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I am working on a 1999 Fiat Punto (176) 55 horse FIRE enging with single point injection.
The injection system was intermittent and I traced it to a break in the wiring for the Crank position sensor I cut the wires (moulded connector on the sensor pigtail) and bothched together with twist connections temporarily and it seemingly fixed the problem. The wiring has 2 insulated wires and a braided shield I am wondering wether the sensor is polarity sensitive and how to find the right polarity. (Want to crimp new EV1x3 connector onto it)
While I'm at it. This fault came to light while re assembling after a head gasket repair and since the valves looked a litte suspicios so I might have rotated the cam so that it is 360 degrees out of phase, could that be te reason for fuel coming up into the intake rather than going into the cylinder?
If i understand you. There is not possibility that crankshaft gets 360 degrees out of phase, because every 360 degres in a 4L engine, both pystons 1 and 4 are at top dead center again. Every 180 degrees of camshaft rotation, camshaft gets synchronization to top dead center of a couple of pystons in crankshaft.
The PCM uses CMP (camshaft) and not CKP (crankshaft) to synchronise injectors firing (in a sequencial system). There are cases which PCM usues cylinder recognition and engine doesn´t have CMP sensor. In that cases while engine is cranking, PCM fires all injectors at the same time until it recognises between cylinder 1&4 or 2&3. At that point starts the programed firing order 1,3,4,2.
Although its an inductive sensor and one wouldn't think that polarity matters it actually does. What happens when you switch the wires around is the signal waveform becomes inverted and may cause issues with your PWM. I haven't experienced this myself but I was folling a thread a while back (iatn I think) where a guy had a similar problem to yours (broken crank wires), turned out the PWM got confused with the inverted crank signal. The shielding on the crank harness is there purely for noise suppression.
From your desription it is a two wire inductive sensor, reversing the polarity on these makes a difference. Also from your description the valve timing may be out by only a tooth or two
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RimmersTechSWE wrote: The engine has a 3 wire crank (TDC) sensor and a 1 wire sensor that goes intor the head so I assume It's a cam sensor but I guess it could be knock.
The one wire sensor that screws into the head I would say is the knock sensor. Cam sensor is normally a three wire (square wave).
Yes might well be out by a tooth or 2 but I guess it might also be related to the fact the the induction side valve on cyl1 does not fully close. I didnt' really want to continue with the car after I discovered that but the owner asked me to put it back together so I did. It did run very briefly on sarting fluid before I cut the sensor connector off so it might well be polarity reversed at the moment. IT stopped running because the battery was out of juice. Maybe I shouldnt say it ran but it rather coughed but the engine was cranking really slowly.
The timing marks are not very clear on this particular example so it would be very easy to be out by just a little on the cam wheel. The car harness for the TDC sensor has also been worked on before so I'm not the first one to discover the problem It's just that the current owner has never noticed.
On this car the crank sensor is called tdc sensor. Since it is a SPI (Electronic carburettor) system it always fires the injector all the time but might fire the spark plugs together 1+4 and 2+3 every time each group is nominally at tdc since it seems to only have 2 coils (Wasted spark?).
It's like an ancient abs sensor and reads a knobbly ring on the crank pulley. Yes I can se that fuel has been sprayed because the mouth of the SPI unit gets wet and It smells like fuel both from the intake an exhaust.
Im not sure it's wasted spark it might have 2 coils in each pack but it has 2 packs and the HT leads marked 1+4 go to one of the and 2+3 goes to the other one so I assume it is because it very much an economy car and 2 coils would be cheaper than 4 coils.
Last edit: 3 years 8 months ago by RimmersTechSWE. Reason: Forgot to answer some questions.
I have seen some systems which before cylinder recognition, primes intake manifold with a little fuel (about 250 ms depending on ECT reading). That could be your case and doesn't mean you have good CKP signal.
For sure if you don't recognise TDC, you cannot fire any coil (i mean PCM.
If you are unsure of CKP connection, you can just swap wires. It is important that noise shield be grounded.
According to your description. It's a waste spark system. You can also prove that by watching plug wires (1&4) firing together.
The car has a light that looks like an injector symbol that comes on when you turn ignition on and goes out like the glow light on a diesel after a few seckonds I assumed that was the priming indicator. The ignition barrel is also very notchy (sticky) so that could also be an issue if all else fails.
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