General Cinquecento won't start when cold

[9XX Girl]

Hi i am new to this forum. I have a 1998 Cinquecento S (900cc OHV engine).
Its been running lovely over the last month until a few days ago when i went out one morning and it would not start. It turns over, tries to fire but never does.

The code light goes out about 1 second after putting the ignition on and the injector light gores out after about 3 seconds.

I had the AA out and started cranking it over and over and over until the battery went flat, they then put a starter pack on and turned it over and over again. He fiddled with the MAP sensor and blew out a few of the vac hoses and eventually, it started He told me to get a new MAP sensor and i drove directly to a scrap yard to get one. When i came out of the scrapyard the car started lovely. I stopped at Halfords next to get new plugs and leads. When i came out of Halfords the car started lovely.
Went home, fitted the plugs, leads, and MAP sensor, started it up, the car started lovely. So i went for a spin.

The car drove as normal. I started and stopped loads of times that day, each time it started again lovely.

Next day, went out, car would not start, cranked it over and over and over, still would not start, eventually it fired just as the battery was about to die.
Again i did about 50 miles, stopping and starting the car about 4 times without issue.

Went out this morning, it wouldn't start AGAIN. It seems to start almost instantly when warm but will not fire up when cold.

Code light goes out, injector light goes out, it turns over but will not fire. It is full of fuel, i have checked for vacuum leaks, I have checked all the plugs and wires, i have got a spark but I just cannot afford to put it in to the main dealer. I don't know what to do but it is just going my head in, :bang:

When it does fire up it idles lovely and drives like a dream.

Any ideas welcome

 

[Discofiat]

Check your crank sensor

 

[9XX Girl]

Check your crank sensor

hmmm.... i was thinking along the lines of a sensor, like ambient temperature sensor, crank sensor, etc. however, i would expect the injector (ECU?) light to come on.

My knowledge of cars is mostly classics and cars without ECUs, i know where i am with points and condenser, so....

how do i check the crank sensor, i know where it is but all the wiring and sensors look good (visually anyway).

I could go to the scrappy and get another but there is no telling that is any good either. I don't want to start swooping new parts in some random fault finding session as that could work out well expensive.

 

[rallycinq]

I'd be looking at the temp sensor first. Its the easiest one to check. You are looking for a high resistance at low temperature, something like 10Kohms at 0 degrees (don't have my own computer here)

Cheers

SPD

 

[9XX Girl]

thanks rallycinq, thats sounding a bit more believable.

You say 10k Ω at 0 deg C.

Hmmm.....the day time temps here are about 18 deg C so i would guess that a cold engine coolant temp would be about 10 deg C.

If you could post (when you get to your own computer) the typical resistance readings for somewhere between that range, (if you have that info) that would be real cool.

I'm at work at the mo and will be working on the car on Sunday. I'll put an ohmmeter across the temp sensor, (the one sticking out the thermostat housing with the two pin Bosch connector on it i assume) plus, i can stick a fixed value resistor in the plug to fool the ECU. If that gets it going i know i am barking up the right tree,

Thanx again for your time.

 

[rallycinq]

Coolant temp sensor
0 10000 ohm
10 7000 ohm
20 4000 ohm
30 3000 ohm
40 1800 ohm
50 750 ohm
80 330 ohm
90 200 ohm
100 replace head gasket

and just in case

Intake air temp sensor
0 degrees 10000 ohm
10 7000 ohm
20 4000 ohm
30 3000 ohm
40 1500 ohm
80 330 ohm

Cheers

SPD

 

[georged30]

i had the same problem with you and fixed it like this in front of the battery thre are two plastic electrical connectors one of them sends power to the ecu disconect them clean them with contact cleaner reconect them and start the car.

 

[9XX Girl]

Thank you rallycing, thats more than useful. I will measure the sensors first as i guess they will be about 7k Ohms if all is well. if one is out of range i will stick a couple off 4.7k Ohm resistors in series into the plug to fool the ECU that the coolant is at 8 or 9 ish degrees. I amuse the air intake temp sensor is the little redish blob on top of the throttle body at 10 o'clock from the butterfly looking from above, (when the black plastic cap removed that is).

If it fails to start i will try your idea georged30, it makes sense. During cranking the voltage drops and starves the ECU of power as it is. High resistance connections will only make things worse.

Its looking likely that i won't get to have a tinker until Tuesday now as i am now working Sunday and Monday too now. Hmmm.... I may get a chance when i get when i get home, who know, anyup, i will post my findings as soon as i know whats going on.

Thanks loads

 

[ycming]

You probably found it by now but the temp sensor is the one bolted onto the inlet manifold.

If the reading is not correct, best just to get another one. No point in trying to fool the ECU.

Ming

 

[9XX Girl]

You probably found it by now but the temp sensor is the one bolted onto the inlet manifold.

Thanks for confirming the location Ming

If the reading is not correct, best just to get another one. No point in trying to fool the ECU.

Ming

No, the resistor idea is only to confirm the correct diagnosis. I wouldn't drive the car with that hack. But it would save the cost of a new sensor if it worked out not to be the fault. I don't like the scatter gun method of fault finding (unnecessary expenditure) Also, the car would scoff fuel and eventual damage the cat too if the ECU thought a hot engine was really cold. Who know what else it could damage too. It might get me the 6 miles up the road the the local scrapyard though (i should buy new i know but, i do like to recycle)

 

[9XX Girl]

OK i have just made some resistance measurements. The coolant temperature sensor (in the top of the thermostat housing) measures 5.5k ohms and the ambient air temperature sensor (plug for this is in the side of the bit that fits on top of the throttle body next to the throttle sensor) this also measures 5.5k ohms.
The daytime temperature today was 11 deg C... so they are ok!!!

These measurements were made at the sensors themselves so i will look in the Haynes manual to find what they pin out at on the ECU plug, and then measure them again from there in case i have a broken wire in the harness.

hmmm.... am at a bit of a loss so i guess i will be up the scrap yard on Tuesday to get a crank sensor as they are £40 new and that still may not be the issue.

I also checked the large plugs from the battery pos and they are all good, clean shiny tined copper.

Has to be crank sensor, throttle sensor, fuel regulator or ECU as i can't get the thing started at all now.and.... i am assuming that the crank sensor, is an inductive type hall effect transducer. Anyone know the resistance values of the crank transducer itself?

 

[rallycinq]

Back to basics.

Do you have a spark?

Do you have fuel at the inlet?

Cheers

SPD

 

[9XX Girl]

Back to basics.

Do you have a spark?

Do you have fuel at the inlet?

Cheers

SPD

Oh yer.... good spark, (new plugs and leads) it doesn't look too regular though.
The plugs are wet when you take them out so plenty petrol. Also, i removed the air filter ducting from the top of the throttle body and cranked it over and over for nearly 2min continuous with the throttle full open. I thought i best stop when i saw the petrol alight licking up from the butterfly while i were sat in the driving seat looking through the windscreen and under the bonnet.

As the spark is a bit regular, i guess its the crank sensor next.

 

[rallycinq]

Oh yer.... good spark, (new plugs and leads) it doesn't look too regular though.
The plugs are wet when you take them out so plenty petrol. Also, i removed the air filter ducting from the top of the throttle body and cranked it over and over for nearly 2min continuous. I thought i best stop when i saw the petrol alight licking up from the butterfly while i were sat in the driving seat looking through the windscreen and under the bonnet.

As the spark is a bit regular, i guess its the crank sensor next.

Yup, would be a choice, but have you checked the connection at the power relay?

Cheers

SPD

 

[9XX Girl]

The two black ones and the fuse next to the ECU,
Yer they are all ok,

 

[9XX Girl]

What size if the fuse meant to be? I have a 25A in there, is that right?

 

[rallycinq]

The two black ones and the fuse next to the ECU,
Yer they are all ok,

It is looking like crank sensor.

Cheers

SPD

 

[9XX Girl]

I now have the crank sensor off, it’s a Magneti Marelli SEN8D3
The same as on VW Golf (1992 onwards) both 8 and 16 valve (handy to know)


I have 0.3MΩ between “+” and “–“ terminals

but no reading between “S” terminal and “–“
or
“S” terminal and “+” terminals.
Anyone know what they should be?

It was only held on by one screw and once off ,I have noticed the bracket is slightly bent so it may not have been seeing the graduations on the pulley wheel square on. I have straitened the bracket and will be refitting it tomorrow to see if that makes difference, if not I will be off to the scrappy to get another either from a Chinq or a Golf



Will keep you all posted

 

[9XX Girl]

Went to the scrap yard today an bought a crank sensor for £5.
Fitted it and it fired up first time.

Thanks everyone for your help. Now I'm a happy bunny!