Z3 Cranks but sometimes does not start.

[bonbon]

Recently I sensed there is a tough start. To overcome the problem I’ve been waiting to turn over 3 seconds after the dash lights disappear. Seems to have worked - but once in a while it really struggles to start (need to wait a few minutes).
Not 100% sure what’s going on - but I sense it’s a failed one-way valve in the fuel pump. I guess I can verify by checking with a pressure gauge.
As I’m really fed up going into the fuel pump - I’m going to try a more superficial option. Today’s plan is to insert a small one way valve inline with the fuel filter (6mm). Any thoughts?
I’ll update.

 

[AntStark]

Sounds like the cam position sensor may be faulty.

 

[t-tony]

I agree, and, they don’t always throw a fault code.

Tony.

 

[bonbon]

Before I proceed, is there a way to confirm it’s the cam sensor if it does not throw a code?

 

[AntStark]

Try it on a code reader..might not trigger the engine warning light but the fault may be stored. If replacing don’t buy a cheap one. If you have an M43 1.9 then I think the OEM ones were made by Delphi.

 

[t-tony]

Before I proceed, is there a way to confirm it’s the cam sensor if it does not throw a code?

Replace it with a "known" good one.

Tony.

 

[bonbon]

1. I guess Delphi or MEYLE
2. For everyone’s benefit - I will diagnose and update before throwing any parts at the car.
3. Just curious - why the cam position sensor and not the crankshaft sensor which seem to make more sense to me?

 

[t-tony]

It does make more sense, but just I'm going on past experience. When my crankshaft sensor packed it wouldn't start at all.

Tony.

 

[bonbon]

Update:
1. Checked codes with a reader - nada. (Bought a MEYLE camshaft sensor which will now gather dust).
2. Attached a pressure gauge inline at the inlet of the fuel filter ( below the LHD driver - easy access when on a lift - only need to release 4 nuts on the protective cover.).
Turning on the pump - pressure went up to 50psi as expected. Turned off the pump and after a 20 minute wait, the pressure went down to 34psi.
I have seen online that a drop of 7psi is ok, but 15psi implies a problematic one way valve in the pump. So “NASA we have a problem”.
3. As mentioned above, I’ve become fed up accessibg the fuel pump/gauge - so as I was already into the fuel line - inserted the one way valve ($5) before the fuel filter. There was room - needed to add a bit of 6mm id pipe.
Pic attached.
I hope this sorts it out. The issue was erratic so I’ll only know on a few weeks.

 

[bonbon]

Ok - first 24 hours was erratic - but seems to have settled down.
Next steps:
1. Continue to monitor before deciding to remove the one way valve (as the way I put it in there is a 180degree bend in pipe and I fear at some point it will bend and limit flow).
2. Try replacing the starter relay - next to my left knee (LHD)
3. One other failure mechanism reported has been the ignition switch. I’ll see how things get on.
4. For completion: the camshaft sensor has solved this issue for some (even though no codes were thrown)
5. If/when I remove the one-way valve, I guess I’lll need to replace the fuel pump as the one way valve is failing.
I’ll update.

 

[bonbon]

So far 14 days no problem. Let’s see

 

[the Nefyn cat]

I'm a bit late to the party, maybe, but a faulty cam sensor doesn't always throw a fault code. There again, it sounds like it doesn't need fixing any more, but, just in case.......

 

[bonbon]

I'm a bit late to the party, maybe, but a faulty cam sensor doesn't always throw a fault code. There again, it sounds like it doesn't need fixing any more, but, just in case.......

What would be the symptoms if faulty?

 

[t-tony]

On my 2000 2.0 Z3 when the inlet cam was failing it would sometimes fail to start straight away and didn't respond to the throttle. Also after a shortish run trying to start with a lukewarm engine it would wind over and over and eventually start and run raf.

Tony.

ps. Read "rough as . . . ."

 

[bonbon]

Does our fuel pump turn off a few seconds after turning the key one position (when lights on the dash go out) - or does it continuously push fuel even before turning the key another position to start the engine?

 

[the Nefyn cat]

What would be the symptoms if faulty?

Much like Mr t-tony says, it was one of those intermittent ones, makes it hard to sort out. In the end I took a punt on a new sensor and it's been fine for the last few years.

Does our fuel pump turn off a few seconds after turning the key one position (when lights on the dash go out) - or does it continuously push fuel even before turning the key another position to start the engine?

IIRC, the pump turns on (with the key) runs for a few seconds to get pressure in the system, and then relies on getting a signal from somewhere to reassure it that the engine has started. I've not had any problems in that direction, so I haven't bothered looking further. Lazy tw@.

 

[bonbon]

Much like Mr t-tony says, it was one of those intermittent ones, makes it hard to sort out. In the end I took a punt on a new sensor and it's been fine for the last few years.



IIRC, the pump turns on (with the key) runs for a few seconds to get pressure in the system, and then relies on getting a signal from somewhere to reassure it that the engine has started. I've not had any problems in that direction, so I haven't bothered looking further. Lazy tw@.

My question was to clarify if in the case where the one-way valve on the pump fails, would it help to wait a few more seconds (say 5) prior to cranking the engine (or does the pump turn off after say a couple of seconds when the lights turn off? (…and in such a case it may help to turn the key off and the on again to pump more fuel - and then turn on the ignition)

 

[bonbon]

So far 14 days no problem. Let’s see

Now a month (cranking 2 seconds after the dash lights disappear). Still not 100% convinced as it was rare beforehand - but for sure the pressure loss was fixed.
End of May 2024 - all ok - so one way valve mod seems to have worked.

 

[bonbon]

Ok a few months later and all is well. The problem was a failing one way return valve in the fuel pump. Adding the small one way valve seems to mitigate the problem - which includes waiting 2-3 secs after the dash lights disappear before cranking .

 

[bonbon]

I think I have it sussed.
It does seem that the non return valve inside the fuel pump has failed (and perhaps even deteriorating).
Cranking exactly 2 seconds after the dash lights go out seems to start the engine all the time - presumably as fuel pressure has built up and just before the ECU turns off the pump.
Seems childish not replacing the unit - but for some reason I am fed up changing it out. I’ll do it again when the fuel level gauge fails for about the 3-4 time. (I’m at 470,000km)