Spark Plug Failure

[Bailes1992]

My Wife drives a Renault/Dacia Sandero with a 900cc Nissan turbocharged 3 pot with 90bhp.

The car is ~5 months old and has ~2800miles on the clock.

When we first had it I was filling it up with Shell V-Power (99RON in the UK which I believe is 93MON in the US) but one week they didn't have any so I filled up with standard Shell Fuel Save (95RON here, 91MON in the US). The following week my Wife was complaining about shuddering and surging at low RPM's under load. Even after going back to Shell V-Power it was still shuddering and generally quite rough running. After a few days in Renault they diagnosed a faulty spark plug and replaced all 3 under warranty (they're £25/each iridium cored plugs with multiple electrodes). The problem was fixed and it was back to being smooth and punchy.

I carried on running it on Shell V-Power once we had it back until around a month ago when again my Wife (who hates spending money) filled up with standard 95RON in a local supermarket in order to save £4. I drove the car the following day and noticed that at low RPM's (Under 2500rpm) and under load the engine was pinking quite badly. Over the course of the 75-100miles I did that day the pinking went away but the car had started juddering again. We are now on our 3rd tank of Shell V-Power since and the judder is still there so I'm suspecting another sparkplug has failed.

The car sticker in the petrol filler flap asks for 95ron or 98ron fuel and a maximum ethanol content of 10% so switching between fuels shouldn't be an issue.

I've booked the car into Renault in 2 weeks time, although I suspect they're just going to put another set of spark plugs in and tell me it's fixed.

Any thoughts on this? Can pinking break spark plugs?

 

[Astro14]

Pinking (pinging on this side of the pond) can break spark plugs. It can put holes in pistons, too. All quite expensive - and to be avoided... When the engine experiences an ignition event (pinking) before the spark plugs fire, a totally different shockwave forms. One that is completely different than the normal combustion shockwave. And that abnormal ignition shockwave can be destructive. Depends on the timing of said events, and the shape of the combustion chamber. Lots of variables.

The engine should have knock sensors (AKA pinking sensors) that retard the timing when it is detected. The shockwave is violent enough that it can be detected, clearly separate from normal combustion events, by piezoelectric sensors.

Sounds like the combination in her case is lousy fuel and faulty sensors.

The expedient fix is better fuel. Higher octane.

But long term I would want to know why the engine is not tolerating the lower octane.

 

[Bailes1992]

The pinking went away after a period of time, so the engine retards the timing eventually. I feel it is taking too long to do so and damaging the spark plugs before-hand.

Maybe I should just keep it on 95ron fuel with a PEA additive like Archoil AR6900 to keep things clean.

The other issue is Dacia is a 'budget' brand usually purchased by people who treat there cars like a white good and don't really care about them. The chances of many people running this engine on premium fuel is few and far between. If this is a programming issue I may never get to the bottom of it.

 

[mk378]

When the timing is retarded to compensate for low octane, you'll lose mpg. Often enough to make it money ahead to buy the high octane fuel.

 

[Bailes1992]

Originally Posted by mk378
When the timing is retarded to compensate for low octane, you'll lose mpg. Often enough to make it money ahead to buy the high octane fuel.

I try to tell this to my Wife but she has none of it. She just sees the slightly inflated figure when she fills up!

 

[Propflux01]

Perhaps is just LSPI, common in many small engined turbocharged cars?

 

[talest]

Originally Posted by mk378
When the timing is retarded to compensate for low octane, you'll lose mpg. Often enough to make it money ahead to buy the high octane fuel.


When Premium is as much as $1 more than 87 in many an area, I have to wonder about this. The power difference can be noticeable, though. Auto ECU timing

 

[Kestas]

Originally Posted by mk378
When the timing is retarded to compensate for low octane, you'll lose mpg. Often enough to make it money ahead to buy the high octane fuel.

That may have been true years ago. But with premium costing 25% more than regular the loss in mpg does not eat up the savings.

 

[Ded Mazai]

I would guess that the knock sensor is the suspect. It may be loose or not sensitive enough. Ideally it should detect knocking before you do.

 

[AC1DD]

Originally Posted by Ded Mazai
I would guess that the knock sensor is the suspect. It may be loose or not sensitive enough. Ideally it should detect knocking before you do.


It's also possibly the ECU not mapping correctly for the retard during use of lower octane fuel. So sensor might be fine but computer isn't implementing data correctly.

When he takes it back into the Renault dealer he should ask if there are any software/hardware updates for the ECU.

 

[Linctex]

Originally Posted by mk378
When the timing is retarded to compensate for low octane, you'll lose mpg. Often enough to make it money ahead to buy the high octane fuel.


Not around here! 92-93 at the pump (USA, Texas) is 50 cents higher!

With a 26 gallon tank, it is NOT worth spending the extra $13

 

[MichiganMadMan]

Originally Posted by Ded Mazai
I would guess that the knock sensor is the suspect. It may be loose or not sensitive enough. Ideally it should detect knocking before you do.


^This

Working on engine calibration in a previous life: If you heard it rattling, something was wrong. A properly working system should be nearly undetectable by hearing. You might notice that the torque is gone and get "fish bites" during acceleration as the ECM plays with the timing, but hearing it means there are multiple events.

I don't have that much experience with Renault products in general other than some rental cars when I was in Germany, so I'm not familiar with their strategy. Most manufactures have a method to detect spark knock events and assign a value to the fuel so it adjusts properly. They are usually aggressive to back off the spark and cautious to put it back.

 

[PandaBear]

Originally Posted by talest
Originally Posted by mk378
When the timing is retarded to compensate for low octane, you'll lose mpg. Often enough to make it money ahead to buy the high octane fuel.


When Premium is as much as $1 more than 87 in many an area, I have to wonder about this. The power difference can be noticeable, though. Auto ECU timing


Usually they are 20c-40c more, mostly 20-25c more. I've never seen $1 more than 87.

 

[vw7674]

Faulty spark plugs?

 

[Bailes1992]

Originally Posted by Propflux01
Perhaps is just LSPI, common in many small engined turbocharged cars?


It's port-injected so I highly doubt it.

Also, isn't LSPI caused by oil, not fuel. Wouldn't explain the differences between fuels.