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2001 laguna 1.9 dci hard hot start

Posted By andytheone 10/2/2005 10:06:59 AM
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andytheone
 Posted 10/2/2005 10:06:59 AM
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i have a 2001 launa in for repair which has a hard starting fault when hot, the coustomer say in the winter time it will restart no problem when cold but when it is hot it is very hard to start

there are no fault codes preasent when it will not start but this is what i have noticed to be the only different between hot and cold starting

when the car is cold it will crank at about 300 rpm and generate about 200 bar of fuel preasure and then start straight away

after driving about 10 miles turn the car off wait a minute then try to restart you get 300 rpm and 80 to 100 bar of fuel preasure and it will not start

when it has been in a none start position i have added easy start and it fires straight away

this is the only thing i have seen that changes i have scoped crank and cam sensors and it only seems the fuel preasure which alters when it does not start

so do you think im looking at high preasure pump failure when hot, or is there something else maybe that alters the fuel preasure of any other known fault

shorty
 Posted 10/2/2005 10:15:41 AM
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hi andy, not sure with renaults but seen this on the experts 2.0 hdi where it has been the injectors.
would always start from cold but sure enough when hot it was impossible.



shorty

 

andytheone
 Posted 10/2/2005 12:36:15 PM
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i did try injectors for leak off and removing the fuel feed pipes to see if any air would go backwards through the injector but nothing

this car has done 30k miles and the coustemer says it will be ok now untill next summer i would think an injector fault would be there all year round but this is only a hot weather fault i guess it night be change one bit at a time

TopGun
 Posted 10/2/2005 2:38:59 PM
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Andy,

As there seems to be a temperature component to his one, have you checked the fuel temperature sensor?

What is the engine code as this is on the change over point. Also is it a Laguna ll?




Regards,

TopGun.

www.ivesgarage.com

andytheone
 Posted 10/2/2005 4:41:07 PM
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thanks for the reply fuel temprature is at 52 C when it is hot and starts and when it is hot and wont start

it seems to be related to the fuel preasure which i think should be around 150 bar before it will let it start

it is a laguna 2 with bosch common rail, it has no pump in the tank either

what i have noticed is when it does start the fuel preasure jumps stright upto 350 within a second of starting and then when i does not start it cranks for ages and generates about 90 to 100 bar

 

 

TopGun
 Posted 10/2/2005 5:50:07 PM
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Andy,

I agree the low fuel pressure would appear to be your problem the question is what is causing it?

The reason I asked about the fuel temp was that the common rail uses  variation in fuel return flow rate to cool the rail & injectors and potentially if the PCM sees a high fuel temp the pump has to deliver a higher flow rate to compensate and if the pump was marginal it could have been a factor.

I am still seeing 5 possible engine codes all F9Q but the numbers vary from 650 to 740 so if you can let us know that detail it will help enormously.

What data sources do you have available?
Clearly you have access to live data, what equipment?




Regards,

TopGun.

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Angus
 Posted 10/2/2005 6:43:29 PM
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Andy

All the data you've quoted suggests inadequate fuel pressure on hot cranking.

Two things come to mind.  Firstly, there was apparently a bad batch of rail-pressure sensors around that year.  I came across a duff one on a '01 2.2DCi Master that was doing odd things too.  If it reads consistently low across the range then it may be affecting hot starting the most.

Secondly; Could it be the primary pump [down by the rack?] failing to reactivate if hot.  I've got an on-going Iveco also with EDC that has had three, very similar, in-line pumps fitted in the last two months because of primary pump related hot starting "known problems."

Thirdly; [just remembered another.] There can be issues with the plug connectors on the injectors vibrating loose and not making good contact.  Whether this would cause a low pressure reading is unclear; but just one loose one certainly can cause non-starting for some as-yet undetermined reason.



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andytheone
 Posted 10/3/2005 12:52:37 PM
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thanks for the replys

the preasure sensor seems to work ok, i say this because when i have got it started when hot the preasure at idle comes up the same at 350 bar @ 800 rpm  the only difference is when cranking

i did look in the tank for a pump but there was nothing but if as you say there is a pump down by the rack from what im geting it seem like its probably that, and its this i need to check next

thanks i will let you know the outcome

Angus
 Posted 10/3/2005 2:16:00 PM
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Andy

Err..... It's the sender saying it's 350 bar. 

What if there's actually 450 bar at idle and the sensor's a bit tired and reading 100 bar low across the board?  So at hot crank it's really 180-200 bar [which is enough to stir the ECU into firing the injectors] not 80-100 bar [which isn't]?

Reading 100 bar low won't really affect running too much: but starting when hot....

There's an in-line pump somewhere around the rack area.  If it fails completely there's not enough primary pressure to the secondary [high-pressure] pump and consequently low rail pressure readings and no injection.  Do you have primary pressure readings on your live-data?  Or a fuel-pressure test gauge?  Should be 2.5-4.0 bar.



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aidan
 Posted 10/3/2005 2:23:06 PM
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Hi

No experience on this system but Just A thought, say the car was in a hot no start situation, could you give it a temporary false temperature sensor reading with a sensor simulator to say the engine was slightly colder and see what effect it had ? I would think that if it then started you would be looking electrical faults if it still did not start would you be looking for mechanical problems possibly worn pump?

Aidan



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