Yet another Annoyingly French Missfire - Please help Tech Guru's????

[godzillar32]

Guys,

My wifes newly aquired 02 172 Cup had a really really distinct but fient missfire on tickover and if held at a set revs position. Having looked through the cars service history it had recently had a plug change for some pants non NGK items so i replaced the plugs with the correctly gapped NGK items.....after staring the cars missfire was worse then ever...causing the engine to move about on its mounts!! So...I then inspected the HT leads to disciver one had a split in its insulation.....so i replaced them and..........the really bad miss has been replaced with the same missfire as the car came with. So............I bought a new coilpack and fitted that............no improvement!!

I noticed that in the cars history it had had one of the injectors replaced so im wondering.........could this missfire point towards a leaky injector?? Pre-empting this i have bought a complete rail with injectors atatched off a good (i.e properly running) 172. These should be here on Tuesday.

So my question to you guys is this..............is there any other common (Read: French) fault(s) that causes missfires on these engines?

Secondly. In order to fit the second hand rail and injectors I presume the best plan of attack is to unclip the fuelpump feeds and start the car until it runs out of fuel (To Depressurise the system)............then pull the fuel feed pipe off the end of the injector rail and unbolt the 2 retaininig nuts....lastly pulling/wiggling the pre-soaked in WD40 injectors out of the lower inlet manifold???? Does replacement require new O-Rings fitting on the end of each of the replacement injectors followed by copious amounts of WD40 on said O-Rings before re-qwiggling/pushing them home into the manifold??? If I need new O-Rings is there a main stealer part number for them????

Please get back to me as her indoors is desperate to get out an drive this car hard.....but ive said No until we stop it doesn minature scooby impressions!!!!

Cheers Godzilla...........

 

[MarcoB]

I wouldn't bother trying to de-pressurise the system because it only sprays a little bit of petrol. Just hold a rag near when you release the connector on the rail.

Don't use WD40 on injector seals either, use some silicone based lubricant.

It might have no compression on a cylinder so you need to check for that as well.

 

[godzillar32]

I worried about the no compression issue and havent tested but why would the missfire go worse when I installed the new plugs then go better (But still there) when I replaced the HT leads? I would have thought a miss due to low compression (Worn rings) would be constantly the same and would also cause blowby and thus nice blue smoke out of the exhaust???

 

[Kerwall]

No compression doesn't have to be rings. Could be a valve?

 

[godzillar32]

True.............but would it not cause a missfire that was constant? What range of pressure should each cylinder be showing and ill test them tomorrow???

 

[dalealtham1]

Crankshaft sensor
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[godzillar32]

Ive been told the Crankshaft Sensor before. Any chance someone can post up a pic of said sensor so i can spy it on the end of the crankshaft...lol??? Cheers

 

[MG cup]

Its attached to the very top of the gearbox where it joins the engine under the thermostat housing. 95% sure it wont be that, renault or most crankshaft sensor faults are usually bad starting or no starting faults.

Put wd-40 on all electrical ignition connections and injector plugs. Disconnect the injector plugs one by one when the car is at revs that are causing missfire and listen for engine note change. Theres a good chance its one of them as most cars are at the age where injectors are needing cleaned or replaced.

 

[godzillar32]

Cheers Swede...im hoping that is in an injector. As the TDC Sensor was only cheap ive ordered one of those too..........as soon as my secondhand set of injectors arive I will ultrasonically bath them, check the two O-Rings are good...lube them up and throw them in.............lets see how that goes!!

 

[dalealtham1]

Its attached to the very top of the gearbox where it joins the engine under the thermostat housing. 95% sure it wont be that, renault or most crankshaft sensor faults are usually bad starting or no starting faults.

Put wd-40 on all electrical ignition connections and injector plugs. Disconnect the injector plugs one by one when the car is at revs that are causing missfire and listen for engine note change. Theres a good chance its one of them as most cars are at the age where injectors are needing cleaned or replaced.

Had same problem with mine lumpy and running bad. Changed crank sensor n now she's running a beaut!!
​

 

[godzillar32]

Ive just bought this.....Ok its not an OEM one but it should do the job.....I only hope it fits onto my cars loom and doesnt require the "new" Style conversion harness from the Renault Stealer.. http://www.ebay.co.uk/itm/221264094...X:IT&_trksid=p3984.m1439.l2649#ht_1274wt_1170

 

[andy-reid]

Ive just bought this.....Ok its not an OEM one but it should do the job.....I only hope it fits onto my cars loom and doesn't require the "new" Style conversion harness from the Renault Stealer.. http://www.ebay.co.uk/itm/221264094...X:IT&_trksid=p3984.m1439.l2649#ht_1274wt_1170

that will fit but are no different to what you have the MODIFIED one is blue and needs a replacement plug to go with it as the connectors are gold to prevent drop in signal streangth

 

[godzillar32]

Cheers Andy. Im not too fussed about fitting the new design with gold contacts...I just want to fit a brand new sensor so i can discount that as the problem. The second hand injectors and fuel rail have arrived this am. All injectors look fine and the o-rings are ok too so ill lube them up with some silicone grease and fit them later on....weather permitting.

 

[godzillar32]

Im also going to check all of the injector loom for any sign of damage etc.

 

[oknights]

How did you get on? I have a very similar issue at the moment, waiting on a fault reader to see if there is anything it can pick up before I start taking parts off..

 

[JoshOm3]

I had a similar misfire as you've described. Mine turned out to be two injectors not functioning properly. Replaced them and it was cured.

​Fingers crossed.

 

[godzillar32]

I've not changed the injectors yet... its tomorrow mornings job. Fingers crossed too as its getting sledge hammered otherwise.. lol

 

[oknights]

I've not changed the injectors yet... its tomorrow mornings job. Fingers crossed too as its getting sledge hammered otherwise.. lol

Yep I know how you feel! But then it runs ok and I realise why I bought it in the first place!

 

[godzillar32]

I know how great french hot hatches can be but the unreliability and illogical designs properly muck me off!! Let hope its sorted soon.... as I need to fix my GT-R which although usually totally reliable (I built it) has developed an electrical fault!!

 

[godzillar32]

Well guys , problem solved.... it was a faulty injector... ...

 

[godzillar32]

I retract the previous statement as the missfire is back. I took off the Crankshaft Position sensor and the metal tip is rusted to hell.......the Ebay replacement part sent is wrong so I filed the tip of the sensors end and reinstalled it.........missfire still there peeps................. its only minor and the untrained ear wouldnt hear it but I know its there.........and it is DOING my head in!!