Smart car (Mercedes engine )

[Walesy]

Hopefully an answer can be given by a Merc forum user
smart car , MERCEDES ENGINE 3 cylinder engine has an injector fault showing on number 3 cylinder
all new plugs fitted , all good
new coil packs , all good
all new leads (all good )
New injector fitted , when listening to injector 1 and 2 with the old method of a screwdriver as a stethoscope they both have a lovely ticking sound , constantly ticking .
number 3 ticks for approx 12 seconds and stops ticking so fuel cuts off and runs on 2 cylinders
moved all injectors around and still does the same , bought a noid light to see the signal and as said stops after around 12 seconds .
switch off engine and the process does it all again .

ANY IDEAS WOULD BE APPRECIATED AS MY HEADS DONE IN
not a mechanic but handy with spanner’s

 

[Ian_T]

Are you able to do a compression test?

And do you have a test light to plug in instead of the injector to see if it continues to flash after the ticking would have stopped?

Sometimes the fault code will be a little more descriptive, saying 'open circuit' or 'short to ground' or something like that.

 

[alexanderfoti]

Yes exactly. What code do you have? If the Ecu thinks is misfiring on a cylinder, it will turn the injector off. These engine do like to burn valve seats, sure you don't have a mechanical fault, and the injector is a symptom?

 

[LostKiwi]

Alex is bang on.
When you changed plugs did you change all 6? Many don't realise there are 2 per cylinder (and those lower ones are a pain to get to).
A decent scan tool will show if it thinks there's a misfire. As he said if it thinks there is it will turn off the injector to prevent damage to the catalytic converter.

 

[Walesy]

Are you able to do a compression test?

And do you have a test light to plug in instead of the injector to see if it continues to flash after the ticking would have stopped?

Sometimes the fault code will be a little more descriptive, saying 'open circuit' or 'short to ground' or something like that.

Not got anything to do a compression test with , plugged a noid light in to the connector which feeds the injector and the light flashes rapidly for 10-12 seconds and then stops flashing .
got a test screwdriver with an earth clamp and does the same
code just came up as an injector fault cylinder 3

 

[Walesy]

Alex is bang on.
When you changed plugs did you change all 6? Many don't realise there are 2 per cylinder (and those lower ones are a pain to get to).
A decent scan tool will show if it thinks there's a misfire. As he said if it thinks there is it will turn off the injector to prevent damage to the catalytic converter.

All 6 plugs changed and the old ones were shocking , possibly the originals , just got a very basic OBD reader

 

[Walesy]

Yes exactly. What code do you have? If the Ecu thinks is misfiring on a cylinder, it will turn the injector off. These engine do like to burn valve seats, sure you don't have a mechanical fault, and the injector is a symptom?

Thanks for the reply , cheap OBD just comes up with an injector fault , cylinder 3

 

[Ian_T]

Was there any difference between the plugs when they came out? When you say they were in a terrible state, how do you mean? Physical damage, running rich? Covered in oil or something else? Were the plugs in No3 any different to the others?

The compression question was because as Alexander and LostKiwi suggested, there could be a mechanical fault rather than an electrical / component fault. And yes, if you're unlucky, it could be due to a burned valve, which seems to happen anywhere from 60k miles.

Given you've moved the injector to different positions and the fault stays with No3, I think we can rule out the injector itself. Do you have spark on those plugs in No3?

Once you can rule out the mechanical faults, there is the remote possibility of the ECU being faulty, still able to drive the injector, but the circuit that measures the current drawn by it could be faulty, making the ECU think the injector is a hard short to ground or something silly. I say "remote" and believe that's highly unlikely.

 

[Walesy]

Plugs which were removed should have 4 tips at the spark point , some had only 2 left on
lots of sparks jumping well on all 6 plugs , felt them first hand and certainly made me jump
finally found someone with a proper test system to plug in to the car but can’t get here until 3rd sept
hopefully he can source a fault and if so will list it here in case someone ever gets the same problem

 

[EmilysDad]

Plugs which were removed should have 4 tips at the spark point , some had only 2 left on
.....

OE plugs are single earth electrode ....

 

[LostKiwi]

OE plugs are single earth electrode ....

LKR8A are twin.

 

[EmilysDad]

LKR8A are twin.

My mistake - confused with my 451's plugs.... I knew they weren't quads.

 

[LostKiwi]

My mistake - confused with my 451's plugs.... I knew they weren't quads.

None are quads as far as I'm aware.

 

[Walesy]

Plugs which were removed should have 4 tips at the spark point , some had only 2 left on
lots of sparks jumping well on all 6 plugs , felt them first hand and certainly made me jump
finally found someone with a proper test system to plug in to the car but can’t get here until 3rd sept
hopefully he can source a fault and if so will list it here in case someone ever gets the same problem

Guy came out today , said cylinder 3 has no compression , other 2 cylinders are fine
looks like it’s the end of the road for this smart car as it looks like an expensive repair ?

 

[Walesy]

Are you able to do a compression test?

And do you have a test light to plug in instead of the injector to see if it continues to flash after the ticking would have stopped?

Sometimes the fault code will be a little more descriptive, saying 'open circuit' or 'short to ground' or something like that.

Guy came out today and said there was no compression on cylinder 3 , other 2 were fine so it looks like the end of the road for this smart car as it looks like an expensive repair?