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Discussion Starter · #1 ·
Hi all,

I have an intermittent start problem with my Megane cabriolet 2.0 IDE (manufactured 2002 with 85,000 miles on the clock). The car can start up perfectly for a number of times then at random it will not start (the engine cranks over well and the dash board lights display ok and no warning lights are shown). This problem first occurred a year ago. I called the break down assistance out who jumped started the car from their recovery vehicle whilst I cranked the car over thus spinning the engine over faster and the it started and was advised that it was a crankshaft sensor problem and this was a common problem with this car. I had a new sensor fitted and all was good. 3 months later it would not start again so I called out break down assistance and whilst I cranked the engine over he pulled at the crankshaft sensor and it started. I was advised that it was either a bad crankshaft sensor or the sensor plugs were not good and so I should replace the sensor and also remove the connector plugs and hard solder the wires together. As a simple and cheap fix I did this which worked for 3 months or so then the problem occurred again.
The problem now occurs in every 3 in 10 start-ups or so. The problem can occur at any time under any condition, eg it can be a warm or cold day, wet or dry, on a cold start or after driving an hour or so and filling up at a pump station. When it won't start you can wait for 1/2 hour or so then it will start with no problems. Or sometimes it won't start even after trying over a number of hours then suddenly the next day it starts up perfectly. I have had 2 garages look at the problem who cannot identify the problem, the last one saying that they have no idea and could be a loom or ECU problem.
The last time it would not start the break down recovery could not start it however they did spray easy start into the intake manifold and the engine ran for a few seconds before dying out to me indicating that the ignition, coil packs, sparks, crankshaft sensor is all ok and that the problem is fuel supply related. They also pulled off the fuel line feed going to the high pressure fuel pump and fuel pumped put well indicating that the fuel pump is good. The car had to be put on the back of a trailer and brought home where upon the next day the car started perfectly well.

So does anyone have ideas of what could cause this problem. I contacted the local Renault dealer to purchase wiring diagrams for this vehicle but they referred me to the Haynes of Megane mk2 manual which is of no use. I have read up in this forum about IDE valve problems and have seen a Renault bulletin which identified this valve as being a weak point and can provide starting issues but without any fault codes showing I am initially at a loss as to where to start the check. The car runs perfectly apart from this start up fault.

Thanks for any guidance that you can provide!
 

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As one of the garages, I also think it is an ECU or wiring problem.
Indicative is that engine started with easy spray which means all is good, spark is created but there is no fuel injection.
Lots of useful info here

Fuel pump is supposed to be good so you can measure voltage on either of injectors to make sure that they are not activated, no fuel is being injected and engine would not start because of that.

To do that, you can use 12V probe with light (light on when 12V measured) or multimer. Reading of above 5V on injector pins during cranking means injectors are working. If not, they are closed, no fuel is injected and engine does not start.

Again, that comes from faulty crankshaft sensor.
Sensor itself, wiring or some of the connectors is losing contact, engine computer does not get signal, it does not know that engine is cranking and it does not open injectors for fuel delivery.
That is the safety measure, all other relays are closed, coil is producing spark but injectors are dead.

How to solve this, that's another problem.
Three new wires from ECU to the crank sensor would hopefully solve the problem. Doesn't matter where you pull them or how thick they are. It is a small voltage and low current, any good wire will do.
Problem is, which ECU pins are connected to the crank sensor. Without proper shema, I am helpless.
 

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Found one but it doesn't help much.

Top picture is for K4J and K4M engines.
Second is F4R engine electronics diagram which is useless.
Crank sensor is modul 1 and is connected to ECU by two wires, designated F3 and E4 (I think).

No color, no ECU pins, nothing. I can not see which wires are connecting ECU with sensor and until we find a good shema, no luck. Unless you want to dismantle whole wiring and test-find which are the wires we need.
 

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Discussion Starter · #4 ·
As one of the garages, I also think it is an ECU or wiring problem.
Indicative is that engine started with easy spray which means all is good, spark is created but there is no fuel injection.
Lots of useful info here

Fuel pump is supposed to be good so you can measure voltage on either of injectors to make sure that they are not activated, no fuel is being injected and engine would not start because of that.

To do that, you can use 12V probe with light (light on when 12V measured) or multimer. Reading of above 5V on injector pins during cranking means injectors are working. If not, they are closed, no fuel is injected and engine does not start.

Again, that comes from faulty crankshaft sensor.
Sensor itself, wiring or some of the connectors is losing contact, engine computer does not get signal, it does not know that engine is cranking and it does not open injectors for fuel delivery.
That is the safety measure, all other relays are closed, coil is producing spark but injectors are dead.

How to solve this, that's another problem.
Three new wires from ECU to the crank sensor would hopefully solve the problem. Doesn't matter where you pull them or how thick they are. It is a small voltage and low current, any good wire will do.
Problem is, which ECU pins are connected to the crank sensor. Without proper shema, I am helpless.
Hi Moxinel and thanks for the message.

The above makes good clear sense and something that I will first try and should not be too difficult (initially I ruled out the crankshaft sensor/cable as being suspect which would have took me off in a wrong direction). As the problem is intermittent I can use this to my advantage, eg take the readings at the injector and crankshaft sensor when I know the car starts ok and then when the problem occurs I will retake the same readings and compare the results. Hopefully it will be a break in the sensor cable which should not be to difficult to fix. I will post my findings/update when I perform the checks and hopefully with success :)
 

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Discussion Starter · #5 ·
Found one but it doesn't help much.

Top picture is for K4J and K4M engines.
Second is F4R engine electronics diagram which is useless.
Crank sensor is modul 1 and is connected to ECU by two wires, designated F3 and E4 (I think).

No color, no ECU pins, nothing. I can not see which wires are connecting ECU with sensor and until we find a good shema, no luck. Unless you want to dismantle whole wiring and test-find which are the wires we need.
Thanks for digging this up. My car is a Megane-1 and not mk2 (the 2.0 IDE refers to the engine size and model which can be confusing). The engine I have is F5R so will refer to the F4R schematic and hope they are similar. I have crawled through the internet and forums for wiring diagrams for this model but there is nothing and others have reflected this. Luckily I have time at the moment so will attempt to test find where sensor to ECU pins... Or I might strike lucky and visually see a break in the sensor cable (fingers crossed).
 

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F5R is a derivation of F4R.
Engine head adjusted to accommodate direct injection, HP fuel pump, different pistons but basically, it is F4R (block, crank, rods,...).
Lots of stuff for F5R here


Cars with that engine are even fewer and nothing comes out on google. Maybe if you try searching for Megane I. Any decent plan should have all types of engines and electricity.

Apparently, only 2 wires to crank sensor. Don't know which type but you can try finding wires of the same color running to ECU. That comes tricky as there are many shades of same color and if you cut the wrong one, hard starting may become least of your problems.
 

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Hi Moxinel and thanks for the message.

The above makes good clear sense and something that I will first try and should not be too difficult (initially I ruled out the crankshaft sensor/cable as being suspect which would have took me off in a wrong direction). As the problem is intermittent I can use this to my advantage, eg take the readings at the injector and crankshaft sensor when I know the car starts ok and then when the problem occurs I will retake the same readings and compare the results. Hopefully it will be a break in the sensor cable which should not be to difficult to fix. I will post my findings/update when I perform the checks and hopefully with success :)
I am positive that no signal from crank sensor equals no fuel injection.
You will find those in relation and such a problem you have, 10 times nothing and then all of a sudden engine starts like new, is a model behavior for that.

You problem reoccurs every 3 months. Look for a sensor wires or harness that is touching car body at some point. Maybe rubbing against it, takes time to bite through and spoil the signal. Or some other part leaning against wires, worth looking into. Would save you a lot of trouble, then you need just a new sensor and a wire fix.
 

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Discussion Starter · #9 ·
I am positive that no signal from crank sensor equals no fuel injection.
You will find those in relation and such a problem you have, 10 times nothing and then all of a sudden engine starts like new, is a model behavior for that.

You problem reoccurs every 3 months. Look for a sensor wires or harness that is touching car body at some point. Maybe rubbing against it, takes time to bite through and spoil the signal. Or some other part leaning against wires, worth looking into. Would save you a lot of trouble, then you need just a new sensor and a wire fix.
Hello Moxinel,

Thanks for all the useful and knowledgeable information that you have provided.

I have not had the start problem since posting on this forum though I have taken of 1.9v from the crankshaft sensor plug to earth and will see if this changes when the start problem occurs. I cranked the car over with the crankshaft sensor disconnected and when spraying easy start into the intake manifold and the engine ran for a second or so replicating the problem and pointing to the crankshaft sensor cable or ECU being the suspect as you said.
Whilst the car is still starting ok I attempted to trace where the crankshaft sensor cables went to the ECU and it was not very successful and I was getting readings that I was not expecting (eg finding low continuity from the crankshaft sensor plug to many different pins on the ECU plug). I was hoping to see 2 pins on the ECU plug with good continuity to the crankshaft sensor plug identifying the pins but this is not the case.
A good looking over the whole wiring harness shows the wiring harness to be in bad repair, eg many sensor plugs are showing bare wiring entering the plugs, there are multiple repairs throughout the main harness and wiring has been cut short then re extended with different colour wires but badly connect and covered with insulation tape. I have found a second hand wiring harness for just over 100GBP and am thinking of replacing the whole harness due to the state of the current harness. Am thinking that i can more easily give the replacement harness a though check over and clean up on the bench and maybe map out where the wiring connects to on the ECU prior to installation. So is installing a replacement harness something that is possible for an amateur to do or would it involve problematic areas or requirement of special tools. For instance, I am not sure how difficult it would be to replace the harness to the injectors as these do not seem to be easily accessible.

Thanks again for any guidance that you can provide.
 

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Never did such a job. It all depends on specific type, how many loops you have to go through, behind the radiator, below brake lines, lights, horn, several sensors etc.
But in general, harness from cabin to the engine bay is single bundle going through firewall and then spreading around.

As for crank sensor, you can not measure that while ECU is connected.
If ECU is powered, then it is probably sending 5 Volts (or 1,9 as you measured) and you can not measure continuity. Only way to do it is to disconnect ECU and then measure from crank sensor to the connector for continuity. And even that may be false reading if shaking from driving is creating contact somewhere that you can not see.

Sorry I can't do more, but one advice.
Before buying new harness, make sure it is absolutely the same like one you need.
 
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