors. On the other side of each of those plugs I get 3.6V on the cylinders that are firing and 0V on the cylinder that is not firing. The resistance of all 4 injectors is 14.8ohms.

I can't find an obvious short on any wiring and I don't want to risk opening the multi pin plug on the engine computer but it looks perfect anyway. Would I be correct in thinking it is likely the ECU is down to ground on that output and if so can it be replaced with a second hand unit or do I have to give it to a fiat dealer to sort.

thanks in advance again.

winston

 

[Deckchair5]

As you have 0v on the suspect cylinder then it could be a poor connection at the ECU connector on that wire. It could also be a poor contact of the temrinal in the ECU ie circuit board to connector pin

I'd do a resistance check for continuity on that wire from the relevant ECU connector pin to connector D81

It could be the ECU that is faulty but check out what you can whilst that's free

I would have hoped for a P0606 PCM processor self test fault if it was not providing a signal at all for that injector and I can't understand why it is not sensing and putting up an injector open circuit fault for that injector. A simple wire break could be the answer

If it IS the ECU then it's usually best to send it away for testing at one of the many ECU repair shops

 

[gamekeeper]

Thanks deckchair. We were thinking alike as I just did an impedance test on the wire from the plug on the injector that measures 0V. I only measured it to ground and got an open circuit reading even on the 20 Megaohm setting. I will try to find the correct pin on the plug on the ECU and test the continuity to there. As it stands the fiatscan program shows no faults even though I have run the car with that injector unplugged.

 

[gamekeeper]

Just tested the continuity from pin 34 on the ecu plug to the plug on the injector and the continuity is good. I also tested the third injector to pin 2 to compare and it was the same. So that narrows it down to the ecu. I also noticed that with the engine running on 3 cylinders there is still alot of excess fuel and white smoke coming out of the exhaust, there is a puddle of petrol on the flloor after a relatively short period of running. I thought that was all coming out of the fourth cylinder as that's the one that doesn't fire and there was the 0v test on it's firing wire. I am now runing it with that fourth cylinder injector unplugged, the spark plug out and laid on to of the engine happily sparking away and no smell or evidence of petrol coming out of the spark plug hole with the air being pushed out by the piston.

So in summary. 3 cylinders are firing but running very very rich. One cylinder isn't firing but it is sparking well with a plug and coil from a sister cylinder, the injector tests ok and is wired to the plug on the ecu but has 0V o that output where the other 3 injectors have 3.6V. Fiatscan shows no faults. Any sugestions ? thanks.

 

[Deckchair5]

I would have expected the ECU to notice an open circuit to that injector so it's a puzzle why it hasn't put up an injector open circuit fault code

The ECU isn't putting out the earth signal to fire that injector so it depends whether you want to investigate for an open circuit inside the ECU or send the ECU off for testing


Normal injector waveform

 

[gamekeeper]

Unfortunately I don't have acces to an oscilloscope these days so it looks like a send away job. Thanks for all your help. I will let you know the outcome.

 

[gamekeeper]

I am back so soon. As it stands I can't find anyone to test the unit for me. Have tried Camco, BBA-reman and ECU testing. None of them can test it and none have a replacement. It is a bosch 0261 207 086 . Does anyone have any contacts that might be able to help.

I may open the unit up and have a look at it myself. If I do would a repair house still look at it for me with the silicon seal broken. Thanks in advance once again.

winston

 

[sixpotman]

You Could try Injection Correction

http://www.injectioncorrection.co.uk/
part of Blue Streak they own intermotor

John

 

[gamekeeper]

Thanks sixpotman but unfortunately they don't do it. It's looking like it's a bit of a rare unit. ECU express have come up with a replacement unit for £390. They can't test or repair the existing unit.

 

[sixpotman]

http://cgi.ebay.co.uk/Brand-New-Fiat-Alfa-ECUs-Engine-Control-Unit-/330382853424#ht_4955wt_907

John

 

[sixpotman]

http://autotekelectronics.com/newau...n=&PartNumber=00468183880&search=Find+My+Part

John

 

[gamekeeper]

Spot on thanks sixpotman. Now I know what it will cost me if I wreck this one it's time to break into it. Any advise on how to get the back off without damageing the pcb.

 

[Deckchair5]

Have a look at the ECU pins before you go in. Find out what pin relates to the fault and see if it's a simple bent pin or a pin that is lower than the rest

Not sure if 1.2 ECU construction is similar to 1.6 but I can post pics of steps i took to get inside my 1.6 ECU later if you think that might help

Do a search for ECU as others have posted pics in the past that you may find useful

 

[gamekeeper]

The pins are all perfect to the naked eye.

I carefully cut round the silicon with a stanley knife as close to the plastic as I could and that allowed me to prize the plastic back off. Inside the 4 rows of pins on the sockets turn into 2 rows of tiny square pads onto which all the wires are spot welded. Most are a very fine gold coloured wires embedded in a soft silicon compound and it's impossible to tell if they are ok or not. Even if one wasn't ok I think trying to mend it would be difficult without damaging the ones next to it because of the silicon. Then there are some larger silver coloured wires, many of which look like earth connections as they are welded directly between the pcb and alloy casing but some which also go to the pin pads. One of those is clearly broken but it's not clear which pad it was connected to. I tried soldering it to one of the pads I thought might be correct just to see if I could but the solder won't take to the pad at all.

 

[Deckchair5]

Can you post up some pics?