Technical Big electrical problems Punto 75

[Karolis]

I have big electrical problems on my Punto 75 (1995, 1242 mpi).

Have anyone got some electrical scheme for checking all the ground connections (don't know if I have them all and where they are) and everything else that could help?

I started to connect the pc for looking what's happening when car goes bad.

My problems are first at all about lambda signal. Some times I have correct bouncing by 0,1 and 0,9v, sometimes I have crazy 0,1 fixed v and -0,8v in cutoff, or 2-3,5V while driving. Can't find by what it depends, it doesn't do this always, every day is a different thing. Obviuosly some times the ecu goes crazy and car moves only in open loop (after 4500 rpm and good pedal), no normal driving.

New bosch lambda sensor. Had problems always always, till I bought the car.

If I disconnect the lambda sensor I have 0,2v signal.

Sometimes it is sensible to the fuel pump load, when turn the key to start the engine and the pump does bzzzz. When I have bzzz I have 1,5v ~ on sensor, when bzz stops sometimes I have 0v, sometimes 0,5, sometimes 0,2...

Going very crazy. No change by moving wires in the engine hood. Different voltages by different humidity and/or temperature.

Probably there's more mess in the hood, problems in different places that come out in different moments and can't be exaclty found in easy way.

Sometimes, by moving the crank sensor, when the key is on but engine off, I have the fuel pump bzzzz again like I turn off and on again the key, sometimes not.

Now I'm driving 3 days with the tester near the driving wheel and always looking what happenings, no logic for the moment.

Will load videos on youtube

Sorry for bad english. I'm from Italy, mechanics don't like my car and don't want even to look (I understand )

Every and any help really apreciated.

Videos:

 

[fingers99]

I think the earth points are in the same place as any Mk1 Punto. No point "checking" them except for continuity between one end and the other. Best to unfasten, scrape clean, coat with petroleum jelly or silicon grease and re-attach.

I think there's an earth tag on the ECU, too.

 

[Karolis]

Yep, I would like to clean very well all the earth points, but don't know how many they're and where, all. Maybe someone is missing too (old car, a lot of messed during years, maybe there's something terribly wrong with wirings, I don't know if everything is where it should be... )

 

[fingers99]

A manual would help. The most obvious ones are: battery -ive to passenger side front wing. Gearbox selector box to driver side front wing. Some have an extra earth to the coil pack bracket, many have an extra earth to the ECU box.

There are more, but these might well do the job.

 

[s and b]

disconnect the battery
remove multi plug from ecu on inner wing
check for no resistance in the multiplug loom from pin outs 17 and 34
repair if resistance found

system type magnetti marrilio 6f,sb/16f/gf.s3???????

is a good a

 

[Karolis]

Thanks, will check as soon as possible.

The ecu is IAW 8f.5t .

Sorry but I'm very bad with electronics. Check if I'm right:

For checking the resistance I put my tester on "ohm" mode, and I have two tester plugs. Where I must put them? Red on the pin 17 and black on the 34? Or red on the 17 and black on all ground points and then the same on pin 34?

 

[fingers99]

Thanks, will check as soon as possible.

The ecu is IAW 8f.5t .

Sorry but I'm very bad with electronics. Check if I'm right:

For checking the resistance I put my tester on "ohm" mode, and I have two tester plugs. Where I must put them? Red on the pin 17 and black on the 34? Or red on the 17 and black on all ground points and then the same on pin 34?

Ohm mode, either probe to either pin. There should be -- according to the instructions -- no resistance between the two.

 

[Karolis]

Thank you It's simplier to do that to say

These "instructions" that you're talking about is some car electrician manual (maybe your job) or I can find the on internet too?

 

[fingers99]

Thank you It's simplier to do that to say

These "instructions" that you're talking about is some car electrician manual (maybe your job) or I can find the on internet too?

I mean S & B's instructions. There's a very good Cinquecento club in Italy (www.clubcento.it) who might be able to point you further.

 

[Karolis]

Tested right now, one tester set to "200" (I also have 20k, 200k, 2000k etc on the tester, everything gives 0) The 200 gives me 0,8 value, other tester, always set to 200, gives me 1,0, sometimes 0,9. Is should be 0,0, right?

 

[fingers99]

According to the instructions, yes. But I'm not sure what that signifies, or that S & B's ideas are right for your ECU -- I've no pin out for the P75 here. Best wait for him to come back.

 

[DaveMcT]

A high ohm setting makes the tester more sensitive. We are measuring car wiring so 0.0, 0.01, 0.001 are all more or less zero.

 

[s and b]

on the ecu find pins 17 and 34 and ground each one with your ohm meter looking for zero

on your wire side ground terminals find the same pins and ground each one with your ohm meter,you are looking for zero

this will tell you whether the circuit board in the ecu is getting earthed properly

thing is with your crazy voltage on the lambda i can only assume that you are getting voltage leak or maybe one of the senseors is wired wrong and putting a voltage either to the lambda and or the ecu


can you rip off everything that isnt engine bay stock wiring loom and start again?
can you try another ecu?
really hard

 

[Karolis]

on the ecu find pins 17 and 34 and ground each one with your ohm meter looking for zero

on your wire side ground terminals find the same pins and ground each one with your ohm meter,you are looking for zero

this will tell you whether the circuit board in the ecu is getting earthed properly

thing is with your crazy voltage on the lambda i can only assume that you are getting voltage leak or maybe one of the senseors is wired wrong and putting a voltage either to the lambda and or the ecu


can you rip off everything that isnt engine bay stock wiring loom and start again?
can you try another ecu?
really hard

Hi, thanks for the dedication attention.

Have no zero between 17 and 34 (like you see in video), must look the other side like you say. That's a sign of problem right? (I notice now that I didn't disconnected the battery when measuring that :bang: )

I think too that I have some other sensor voltage that goes on lambda circuit.

Can't try another ecu (have a Panda, with a 16F, but I don't think the engine will start with that instead of my 8F, also che key CODE problem is there).

Will remove the lpg system cables (very simple, + - on battery, rpm signal on a coil wire and injector plugs). Maybe it disturbs.

Hard, yea, frustrating too, but not impossible I think. Only need a ton of time and patience

With all you helping me with tips will find the problem for suree :slayer: :yuck:

I think also that I have maybe some ground missing or something, where I could find a "ground places" list of my car?

 

[fingers99]

If you can get a factory manual for the car, that'll give you all the earths. Otherwise, the Seicento technical manual (in the downloads library here) will give you some clues.

AFAIK, the P75 ECU is exceptionally reliable (if only the same could be said to be true of the Mk.2 Punto ones!).

But -- general rule is -- you can't have too many earths!