renault clio 1.4 priviledge - Lambda sensor & misfiring - burge

My son has been experiencing rough running at tickover, we took it to the garage and their scanner indicated that the pre-cat lambda sensor reading was all over the scale, they replaced the sensor but this did not improve things the readings were still way out, so they got another in in case this one was faulty and the same has happened again. has anyone experienced this problem that can help us sort it out.

Thanks Burge

renault clio 1.4 priviledge - Lambda sensor & misfiring - unthrottled

Then the lambda sensor wasn't faulty! Didn't they test the sensor to see if it was working?

Let's start with the obvious: is there a leak in the exhaust upstream of the cat? Partial vacuum pulses at low load can draw air into the exhaust confusing the lambda sensor.

Failing that, is there a consistent misfire in one of the cylinders? This would pump air and fuel into the exhaust, again confusing the lambda sensor. Take the plugs out and examine the tips-they should all be tan brown. If one of them has a very different colour to the others-that cylinder has a problem.

Moving further upstream, the fuel pressure regulator could be faulty (unlikely) or the MAF could be dirty/malfunctioning.

No, changing ther air filter will not help matters!

It's disappointing that the garage assumed that the lambda sensor was faulty simply because the readings were out of range.

renault clio 1.4 priviledge - Lambda sensor & misfiring - burge

The garage said they do not have any means of testing the sensor, I have checked around the engine and cannot find or hear an air leak, the plugs all looked the same not tan though more dark, anyway as I had a new set I put them in, this has made no difference! in the days before my son got the misfire he said that he had been getting a slight hesitation when pushing the throttle pedal down. at present trying to work out which bit is the maf sensor so that we can take it off for a clean, I believe I can use carburettor spray on it is this correct?

Burge

renault clio 1.4 priviledge - Lambda sensor & misfiring - Railroad.

A very typical example of a garage that does not have a clue about engine management systems. Sadly they are not alone either. They plug in the scanner and there's a mention of lambda sensor. They take this as gospel and assume it's faulty, whereas in fact the sensor is reading correctly telling the story as it is, and the fault actually lies eleswhere.

The oxygen sensor on your car contains zirconia which is a substance which is sensitive to oxygen. As oxygen passes the sensor small voltage is produced. The more oxygen the higher the voltage. The sensor actually compares the oxygen inside the exhaust with ambient oxygen outside. Since a richer mixture consumes more oxygen than a lean one If there is little difference (low voltage) the ECU knows the mixture is rich. If the difference is high then it knows the mixture is lean. Prior to this the ECU needs to know engine speed and position, throttle position, mass air flow for load and the temperature of the intake air as well as engine temperature. With this information it can calculate how long to keep open the fuel injectors to provise the precise quantity of fuel for all engine conditions in real time. Longer injector duration means more fuel injected, and shorter means less.

The oxygen sensor will continuously switch from low to high and back (0.1v - 1v) as the ECU richens up and leans off. This cycling is known as 'Closed Loop'. If the engine is running badly because of a misfire due to a faulty spark plug or coil, or incorrect valve clearance, air leak, fuel pressure fault etc then the closed loop system will not happen. The sensor readings will be erratic and a fault code relating to the sensor may be generated. This does not mean that the sensor itself is faulty.

Most oxygen sensors have 4 wires. 2x white which are a 12v supply for the heater circuit and ECU supply voltage. Black which is earth and grey which is the signal return to the ECU. Use a voltmeter to see what the sensor is doing by probing the grey wire and earth. As I mentioned earlier you should see a continuous rise and fall between 0.1 and 1 volt DC.

renault clio 1.4 priviledge - Lambda sensor & misfiring - burge

Thanks for all that info, only problem is I am good with old car oily bits but come unstuck with these modern one's and would not even know where to look and maybe even making things worse, plus do not have a voltmeter with probes. If you could recommend a good diagnostics firm in the Grimsby area so that I can get it checked out if that is not to much trouble, I do not know if you carry lists of professionals that come recommended!

Thanks burge

renault clio 1.4 priviledge - Lambda sensor & misfiring - unthrottled

Hmm. You say it is running rough at idle, what about under load?

Are all of the spark plugs fed by the same same coil pack (if it isn't a distributer)? I wonder if a weak spark is causing misfiring. That would explain blackish wet plugs.

Does the exhaust smell 'fuelly' ie is it obviously running rich (although misfire can also make an exhaust smell of fuel)?

I'm betting this problem is simple and well within the bounds of a DIY mechanic.

renault clio 1.4 priviledge - Lambda sensor & misfiring - burge

all the plugs are fed from separate leads which end with a coil pack bolted over each plug, and yes there was a smell coming from the car after it came home but I'm not sure it smelt of petrol.

Burge

renault clio 1.4 priviledge - Lambda sensor & misfiring - unthrottled

Ah, coil on plug-so it's a bit newer than I thought-I must have been thinking of the old liberty.

Well, since they have their own coils, they are unlikely to all be misfiring. The MAF is situated upstream of the throttle body. You could try cleaning that next!

renault clio 1.4 priviledge - Lambda sensor & misfiring - burge

sorry missed first bit when under load! it seems better when doing about 50mph there may well be a misfire but it does not seem noticeable not like when you have a plug down. just going out to see if I can locate this maf, in the haynes it mentions a map but not a maf are these one & same?

Burge

renault clio 1.4 priviledge - Lambda sensor & misfiring - injection doc
renualts are very good at storing onformation about misfires ! even on one or all cylinders as it uses the crank sensor signal to detect the misfire and even counts how many times the misfire has occured.
I would suggest a good diagnostic tech to scan the vehicle and read the live data.
It sounds like your original garage hadnt got a clue about diagnostics. It really does sound more like it has a small air leak ! could be pin prick size ! that would cause a hesitation and throw the lambda out.
All the diag tech has to do is to look at long and short term fuel trim calculations and this will soon show up where to look ! they should also check coolant sensor live readings and map sensor reading as coolant sensors are common place on renualts , often read widley out but do not flag up a fault !
renault clio 1.4 priviledge - Lambda sensor & misfiring - unthrottled

no, MAP and MAF are not the same thing. For one thing MAP is located after the throttle plate and measures Manifold Absolute Pressure. the MAF is before the throttle and meassures Mass Air flow. Immediately after a cold start and during hard acceleration, the ECU uses the MAP to estimate air flow and calculates the amount offuel required.

During normal operation, the MAF provides a more accurate estimate and the ECU uses the MAF to calculate the fuelling. The lambda sensor in the exhaust is just a feedback loop to ultra fine tune the fuelling. It has the 'authority' to change the fuel trim by about +/-10%. Outside of thatthe ECU will assume that the lambda sensor is talking b***** and will ignore it!

Back to the leaky exhaust. At idle, the leak will tend to be going IN to the exhaust-so you won't hear it. Try getting an assistant to plug the exhaust briefly with a rag while you listen. It's as well to be sure of the simple things before the diagnosis by buying new stuff starts. Everyone worries about how hard the electronics in modern cars is to understand, but on the whole it works very well.

renault clio 1.4 priviledge - Lambda sensor & misfiring - burge

have tried the exhaust test and could haer no leaks, clean out what I thought was maf sensor but still no joy. then was given a garage that was good by a neigbour who used to run one. the end result is the problem has now been sorted, I took it to them and they did a scan and agreed that the lambda was getting a indication that there was a problem upstream, from their experience they tried a few things and came up with trying a new coil pack on each cylinder it turned out to be the last one was breaking down and giving an extra pulse therefore causing the misfire, this error never registered on the scanner.

Thanks for all the help. Burge

renault clio 1.4 priviledge - Lambda sensor & misfiring - unthrottled

Glad it's sorted!

renault clio 1.4 priviledge - Lambda sensor & misfiring - Railroad.

The ignition coils on Renaults are wired in pairs (cylinders 1 + 4, and 2 + 3), and each pair are also wired in series. This can lead to a little bit of confusion when trying to establish which coil is actually faulty. They do commonly fail, and I'm glad you managed to get to the bottom of it.

renault clio 1.4 priviledge - Lambda sensor & misfiring - unthrottled

That's what I assumed-but newer cars use fully sequential ignition ie one coil per cylinder.

 

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