Big thanks to Humour for his help , we managed to get a comparison of fuel pressure and cranking speed from his 1.3 multijet which shows my car definitely has a much slower rate of pressure increase when starting and achieves a significantly lower pressure for the same cranking speed. For reference to any others reading this thread with a similar issue, the fuel rail pressure when cold is about 198 bar at 165 rpm on a good engine. I am getting around 180 bar at 194 rpm.

As expected , on a healthy engine the cranking speed never reaches maximum before the fuel pressure is sufficient for the engine to start ( As seen on Humour's car : 198 bar at 164 rpm)

When the engine is hot on my car , I manage a higher cranking speed but the pressure struggles to get above 150 bar. Having spoken to diesel specialists I am advised a diesel needs between 150 -160 bar to start. Since i am borderline on the required pressure even with the engine turning at its maximum cranking speed. it would seem the issue points to the fuel pump.

Glad I was able to help Mike, even though I did nothing in practice but banter


I hope you are now at root cause and the next fix will rectify your nice looking Grey GP.


Also it was interesting to hear a very quiet 1.3 Mjet in comparison to mine, it suggests that the rattle on mine is due to wear on the chain tensioner which I will be budgeting to sort before I hit the 100K mark.


Will keep in touch


Hum

Picked up a reconditioned fuel pump today and fitted it this evening . A 20minute job and relatively straight forward. Cranked over the engine and it started after about 5 revolutions to prime the pump. Put the diagnostics on the car to check the ramp rate on fuel pressure and the pressure vs rpm. Looking much healthier and closer to Humour s punto. Real test will be after the drive into and back from work tomorrow.

Fingers crossed


A couple of questions for clarity if I may;


1. Is the fuel pump you are referring to in the fuel tank, or that bulky item on the side of the head at the end of the fuel rail?


2. How did you depressurise the system before disassembly? 600Bar of pressure is DANGEROUS


3. Did you notice any visual failure points, such as seals etc. on the component you removed?


Would be interesting to understand what failed inside.


Humor

Think you can depressurise the system with mutliecu scan. Know can do some sort of depressurise with it.

Hi guys,
No I didn't use any special tools or techniques to de pressurise the system before dis assembly. The beauty of hydraulics is that providing you have no driving force ( ie active pump) you only need to release a very small amount of fluid to drop back to zero pressure. Typically when the engine is at rest , the measured fuel rail pressure is anywhere between 0 and 2 Bar , so not a pressure to be concerned about. I suspect that the fuel rail solenoid is active after the engine stops running to ensure the system is de pressurised to reduce the wear on the seals etc. It would also make sense from the stand point of heat build up not to block / trap the fuel in the rail as it will expand and increase in pressure.

I am pleased to confirm that since changing the fuel pump ( the one on the side of the engine driven from the camshaft) hot starting has not been an issue. I have repeatedly tried hot starts after leaving the engine stopped for various periods of time, in all cases the engine catches and fires up after the same number of revolutions / time as when its cold ( trpically 1-2 seconds).

As a reult of being supplied refurbished injectors , one without a new IMA code , I can also announce another observation. If the injector IMA code is wrong , the engine will run , but its likely to exhibit a flat spot , a louder injector ignition and excessive smoke on start up and under acceleration/ deceleration.

Having swapped the injector (without a correct IMA code) back for the original injector and then recoded to suit , the symptoms I mentioned above were resolved.

I did some reaearch and it appears the IMA code is the characteristic of the injector as derived under test using Bosch diagnostic equipment. The ECU uses this figure ( 8 digit hexadecimal value) to adapt the timing and quantity of fuel injected to reduce the noise and smoke generated when the fuel ignites. Its unliley that you will ever find two injectors with the same identical IMA code.

Hopefully this thread will be useful for any others experiencing similar symptoms in future.

Regarding reasons for failure , this I suspect would require some detailed inspection of the internals of the pump and validation of tolerances from the factory when originally built. Since i need to take the pump back as an exchange , I am a little reluctant to open it up and look inside. Past experience has shown there can be a number of small components held in with springs that disappear over your shoulder never to be seen again.

What I can confirm is there were no visible external leaks from the pump or any of the pipework fittings.

It only takes literally half an hour to change the fuel pump , and I can now do injectors in around the same time , the fiddly part is getting the screws started when refittiong the pump to the engine and aligning the drive dog on the pump to the camshaft cut out.

Feel free to drop me a line if you need any tips on how to remove the fuel pump, injectors, fuel rail opr any of the other tasks I've undertaken in persuit of fixing this issue , Im only too happy to help.

Quick update and hopefully final one on this topic !

After replacing two injectors with refurbished ones , the engine hunted , had terrible flat spots and smoking at certain rpms under load. Car would start but certainly didn`t run smooth , even though i re coded the injector IMA numbers into the ecu.

Swapping back to the original injectors and IMA codes , the engine runs fine , no flat spots or smoking.

Word of warning to anyone changing injectors on a multijet , make sure you buy from a supplier that fully tests and characterises the injector , to provide a new IMA code. If you use the factory original IMA its likely to be a mile out after refurb and the consequences are probably worse than the original fault

In my case the two original injectors i changed were giving higher leak back, which can cause starting issues. The high leakback doesn`t seem to affect the original fault of poor hot starting , the issue has been fixed by the new diesel pump.

With original injectors and a new diesel pump fitted , the car starts fine ~ hot , cold, or anywhere in between. No smoking under load or lumpy flat spots.

Well done Mike, glad the issue is now solved.


Also thanks for the explanations, the feedback will undoubtedly help others.


Interesting to note the refurbished injector's IMA calibration code is no longer valid. Looks like stealer prices will apply if one should need to replace these.


Humour

Hi there
Great Post and I can see you've really covered all sorts!

I message because I have the same issue with my 2007 diesel, 49000 miles

Starts fine cold but once warm often struggles, not always but often.

Was gonna change the glow plugs and starter but this doesn't seem logical considering it starts totally fine cold and battery all checks out too.

Should we go straight for the new fuel pump you reckon or are there other things to rule out first? As a fuel pump takes 30 mins to fit then I'm tempted to go that route as long as I can source a cheap part.

I must add the diagnostic did show up code P0683 which indicates a glow plug issue but this would be strange as it starts fine cold.
Many thanks

Mal

Here's the code :

Malnisbett said:

Here's the code :

Click to expand...

What car and year..?

I take it thats the 1248mj ?


I have 3 grande punto in that age range

Your glow plugs are unlikely to be your problem..




Is it difinitely cranking the engine over at speed once warm?

What rail pressures did the diagnostic show?

I havent read every post on this topic so if its been covered I apologise

Have you ate all changed your fuel filter to rule any of this out?

I have had a problem of the engine cutting at idle, MES said water in fuel filter, I didnt know how to drain the fuel filter of water so I just put a new filter on and it was fine.

@mainisbett

The classic difficult hot starting fault would be caused by intermittently failing ckp sensor (crankshaft position sensor). It just gets worse over time.

Edit: If the car started fine after letting it cool down, it'd be one of the suspects.