High hydrocarbons

[oVerboost.]

Had my car checked today, and found that the hydrocarbons are really high. The car has a very slight misfire at idle which I put down to being a charactaristic of the 172 but perhaps this is more serious.

When driving the car seems fine, and has no misfires or hesitation in any gear but at very low rpm and idle the car has a very slight misfire.

There are no airleaks, the idle control valve is working as it should as is the map sensor and the lamda readings when tested were fine too.

Any ideas? It is booked in on Thursday for a compression test... as I am now thinking possibly a valve or head gasket.

Thanks.

 

[Gaz_]

All info in here

http://www.cliosport.net/forum/showthread.php?t=477295

 

[oVerboost.]

But that does not explain why the hydrocarbons were high, I had it retested today and the car was hot - really hot engine wise had been on an hour drive. Yet the HC level was sky high.

 

[NWPerformance]

When did you last change your plugs?

 

[oVerboost.]

Plugs changed 2 days ago, leads all checked and working correctly and the coilpack is also working fine.

However plug 3 looked quite black in comparison when changed. New plugs did not make any real difference to how the car behaves.

 

[NWPerformance]

Take your map sensor out and clean in. Its near the R on the Renault sport.

 

[oVerboost.]

Done that as well today, with it disconnected it still runs the same.

One thing I did notice was that when you disconnect the lead from the coilpack with the engine running (on cyl.3) the engine sounds the same, which suggests its not doing much. There is a temporary drop in revs but the engine sound etc is the same.

 

[K-Tec Racing]

weak spark, would mean poor burn in that cyl, meaning HC's

you need to check the leads and change the coilpack after that

also check all fuel inj are correctly opperating

 

[oVerboost.]

The coilpack is giving a spark though, to the lead going to that plug.... Would that illiminate the coilpack or not?

I shall try some leads and change the coilpack over as well and see whats what, any other ideas greatly appreciated.

Could it perhaps be an exhaust valve or something?

 

[rob_clio197rs]

check that the spark plug on that cylinder is not damaged, maybe the gap is incorrect maybe too large or maybe its been tapped and the gap is very small like almost touching

 

[oVerboost.]

Plug gaps checked, all correct. Keep the ideas coming though, thanks for all the suggestions and advice.

 

[oVerboost.]

I would of changed the lambda but those readings are okay, and if a catalyst had failed it would be noticable when driving and the other readings would be out too wouldn't they?

 

[NWPerformance]

Is your engine light on?

 

[oVerboost.]

No engine light on, or other warnings. :-(

 

[oVerboost.]

Also just having a play around with the ht leads on the coilpack, swapped 1 and 2 and 3 and 4 around and it makes no difference is this normal?

 

[oVerboost.]

Does anyone know how much the hc level would drop at a fast idle (mot type) rather then standing idle at 700rpm?

 

[oVerboost.]

Injector fault?

Still got no further with my misfire at idle, and high hydrocarbons (Hc).

After doing some research today, Im wondering if it could be the injector at fault? Are these common anyone else had any problems with them before?

The lead going from the coilpack to the plug/cylinder when removed makes no change in engine noise, yet when you remove the others the engine drops noticably and almost stalls.

Under acceleration the misfire goes away, so maybe a clogged injector or a fault with the wiring?

Any experience of similar problems anyone? Thanks.

 

[legohead01]

Re: Injector fault?

im havin the same thing mate. put off the plugs for the injectors 1 at a time see which 1. i have this b4 and just changed 1 injector but now its a different 1 now so replacing them all this time.

starting to become a comon fault in the last few months.

 

[oVerboost.]

Thanks for the info will try the injectors tomorrow, doing a compression test as well just to make sure. Fingers crossed!

 

[JonC]

It could also be the CAT and/or the lambda sensors. My last MOT reported high really hydrocarbon and CO. Took the car out for a real good blast for about a hour and took it back to the MOT centre and passed with normal readings.

 

[oVerboost.]

JonC - what was your idle like and did it misfire? It was quite hot and had been driven hard for a while before the hc were checked... I am going to check the injectors tomorrow and do a compression test to rule out a valve. Thanks.

 

[oVerboost.]

Well the compression test confirmed my fears, it has to be a valve at fault. 160 on all cylinders except the faulty one which is 110. :-(