Hello All,

I have recently become the owner of a Dacia Logan 1.4 mpi (benzine). The car is from 2006 and has, as of now, 126 000 KM on the dash. Unfortunately, we began to have problems with the car fairly soon after we bought it. The problems may not be related to eachother, but they come in this form:

1 - Intermittent misfire (when starting the car and putting some load on it when cold the engine light starts to blink and shortly after stops. My cheap OBD scanner diagnoses this as a Cyclinder 4 misfire fault code).

2 - roughness at idle and when stopped. This comes in the form of a vibration sometimes stronger and sometime weaker, but constant. Engine temperature seems to not affect this issue and it is most apparent when at stopped at a light. Clutch engaged or disengaged does not affect the vibration. The vibration disappears when putting load on the engine.

3- Sudden stalling at cold temperature. When driving down the road shortly after cold start and putting some load and raising the revolutions on the car if i engage the clutch and hold it pressed down the revolutions will zero out (i see the dial just go down to zero) and the engine will cut out. This only happens when cold and once the engine reaches normal operating temperature this problems disappears entirely. The solution for this is that when i need to stop upon cold temperature i use the engine break and do not allow the revolutions to reach the zero mark.

Things that i have changed after lots of researching on the internet:

Air filter
Intake air temperature sensor
Throttle position sensor
Manifold air pressure sensor
Crankshaft position sensor
Entire ignition systems (coil pack/bobine, spark plugs, spark plug leads)
IAC valve
I have taken apart and cleaned out the entire air intake manifold to the best of my capabilities.

Checked engine mounting, as possible cause of vibration, and they seem in perfect shape

Checked all relays and fuses for the injection system and fuel pump and they are ok

I have used two treatments of fuel injector cleaner and checked resistance of all injectors and they are within specifications of the logan manual.

Cleaned all harnesses on fuel injectors.

Checked for vacuum leaks but this engine does not have many vacuum hoses to check.

Things which i have not yet changed/done but might be the cause of the issue:

Upstream O2/Lamba sensor (even though i have run several time tests on this sensor through the OBD scanner and I get good feedback from this sensor) I have a new one of these but havent managed to take the old on off the engine as it is rusted in place.

Fuel pump

Fuel injector(s)

Compression test on the cyclinder to see if the issue is mechanical.



I m not really sure at this point in which direction to continue and any advice that someone who had the same issue and managed to solve it could give would be very welcome.

Thank you very much in advance.

Regards,


Mark

swicth between nr 4 fuel injector and nr 1 and see if fault follows the injector. Be carefull of orings when pulling injector out of the fuel rail. If fault switches to nr 1 cilinder, replace faulty injector. If not, check for mechanical issues (tight valve clearence, low compression) on nr 4
do you have LPG on it also? If so, some ecu parameters might us ea reset before anithing else.
good luck

Hello,

Thank you very much for your reply. I appreciate it. I will try to see if the injector might be the problem. I considered doing this procedure before, but having no way of relieving pressure (unfortunately it is not clear to me which relay controls the fuel pump) from the fuel lines i somewhat gave this up.

About LPG - the car has no LPG

I will try to see if i can find a way to carry out this procedure and carry out your suggestion.

Thank you

maybe it's the catalyst converter...

Good Morning,

Thank you for your answer.

I understand that the repeated misfiring might damage the catalytic converter, but how can a faulty cat affect the overall performance in this way. is it plausible?

Also the rear end O2 sensor has been monitored quit closely by me. The voltage reading according to my information is good and it doesnt seem to me that (high amounts of) raw fuel is getting in there or anything that might damage the catalytic converters performance in any way. I might have to check this again as it has been a couple of months since i did this inspection.

Personally, I think this is an injection problem overall. I think that the misfire is a lean misfire caused by a clogged or partially clogged fuel injector(s). When the misfire occurs and i read the freeze frame data from the OBS tool the fuel trims are showing lean mixture (negative) in all cases. When the engine is cold before the O2 sensor kick in i believe the ECU is programmed to apply a biased rich fuel mixture until it is in open loop. Since the injector might be clogged then it might be that not enough fuel is getting into the injectors, and therefore cyclinder, to keep the power in the car when load is relieved (stalling issue.)

The shaking at idle/stopped could also be cause by a clogged injector relieved from load being shy and not spraying enough fuel into the cyclinder causing this shaking condition and causing the O2 sensor to go crazy while trying to adjust for this condition.

It would be nice if someone could confirm my logic


I have booked myself in for a inejctor check at a local mechanic and a thorough fuel system cleaning. I think that it is the best place to start as proposed by Einstein

You have figured it out, kudos!, the clogged injector is also my guess.

Hello,

Thank you for your answer. I appreciate it. I will post something after the diagnose from the shop to update on whether the issue has been solved or not.

Regards,

Good Evening,

Quick feedback on the issue below. Turned out that this was not an issue with the injectors in the first place.

We brought the car to a mechanic who had experience with first generation renault engines and he immediately saw the issue that so many meganes and clios had before:

VALVE MIS-ALIGNMENT!!

The previous owners of the car never had had a proper service done to the car and the exhaust valves were completely out of standard. This was more pronounced when the engine was cold and repeated misfire + engine stalling occurred until the engine heated up to operating temperature and the metal components of the cylinders expanded just enough to make the problem disappear.


The man popped open valve cover, calibrated the valves and that was it. Problem solved.

If you are experiencing similar problems as the one we had the above is definitely something to keep in mind

if the injector permutation turned out same result, that would have confirmed a mechanical problem so probably valves.
glad you solved it.

Try using a petrol with the least ethanol. Ethanol attracts humidity and so causes low temperature misfiring. It certainly helps with older vehicles.
Here in France, the 98 octane is best.
Bon Chance, Barrie