STill experiencing slight misfire type fault ....HELP

[roadrunner_182]

I posted a while ago about a fault that had developed on my 172, the car started to misfire in 3rd gear, eventually got so bad car would barely drive, kangarooing then eventually died.

Took to local garage who replaced coil plugs and leads, problem persisted and actually worsened car would start and if it did would stall.

Took to renault specialist, they played with the cam sensor and loom and car started straight away, but misfire remained, no fault codes whatsoever at any time during problems. Renault specialists found problem with 1 injector so replaced it. Car appeared much improved, however low down misfire / cough remained.

Took back to renault specialist, who replaced all remaining injectors. Ive since had car back, but the problem is still fu*king there, its so frustrating. ALthough its greatly improved if i remain in say 3rd gear at low revs then push the accelerator, its seems to hesitate / cough slightly then picks up fine, ive lost confidence in the car completely.

Booked into another specialist next week Birchwood as im all out of options really. The fault is so intermittent and not throwing codes that most mechanics are scratching their heads! Anyone got any ideas? Ive done a search others with similar faults have had it rectified after replacing injectors or cam sensor?!

 

[MicKPM]

Problem 1:
If they're looking for codes on what is most likely a mechanical issue rather than an electrical issue they're bound to fail.

Problem 2:
You really shouldn't keep taking it to different people; Pick a "Specialist" you trust, stick with your decision and let them see the job through.

My advice, which you or anyone else is welcome to disagree with is if it's an electrical issue then it really should go somewhere a little more electrically biased rather than a jack of all trades grease pit garage. People put too much stock in the term "diagnostics" and assume it will tell you exactly what is wrong in seconds which it won't especially as in most cases "diagnostics" simply means the garage employee plugging in a Launch, Solus or Vantage device and "Code Reading" because they're ignorant on the subject and can't use the equipment properly so don't know any better. The basic mechanical condition of the engine should firstly be checked; that means engine compression and confirming correct timing before then moving on to the electrical items. Ignition and injection drivers need scoping along with the vehicles main trigger pattern to ensure they wave forms are right and in sync (for this you'll need access to a decent bit of kit with 4-channels as 2-Channels won't allow you to overlay the lot). Then, as it appears to be load related (from previous posts) the fuel pressure and MAP sensor, including the rubber seal and associated wiring should be checked as it could be a simple fault with this sensor itself OR it could even be the ECM at fault. What "Cam Sensor" did they play with exactly as the F4R doesn't run a dedicated camshaft position sensor?

Mick

 

[davemittell]

Where in north wales are you and where have you been with it?

 

[roadrunner_182]

Hi Mick,

I think the reason they are pointing more towards electrical, is due to the fact the problem is intermittent, they said if the injectors didn't solve the issue they would be scratching their heads really and they think the issue is going to start becoming expensive as all the common parts have been replaced, next would be ecu etc...

The first garage i went to were shocking, never will i set foot there again, they had shi*e diagnostics equipment and skills, they just replaced parts and hoped for the best, told me it was fixed for me to drive 100metres and it to die on me! This is the reason i moved it to another more specialised garage they had the proper renault diagnostic tools, they hooked it up to an oscilloscope etc found no issues and they advised me that they might not be able to get to the bottom of the issue! I feel my hands are tied really as im not a mechanic and just want the car sorted without having to replace parts hoping its going to resolve the problem!

The sensor and loom replaced where from the tdc sensor, apparently this is connected to the gear box, what they did say was that upon inspecting the sensor it was faulty but also it appears the gearbox had been out at some point in the cars life and some1 might have dropped it as there was only one bold holding the sensor in place, the other had been sheered off, so they replaced the sensor and secured it with 1 screw , hooked it up to the oscilloscope to check it was working ok and all seemed fine. Prior to replacing all injectors they were apparently showing fine?!Where is the map sensor located and what is the ECM?

Thanks for your help by the way - appreciate it! Im fed up with the car now seriously considering getting rid....

 

[roadrunner_182]

Im near Rhyl, been to a garage in Denbigh - complete waste of time, and ended up in reno tech in llandudno

 

[MicKPM]

I sympathise mate as these intermittent problems are indeed frustrating for everyone involved but keep with it and don't let it put you off the car. From the sounds of it the second place (reno tech?) do know their stuff if they're even in possession of a scope so let them at it again.

First thing I'd suggest you get fixed: "CPS" mounting.
If the crank position sensor is incorrectly secured it will give nasty, unwanted results as it will lose resolution as it moves away (or closer) to the target on the flywheel so this should be the first thing you rectify... take the sensor off the gearbox and have the snapped bolt removed. I know, its hassle but by doing this and ensuring the CPS is correctly secured will rule out and basic but essential signal that the ECM (Engine Control Module or ECU) needs to be able to correctly control the ignition and fuelling so could be the root of your problems. I've seen these "secured" by one bolt before and it still allows for the silliest bit of movement but thats all it takes sometimes to fudge things up.

Mick

 

[roadrunner_182]

Yea, ive taken your advice and booked it back in with them as to be fair they have been great so far just one of those problems thats not been easy to identify.

Just a query with the CPS mounting, apparently the gearbox housing is cast iron and the broken bolt cant been repaired for some reason, as i asked this when it was first identified and they said it would need a new gearbox to rectify the problem. They said the same, a tiny bit of movement can cause problems but the scope readings when testing showed it was all ok, and they dont want to start changing things (mega bucks wise) and it not resolve the problem...so im into catch 22 really.

 

[lemonnobby]

it is a cast but not iron. you could drill it out or drill it out and helicoil

 

[MicKPM]

It may not be moving when the car is running and standing but when its moving, say you hit a bump, it could force it to vibrate and so move. Like throttle position sensors any kind of abnormal movement in the mounting or assembly effects the output signal and so causes running issues which is why they need to be solidly mounted. Wouldn't even have to helicoil it, its an aluminium cast so would simply take a re-tap as the old bolt *should* come out with ease and there's enough room in there with the battery and airbox out to get full access. Just don't touch it with a hammer or else it'll snap the lug and then you are bolloxed!

Mick

 

[roadrunner_182]

Yea this is what im worried about, from what i can gather the damage to the bolt is beyond repair as the garage said it looks like something has snapped off :-s so it may be a case of having to replace the whole gearbox even though the internals are in perfect working order i might just have to get rid instead, ive injected almost a grand into it already...

 

[davemittell]

Well I'm only based in Buckley which is about as far as llandudno is from you.
I have a scope! And the knowledge to use it! Also have clip.
If you still have no joy with the other place look me up serviceyourcar.co.uk I will happily take a look. I am not one to guess at diagnostics and I am an ex renault mechanic and enthusiast. Can probably come up with a decent fix for the crank sensor lug too! This could be the root of your problems. Just looking and it may be possible to weld another lug to your box in situ or fabricate a bracket to compensate for the lug if it is missing.
Sometimes a fresh approach is needed starting at the basics.
pm me for more details if your getting stuck!

 

[MicKPM]

It will need TIG welding if you try but agree, a bracket *could* help resolve the issue if it rules out movement and ensures the correct positioning.

 

[roadrunner_182]

Just an update for anyone who may be experiencing a similar issue.....

The problem started with a misfire type symptom kangarooing and not starting, took to a local garage, that did not correctly diagnose the problem as having a faulty tdc sensor, and so decided to replace coil plugs and leads, to no avail.

Towed car to Reno-Tech Llandudno North Wales, they identified the fault, replaced the sensor and loom, however a slight misfire remained. Garage asked me what had already been replaced; I advised coil plugs and leads. No fault codes were showing, and no problems were showing when connected to a scope.

Reno tech checked injectors, found slight fault with one and replaced it, car ran better, misfire remained. Mechanics were at a loss as to what to replace next, replaced ecu with one off another 172, misfire remained, so this eliminated the ECU.

Eventually mechanics at Reno Tech had hit a wall and were at the point of considering trial and error repairs as all other parts had been replaced, as a last ditch try before spending major bucks mechanics suggested ordering new leads as the ones fitted in other garage did not seem to be sitting correctly, also new inlet gasket due to the amount of times it had been taken off it could have lost its seal.

Night before it was due in the garage, misfire came back worse, eml flashing indicating misfire; car limped home, towed to Reno – Tech next day. Fault code showing misfire cylinder 1…..turns out it was all because of the shitty non reno leads fitted by the first garage, they hadn’t been fitted in place correctly and had been causing the misfire, cylinder 1 lead had a hole through it and covered in soot like powder.

Replaced with Renault leads, misfire has now gone completely - thank god for that.

Went back to original garage and thanked them for misdiagnosing initial problem and shoddy workmanship with cheap parts, demanded money back for leads.

If your experiencing a similar fault, and have exhausted all other possible causes, just double check those leads. I could have saved a fortune.

Lesson learnt there are garages and garages….initial garage also dented my bonnet…great! So if anyone knows of a bonnet in silver going cheap pm me please

Thanks to everyone who offered advice on here anyway!