P0300 Misfire.....Here we go again!

[Sir Nancy Flowers]

If the resistance is within spec, and you have noticed that one plug is different from the rest then to me at least it points to an ignition issue if you have some random crappy HT leads then get them swapped over and check again.

That was my thinking. I haven't researched those specific ht leads but why change from the oem ones? Just says to me that someones trying to cut corners

 

[william84]

Spray pattern has alot to to with combustion if not vaporised correctly it won't combust correctly 🤔

Always clean dirty plugs as soot can cause it to fire irregular as well.

So to some up after injector change ensure you clean the dirty plug.

I.e. misfire

 

[Sir Nancy Flowers]

Well that could be our entire issue here. Fault injector initially and the dirty spark plug could still be causing a misfire. New plugs on the way so I'll give that a switch when they arrive too!

 

[bloke]

majority of faulty injectors i've seen break down when they are hot/been running for a while. checking spray on cranking can be a red herring.

 

[Sir Nancy Flowers]

majority of faulty injectors i've seen break down when they are hot/been running for a while. checking spray on cranking can be a red herring.

Yeah that's a fair comment. Mine tends to throw its code about 10 seconds in which made me think more that it was a blockage or the injector is dead altogether. I guess we will see when I do the crank test!

 

[bloke]

ecu doesn't know if it's blocked so it won't throw a code. works on the resistance of the circuit for fault finding.

for the price if you're having injector issues unless it's a low mileage c\ar you might as well throw a set of new ones in, new lambda at same time as well if you want to push the boat out.

bosch give about 90,000 miles for replacement of lambda but not seen anything for mm injectors.

 

[william84]

I was under the impression the knock sensor throws the code for a misfire.

 

[Sir Nancy Flowers]

For science sake, I'll be testing the injector flow tonight.

I'm resentful to be throwing a bunch of parts at my car when, once isolated, I can just change 1 part and then use the other money for other upgrades or fixes

 

[william84]

Generally imo if it was ECU codes are instant as the circuit could not be completed. With all your resistance checks pointing to them being working

 

[Sir Nancy Flowers]

So, from what you've said, it's either gonna be a blocked injector or coils or leads?

Flow test might give us more evidence to a blockage but if not, it's the other two?

 

[william84]

Double check you've not trapped a ht lead by mistake clean all plugs for good measure aswell.

 

[Sir Nancy Flowers]

New plugs arriving soon. Advice on cleaning the old ones?

I'm pretty sure I have trapped a lead as the inlet manifold is a tad tricky to line up and defo wouldn't bolt down if I had! But I double check!

 

[william84]

So, from what you've said, it's either gonna be a blocked injector or coils or leads?

Flow test might give us more evidence to a blockage but if not, it's the other two?

To definitely rule your injectors swap the one with the issue with say number 4 injector as we know that's working then your fault will go to that cylinder.
If not then it's not the unit it's self.

 

[william84]

New plugs arriving soon. Advice on cleaning the old ones?

I'm pretty sure I have trapped a lead as the inlet manifold is a tad tricky to line up and defo wouldn't bolt down if I had! But I double check!

That could be the whole issue
HT lead will be shorting through the rubber coating to the engine

I use carb cleaner an a cloth to clean dirty plugs

 

[Sir Nancy Flowers]

To definitely rule your injectors swap the one with the issue with say number 4 injector as we know that's working then your fault will go to that cylinder.
If not then it's not the unit it's self.

Unfortunately my obd scanner just gives me a random cylinder misfire. So it doesn't tell me definitively which cylinder is misfiring. I assumed it was 3 as that tends to be the one that always goes. Also, it was the one with the nasty spark plug which obviously says poor ignition

 

[Sir Nancy Flowers]

That could be the whole issue
HT lead will be shorting through the rubber coating to the engine

I use carb cleaner an a cloth to clean dirty plugs

I'll clean up the plugs as best I can and see how that changes things too. Might have been a load of fuss over nothing 😂

 

[william84]

I would have to agree dirty plug indicates your fault is on that cylinder.

Yeah just checked p0300 is random misfire.
If it was narrowed to a cylinder it should read p0301for cylinder 1 so on so forth.

Keep us posted

 

[Sir Nancy Flowers]

I would have to agree dirty plug indicates your fault is on that cylinder.

Yeah just checked p0300 is random misfire.
If it was narrowed to a cylinder it should read p0301for cylinder 1 so on so forth.

Keep us posted

I wish it did show me which cylinder but alas I am here to make educated guesses.

Expect an update this evening.

See below for the spark plugs. They're in order. Spot cylinder 3!

 

[william84]

I wish it did show me which cylinder but alas I am here to make educated guesses.

Expect an update this evening.

See below for the spark plugs. They're in order. Spot cylinder 3! View attachment 1439346

Definitely agree looks very dirty carbon build up.

 

[bloke]

Plug gives it away but if the reader just brings up a generic misfire see what it says under freeze frame data, that normally tells you what cylinder.

 

[Sir Nancy Flowers]

Morning all. At the car. With the ignition on but engine off, I've cleared all the faults. Now cant get the eml light back on 😂. Its still not idling right. Even more lumpy than usual. I'm going to get the sparks out, clean them up and go from there. At least I can get it MOTd now lol

 

[Sir Nancy Flowers]

Okay. Brilliant news. After 10 mins of idling, the eml starts flashing and I've had cylinder 4 misfire. I'll do the usual checks once its cooled down and report back.

 

[Sir Nancy Flowers]

Okay so. Swapped a spare injector into cylinder 4. Still idles like crap. Waited the near 5 minutes for it to throw its fault and again, cylinder 4 fault flashing eml. This is making me think the leads or coil are faulty? Anyone?

 

[william84]

Okay so. Swapped a spare injector into cylinder 4. Still idles like crap. Waited the near 5 minutes for it to throw its fault and again, cylinder 4 fault flashing eml. This is making me think the leads or coil are faulty? Anyone?

Remember on some readers they work back to front to Renault.
4 could really be 1.

 

[JamesBryan]

Unplug an injector one at a time while the engine is running.

If one of them doesn't make the idle bog down, then that's your culprit. If the idle does drop then that one is ok.

 

[Sir Nancy Flowers]

Remember on some readers they work back to front to Renault.
4 could really be 1.

And the f**kery continues 😂

 

[william84]

Not sure if your aware of cylinder order.
From gearbox side it goes 1234.
From cambelt side it goes 4321.

To check HT or spark plug swap number 4 HT on coil with no2 then it will move to no2 for misfire. Then you know it's not injectors.

I'm sure 2 n 4 fire together 1 n 3 could be wrong though.

If fault moves to no2 then you know the fault is with ht or plug.

 

[Sir Nancy Flowers]

Not sure if your aware of cylinder order.
From gearbox side it goes 1234.
From cambelt side it goes 4321.

To check HT or spark plug swap number 4 HT on coil with no2 then it will move to no2 for misfire. Then you know it's not injectors.

I'm sure 2 n 4 fire together 1 n 3 could be wrong though.

If fault moves to no2 then you know the fault is with ht or plug.

Just about to go test this.

 

[Sir Nancy Flowers]

Switching the 2 plugs made it run the worst I've ever heard. And it was making it pop and bang really bad so I cut it after a second or two.

 

[william84]

If it's not 4 n 2 it's 4 n 1

 

[william84]

Remember clear codes

 

[Sir Nancy Flowers]

Switching 1 and 4 made it actually run so that would be that. Unfortunately, it's still showing cylinder 4 misfire. What does that mean?

 

[Sir Nancy Flowers]

Switching 1 and 4 made it actually run so that would be that. Unfortunately, it's still showing cylinder 4 misfire. What does that mean?

Having thought about this, surely it means that the leads and coils are fine. When I switched the leads around, it still showed the same fault.

I'm going to switch the injectors from cylinder 1 and 4. If the fault moves then it must be injector based. If not, its spark plug based.

 

[william84]

You've now ruled out plugs and HT.
So would point to fueling.
If resistance is all in threshold on injectors then its delivery. Side note test resistance hot and cold.
Spray pattern looks fine then it would point to O2 pre cat

 

[Sir Nancy Flowers]

After switching injector 4 and 1, the fault has moved to cylinder 1. To eliminate not knowing which way my obd scanner reads, I'm going to switch cylinder 1 and 2. If the fault moves to cylinder 2, its injector located in cylinder 2. If not, it's the injector located in cylinder 4. Back soon.

 

[william84]

Injector needs changed No1 bin

 

[william84]

Go through your ones you have and swap

 

[william84]

I hope that's you mate smiles for miles.

 

[Sir Nancy Flowers]

Just switched injectors. Feels lumpy but better. Maybe I'm just used to the daily. No flashing light just yet. THIS COULD IT BE LADS

 

[Sir Nancy Flowers]

Well chaps. After a short test drive (on public land of course as my mot has expired) I can safely say it was injectors all along. So. All you gits that said injectors early on, you can be feeling pretty smug round about now 😂😂.

Thanks for everyones help. Especially @william84