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172 misfire on cyl2 - any ideas?



  172, S2000, S1 Elise
I've been struggling to diagnose a misfire for the last couple of weeks, hopefully one of you lot with vastly superior knowledge of these cars might be able to help.


The initial problem occurred during heavy rain, car was running perfectly, then I parked up, returned it it and started it up. Immediately it was running on 3 cylinders. The check engine light was on.


Thought it was an electrical issue (due to torrential rain), got it on Torque Pro android OBD2 app, which read an injector fault on cyl 3.


Replaced this injector with a renault one, problem went away, car was running perfectly for next 100 or so miles.

Then it started running on 3 cyls again. This time it's misfiring on cyl2. I know it's cyl2 (second from right) as when I pull the injector leads off, this is the only one where it has no effect on the running of the engine. The check engine light has not come on again, though.


What I've tried so far:


- swapping the injectors over between cyl2 and 3 on the fuel rail - which makes no difference, misfire is still on cyl2.


- swapping power leads between injectors 2 and 3 - no difference - misfire stays on cyl2, so I know power is getting to cyl2 injector (also tested with multimeter).


- Swapping plugs over between cyl2 and 3 - again no difference.


- Changing coil pack for a used one - no difference.


- Changing leads for another used set - no difference.




Any ideas of what to try next? as it has me stumped.




If I can't resolve it myself, can you recommend someone who could take a look at it, preferably in Bristol, as I'd like to avoid driving it if poss in its current state. Even though it's just about driveable on 3 cyls, until I know what the fault is I don't want to risk damaging the engine.

Thanks,

George
 
  172, S2000, S1 Elise
Check the wiring for the injector itself
Hi,

I've checked the wiring by swapping the cables from cyl2 and cyl3 over - the misfire remains on cyl2.

I've also checked with a multimeter that power is getting to both injectors, which it is.

Is there anything else I need to/can check, wiring wise?

Thanks
 
  172, S2000, S1 Elise
I'm over in street if you'd like me to have a look.
Dan,

Thanks, the car's been down to your place before and I'd definitely bring it down again if I thought it was ok to drive, but without a diagnosis I wouldn't want to drive that far on 3 cyls in case I caused damage.

Thanks though mate
 
Dan,

Thanks, the car's been down to your place before and I'd definitely bring it down again if I thought it was ok to drive, but without a diagnosis I wouldn't want to drive that far on 3 cyls in case I caused damage.

Thanks though mate
Oh really? What's the reg? I'm betting it's an injector (I have a few spare if you want to borrow one?)
 
  172, S2000, S1 Elise
Oh really? What's the reg? I'm betting it's an injector (I have a few spare if you want to borrow one?)
It's RX51***, you had you had it in for an engine swap when it blew a plug out of the head.

I thought it was injector too, especially as cyl3 injector had failed 100 miles ago, but I've tried swapping cyl2 with cyl3 (which runs fine so the injector must be good) and the misfire stays with cyl2. That rules out the injector as a possibility, doesn't it, or am I missing something?
 
Ah yes I know it, Monaco.

Ah I skim read it, I understood you'd swapped the plug leads and the misfire hadn't moved.

Does it sound normal when cranking it over or does it have an 'easy' spot?

Do you have access to a noid light to see if it's triggering the injector? As it earths it to fire.
 
  172, S2000, S1 Elise
That's the one, Monaco. Hasn't missed a beat since you had it, until this!

Sounds normal to me while cranking, yep. You thinking that would be a sign of low compression on that Cyl?

Na I don't have a noid light, I could possibly get hold of/buy one, but again if it wasn't firing the one injector right, then when I swapped the leads around wouldn't the misfire move with the lead?

Cheers
 
Yes the compression was what I was getting at.

If you swapped the ht leads and it didn't move, that says its it's not the lead or coil at fault.

If you use a multimeter across the 2 pins it should flash voltage if it's receiving a signal when cranking.
 
  172, S2000, S1 Elise
I meant the injector leads - I swapped these around between cyls 2 and 3 and the misfire didn't move...

Haven't tried swapping ht leads around between the cyls, but swapped for a whole spare coil pack/set of leads. No difference. So I think that rules that out.

I guess the logical next thing to try would be a compression test?
 
I meant the injector leads - I swapped these around between cyls 2 and 3 and the misfire didn't move...

Haven't tried swapping ht leads around between the cyls, but swapped for a whole spare coil pack/set of leads. No difference. So I think that rules that out.

I guess the logical next thing to try would be a compression test?
Ah I see. Have you swapped the actual injector from 2-3? If it doesn't move then that pointing towards a cylinder fault.
 
  172, S2000, S1 Elise
Yep, I've tried that too, swapping the injectors over on the rail... And the damn misfire just won't move.

Wouldn't a cylinder fault be more likely to come on and get worse gradually though? The fact it was running perfectly one moment, and then as if a switch flicked, it was running on 3, made me think it was more likely electrical?

Clinging to that hope!
 
In theory, yes but if everything else has changed it's pointing to something mechanical. Especially if you've swapped the injector plugs over and it's still there.

Next step is a compression test..
 
  172, S2000, S1 Elise
Sorted. Compression was identical across all 4 cylinders, so I went back through everything electrical today. It was a dodgy HT lead on cyl2, after all that! (I'd tried my spare set, but not since swapping the injector).

Running perfectly again.

Last couple of Q's.

Can I reset the check engine light myself? Torque on my phone can't reset it.

Also, does anyone know the part number for the metal clips that hold the injectors to the rail?

I lost one...

Cheers
 


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