REnault Megan 2000 Misfire

[Vincent]

Hi all, Love the vids so thanks ALOT for those.. actually got me thinking about leaving my design job and picking up the wrench for a living… get of that tangent Vincent!

So the car throws up an electrical problem light, the battery symbol and the STOP light persistently flash. That is unless revving hard, they will go out briefly but come on when back to the very rough idle speed. The headlights, clock and any other light flashes the same frequency as the stop and battery warning lights. The problem cylinder is number 3, diagnosed via power balance test (thanks for teaching me that one Eric). I pulled out the sparks, number three is decidedly more dirty but it does still spark with a healthy colour after a clean.

Next step, I am thinking (hoping) it is a faulty injector so I had a listen to them all. Great I thought, number three is not making a clicking sound and the others are.. got to be the problem. Now, for some reason, before making the purchase of a new fuel rail I would just double check the next day as I was in a little bit of a rush the first time round. Unfortunately, I can now hear all four injectors clicking away. What happened, I am thinking I just didn’t put the driver on the right part of the injector before hand. Although, number 3 injector does sound a bit quieter than the others so perhaps it is a bit clogged or has a warn mechanism or just an intermittent fault. The Stop and battery lights are still flashing even when I can hear the injector click.

I have purchased a multimeter and heard the beep on all four injectors to confirm continuity.

What ohh wise ones of mechanical joy should be my next step? Get a compression tester to check the suspect cylinder or just whip out the injectors and give them a good old clean whilst checking they are firing properly?

Thanks for all the pointers in advance, I know my way around a bike but fairly new to cars. Would I need to depressurise the fuel system before removing the rail or can I just go for it with my eyes squinted?

Vincent

Topic

[Daniel]

Well the battery light is probably just a result of lower than normal idle speed. Hopefully that will go away after the engine is back to health.
I wouldn’t worry about a compression/leak down test right now because (unless you are getting sooty, blue-ish, or odd smelling exhaust) we have no reason to think compression might be an issue.
Try pulling number three fuel injector and trade it places with, say, injector two. Clean the plugs, run the engine for a while, then pull plug two and see if it is fowled like three was. if it is, you know the injector is faulty.
You could try soaking it in carb cleaner or acetone to clean it out, but most likely it will need to be replaced.
If you have the money, and think the car is worth it, change all four. Keep in mind that replacing all four is not necessary at all, but it might make the engine run a little smoother by keeping all cylinders balanced.

For a novice you seem way ahead of the curve. Be careful where and who you get advice from. The internet is full of people who think they know what they are talking about. I’ve found this forum pretty reliable.

Good luck. Let us know what you figure out.

[Vincent]

Hi,

Thanks for that fast reply! I agree, swapping the injector seems like a good idea. I unfortunately do not think it is as simple as just pulling it out and sticking it back in and I think I have to remove a fair amount of the inlet to get at the rail which must be removed before the individual injectors. Just a little concerned with the whole fuel pressure issue, I just don’t know if we are talking 200psi or just enough to get to the injector?

Thats good to hear about changing one and not all four, I guess it makes sense for a supplier to encourage changing four at a time. It does make sense to do that on a new model but not a 14 year old car.

Thank for the knowledge cred… I have read some awful advice on other forums that just didn’t make any sense. I will keep you posted with what I find on the weekend as this does sound like a dirty Sunday.

[Jon Hart]

Might be worth checking the injector wiring using a noid light quick and easy to do and will tell you if you are getting the correct pulse frequency and duration from signal to each injector.

Swapping injectors out isn’t always that simple cant be 100% sure on that car but most modern cars the injectors are coded to the car and the cylinder so swapping them around isn’t an always an option.

Check your coils/ht leads as they can also present a misfire.

As for the fuel system the system should only pressurize with the ignition on, there will still be some fuel in the system but you an always release the pressure before you work on it for added safety.

[Daniel]

The fuel system should retain pressure evem with the car off. There is a valve at the fuel pump that keeps the lines pressurized. I’ve never heard of a fuel injector being cylinder specific.
If there was a misfire, there would probably be a code.

[Jon Hart]

Well Off the top of my head I know SAAB Vauxhall and VW and peugot that have cylinder specific injectors It is fairly common on new cars today, not sure how much of it a 2000 reg car will have on it dont see much older than 2007 come through the garage.

[Daniel]

I think you are confused because I haven’t ever heard of cylinder specific injectors and I’ve been working in a garage for a few years now. I called my buddy who has been a master mechanic for 20+ years and he has never heard of it. So I think you have been told incorrectly. Sorry.

[Jon Hart]

Do you work on European cars?

Well For the SAABS (Vauxhall Engines)they are coded to work with each cylinder so while you can swap them they have to be recoded with security access in order for them to work.

On Seats (VW engines) have the codes printed on top of the injectors you can look on the online data sheet to see which code should be on each injector,

I’m not saying this is on every car but the cars I Work with this is the case. both can be swapped but not without dealer level software.

[Daniel]

We work on a variety of cars. Maybe things are different where you are, but I’ve never heard of this and didn’t see anything on the internet supporting it. OBD can identify which injector is malfunctioning because the power supplies for the injectors are cylinder specific.Maybe that’s what is causing the confusion. When I order fuel injectors for a customer they all have the same part number. I’ve never seen a car call for multiple part numbers as far as injectors go.

[Jon Hart]

[quote=”thisisbuod” post=129730]We work on a variety of cars. Maybe things are different where you are, but I’ve never heard of this and didn’t see anything on the internet supporting it. OBD can identify which injector is malfunctioning because the power supplies for the injectors are cylinder specific.Maybe that’s what is causing the confusion. When I order fuel injectors for a customer they all have the same part number. I’ve never seen a car call for multiple part numbers as far as injectors go.[/quote]

Had a chat with are master tech today on this subject and he confirmed on the new Seat diesels and some petrol models the Injectors are cylinder specific they cannot be swapped and when ordering a new one the code on the top is needed to insure the correct injector is sent out.

[Daniel]

All I know is; in America this is not the case. I said this earlier. Not to be rude, but I’m still not 100% sure you’re not misunderstanding something. I see no purpose for having cylinder specific injectors when the engine can easily identify the injector for each cylinder by using the wiring harness. Before we digress further…. I’m interested to see what Vinchenzo found.

[Vincent]

So I am a day ahead of schedule…

I took off the fuel rail today and had a look at the injectors. They appeared to operate ok and I flushed a bit of cleaner through each one. I couldn’t observe the injector spraying because I have no way to pass the cleaner with pressure… I will get a syringe for next time.

I swapped injector 3 with injector 2 so I can test to see if we get the same problem in cylinder 2. Unfortunately, when refitting I noticed that injector 4 had a damaged connector, the clip was not properly attached to the body of the injector as the plastic has perished. It wobbled easily and could be the reason why the stop and battery lights are flashing as the connection was being broken and remade in time with the engine vibration.

With a gentle poke, it snapped right off so I don’t think it is a good idea to drive on an engine with a suspect injector in cylinder 2 and no injector in cylinder 4. I am a little bit confused because the engine actually runs smoother now than before. Is it possible the injector 4 is stuck in the open position allowing, all be it badly, fuel to enter the cylinder? A power balance test now reveals show the expected drop in revs for each cylinder so not really sure what is going on at all now.

I have ordered another fuel rail with injectors and will report back after fitting it. Not really sure what else to do as I cannot drive around to see if cylinder 2 now exhibits the same errors that 3 previously did.

[Daniel]

The problem could have been that connector and when you re-attached it fixed the problem. Replacing it is the best course. It would have only gotten worse. If it was stuck open you, probably, would have had sooty exhaust and severe idle issues.

[Vincent]

So I have had a few changes since last weekend.

Firstly I have changed the fuel rail for another, second hand but fully tested one. Brilliant, the car runs great with no misfire. However, 10 minutes down the road, I hear a sort of hissing/rattling noise (like a rattle snake) and the misfire returned. The noise sounds as if it is coming from the front far side. Not really sure about the rattle noise, which is not permanent and only sounds under heavy engine load (like accelerating hard or accelerating up a hill) any ideas as to what it might be? Thinking the misfire could be due to the blackened and old spark plug as the performance has improved with the new injectors so I got 4 new plugs and some cleaning additive hoping the misfire would resolve with a cleaner fuel and a brighter spark. On replacing the plugs I noticed that the coils are from different manufacturers, two are original and two are aftermarket so they must have been replaced at some point. I decided that the relatively little cost of 4 new coils was a worthwhile investment, as research showed that the original coils are prone to malfunction and common sense suggests they should all four be the same. Definately an improvement in performance and running but that misfire is still there.

Performing another power balance leave me a little unsure.
Cylinder 1: Behaves as expected with a significant drop in power leading to engine stall if not reconnected quickly
Cylinder 2: Runs badly with a small drop in power, a definite change in revs but the engine persists even without without this cylinder firing.
Cylinder 3: (the original problem cylinder) Runs badly, a drop in power and a less noticeable change in revs, again the engine persists without this cylinder
Cylinder 4: Behaves as expected with a drop in power and reduced revs, the engine stalls if not reconnected quickly.

This engine follows the 1342 firing order with 2 and 3 being the paired cylinders. I guess this explains why removing the spark from either 2 or 3 results in no stall but removing from 1 or 4 causes a stall because 1 and 4 are doing the majority of the work. I think I have got that right. There is no oil or soot from the exhaust so I do not suspect the bottom end or rings, leading me to think this could be a broken gasket between 2 and 3? I mean an actual broken gasket and not just the phrase ‘broken head gasket’, which has come to mean any number of serious engine problems. In other words, I am thinking it could be the physical sealing gasket between the two cylinders. I decided to test this theory by spraying some maintenance spray ( I didn’t have any washing up liquid at the time ) and it seems that consistently I get a little bubble forming in the same spot between the two cylinders. This may not be conclusive as firstly, I don’t know if this is a recognised method for testing a leak but seemed the logical way to go about it and secondly, the spray is fairly oily and bubbly any ways and the bubble could be down to just the vibration of the engine? I did test a few time and it was fairly does seem that bubble forms in the spot between the two cylinders where the engine head meets the body and that although other bubbles are there, they are not as large.

Once again, thanks for taking the time to read, any suggestions on the next stages of diagnosis will be warmly received.

[Daniel]

I think you are on to something with the gasket.
First: did you put a bit of oil on the injector seals before you installed them? That noise you described could be a vacuum leak if the seal(s) got torn during installation .
Go get/rent a compression tester. pull all the plugs. Pull the fuel pump fuse and ignition fuse (if the car has them). Connect the compression tester to each cylinder, have someone crank the engine a few revolutions, and record the reading. Also note how quickly each cylinder looses pressure when the engine is not being cranked.
Now you want to do the same thing, but first squirt just a little oil into each cylinder. Record the readings.
If one or two cylinders do not build up pressure as well as the others, than you probably have a bad headgasket.
If there is a dramatic difference in a cylinder with the “dry” test compaired with the “wet/oiled” test than you probably have bad piston rings.

[Vincent]

Hi, Compression tester got her ok and I spent the afternoon putting it to good use.

here are my results:

DRY: 1: 220, 2: 220, 3: 10, 4: 220
WET: 2: 270, 2: 270, 3: 10, 4: 270
(PSI)

Shining a bright light into the cylinder I can see that 3 is really roughed up. It looks black and tar like with lots of texture. All the other cylinders look the same, black but smooth. No Cylinders lost pressure when the engine was not being cranked, including the 10 psi in cylinder 3.

I think it is very obvious that cylinder 3 is the problem with only 10psi. As there was no real difference between the dry and wet tests, what does this indicate to you? Piston rings in that cylinder or could we still be looking at a gasket issue with a tear right next to that piston. I guess it could not be a valve stuck open as there would just be no pressure at all, not even 10 psi? It is interesting to note that the problem cylinder had a very oily spark plug (before the wet test), whereas the others still look new.

I am happy to continue trying to fix the car as it has become a bit of a welcome challenge and I don’t really have anything to lose from taking the head off, apart from making a bit of a mess.

Thanks, Vincent

[Author]

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