Today I changed the EYQUEM RZC58LS spark plugs and I put the OEM - NGK DCPR7E, those that do not last more than 15k miles. I don't mind that, at least they are OEM.

But, literally nothing has changed with the new spark plugs. I had the EYQUEM for 7500 miles. Weak acceleration and bad throttle response when engine gets warm remained.

Spark plugs are not put in order. Please check them and tell me your opinion.

Quite clean..

2 x sizes of gap..?

1 has a deposit on outer edge..

As said the gap in two of the four seems small, but it's hard tell for sure from a photo, did you check the gaps on them and the new ones before fitting them?
How long has the weak acceleration/throttle response been a problem?

I am not much familiar with spark plugs.

Can you tell me what small spark plug gap means? Or big? Is it getting smaller / bigger as they age? Or wrongly fitted?

I didn't check anything because mechanic fitted them as I told him.

Weak acceleration/throttle response has been here for at least 12500 miles, when I changed the cam belt, tensioner and water pump.

Wasgehabendas said:

I am not much familiar with spark plugs.

Can you tell me what small spark plug gap means? Or big? Is it getting smaller / bigger as they age? Or wrongly fitted?

I didn't check anything because mechanic fitted them as I told him.

Weak acceleration/throttle response has been here for at least 12500 miles, when I changed the cam belt, tensioner and water pump.

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oh- timing belt change and since then it's a slug.... it all makes sense now did the mechanic that changed the plugs do the timing belt?

Jockcl500 said:

oh- timing belt change and since then it's a slug.... it all makes sense now did the mechanic that changed the plugs do the timing belt?

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It was a different mechanic because the one who did the timing belt was not a good one. He wrongly fitted many things on a car.

Is spark plug gap somewhat in correlation with the timing belt?

plugs are normally pre-gapped with cardboard protection but a mechanic should still look at them, to make sure they look ok, maybe they have been dropped but the gaps should be even across all the plugs, hopefully the new ones are evenly gapped.
Anyway my guess is the timing belt has been fitted on the wrong tooth, meaning the valves have been opening at the wrong time, if this is picked up quickly after the belt change then no damage is likely.
Unfortunately as you have done many miles, the valves will be burnt and need replaced, a strip down and new valves gaskets etc and a new belt fitted correctly.

Wasgehabendas said:

It was a different mechanic because the one who did the timing belt was not a good one. He wrongly fitted many things on a car.

Is spark plug gap somewhat in correlation with the timing belt?

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Happy you changed mechanics but
Sorry to be the bearer of bad news, but you are quite correct the mechanic who did the belt has made a right mess and now there is nothing other than a strip down that will cure it.

Wasgehabendas said:

I am not much familiar with spark plugs.

Can you tell me what small spark plug gap means? Or big? Is it getting smaller / bigger as they age? Or wrongly fitted?

I didn't check anything because mechanic fitted them as I told him.

Weak acceleration/throttle response has been here for at least 12500 miles, when I changed the cam belt, tensioner and water pump.

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You ask what spark plug gap means ? It's the gap between the end of the centre electrode and the side electrode so it's the gap the spark has to jump. I enlarged your pictures on my computer and it's obvious, from the first picture, that the gaps are all over the place. Who ever fitted them should have checked these gaps before fitting and adjusted, by gently bending the outer curved electrode until the gap was correct. The long life iridium type plugs should never be "fiddled" with as you can damage them. A common reason why the gaps are too small is often that the fitter bangs the end of the plug against the side of the plug hole in the head as he/she is trying to start then in the hole, maybe that's what happened here?

Here are the plugs I took out of our Panda last time I serviced her and you can see the gaps are all the same and you can get an idea of what a correct gap looks like:



The Haynes manual is not very helpful stating that the gap is "preset" and, to be honest, I've not had a problem with plug gaps since they started boxing them up with that wee cardboard tube over the end, but if you want to check, a gap of around 30 thou (0.030") is a pretty good average setting.

From what you are telling us about your running problems coming on after the timing belt was changed, my bets would all be placed on the timing not having been been correctly carried out - by that I mean I think it's very likely the cam shaft and crankshaft are not correctly synchronized, maybe one or two teeth out?

As Jockcl500 says damage may have been done but also maybe not. If it were me I'd be getting the cambelt correctly fitted and than doing a compression check on the engine before making any decisions about taking the cylinder head off. If the compressions come up good then you've likely got away with it?

I have to say you do seem to be very unlucky with your choice of mechanic. Maybe third time lucky?

Pugglt Auld Jock said:

You ask what spark plug gap means ? It's the gap between the end of the centre electrode and the side electrode so it's the gap the spark has to jump. I enlarged your pictures on my computer and it's obvious, from the first picture, that the gaps are all over the place.

Here are the plugs I took out of our Panda last time I serviced her and you can see the gaps are all the same and you can get an idea of what a correct gap looks like:

View attachment 216732

The Haynes manual is not very helpful stating that the gap is "preset" and, to be honest, I've not had a problem with plug gaps since they started boxing them up with that wee cardboard tube over the end, but if you want to check, a gap of around 30 thou (0.030") is a pretty good average setting.

From what you are telling us about your running problems coming on after the timing belt was changed, my bets would all be placed on the timing not having been been correctly carried out - by that I mean I think it's very likely the cam shaft and crankshaft are not correctly synchronized, maybe one or two teeth out?

As Jockcl500 says damage may have been done but also maybe not. If it were me I'd be getting the cambelt correctly fitted and than doing a compression check on the engine before making any decisions about taking the cylinder head off. If the compressions come up good then you've likely got away with it?

I have to say you do seem to be very unlucky with your choice of mechanic. Maybe third time lucky?

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Nice pic of evenly gapped plugs.
I think "at least 12,500 miles" with a belt on wrong is very likely to have done valve damage, I would not waste time with belt refit and compression testing, I would just take the head off and get the valves replaced and reseated, it may not need all of them, but experience says a couple of hundred miles may get away with it, 12,500 says no chance to me.

take a picture flat on a desk as P & G has done


they look okay to me except its hard to judge as some look bigger because they are closer to the lens. Maybe running a bit weak


Take the MAP sensor out and look for oil on the tip ? You don't have to undo the electrical connector


Do you have a scanner ? to read and clear codes, Read data


What engine CC and year ?

Jockcl500 said:

Nice pic of evenly gapped plugs.
I think "at least 12,500 miles" with a belt on wrong is very likely to have done valve damage, I would not waste time with belt refit and compression testing, I would just take the head off and get the valves replaced and reseated, it may not need all of them, but experience says a couple of hundred miles may get away with it, 12,500 says no chance to me.

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Of course if I was doing the fault finding I'd not be charging myself labour charges. It also occurs to me that you're going to have to strip out the engine mount and dismantle the belt guards regardless of whether you're going to do the head or just refit the belt? All about the labour I suppose isn't it? Please don't think I'm saying one of us is more right than the other, just different approaches?

Thank you for exlaining me the spark plug gap. I understand now what it means.

koalar said:

take a picture flat on a desk as P & G has done


they look okay to me except its hard to judge as some look bigger because they are closer to the lens. Maybe running a bit weak


Take the MAP sensor out and look for oil on the tip ? You done have to undo the electrical connector


Do you have a scanner ? to read and clear codes, Read data


What engine CC and year ?

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Could you tell me where is the MAP sensor located? Maybe you wanted to say "you don't have to undo the electrical connector"?

Yes I have a scanner. No fault codes. Every parameter looks normal.

Timing advance from MES shows 10 degrees at idle. If it it was one tooth off timing would be different right?

Jockcl500 said:

plugs are normally pre-gapped with cardboard protection but a mechanic should still look at them, to make sure they look ok, maybe they have been dropped but the gaps should be even across all the plugs, hopefully the new ones are evenly gapped.
Anyway my guess is the timing belt has been fitted on the wrong tooth, meaning the valves have been opening at the wrong time, if this is picked up quickly after the belt change then no damage is likely.
Unfortunately as you have done many miles, the valves will be burnt and need replaced, a strip down and new valves gaskets etc and a new belt fitted correctly.

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Maybe he did something else wrong and retarded the timing e.g harmonic balanser?

its rare for a garage to get a belt change wrong


A compression test would be a Good start if the poor performance start exactly at the same time as the belt change.

MAP is located on the left of Black plastic inlet manifold. You can get to it without removing the air filter box

well it is on a 1.2L, 2011

You have MES


hows the ambient temperature look ?

koalar said:

its rare for a garage to get a belt change wrong


A compression test would be a Good start if the poor performance start exactly at the same time as the belt change.

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Yes I know it is a rare to get the belt done wrong. As I said above, maybe mechanic did something else wrong by mistake which affected the throttle response.

I got much better throttle response when I changed the fuel pump (lasted 1000-2000 miles). Also throttle response got better with injection cleaner (lasted 300 miles).

Head gasket is leaking oil too. Along with the pump and injectors they should be checked first.

I don't give up with the car! No matter how many troubles it may have.

koalar said:

MAP is located on the left of Black plastic inlet manifold. You can get to it without removing the air filter box

well it is on a 1.2L, 2011

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Okay will check for it

koalar said:

You have MES


hows the ambient temperature look ?

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There are 2 temperatures.

Engine temperature - it is normal. Up to 95 celsius.

Air temperature - what are good values? I need to check them

are you seeing oil on the throttle body butterfly. When you take the air filter off?

koalar said:

are you seeing oil on the throttle body butterfly. When you take the air filter off?

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If you mean here, on the surface, I don't see any oil.