Technical Car won't start from cold without pressing acceleration/throttle and stall when hot

[akman88]

Hi Fiat experts,

I have been having issue with my 2006 1.2 Grande Punto (60, 251 miles)

It has been going for a month and been scratching my head over this issue. :bang:

It started with the car had a rough idle with the rpm meter jumping up and down around 1500 - 2000 rpm. The car then started to stall at the junction once the clutch is down or braking ,i.e. at low speed/rpm. The car won't start when turning the key normally. It will only start with pressing the accelerator pedal down while turning the key.

The next day, went to the local garage to get it checked. The mechanics:
- ran diagnostic
- cleaned the idle control valve
- changed the camshaft sensor

The fix improved the rpm meter jumping for a day and car started from cold normally. On the way home from work, the car stalled at the junction again. Had to wait for a while to restart the car and only started when pressing the accelerator pedal.

The next day the car won't cold start without pressing the accelerator pedal down while turning the key. Once started, the car ran nominally until the engine is hot around the middle temperature mark and the car stalled at stationary, see attached image. It is similar to someone turning off the engine. The car also stalled at junction when braking or clutch is down at low ~ 500 rpm. Rpm meter did not jump up and down anymore.

Second trip to the mechanics:
- Changed knock sensor since the reading was jumping up and down.
- Changed spark plugs
- Cleaned throttle body
- Tried a brand new throttle body, but that did not improve the issue, returned the part to the supplier

After a week of looking at the car, the mechanic could not fix the fault and suggest a different mechanic with more electric/ECU experience.

Current issue:

- Doesnt cold start without pressing the accelerator down
- Stall at stationary when the engine is hot around the middle temperature mark.
- Stall at junctions at low rpm when the clutch is down or braking


No fault code error and no warning lights appear on the dashboard either.

Been looking around for similar threads, it seems to be a crankshaft issue with similar-ish symptom.

Recent car history:
- Cambelt, water pump kit and temperature sensor changed 3 months before this issue.

Going over to the other mechanic in the next few days. Hoping that maybe one of you had a similar issue and could shine a light to this problem.

 

[akman88]

Also, new battery was fitted 2 months ago

 

[GrandePunto PL]

- cleaned the idle control valve
- changed the camshaft sensor

Idiots not "mechanics". There's no such thing as "IAC valve" in this car. It's an "EVAP system" valve (to burn some fuel vapors). Yes I know, some sellers on eBay push this thing as a "idle air valve" - wrong.
Second thing is camshaft sensor - bad decision again. CRANKshaft sensors were much more faulty when we look at the history (previous generations of Punto: MK1, MK2, and similar models - Uno, CC, SC, Panda).

- ran diagnostic

So what? Simple code reading/erase is NOT "diagnose".

1. What about valve clearances? Manual adjustment (shims), not automatic (hydraulic). Because of age (2006) it must be done (should be done long time ago). Normally you do/check this during timing belt job. These are not separate jobs (should be always done together, there is a "connection" between the two) - even tho "professionals" do it separately.

2. Other sensors or wiring: MAP (it's 2in1: pressure and temperature), coolant temperature, exhaust (2 lambdas), brake pedal switch, clutch pedal switch (and/or clutch is faulty somehow, mechanically or hydraulics). Wrong temperature reading will not trip the error code (but will fool, spoil the ECU, fuel dose, ignition timing etc.).

3. Intake (vacuum) and/or exhaust leaks.

4. Fuel system (pump), pressure.

5. Gas pedal and/or throttle sensors (potentiometers).

6. Breather hoses (PCV system).

7. Timing belt job - done properly? Really?

8a. New battery? Why? What about alternator? You have 2006 Punto, there are improper water drains (too short), rain falls down right into the alternator killing it over time (then you have bad battery, plus, seized alternator can stall the engine mechanically). You must replace it with modified one, longer. Mind there are 2 drains.

8b. "Earthing points" - corrosion. Check Guides section (as a home work): https://www.fiatforum.com/grande-punto-guides/ - study this before posting new questions (or starting multiple threads) !

8c. Same with corrosion in general - for example fuse box (one under the hood/bonnet). It will rot from the bottom (where cables go) - top view (when you open it) will be "OK" at first glance.

9. Early ones (2006, 2007, 2008 maybe) had a bit faulty ECU software (throttle handling). Unstable idle RPM and RPM drops during braking/clutch - but not so much to stall the engine or prevent it from starting! But this can still be a problem - a part of it. There was a service recall in some countries (replacing ECU soft).

 

[akman88]

CRANKshaft sensors were much more faulty when we look at the history (previous generations of Punto: MK1, MK2, and similar models - Uno, CC, SC, Panda).

Thanks a lot for the comprehensive advices. Went through the Grande Punto Guide. A lesson learned here is that always check the forum first.


I am planning to go through the checklist within my ability this weekend and change the crankshaft sensor myself. Hopefully this will save me some money and time.

Any advice/tip on the crankshaft sensor replacement? I could not seem to find a thread on the forum on replacing the crankshaft on a 1.2 Grande Punto.



Thanks a lot GrandePunto PL!

 

[OldEngineer]

It will be the MAP...

https://www.fiatforum.com/grande-punto-guides/227405-1-2-1-4-map-sensor-replacement.html

 

[akman88]

Recent update:

I spent the weekend diagnosing the three parts 1) MAP sensor, 2) crankshaft sensor 3) camshaft sensor. It is my first time working with cars. Any advice will be highly appreciated.

1st test: Bench test and measured the resistance between the pins on the sensor.

• MAP sensor (Bosch 0 261 230 030)
  • There was resistance across all pins and ground. I forgot to take pictures and resistance value.
• Crankshaft sensor
  • There was 1 k ohm resistance between the two pins [see image].
• Camshaft sensor ( Bosch 0232103048) [see image for pin outs]
  • There was no recorded resistance between the voltage signal and the ground.
  • 267.4 k ohm between voltage supply pin and ground.
  • This is strange since I would of expected a resistance between the voltage signal and the ground?
    

2nd test: Check continuity with the sensor connector and back probe while the connector is attached. Can only test MAP and camshaft. The crankshaft gives out AC voltage hence no ground pin for continuity.

• Connector for the MAP and camshaft and continuity confirmed.
• Backprobed the MAP and camshaft continuity confirmed.

3rd test: Backprobed the MAP sensor and measured the voltage across ground and pin 4 (pressure signal) when pressing the accelerator down.

• Voltage dropped from starting 1.4 V with the accelerator down.
  • Is this expected? Read online that it typically goes up.
  • The voltage supply is reading 5V
  • Continuity exist with ground
    
  • The voltage signal for the pressure pin is less than 5V (can't remember exactly)
  • The voltage signal for the temperature pin is less thand 5V
    (can't remember exactly)

4th test: Bench test crankshaft sensor by measuring the AC voltage and phasing a wrench across the sensor.

• The voltage varies, seems to be behaving as expected. I don't have an oscilloscope to confirm. Not sure what the voltage peak to peak should I expect.

5th test: Backprobed the camshaft sensor with key turned and engine off

• I measured the voltage supply pin and ground to be 0.047V.
  • This is strange since I would of expected 5V
• Measured the voltage signal pin and ground to be 5V
  • Since it is a ratiometric measurement, I would expected this value to be lower than 5V?
• I also checked the wire connector.
  • Voltage supply pin = 5V
  • Votlage signal pin = 5V
  • Continuity exists between the ground.

There is a lot of information here. I don't have enough experience to make a judgement. Maybe one of you can share some insight, or maybe this information could help someone.

In my opinion, it seems that the issue is the camshaft since it is behaving strangely. For instance, there is no resistance between the voltage signal pin and the ground. Also, the voltage reading when back probed is also strange compared to the reading when back probing the MAP sensor.


I bought a camshaft sensor and will try it out once it is here. I will keep the thread posted.

 

[jackwhoo]

Hi,

Go online and Google how the sensors work and what signal out put is expected from each one.

Consider getting MES and using it to read what the engine ecu is detecting.

Best wishes

Jack

 

[akman88]

Hi,

Go online and Google how the sensors work and what signal out put is expected from each one.

Consider getting MES and using it to read what the engine ecu is detecting.

Best wishes

Jack

Thanks for the advice Jack.


I could not find an online datasheet that provide information on signal reading.

Recently changed the camshaft sensor. Unfortunately that does not solve the issue i.e., the car turn off itself when its hot around the middle temperature mark. Still stuck with it :bang:


I also purchased the MES. Ran diagnostic and three intermittent errors came up

1) P0105-14-Intake pressure sensor
2) P0110-15 Air temperature sensor
3) P0135-14 Preheating resistance 1 above catalyser

Cleared the error fault and drove it for a few days with the problem. Checked it today, the error doesnt come up again but the problem is still there.


Can you advice what readings from the ECU should I check?

 

[jackwhoo]

Thanks for the advice Jack.


I could not find an online datasheet that provide information on signal reading.

Recently changed the camshaft sensor. Unfortunately that does not solve the issue i.e., the car turn off itself when its hot around the middle temperature mark. Still stuck with it :bang:


I also purchased the MES. Ran diagnostic and three intermittent errors came up

1) P0105-14-Intake pressure sensor
2) P0110-15 Air temperature sensor
3) P0135-14 Preheating resistance 1 above catalyser

Cleared the error fault and drove it for a few days with the problem. Checked it today, the error doesnt come up again but the problem is still there.


Can you advice what readings from the ECU should I check?

Hi,

Look at the live data using MES .
Maybe even display it in graph form.
Start with ecu voltage,engine coolant temp, map readings, inlet air temp, rpm and
Anything else you fancy.


When it does cut out go back to basics, check for sparks at plugs, fuel , power to coil pack.

Good luck
Let us know

 

[akman88]

Update:

After a new temperature coolant sensor and new a crankshaft, the problem finally went away. I suspect that the crankshaft sensor was the main culprit.

Note: The MES recorded that the engine cut off at 71 deg C and throwing P0115-62 - Water temperature sensor error.

Thank you all for your advice! This is a great community.