UK Car Repair Questions? Ask a Mechanic for Answers ASAP
sorry about the delay
This sounds like a lack of fuel and could be a lack of fuel pressure from the electrical pump at the tank.
1st thing to try is to remove the fuel filler cap and then flick the ignition on whilst listening for the brief ‘buzz’ of the pump
If the connections to the pump are corroded or damaged then the pump could stop at any time or could not be running at full speed. Check that its relay switches in and out and the relay contacts are clean and bright – replace the relay if in any doubt and do the same for the fuse,
Ideally measure the pressure at the injector rail (should usually be around 3Bar / 45psi +) and if this is low check the pump as described and also consider changing the fuel filter as if this partially blocked this too will reduce pressure.
OK thanks for the extra info
that sounds like the fuel pressure is probably fine then
in that case I'd say to check the breather system next
if you loosen the oil filler cap a 1/4 turn and secure it with some tape so it can't fall out but leaving a gap so the engine can 'breathe' and then try to repeat the test ?
this will show if any of the breather valves etc are at fault with the hesistation
that allows internal engine air / breather gas to exit instead of being piped back into the inlet manifold or pre-turbo
I'm thinking that you may have a faulty PCV thats not venting as it should
and by allowing the gases to exit all the time under the bonnet this will show if the breather system is at fault
if you have a blocked or sticking breather then opening the filler cap should stop any hesitation , as I'm thinking a sticking PCV will suddenly 'burp' a load of blow-by gas into the engine which will lean it out
so yes a the collapsing breather hose may be the issue
OK I'd agree that heating the N75 valve up to do its resistance check is a good idea
also I'd do a vacuum leak test
The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane around each joint in turn. If the engine rev's up you've found your leak.
Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.
Work your way through each possible joint one at a time and you should find it. I use a slightly flattenedpiece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.
good progress I'd check the rest of the breather pipes for leaks and blockages as you've already mentioned