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Old 15th August 2010, 22:50   #1
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Default Fiat Siena, very stubborn problem.

Hi All,
I have been living with a very strange but stubborn problem with my 2000 FIAT Siena 1.2 Petrol for a couple of year now. It is an intermittent problem which makes it especially difficult to diagnose. Thank you for any help in advance. I sure do need it.

Sometimes after driving the car under load say with 5 people a/c on, for a while in heavy city traffic, if I stop to get something for 5,10,30 minutes - a few hours and try and start my car, it wont start. I have to press on the gas for the car to start but as soon I take my foot off the accelerator, the car stops. It just wont idle. Oddly enough, if I leave it alone for half an hour, the car starts just fine, as if there was never a problem.

Like I have mentioned, this only happens SOMETIMES, ONLY WHEN
1. I run the car. (usually occurs when there are 5 people and the a/c on)
2. Stop the car for a while. (noted to vary between 5 minutes up to 6 hours, mostly 5 mins to 30 mins.)
3. Try and start the car for a while, unsuccessfully.
4. Leave the car alone for a while. (usually 15-30 mins)
5. Car starts fine.

This is what I have tried:
checked and increased the idling screw.
cleaning throttle body

These are the conditions under which this problem usually occurs:
Car is fully loaded - 5 people.
A/c is on.
Note that this problem does not always occur under these conditions.

These are the observations whenever the car is checked by various mechanics (of course, the car doesn't act up then):
ECU reading are normal.
Idling settings are fine.
Throttle body is clean.
Fuel pump motor is fine.

Its very embarrassing when it happens in the presence of family and friends, It is my first car , i love it, but its become an object of ridicule. The car becoming increasingly unreliable because of this.

I would appreciate any pointers at all. People have told me it is most likely an electronic problem. I'm willing to undertake changing parts as a calculated guess but I need help doing this. Please help.

Thanks,
Aninda.
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Old 16th August 2010, 01:22   #2
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I would suspect it as dirty spark plugs and clogged fuel Injectors.
get these checked at least.
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Old 16th August 2010, 11:49   #3
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Hi ghpk,
I'm sure I had the sparks checked and if memory serves me correct, a couple of them were changed too.

Don't know about the fuel injectors though. I will follow up on that one.

Thanks! Let me know if you can think of anything else too.
Regards,
Aninda.
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Old 16th August 2010, 13:27   #4
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Airlock in the fuel pump when engine is warm. Try insulating the fuel lines. Also , Fiats used to let fan run on when ignition off. If this is not happening that is your cause
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Old 16th August 2010, 14:23   #5
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so I should -
Get the Fuel lines insulated?
Check that fan runs when ignition is off ?
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Old 16th August 2010, 15:38   #6
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Quote:
Originally Posted by ajmat View Post
Airlock in the fuel pump when engine is warm. Try insulating the fuel lines. Also , Fiats used to let fan run on when ignition off. If this is not happening that is your cause
The pump is fully submerged in the tank. Shouldn't give you the problem.

As I don't know the Siena this well I have to ask, whether you have 2 coils at the side or is it individual coils sitting on top of the spark plug.

If it is 2 coils at the side: When were the spark plug leads changed the last time?

When was the fuel filter changed last time?

The fuel pump has got a filter in its housing and a filter before the housing. Check for clogging, which can occur when load in the rear is extreme.
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Old 16th August 2010, 15:49   #7
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Quote:
Originally Posted by CPH View Post
The pump is fully submerged in the tank. Shouldn't give you the problem.

As I don't know the Siena this well I have to ask, whether you have 2 coils at the side or is it individual coils sitting on top of the spark plug.

If it is 2 coils at the side: When were the spark plug leads changed the last time?

When was the fuel filter changed last time?

The fuel pump has got a filter in its housing and a filter before the housing. Check for clogging, which can occur when load in the rear is extreme.
I'm really sorry ... I'm not very knowledgeable about the working of my car. I'm learning as I try to solve this problem. I will get back to you with this information as soon as I can.
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Old 16th August 2010, 16:01   #8
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Quote:
Originally Posted by spacefugitive View Post
I'm really sorry ... I'm not very knowledgeable about the working of my car. I'm learning as I try to solve this problem. I will get back to you with this information as soon as I can.
Pm/email me a picture of the open engine bay or put one up on the forum.
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Old 16th August 2010, 16:19   #9
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This is an image of the engine bay I found on the internet @ : BUYING USED FIAT SIENA

I will post one with a better resolution once I have the car back from the garage.
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Old 16th August 2010, 17:17   #10
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When the Engine gets too hot,this kind of things will happen.
1.
For example : If the engine is in good condition and the radiator cooling fan is not working while you driving a car and you are not aware of it.The engine will automatcially stops after getting too much heated.

If you start the engine again without noticing what happens,it will not start.But after the engine gets cooled,it will start again.

Check the radiator in the morning,Start your engine and check the radiator (open it before itself),whether there is any bubbles.

2.As you said the Spark plugs are changed.So no need to worry about that area.

3.If there is any water mixed and the filter not working properly also this can happen.

4.The injectors whicih is the main one for firing.It may create some problems.

plz Update total kms done in ur car and also the temperature your engine is producing.

Last edited by dmaheshkumar : 16th August 2010 at 17:20. Reason: spelling mistakes
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Old 16th August 2010, 18:23   #11
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Quote:
Originally Posted by dmaheshkumar View Post
When the Engine gets too hot,this kind of things will happen.
1.
For example : If the engine is in good condition and the radiator cooling fan is not working while you driving a car and you are not aware of it.The engine will automatcially stops after getting too much heated.

If you start the engine again without noticing what happens,it will not start.But after the engine gets cooled,it will start again.

Check the radiator in the morning,Start your engine and check the radiator (open it before itself),whether there is any bubbles.

2.As you said the Spark plugs are changed.So no need to worry about that area.

3.If there is any water mixed and the filter not working properly also this can happen.

4.The injectors whicih is the main one for firing.It may create some problems.

plz Update total kms done in ur car and also the temperature your engine is producing.
It may not be over heating, as I have noticed the heat indicator is where it should be. The other thing is that even in the problem condition I can start the car with the accelarator and continue driving as long as the accelarator is pressed ... only when I step off the gas does the car stop again and again.

Having said that .. I will check the injector filters. Thank you very much for replying!
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Old 16th August 2010, 21:13   #12
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Thank you all for your help so far ...

some more additional information I should share :
RPM PDC Sensor replaced along with timing belt.
Valve timing verified.
Fuel Filter replaced.

Does not seem to solve the problem.

The guy at the garage suggests I replace the throttle body assembly and the fuel pump.
Throttle body assembly because : of wear and tear the throttle angle might have some play causing this issue.
Fuel pump : heating up of the fuel motor could cause this problem.

Im told these are quite expensive .. and are as good as calculated guesses. What do you guys think of this?
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Old 17th August 2010, 09:11   #13
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Replacing all the things will be very expensive,but already u have done some changes.
But without identifying the problem please dont spent money,bcause Fiat Sienna (Revalueation) is very less in the market.

If you like this vehicle a lot and you love it,then try to work out the things.Otherwise please go for another (Only if interested).

You are very much interested in your car,then spent for it and change the assembly.What are all the parts you are replacing ,please take and keep it with you (Old parts).It will be very helpful in future.

Take your car to different mechanics,Dont go to the company service centers.There are very very good mechanicas outside in a small size garrages.

Last edited by dmaheshkumar : 17th August 2010 at 09:13. Reason: Spelling
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Old 17th August 2010, 12:16   #14
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Check fuel pump motor. It is housed in the fuel pump assembly. If the motor is weak, it does not throw out fuel at the required pressure and under fully loaded conditions, the fuel supply is limited.

The entire assembly will cost you approx Rs.10-15000. Instead just tell your mechanic to open up the fuel pump assembly and try another motor. The motor is of Bosch make and costs Rs 1500-2000 here at the Mumbai Bosch authorised outlets.
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Old 17th August 2010, 18:29   #15
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Quote:
Originally Posted by mohit333 View Post
Check fuel pump motor. It is housed in the fuel pump assembly. If the motor is weak, it does not throw out fuel at the required pressure and under fully loaded conditions, the fuel supply is limited.

The entire assembly will cost you approx Rs.10-15000. Instead just tell your mechanic to open up the fuel pump assembly and try another motor. The motor is of Bosch make and costs Rs 1500-2000 here at the Mumbai Bosch authorised outlets.
Thanks Mohit, Thats very useful, I will definitely try that. My car is at a bosch service center right now, and that should be easy enough for them.
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