C5 X7 no start (or only runs for fraction of a second)

[MattBLancs]

Latest news, and it's not good news!

Turns over lovely but won't flipping start. Stupid thing

[bobins]

OK, so back to basics. What would stop it starting ?
Cam/crank synch.
Fuel rail pressure - stuck or intermitent injector / leak off.
No fuel - HP pump.
Low compression - either hydraulic tappets or piston blow by or knackered valves.
We know it can actually get air to the combustion chambers so that side should be OK.
Presumably a fubar'd MAF/MAP wouldn't stop it starting ?

What else ?

[moizeau]

Partially blocked exhaust and towing it (higher revs) forces the start?

[MattBLancs]

Thanks for the ideas folks, will accumulate my thoughts and reply shortly with more

[Hell Razor5543]

If the hydraulic tappets are dry (no oil in them) the valves do not open properly. This means that the engine cannot run for long enough to fill the tappets with oil. Towing the car will get the oil flowing into the camshaft area, which will allow the tappets to get oil into them, and then they will work properly. I know other Forum members (who are professional mechanics) do this as a matter of course when they have situations similar to this.

[moizeau]

My further thoughts would be
1 - a compression test
2 - take the exhaust off (and be loved by the neighbours)

My old 350LC wouldn't start on the kick due to worn rings but would with a bump.
I had a water pump that wouldn't start, there was wasp's nest in the exhaust.

The other things have already been checked in Diag I think, but worth a recheck.

[MattBLancs]

Ok a brief situation update and then I will reply to the points raised in a mo.

Car has been in use recently. After the tow start (Via Defender) it drove to Preston garage, ran fine for them, and their MOT man too. No faults found.

Picked up and drove straight to Cumbria = started in -3°C conditions fine. Then again for the return to Lancashire the next day (-5°C and exposed car park position, little uneven for 1-2 seconds but put that down to lack of glow plug function) ran perfectly - short stop about 20 minutes from cold start, then restarted and back (2.5 hours) run home.
Has done little bit of day-to-day driving over the Christmas hols.
Started fine at home then no start in busy car park.
Bump started (via Space Tourer) then fine again.

Another 5/6 starts and relatively short trips since then (2x 30 minutes, 2x 10 minutes= started fine for each of those) all these on the old starter motor.

Started fine this morning for drive round the back to jack it up for starter motor change (and swapping tyres about and refitting undertray)
Starter motor fitted and now non-starter again.

When running is nice healthy power output (goes well!)
Economy seems ok (high thirties MPG but I haven't tried driving gently yet.

[MattBLancs]

OK, so back to basics. What would stop it starting ?
Cam/crank synch.
Fuel rail pressure - stuck or intermitent injector / leak off.
No fuel - HP pump.
Low compression - either hydraulic tappets or piston blow by or knackered valves.
We know it can actually get air to the combustion chambers so that side should be OK.
Presumably a fubar'd MAF/MAP wouldn't stop it starting ?

What else ?

Cam/crank sync= checked previously and reported as Synchronised in Diagbox. Laptop on charge, will check this again (after tea)

Compression= not got means to check (yet)

As per "situation update" when running seems to run well.

Air filter few thousand miles old. Anti shudder valve thing checked (is open)

Not tried with MAF unplugged, but my thoughts same as yours = should not stop it running, I don't think.

[MattBLancs]

Partially blocked exhaust and towing it (higher revs) forces the start?

When running seems ok (not restricted)
I'm used to the 16v DV6 HDi (which is the most rev-happy diesel ice ever come across!) And it's not as keen to be in the upper revs as that (flattens off a touch about 4000, where as the dv6 is happy to approach 5000)

[MattBLancs]

OK, so back to basics. What would stop it starting ?
Cam/crank synch.
Fuel rail pressure - stuck or intermitent injector / leak off.
No fuel - HP pump.
Low compression - either hydraulic tappets or piston blow by or knackered valves.
We know it can actually get air to the combustion chambers so that side should be OK.
Presumably a fubar'd MAF/MAP wouldn't stop it starting ?

What else ?

Sorry fuel pressure - missed that - figures quoted in Diagbox seemed ok, but will check them again shortly.

Intermittent injector fault not more likely throw a code / lumpy running on one cylinder down??

[bobins]

I can send you my leak-off test kit to borrow if:
A: You've not got one.
B: You want to go down that route.

It could help narrow it down one way or the other.

[MattBLancs]

If the hydraulic tappets are dry (no oil in them) the valves do not open properly. This means that the engine cannot run for long enough to fill the tappets with oil. Towing the car will get the oil flowing into the camshaft area, which will allow the tappets to get oil into them, and then they will work properly. I know other Forum members (who are professional mechanics) do this as a matter of course when they have situations similar to this.

I agree with this, and further, thought that was the cause of my issues, resolved by the (1st) Defender pull start, right up to the point I had my second "failure to start" situation. At that point, car having started and run fine for about 20 minutes, stopped for about 5 minutes that wouldn't go again, I was pretty sure hydraulic tappets were not the cause of at least my second failure to start.

[MattBLancs]

I can send you my leak-off test kit to borrow if:
A: You've not got one.
B: You want to go down that route.

It could help narrow it down one way or the other.

That's very kind of you to offer, thank you.

I'll probably buy a kit as have a bit of a tool collecting habit, so like to "build my arsenal" especially in pursuit of a problem

[MattBLancs]

My further thoughts would be
1 - a compression test
2 - take the exhaust off (and be loved by the neighbours)

My old 350LC wouldn't start on the kick due to worn rings but would with a bump.
I had a water pump that wouldn't start, there was wasp's nest in the exhaust.

The other things have already been checked in Diag I think, but worth a recheck.

As above, not the means to diesel compression test (yet)

Taking exhaust off - likely next weekend but will try. Unless I believe the diagbox reported figures then guess needs to be ahead of the catalyst+ DPF unit.

Diesels used to suffer collapsed catalyst occasionally, is that still a thing?

[H4wkeye]

Quite odd seeing how it's intermittent. Guess some really persistent gremlins snuck in this time. Keep us posted Matt, curious to see what it was eventually. Hoping for a quick fix!