Leak Off Test Hard Starting

[adam03031980]

Hi All

Im thinking of doing a leak off test see if it gives me any indication as to the state of the injectors and if they are causing the hard start the reason i say this is i seem to be getting air in the system and also when my dad put the car on diag it showed the injector on the passenger side as working at 115% yet the drivers side one working at 84% and the 2 middle working around 100%, has anyone had this isse re the injectors working at different %'s

[Doggy]

In some cases, leaky injectors can reduce the fuel pressure enough so the car won't start, but I think it has to be pretty bad or acompanied by other issues, (slow cranking speed / dodgy glowplugs / low compression / marginal fuel pressure). I had at least two clearly faulty injectors, but no starting issues.

I don't look at this often enough to be certain, but don't recognise the percentages as you describe them. IIRC the diagnostic system reports the % corrections applied to each injector to attemp to compensate for wear etc. I read up a fair bit about this & apparently the cam sensor is used to determine how much the engine 'accelerates' in reponse th each injection cycle, if one cylinder does more than the others, then it has the calculated injection volume reduced to comensate, (or vice-versa).

A big difference in these numbers can't be good - after changing mine, all the percentages / volumes were virtually identical, the idling speed was much steadier and the air flow appeared much lower.

[adam03031980]

Well just called out the AA as getting fed up with the car still hard to start but he picked up these fault codes though i havent noticed and engine light on they were
p1351 pre post heating relay control circuit failure
p0113 inlet eir temp sensor
p0102 air flow circuit low

could these be the issue and where are they on the car i know where the glow plug relay and maf sensor are but not the air temp sensor.

[Doggy]

On most HDi's the IAT sensor is part of the MAF.

[adam03031980]

i did disconnet th maf sensor when idling the other week as i was told if the engine speed changes that will tell me if its faulty or not would that have brought those codes up

[Doggy]

I was thinking that too.

I think the pre/post heating is a very common message, you can probably ignore, (assuming the glow plugs are working).

[adam03031980]

i was thinkinf that when i change the air filter and coolant temp sensor i removed he maf when i did that the flat spot in acceleration disappeared for a couple of days when changing gear but then reappeared im wondering if thats maf related can they be cleaned.

[adam03031980]

Just out of interest im going to do a leak off test this weekend just need som pipe but how long should i leave the engine running for and what amounts of diesel are acceptable for leaking off

[Doggy]

I tried cleaning my MAF, but since it wasn't faulty, it made no difference. It has a couple of fine wires across the airstream, think it works by applying a fixed excitation supply & calculating air flow from the chilling effect of the air, (which will alter the resistance and hence the current or volt drop across the sensing wires). It includes a thermistor temperature sensor as well. It may help to gently clean these parts with a solvent, or petrol. Probably easier to eliminate it by substitution if you know anyone else with a similar setup.

The behaviour you describe suggests disconnecting the MAF forced the ecu to abandon the settings it had 'learnt' during normal driving and re-adjust itself over the following days - it just might respond to an occasional, 'Italian tune-up'.

Regarding the leakoff test, the bigger the sample, the more accurate the results. I used 4 small mineral water bottles & left it idling until the fullest bottle was about 3/4 full. Weigh one of the bottles first, then all of them individually after the test for accurate results. A variation from fullest to emptiest of about 10% is considered OK, AFAIK.

[adam03031980]

Well just checked my MAF and there is like a resistor sticking up and above that what should be 2 thin little connections though it seems one is missing presumably broke, is there supposed to be 2 of them and what affect would this have as the engine light didnt ever come on just stored thouse fault codes.

[adam03031980]

Done a leak off test today but looked all ok starting from injector 1 on the drivers side the weights after 10 minutes were 1)68g 2)71 3)67g 4)68g not sre if thats a lot to leak off in 10 mintes

[Doggy]

I'd say that's as near a perfect result as you're likely to see.

Guess it doesn't help you with a solution, but at least it's not injectors......

[adam03031980]

In i bad way i was kind of hoping it would be an injector my next porty of call i think will be to clean out the egr valve as it is only getting 42 mpg as opposed to my 110 that got 60mpg and i only ever sit at 60 as im up and down the A1 and also take a look at the TPS as i have a hesitation in acceleration only slight but seemed to go away momentrily when i moved the TPS also get a bit of black smoke when i boot it not so bad now i have used cleaners and replaced the maf and coolant temp sensor just lucky my brother works in motor factors and gets me some cheap bits