TD4 leak back query

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Dunk89

New Member
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14
Hi guys

Ive read many threads on here with reference to TD4's not starting when hot but I have a question I cant see the answer to.

My TD4 starts perfectly when cold but once up to temperature refuses to start.

Had the rear fuel pump under the back seats replaced as this wasnt working.
Had the crank shaft sensor replaced (one in front of oil filler cap)
Front lift pump is audible.

I have just got a leak back test kit together. So how does the leak back test prove anything other than a leaky injector? Is the test done with a cold or hot engine with ignition on? Why would a leaky injector work when cold but not when hot?

If someone could give me any more pointers I would be very greatful.

Dunk
 
Just to add, once it fires after turning over for around 30+ secs there is no smoke at all.

Crank shaft sensor is what im thinking after changing rear fule pump and cam shaft sensor?
 
Don't know, but I had this problem a couple of years ago. After proving it wasn't the camshaft or crankshaft sensors I did a leak back test and found that one injector was knackered.

It only ever caused a problem when the engine was warm tho.
 
Thanks for the reply.

Had the AA out today, told them of the history, they then sprayed some quick start down the air intake and it started straight away whilst hot.

He is 99.9% sure it is an injector so it's off to the garage for a leakback test, which should hopefully clarify the problem.

Sounds similar to your problem.
 
Dunk89 said:
Thanks for the reply.

Had the AA out today, told them of the history, they then sprayed some quick start down the air intake and it started straight away whilst hot.

He is 99.9% sure it is an injector so it's off to the garage for a leakback test, which should hopefully clarify the problem.

Sounds similar to your problem.
Click to expand...

If it's not injector related, it sounds very similar to one I had, which needed an HPFP in the end
 
Dunk89 said:
Is this the front one behind the battery?
Click to expand...

No. HP = High Pressure. That's the diesel injection pump that pressurises the fuel prior to it reaching the injectors. It's attached to the engine and rather expensive to replace, I would imagine.

The one behind the battery (or in the rear wheel arch on later models) and the one in the tank are both low pressure pumps. Simply there to deliver a constant supply of fuel to the HP pump.
 
Creeeg said:
No. HP = High Pressure. That's the diesel injection pump that pressurises the fuel prior to it reaching the injectors. It's attached to the engine and rather expensive to replace, I would imagine.

The one behind the battery (or in the rear wheel arch on later models) and the one in the tank are both low pressure pumps. Simply there to deliver a constant supply of fuel to the HP pump.
Click to expand...

Thanks for that, fingers crossed it isn't that particular problem!
 
Creeeg said:
Yes, good luck.

Mind you, an injector isn't cheap and they can be swines to remove :eek: Should be cheaper than a new HP pump tho ;)
Click to expand...

It's booked in to go in the local independant LR garage on Monday, they do self refurbed Bosch injectors for £100 each, plus labour and then £55 for a 1 hour diagnosis check to start with - sigh!
 
They'll do a leak back test pretty quickly and that will be a straight yes or no regarding one or more knackered injectors. That seems a good price for an injector. I paid about 200 quid for a new one. Plus fitting, as I didnt fancy wrestling it out of the head on my drive in the snow in January ;)

Only the 5th time I've trusted to put a vehicle in a garage for a repair in 26 years of motoring. It goes against the grain, but sometimes needs must :rolleyes:
 
:hijacked:
I would just like to congratulate the OP on being chosen totally at random, to host my totally innocuous 2000th post.
Normal service may now be resumed...
:hijacked:
 
Why would a leaky injector work when cold but not when hot?
Click to expand...

The system allows a small amount of diesel to leak back to lubricate the injectors, as this fuel returns to the tank it gradually warms the fuel in the tank making it thinner, together with this as the injectors heat up with the engine running the tolerances within the injectors expand allowing more fuel to pass. Being a single rail it only takes one to leak excessivly to prevent enough pressure to build up and atomise.
If your not confident enough to do a leak back test run it till its hot enough to not start
trace the return pipes to the last injector and clamp it off beyond this with a pair of mole grips. If it starts you have one or more leaking, do not run it for more than a couple of moments like this.
They can be a nightmare to remove but most prise out easily enough with care.
I bought four second hand on ebay for £40 and after identifing the leaky one replaced it and it ran without starting problems for another 80,000 miles, then sold it but probably still fine.
 
Davidspect said:
The system allows a small amount of diesel to leak back to lubricate the injectors, as this fuel returns to the tank it gradually warms the fuel in the tank making it thinner, together with this as the injectors heat up with the engine running the tolerances within the injectors expand allowing more fuel to pass. Being a single rail it only takes one to leak excessivly to prevent enough pressure to build up and atomise.
If your not confident enough to do a leak back test run it till its hot enough to not start
trace the return pipes to the last injector and clamp it off beyond this with a pair of mole grips. If it starts you have one or more leaking, do not run it for more than a couple of moments like this.
They can be a nightmare to remove but most prise out easily enough with care.
I bought four second hand on ebay for £40 and after identifing the leaky one replaced it and it ran without starting problems for another 80,000 miles, then sold it but probably still fine.
Click to expand...

Thanks David, great explanation.
 
Yes we got success in the end.

Took it to the garage who performed a leak back test and found one very leaky injector and another that was right on the limit, so we got both changed for genuine reconditioned Bosch injectors (£100 + vat each) around £400 inc labour, testing etc - sigh!

Starts first time every time, but just had his MOT and cost us another £900 for 2 new tyres and a whole new brake system - pipes all well corroded , hand brake cable kaput, rear drums seized solid and wouldn't come off so new ones fitted, new shoes, and cycling ears, new front discs as both had cracked and pads. Oh and a track rod end and rear light cluster.

Just got her back and rear door won't open - Sigh!

so why do they call these Three Granders again?

Wouldn't change it for the world though, God bless Freddie.
 
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