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[Gareth79]

Just posting while I'm waiting for the recovery truck really. My ForFour lost power in the outside lane of the M25, I managed to get it to the hard shoulder. It turns over but won't start, in fact no sign of if even catching. I don't recall there were any warning lights beforehand and no noises.  It has all fluids, Inc petrol which was my first suspicion (i put in half a petrol can of fuel just in case)

I'm away for a week (missed my flight!), any ideas for what to look at or point a mechanic at when I get back?  Quick search reveals clutch actuator might cause this?

[Ocracoke]

Fuel pump failure is possibly my first thought given the description though I have never heard of failure of that type on the ForFour before. As I understand it, your car is a manual so it won't have a clutch actuator.

[Gareth79]

Yes I was just reading more and it's a part on autos.  Fuel pump or something in the ignition was my next thought too.

[Ocracoke]

I guess it does spin over with the starter motor... If that is the case, then for ignition, you need air, a spark and fuel. The air intake is unlikely to be blocked up given where it is which leaves fuel and a spark, which means either the fuel pump or perhaps the fuse to the ignition coils (#34- 10A), the pump (#11 - 15A) or the starter switch (#40 - 40A). There is also the chance it might be relay failure.

Given the relative ease of getting to the fuses and the relays (which are peanuts to replace), I'd check all of those are in good order before digging out the pump.

[Gareth79]

I have a big bag of fuses and relays actually - I bought an entire panel when investigating a previous issue (which was something completely different), I'll have a play, might have time before leaving for the replacement flight.

[Ocracoke]

Good luck, hope it is that. As always, be careful when messing around with fuses/relays and always disconnect the battery if not sure, you don't want to add electrical issues as well.

[Alex]

Relays sometimes come back to life after they cool down a bit.

You need a star diagnosis, you can have all 3 elements of combustion but the ECU waits for the engine to reach a certain RPM and position before firing.

If those sensor are dead (the crankshaft or the camshaft position sensor?) you have no chance of starting the car even if you tow it in gear.

I would not attempt to repeatedly start the car if it doesn't seem to start, or at least let the starter motor cool between tries. I don't know if flooding the cylinder can also be a risk with electronic fuel injection.

[Gareth79]

Thanks all.  I had time to pull the relevant fuses and all looked ok, I put the larger #41 on a meter too, it had continuity. I need to wait until I'm home to test the relays.

What are the options for diagnosics, is the star system very specialist?  It's currently on my drive so getting it transported anywhere will obviously cost money and time, and the car is only worth £800-1000 when running so it's on a knife edge. I do recall having a crank position sensor fault last spring when I got it, but I think it happened once or twice, so I guess that's a real possibility there.

[Ocracoke]

STAR is the Mercedes diagnostic equipment and the recommended diagnostic equipment for Smarts in general because it can drill down a fair way into what a fault could be. That isn't to say another diagnostic machine can be used but it will be less capable.

With that said, if it does have a crank sensor fault anyway, it'll be worth getting that replaced anyway, if only for that to be eliminated as a cause.

[Problemchild]

sorry to hear that

the cars are v reliable and i've seen very few failures that would make a car un-affordable to fix.

sounds like a fuel prob to me

no key on the dash? immobiliser

engine management light would be showing if it was something that the ECU had decided was wrong (airflow, crank position etc)

JJ

[mr singh]

you say the EML would come on if a code is logged JJ, BUT i have seen cases where a sensor has failed but the EML hasn't come on. X-Type diesels when a cam sensor fails, there is no EML but the car will run till its switched off, then it wont start again...

[CrazyG]

If as you say, it had an issue previously with the crank position sensor
and it was not replaced, then that would to all intents and purposes
be the first thing to get fixed/changed.
But....if it had a Star diagnostic's plugged into it, then the answer
would be plain to see (to the operative of it).

Unfortunately, this will require your car to be transported to a Smart
independant.....and the closest to you I think would be in Guildford..
Smart Car Specialist (Sasha), an alternative would be S2smarts
between Rickmansworth and Watford. Call either for advice, and
when they could fit you in...as well as a rough idea of the cost for
the diagnostics and replacing the sensor, then get quotes from
local transporters to get your car their. (I suspect SCS has a contact
who they could suggest to get your car transported to them....I do
know that S2 definitely does.)

[Gareth79]

Many thanks for the detailed replies!   I am back in the country and had a short while to test a few things before it got dark (and more importantly, I got tired).

- I put a probe stethoscope on the fuel pump while somebody turned the key, I couldn't hear it prime when the key was turned (does the FF do that?), but when it was cranking/running I heard a definite whine.
- Spraying a little bit of brake cleaner into the intake hose while it was being cranked, it ran for a short while. Then when cranking it after that (but not changing anything else) it catches and runs for a short while before stuttering to a stop - it did this several times.
- I changed both fuel pump relays with ones from my spares and there was no change, I haven't tested the ones that I pulled yet, but imagine they were fine.
- I used Torque to read off any fault codes, none were found (this was most interesting).
- I didn't remember to check the immobiliser/key symbols, and sorry my memory of what I saw before was not clear.

One important thing is that the battery is quite weak due to cranking and having the hazards one for 3+ hours, I have it on charge and will test some more tomorrow.

I'm leaning towards it being a weak fuel pump though - ie. there is enough to get a bit of pressure so it can start, but not enough to supply the engine running.

edit: I next plan to put a meter on the pump connector to check that it is getting power both when the ignition is turned on and then cranked/running.

[Problemchild]

blocked fuel line??

water in fuel??

diesel instead of petrol??

maybe pop back to the garage you topped up with last?

JJ

[Gareth79]

I'm pretty sure the fuel is fine, The gauge had just dropped to 1 bar and it had run fine for the whole tank. I probably filled it sometime in January.